Physical geography

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Material Information

Title:
Physical geography
Series Title:
Maury's geographies. New series
Alternate Title:
Maury's physical geography
Physical Description:
130 p. : ill., col. maps ; 29 cm.
Language:
English
Creator:
Maury, Matthew Fontaine, 1806-1873 ( Author, Primary )
Maury, Mytton ( Author, Secondary )
University Publishing Company ( Publisher )
J.J. Little & Co ( Printer )
Publisher:
University Publishing Co.
Place of Publication:
New York
Manufacturer:
J.J. Little & Co.
Publication Date:
Edition:
Rev. ed.

Subjects

Subjects / Keywords:
Physical geography -- Juvenile literature   ( lcsh )
Baldwin -- 1891
Genre:
non-fiction   ( marcgt )
Spatial Coverage:
United States -- New York -- New York

Notes

Statement of Responsibility:
by M.F. Maury ; revised by Mytton Maury.
General Note:
Includes index.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 002879464
oclc - 04990822
notis - APB0711
System ID:
UF00081060:00001

Full Text






































































































IThe Baldwin Library
-Univsity
RIorida





ItEVISED EDITI0701.


Physical




Geography.



BY
M. F. MATTRY, LL.D.,
AUTHOR OF "PHYSICAL GEOGRAPHY OF THE SEA," LATE SUPERINTENDENT OF THE NAVAL
OBSERVATORY, WASHINGTON. D. C., ETC.


REVISED
BY MYTTON MAURY, D.D.


UNIVERSITY PUBLISHING COMPANY
NEW YORK.
1891.










MAURY'S


GEOGRAPHIES.


NEW SERIES.



ELEMENTARY GEOGRAPHY:

A revision and abridgment of the "First Lessons" and the "World We Live In." Designed for Primary and
Intermediate classes. The style is familiar and interesting. The arrangement of the text is in harmony
with the latest and best methods of instruction. New Maps and numerous illustrations.


MANUAL OF GEOGRAPHY-REVISED:

A Treatise on Mathematical, Physical, and Political Geography ; in accord with the most recent methods
of teaching. The subject is presented in a bright and attractive manner. Abundant explanations are
employed to awaken and sustain the interest of the pupil in intelligent study. Beautiful new Maps
and Illustrations.


PHYSICAL GEOGRAPHY-REVISED:

In which the Natural Features of the Earth, its Oceanic and Atmospheric Phenomena, and its Animal and
Vegetable Life, are fully treated. The fresh, attractive style of the work and the interest of its detail
charm the pupil and the general reader. Illustrated with numerous beautiful Maps and Engravings.


WALL MAPS:

With new and original features ; furnishing invaluable aid in teaching Geography in classes, and comprising,
I. The World. II. North America. III. The United States. IV. South America. V. Europe. VI. Asia.
VII. Africa. VIII. Physical and Commercial Chart of the World.


MAP-DRAWING:

From Maury's Revised Manual of Geography.

In ordering the Manual or the Physical, specify whether the revised or the old is wanted.




OLD SERIES.


FIRST LESSONS IN GEOGRAPHY.

THE WORLD WE LIVE IN.

MANUAL OF GEOGRAPHY.

PHYSICAL GEOGRAPHY.

In ordering the Manual or the Physical, specify whether the old or the revised is wanted.


***1243 Entered according to Act of Congress, in the year 1878, by
M. F. MAURY,
In the Office of the Librarian of Congress, at Washington.

Copyright, 1883, by the University Publishing Company, New York.


Press of J. J. Little & Co.
Astor Place. New York.















PREFACE.



THIS volume, together with the three graded Geographies previously published, and a treatise on Astronomy, forming
the Author's contribution to the University Series of School Books, was commenced in 1866. It is the joint labor of his
wife, daughters, and self, and constituted one of the chief sources of their home recreation during their residence in
England. There the best sources of information were kindly and freely opened to him. This, combined with the
knowledge and experience acquired or perfected in the superintendency, for fifteen years, of the 'iV. hi.i_ .... Observatory,
made the undertaking congenial, and the occupation as charming as labors of love always are.
The aim throughout the series has been to strip these two most important branches-Geography and Astronomy-
i of dry details and mere technicalities, to popularize these fields of knowledge, and make them as interesting and
instructive to students as possible.
The Author's investigations for his "Wind and Current Charts," in which he was aided by the vessels and
governments of the maritime nations, and the insight that these gave him into the PHYSICAL GEOGRAPIY OF THE
SEA AND ITS METEOROLOGY, also afforded him some rare advantages for preparing the present general treatise on
PHYSICAL GEOGRAPHY.
Besides these special and original sources of information, hlie has, in the preparation of this work, had access to
the best and choicest fountains of recent geographical and scientific knowledge, and has revised his MS. up to the date
of going to press.
A science of recent growth, PHYSICAL GEOGRAPHY depends for its truths and general principles upon extensive
and prolonged observations. These observations have been made for too short a time and over too limited an area,
to furnish more than the basis for a complete science. The quickened and enlarged interest that has been awakened
in physical researches, the more perfect instruments and appliances that are now used and that will be still further
improved, and the patronage and encouragement of i l-... -I governments, will doubtless lead to the solution of
many of its yet unsolved problems.
It has been one of the great aims of the author of this book to prepare its readers and students to understand and
take an intelligent interest in this noble science, and especially to awaken in the minds of the young that spirit of
observation and patient inquiry which has already won from nature so many of her most hidden secrets.
In the preparation of the numerous charts which enrich the volume, the author has had the assistance of one
of the most accomplished chartographers of the country; and the skill and beauty with which they have been
engraved upon copper are very gratifying. The pictorial illustrations, which so abundantly explain the text and
adorn the pages, have been designed and engraved by some of the first artists in the country, or obtained from
European sources, and testify to the liberality of the publishers, and their purpose to present this work to the
public in a most attractive garb.
M. F. MAURY.
LEXINGTOsN, VIaGuNA, November, 1872.





PREFACE TO THE REVISED EDITION.

THE progress of science anticipated by the author in the foregoing preface, has rendered desirable the preparation
of a revised edition of the PHYSICAL GEOGRAPHY. While engaged in this labor, the reviser has sought to meet the
demands of our schools for brief books by abridging somewhat the earlier edition, without, however, impairing its
completeness. To a considerable extent a re-arrangement of the materials has been adopted. But the aim lihas been
throughout, to preserve, so far as possible, the charm of the author's style.
The typographical arrangement of the text, the topical analysis at the end of each chapter, and the test
questions will, it is believed, greatly facilitate the use of the book in the class-room.
In the prosecution of the work the reviser has invoked the counsel of many eminent scientists and experienced
educators. To them all he begs to express his obligations for their valuable suggestions. The book owes much to
their kind assistance. It is hoped that it will be found abreast of the times, and well adapted to lighten the labor
of the teacher, and to kindle the interest of the pupil.
MYTTON MAURY.




II .. .. I..













CONTENTS.


PART I. THE EARTH.


I. The Earth as a Planet.......................
II. Planetary Movements.......................
III. Magnetism of the Earth ....................
IV. Internal Heat of the Earth....................
V. Volcanoes ...................................
VI. Earthquakes.................................


PART II. THE LAND.


I. Arrangement of Land Masses ...............
II. Forms of Land ..............................
III. Relief Forms of the Continents...............
IV. Islands ..... ... ....................


PART III. THE WATER.


I. Properties of Water.........................
II. Waters of the Land.... .....................
I Drainage ....................................
IV. Continental Drainage.......................


PAGE
V. TheSea ..................................... 52
VI. The Oceans.................................. 54
VII. Waves and Tides........................... 55
VIII. Currents of the Sea......................... 61


PART IV. THE ATMOSPHERE.

I. Physical Properties of the Atmosphere ......... 69
II. Clim ate .... ......... ...................... 70
III. Winds and Circulation of the Air............. 7.5
IV. Storms ...................................... 81
V. Moisture of the Air....................... 85
VI. Hail, Snow, and Glaciers.................. 94
VII. Electrical and Optical Phenomena............ 98


PART V. LIFE.


I. Relations between Plants and Animals.........
II. Range of Plants and Animals ................
III. Man ............... .......................
IV. Geographical Distribution of Labor............


LIST OF OHARTS.


Solar System ................................ 7
Lines of Equal Magnetic Declination........ 12
Distribution of Volcanoes .................... .- 1
The World ............................ . .,
North America ............................ 3
South America............................. 3
Europe ................................. .. 33.
Asia ................................... ..
Africa ................................ 37
Australia .................................. 3,


Thermal and Tidal Chart., ................... 59
Curr.tri ,:.f lit- S,.1. aimi Driirri.- .t th.- Land.62. 63
1-,tFi_-ruj.d Lirn:- an'I Z.:.rin.- .:t Temp rature .7;. 73
Winr-. ............................... .79
R.i9n ... .. .. ........................ 9. 91
Distrithuti,:n --f Prnri.,:-Il Veg,-t-al:le Gr,:wths.104, 105
Di-ril:utin if B,- .ti. Bird-., and Fih-he- ..111)0, 111
D)i-tribLtior .,f the Ra,.,-; :,t MN -n ............ 119
Prin;,ipal Indurtrii l Pur-iits ot Different Coun.
tries ............... ..............1232, 128





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:=. + : ,,.' A+














RE ENT


FACTS


CONCERNING PHYSICAL GEOGRAPHY.


A SUPPLE)IMENT TO iMAURY'S PHYSICAL GEOGRAPHY.


S Course of the Gulf Stream.-The theory that a
Sr.rtkin of the waters of the Gulf Stream makes the circuit
of the Gulf of Mexico-has of late been called in question.
In this connection the following letter from B. A. Colonna,
Assist. Chief Officer in the U. S. Coast and Geodetic Survey
DI.r,]:ri t, is exceedingly interesting and important

U. S. COAST AND GEODETIC SURVEY OFFICE,
WASHINGTON, NSombe 241tA, 1887
DEAR SiR:-Your letter of 17th inst. was duly received
by Superintendent Thorn who referred it to this Office.
Press of work on my return from a short leave has pre-
vented earlier attention. I now have the honor to say by
direction of the Superintendent that the exact facts in re-
gard to the circulation of the water in the Gulf of Mexico
Cannot be stated; we have not had sufficient observations.
SThe observations of deep sea currents, and the usual sound-
r_,.i_ were, during the season of 1885-6, confined to the Gulf
Stream, on a line from Cape Florida (Fowey Rock Light
Mouse) to Great Bahamas ; during the season of 1886-7 the
work was confined to the vicinity of west end of Cuba, Key
SWest, and Yucatan. None of this work has been published,
and none of it would shed any particular light upon the
Question 'propounded by you as to the circulation of the
waters in the Gulf of Mexico. Our late explorations indicate
that the axis of the Gul-f Stream hugs the west coast of
Cuba closely, and that the Gulf Stream currents are much
influenced by the moon in accordance with her time of
ti,,Ir,-it I r.l I, r: r declination.
r._ I. i he Gulf of Mexico is concerned I do not think
ih.i. i.-i, any circular, well-defined current about its
...i'.i- i..u:.. The warm surface water probably flows
rir,'i, _ii r. ,,ard the west coast of Florida than it does
.,.. .I ,.- .. ist of Texas or of Mexico. Although this view
S1i...1i.. ,i -...iewhat on climatic and tidal indications, it is
I -.i., i|.=,:rtial. As I have said before, the matter is
o.,- ,l..r' .-o.,sideration ; when we know more about what
t-ckes place at the east end of Cuba and thence westward
il.,ri: its north shore to the Strait of Florida, we will be
Ready to give more particular attention to matters in the
Gulf. The great flow of water through the Strait of
Fl. .1 i ,. northward, must be supplied from somewhere; its
',;r',.. temperature indicates its recent arrival from the
r"'"-:, presumably set into the Caribbean Sea, and up into
the Gulf of Mexico,.by the trade-winds, and thence pro-
-pelled in accordance with the laws of fluid motion. Whether
the whole supply of water for the Gulf Stream reaches the
FPI 'ild- Strait around the west end of Cuba, or not, cannot
now be asserted. It is hoped that the season's work of
1887-8 will shed light upon this subject.
Yours, respectfully,
B. A. COLONNA.


The Velocity of the Gulf Streamn.-Recent ob-
servations of Lieutenant Pillsbury, of the United States
Navy, show that the velocity of the Gulf Stream varies with
the position of the moon. "The greatest velocity is about
nine hours before the upper transit of the moon. The
strongest surface current observed was five and one-fourth
knots-the weakest, one and three-fourths-the average
three and six-tenths knots." These results are, as a rule,
higher than those hitherto given.
It appears also that the speed of the surface water of the
Gulf Stream is retarded perceptibly by northerly and north-
easterly winds, and accelerated by those from the south-
west.
During the coming winter the United States vessel Blake,
under command of Lieutenant Pillsbury, will continue to
investigate the Gulf Stream current. She will anchor six
hundred miles north-east of Barbadoes, during January and
the first part of February, and will be in the track of
ships from South Atlantic ports to the United States.
The last part of February and until May she will be
between the West India Islands, beginning at Trinidad
and ending at the cold Bahama Channel. It is expected that
Lieutenant Pillsbury's report will be of value, and that
some points regarding the Gulf Stream currents will be de-
termined with greater exactness than as yet is possible.
Early Polynesian Navigation.-Mr. Formander
has recently made some interesting and instructive discov-
eries in the folk-lore of the Polynesian islands. He says
that "from about the commencement of the eleventh cent-
ury, for two or three hundred years, the folk-lore in all the
principal groups becomes replete with the legends and songs
of a number of remarkable men, of bold expeditions, stirring
adventures, and voyages undertaken to far-off lands."
For seven or eight generations, the navigators of the lead-
ing groups, from the Sandwich Islands in the north to the
Society group in the south, and from the Friendly Islands
in the west to the Marquesas in the east, were accustomed
to interchange visits, and to voyage freely to and .fro, with
far more assurance and better seamanship than were dis-
played by the early Greek and Italian sailors in the Medi-
terranean. Yet the distances thus traversed sometimes
exceeded 2,000 miles, and crossed the region of both the
north and the south trade winds, and the equatorial calm
belt.
Such facts show that, in accounting for the movements of
population in primitive times, mere distance and difficulties
of navigation need hardly be taken into account. The pos-
sible bearing of this upon such questions as the Asiatic
origin of the North American Indians will at once be seen.
Sea-level.-Recent observations seem to indicate that
along the coast there is no such thing as the popular sea-


Copyright, 1887, by the University Publishing Company, New York.


**, .1270









4 RECENT FACTS CONCERNING'PHYSICAL GEOGRAPHY.


Albatross has been specially constructed .for the work of
dredging, and she is manned by a very expert body of naval
officers and scientists. Every summer, at least, she cruises in
deep ocean waters, and brings back the results to the head-
quarters of the United States Fish Commission, at Wood's
Hole. In the Challenger expedition, only one deep-sea
dredging could be made in a day, and very little of the
bottom was secured at that. On the Albatross two to four
dredgings per day are made in water over 1,000 fathoms
deep, and five in water between 500 and 800 fathoms.
It has been conclusively shown by these later researches
that the proportion of animal life in ocean depths is far
greater than was indicated by the Challenger's results ; and,
furthermore, that instead of the abyssal forms being com-
paratively small, many of them are even larger than the
analagous forms existing in shallower waters. Among the
echinoderms (spine-covered animals, of which our common
sea-urchin is a type), taken in depths of 1,346 to 1,735
fathoms, two species are gigantic, one specimen being
eighteen inches long.
RESULTs.-Reporting the results of the work done in 1884,
Professor Verrill says : Many additions to the fauna of
great depths were made, and a large proportion of them
are undescribed forms. Some of the fishes were of great
interest. Huge spiny spider-crabs, the outstretched legs of
which measured over three feet from tip to tip, were taken in
1,009 to 1,230 fathomns, and another very large crab occurred
in great abundance in 500 to 1,000 fathoms. Numerous spe-
cies of shrimp, many of them bright-colored, and some of
very large size, occurred, as usual in the deeper dredgings."
"A striking characteristic of the deep-sea crustacea,"
says Professor Verrill, "is their red or reddish color. A few
species are apparently nearly colorless, but the great majority
are some shade of red or orange ; and I have seen no evidence
of any other bright color, A few species from between 100
to 300 fathoms are conspicuously marked with scarlet or
vermilion, but such bright markings are not noticed in any
species from below 1,000 fathoms."
Perhaps more remarkable than the matter of coloring is
what we learn about the eyes of deep-sea forms of life. Of
sixteen species taken below 2,000 fathoms by the Albatross
every one had eyes, and these were distinctly faceted. "In
at least three of these species the eyes are not conspicuously
,different in size from those of allied shallow-water species."
However strong, therefore, may be the arguments of
physicists against the possibility of light penetrating the
depths from which these animals come, the color and struct-
ure of their eyes, as compared with blind, cave-dwelling
species, show conclusively that the darkness beneath 2,000
fathoms of sea-water is very different from that of ordinary
caverns."

Red Sunsets and Sunrises.-In the autumns of
1883 and 1884, the sky at sunset, and in a measure also at
sunrise, was illuminated with a peculiar rosy light, which
diffused itself far up toward the zenith. The phenomenon
seems to have been observed all over the world.
Various causes were assigned to account for it. Many
scientific men considered that it was due to the presence in
our atmosphere of minute volcanic dust emitted during the
celebrated eruption of the volcano of Krakatoa, which oc-
curred during the prevalence of the red sunsets. This ex-
planation, however, must be abandoned, for the phenomenon


made its appearance, certainly in one region of the world,
long before the eruption.
In the "' Proceedings of the Manchester Literary and Phil-
osophical Society, Vol. XXIII., Sessions 1883-4," is to be
found a letter dated Taranaki, New Zealand, in which the
writer says that for many weeks before that eruption this
lurid glow was most strikingly perceptible in New Zealand."
In commenting on this letter, in his report for 1885, Dr.
Draper, of the N.Y. Meteorological Observatory, says: "The
latest opinion expressed by scientists is that the red sun-
rises and sunsets were due to the earth passing through
meteoric dust in space." And in explanation of the phe-
nomenon being observed first in New Zealand, he says :
"May we not conceive that the earth in 1883 was passing
through a meteoric cloud, and that the southern hemisphere
was the first to enter that cloud ? "
Temperature of Deep-sea Waters.-Observations
made on the Albatross, during 1884, indicated that the
temperature at depths of 2,000 to 2,600 fathoms was about
37 Fahr. This temperature, however, was also found at
the comparatively shallow depth of 1,000 fathoms. Hence it
would seem that, at least in the region of the observations
alluded to, the minimum temperature is reached at 1,000
fathoms. The surface temperature taken at the same dates
was about 72' Fahr.
It is either owing to the change of temperature experienced
min coming from great depths to the surface, or else to the
removal of the pressure to which they have been previously
subjected, that nearly all the deep-sea animals are dead
when brought up in the trawl. Some have enough vitality
to make a few feeble motions, but "in all cases they ap-
peared," says Sir W. Thomson, "to have received their,
death-stroke before they had come out of the water." An
exception to this general rule was the case of some coral
polyps brought from a depth of 1,000 fathoms. These were
alive and expanded when placed in sea-water.

Power of an Ocean Wave.-In a paper by the-
Rev. Philip Neale, late British chaplain at Batavia, in,
Leisure Hour, speaking of the great, inundation from the
sea caused by the Krakatoa earthquake, Java, he says:
"One of the most remarkable facts concerning the inunda-
tion remains to be told. As we walked or scrambled
along, we were much surprised to find great masses of white
coral lying at the side of our path in every direction. Some
of these were of immense size, and had been cast up more
than two or three miles from the sea-shore. It was evident,
as they were of coral formation, that these immense blocks
of solid rock had been torn up from their ocean bed in the
midst of the Sunda Straits, borne inland by the gigantic
wave, and finally left on the land several miles from the
shore. Any one who. had not seen the sight would scarcely
credit the story." The feat seems almost an impossible one.
How these great masses could have been carried so far into
the interior is a mystery, and bears out what I have said in
previous papers as to the height of this terrible wave. Many
of these rocks were from twenty to thirty tons in weight,
and some of the largest must have been very nearly double.
Lloyd's agent, who was with me, agreed in thinking that
we could not be mistaken if we put down the largest block
of coral rock that we passed asweighing not less than fifty
tons."
compare page 21, paragraph 4, and examples on page 22.















PHYSICAL GEOGRAPHY.


t



SPHYSICAL GEOGRAPHY invites you to consider the terrestrial machinery which makes day and
aight, seed-time and harvest ; which lifts the vapor from the sea, forms clouds, and waters the earth
which clothes it with verdure and cheers it with warmth, or covers it with snow.
SPhysical Geography treats of the agents that cause the wonderful circulation of the waters of
ilth. sea, that diversify the surface of the earth with hills and valleys, and embellish the landscape
{with rivers and lakes.
SPhysical Geography views the surface of the earth, its waters, and its enveloping atmosphere as
the scene of the operations of great physical forces, which by their united action render possible the
]if.- of plants and animals. It studies the life of the globe whether on its surface or within its waters,
taking note particularly of the circumstances which are favorable or adverse to the development of
organic forms. It is especially interested in the earth as the abode of man.
i Observing in careful detail the various features and agencies of our planet, it considers them as
.ar'ts of a magnificent machine, by whose operations, under the guidance of the Great Designer, this
1 1.i-et is made a dwelling-place fit for man.
It has been judged most convenient to present the topics treated in the following order :


I. THE EARTH.
II. THE LATD.


III. THE WATER.
IV. THE ATMOSPHERE.


V. LIFE.















PART I.


THE EALTH.



I. TIHE EARTH AS A PLANET.


1. What is the Earth ?-The first question
which requires to be answered in discussing the
Physical Geography of the earth is, what is the
earth ?
ANCIENT THEORY.-Many centuries of human
history passed before any one was able to answer
this question correctly. Men saw the sun in the
same part of the heavens morning after morning,
and when his light faded, they observed that the
stars were apparently just where they had been
the night before. It was concluded that the sun


';*'. "- .. - -" .- -" -




J.,
''~~ ~~ i.i' :'"" -.
EARTH MO ISP



EA T .A!.-N ;,D -. :NO -N --- -I SPA.:C.-E----- ---


EARTIU 2kND MIOON IN SPACE.


and stars all moved round the earth once in twen-
ty-four hours.
Thus the early answer to our question was that
the earth was the centre of the Universe.
Careful observation seemed to confirm this idea.
Astronomers watched the heavens. They mapped
down the stars, and recorded from night to night
the places of the brightest among them. They ob-
served that some of them did not change their
position with reference to their companions, while
others very perceptibly Naried theirs. The former
were called fixed stars. The latter received the
name planets, or wanderers, from a Greek word


meaning to wander. What did their wandering
mean ? It was found that after certain periods
each of the planets returned to its old place in the
heavens. This was deemed conclusive proof that
the planets, together with the sun and moon, re-
volved in circles round the earth. This explana-
tion was satisfactory to the majority of mankind,
but not to thoughtful astronomers.
THEORY OF COPERNICUS.-In 1542, Copernicus,
a Prussian astronomer, startled the world by an-
nouncing that the ancient theory was a mistake ;
..______ .that the sun, not the earth,
is the centre of the Universe;
S.-- that the planets, instead of
S circling round the earth, re-
- volve round the sun; and
that the earth itself is only a
planet.
S Thus the true answer to
our question, learnt only
: ... about three hundred years
,...... ... ago, is that the earth is not
.-...* utterly unlike the heavenly
.: -\ bodies, as it seems to us to
..... b ..'" be; but that it is actually
*.5 o ....."-:i one of them, and that, if we
:."-....-- : ..' .";;,i' were placed upon one of the
_.'f'. -W s. other planets, the earth would
'r -^"-_ =Y ?.."'*. ***' ^ ^ *'-:"':S ^: y? .
: .~;.?-- ^- ~appear as a shining star-like
:;'....?-,!.:;fI point in the sky.


-The Sun and its


2. The Solar System.
attendant planets with their


satellites, together with the planetoids and comets,
constitute what is known as the Solar System, so
called from the Latin sol, the sun.
A "system" consists of one central body, together with
other smaller ones which move round it.
THE SuN.-The sun is the centre of the Solar
System. From it all the planets derive both
heat and light.
The sun is a vast sphere or ball, more than a
million times as large as the earth. If we could
place its centre where the centre of the earth is,
then the sun would reach so far into space that it









THE EARTH AS A PLANET.


would extend almost 200,000 miles beyond the
orbit of the moon.
The sun is shown by the spectroscope to contain
many of the same materials as those of which the
earth is composed. It is in a state of intense heat,
and columns of incandescent gases project from
its surface tens of thousands of miles into space.
The heat received in one year by the earth from the sun,


than 200 in number. They arc so small as to be,
for the most part, invisible to the naked eye.
The Secondary Planers revolve round the Pri-
mary Planets, as the Primaries revolve round the
sun. They are also called moons and satellites.
Our moon is the satellite of the Earth.
The Nebular Theory, which is held by many astronomers,
supposes that all the bodies constituting the Solar System


s\,
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")URANUS


T I -


SATURN -.


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k__LANETOIDS'
I. N E T 01 DS

_N1 ARS
._ EARTH
S'--- ENUS
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JUPITERi- .'-ez


. NEPTUNE


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THE SOLAR SYSTEM.

would, if distributed uniformly, melt a layer of ice 100 feet were originally one mass of matter in a nebulous or cloud-
thick covering the entire globe, like condition. This was widely diffused through a certain
THE PLANETS.-TiThe planets are classed as Pri- portion of space, and had a rotary motion. From causes un-
mary and Secondary. known to us, parts of it successively condensed and became
The Primary Planets are eight in number. semi.solid. Being detached or thrown off from the general
They are Mercury, Venus, the Earth, Mars, Jupio mass, these formed the various members of the Solar Sys-
ar c Mercury, enusad the E h M ar, tem, the most distant from the centre being the earliest
ter, Saturn, Uranus and Neptune. These names formed. The sun is considered to be a portion of the nebu-
are given in the order of thcir distance from the lous matter which is in an incandescent state, owing perhaps
sun, Mercury being the nearest. Between Mars to chemical and physical changes going on among its ele-
and Jupiter are the Planetoids, or Asteroids, more ments,








PLANETARY MOVEMENTS.


If t he earth be represented by a globe one foot in diameter,
the sun must be represented by a sphere 35 yards in diame-
ter, and be 21 miles from the globe, so as lo show in proper
proportion the real size of the two bodies and the distance
between them. Jupiter, the largest planet, would be repre-
sented by a globe 8& yards in diameter at the distance of 11
miles. The relative sizes of the disks of the sun and planets
are approximately represented below.


TOPICAL ANALYSIS.
I. THE EARTH AS A PLANET.

1. What is the Earth?
Ancient Theory. Fixed Stars. Planets. Theory
of Copernicus.
2. The Solar System.
Classes of bodies included in it. The Sun. Relation
to Solar System. Size. Materials composing it.
Its heat. Planets. Primary Planets. Planetoids.
Secondary Planets. Nebular Theory. Relative
sizes of Son and Planets.


3. Actual size of the Earth.
Diamieter. Circumference. Volume.
gravity.


Specific


RELATIVE SIZE OF THE SUN AND PLANETS.


3. Actual Size of the _Earth.-The equa-
torial diameter of the earth is 7,925.65 miles; the
polar, 7,899.17. The difference is about 26. miles.
The region about each pole, therefore, must be com-
pressed 131 miles. The circumference of the earth
at the equator is 24,899 miles. Its volume, or
solid contents, is about 260,000,000,000 cubic
miles.
The specific gravity of the earth is about 5}-,
that is, the earth is five and a half times as heavy
as a globe of water of equal dimensions would be

4. Comparative I)i.fiiiif ivr o. of the
Earth.-If now we bear in mind that all the
fixed stars are the suns of other systems resem-
bling our own, and in many cases vastly larger *
than our own, and reflect that the heavens above
and below us are filled with untold numbers of
such systems, we shall appreciate the comparative
,i- ii ii'. ,,., of our earth.
The earth is only one of the smallest members of
one of the numberless systems which fill the immen-
si4y of space.
The subordinate position of the Solar System in the universe is
strongly suggested by the fart, that the entire system appears to be mov-
ing through space in the direction of the constellation Hercules. Mo-
tion towards indicates an attracting force ; and implies that the body
exerting that force is larger than the body which is attracted. How
vastly grander than our system must that one be which candrawtoward
itself our sun with its inconceivable volume, and tlhe attendant planets !


S 4. Comparative insignificance of the Earth.

TEST QUESTIONS.- [The test questions are to be used at tlhe
option of the teacher. They are not directly answered in thetext.
Their design is to awaken though ton lthe part of the pupil.] Name
all the bodies you can that may be seen in the heavens, WhatL
would be the consequence to the earth, if the heat of the sun
should be withdrawn ?


II. PLANETARY MOVEMENTS.

1. Effects of the Earth's fMotions.
-The nature of man requires for its highest
development that he shall have certain alternations
in the degrees of light and heat to which he is
subjected. The planetary motions of the Earth
produce just the changes which he needs. They
are those of day and night, and summer and win-
ter. Let us see how these are brought about.

2. notation.-All of the planets rotate on
their axes from west to east.* This motion causes
alternations of sunshine and darkness.
The nearer a planet is to the sun, the less rapidly
it rotates. Mr [,. r,,'y, Venus, and the Earth rotate
in about twenty-four hours. The more distant
planets, so far as their rates have been ascertained,
require only about nine or ten hours for their rota-
tion. Their day is less than half of ours.
It is easy to see that its brevity would be very
inconvenient to beings like ourselves.

3. Jevolution.-The planets, while rota-
ting, also revolve round the sun.
The direction of this planetary revolution is, like
that of rotation, from west to east, and, with the
exception of the satellites of Uranus, and possibly
those of Neptune, all the secondary planets revolve

An interesting evidence of the earth's rotation is that. suggested by
Newton. It is easy to see that a body at the top of a tower will, if the
earth really rotates, move with greater velocity than will the base of the
tower. Let a ball be dropped from the top of such a tower, and it will
strike a point on the ground some distance from the foundation. Ex-
perimnents of this kind have all clearly demonstrated the easterly motion
of the earth, the balls dropped always striking to the eastward.








PLANETARY MOVEMENTS.


in the same direction. The time required for a
single revolution is called a year.
The nearer a planet is to the sun, the more
rapidly it revolves, and the shorter is its year.
The year of Mercury, the nearest planet, is only
eighty-eight days long : Jupiter's year consists of
about eleven of ours: Neptune's of more than 160.
The earth completes its revolution in 3651 days.

4. Inclination of Planetary Axes.-
The axes of the planets are inclined to the planes
of their orbits. The angle or amount of inclina-
tion is not the same for all the planets. Each has
its own. But it is important to-observe that the i
angle of inclination of each planet undergoes no
change. It is said to be "constant." And again
the axis of each planet preserves invariably the
same direction at every point of the
orbit; in other words, at any two ,/,....
points of the orbit the axis is par- '..' ,'
allel to itself.
The facts that the planetary axes
are inclined at constant angles, and
preserve unchanging directions,
bring about, in combination with
the revolution of the planets, two A ,
results : (1) changes of seasons; f..
(2) variations in the duration of -.
day and night. I-! : ..
SEASONS.-An inspection of the *i_
cut opposite will show that as each 'uI-'-.E 21,
planet passes round the sun, the
upper portion of its surface will
be directed toward the sun at one
part of its orbit, the lower at the
opposite part. In other words, the
northern hemisphere of each planet ,. .. .
will receive the more direct rays of 'V.....
the sun at one time, the southern
at another. A hot season, or sum-
mer, will therefore alternate with a cold season or
winter.
The Earth's Axis is inclined to the plane of its
orbit at the constant angle of about 23v. This
inclination, combined with the earth's orbital mo-
tion, makes our seasons.
The sun appears every year to move through the heavens
northward as far as the Tropic of Cancer, and southward as
far as the Tropic of Capricorn. In the course of this jour-
ney he is directly over our equator, or, to use the sailor's
phrase, "crosses the line," on or about the 21st of Mlarch.
Just as soon as he passes northward of the equator, his light
leaves the south pole, and extends to and beyond the north.
The winter of the south polar regions now begins, and that
of the north polar regions ends. Still travelling north-
ward the sun carries the hot season with him, and summer
prevails throughout the northern hemisphere.
The reverse of all this occurs while the sun journeys
southward.


VARYING LENGTH OF DAY AND NIGHT.-A
second effect of this inclination of the axes of the
planets to their orbits is that their periods of light
and darkness, or day and night, vary in length
according to the apparent position of the sun at
the different seasons.
In the ease of the earth, twice every year, in March and
in September, when the sun crosses the equator, the equinox
occurs; that is, daylight and darkness are of equal dura-
tion all over the globe. Each is twelve hours long. This
is because the light of the sun, when he is on the equator,
extends from pole to pole, and one half of every parallel is in
sunlight and the other half in shade. But, as the sun moves
northward, the duration of daylight is greater and greater
for all places north of the equator, until about the 21st of
June, when the summer solstice occurs. Then the north
pole of the earth is turned toward the sun and the northern
hemisphere has its longest day.


ORBIT 01F THE EARTH.


The summer solstice being past, the sun begins to recede
toward the south. Our days then become shorter and
shorter, until, toward the end of December, we have our
shortest day. The sunshine then lasts for us only about nine
hours. The winter solstice being past, the days again be-
gin to lengthen. [For the effect of this upon the climate
of northern latitudes see paragraph 2 on page 70.]

5. Adaptation of the Earth for Hu-
man lfabitation.-Comparing the earth with
the other planets, we observe two points which
render it specially adapted for human habitation:
(1) its position with reference to the sun; (2)
the moderate inclination of its axis.
Owing to its distance from the sun, and the
consequent moderate intensity of its heat and cold,
as well as the medium length of its year, the earth
occupies a most favored situation in the Solar Sys-
tem. We are not so near to the sun as to be,









ro MAGNETISM OF THE EARTH.


like Mercury, exposed to destructive heat; nor are
we so remote as to encounter unendurable cold.
The nearer planets must be too hot; the more dis-
tant quite too cold for human habitation.
Again ; the length of our year and the dura-
tion of its seasons are admirably suited to human
needs. Supposing Mercury, Jupiter and Neptune
to have four seasons as we have, it is obvious that
they would be entirely unsuited to be the resi-
dence of beings like ourselves. The seasons of
Mercury would be about three of our weeks in
length; those of Jupiter, three of our years ; while
on the planet Neptune a single season would be
forty earthly years in duration.
Owing, moreover, to the moderate inclination of its axis,
the earth has polar regions of restricted extent. The vast
proportion of its surface is habitable for man.
It is obvious [ see cut, p. 9 ] that what we call the polar
regions of each planet are of greater or less extent in pro-
portion to the amount of inclination of the planetary axis.
The inclination of the axis of Venus is believed to be 75.
Consequently its polar regions will extend 75 from either
pole. Nearly the whole surface of the planet, therefore,
must have only two seasons ; one of intense heat, the other
of equally intense cold.

TOPICAL ANALYSIS.

IT. PLANETARY MOVEMIENTS.

1. Effects of the Earth's Motions.
Influence upon the needs of man.
2. Rotation of Planets.
Direction. Relation of velocity of rotation to dis-
tance from sun.
3. Revolution.
Direction of the motion. Relation of velocity of
revolution to distance from sun. Illustrations.
4. Inclination of Planetary Axes.
Unchanging amount and direction of the inclina-
tion. Results in change of seasons. In varying
length of day and night. Equinoxes and sol-
stices.
5. Adaptation of the Earth for human habitation.
Two causes of this adaptation. Seasons of the
other planets.

TEST QUESTIONS.-If the inclination of the earth's axis were increased,
how would that affect our seasons? now, if the inclination were dimin-
ished ? Where are the sun's rays vertical when we have our longest
day? Where are they vertical when the days and nights are equal ?


III. MAGNETISM OF THE EARTH.

1. Howv demonstrated.-Among the prop-
erties which belong to the earth as a whole, is
its Magnetism. An understanding of this subject
is best reached by noticing the phenomena of those
bodies which we call Magnets, and then comparing
with these phenomena, certain ones which are ex-


hibited by the earth. The result will demonstrate
that the earth is a magnet.

2. Magnets.-Magnets are either natural or
artificial. The properties exhibited by both are
identical.
NATURAL MAGNETS are pieces of a kind of
iron ore commonly called the loadstone. This
ore was first found near a city of Asia Minor called
Magnesia; and hence the magnet received its name.
ARTIFICIAL MAGNETS are readily made by rub-
bing a piece of tempered steel upon a natural
magnet, or upon a bar of steel already magnetized,
or by the employment of currents of electricity.
According to their shape and size artificial magnets
are called bar magnets, horseshoe magnets, or mag-
netic needles. The last are such as are employed
in compasses.

3. The Properties of the Magnet are
among the most extraordinary of material phenom-
ena. They are closely akin to those of electricity.
MAGNETS ATTRACT pieces of iron and steel. They
also attract other magnets. This action will occur,
even though the magnet and the body attracted
are at a considerable distance from each other, or
even if some substance, like glass, intervene be-
tween the two.
MAGNETS HAVE POLES.-If a magnet be sus-
pended so as to be free to move, one end of it points
invariably to the north, the other to the south.
The two ends are, therefore, called the north pole
and south pole of the magnet.
If now we bring two magnets near one another,
a very singular effect is produced. The north pole
of the one is attracted toward the south pole of the
other; the south pole of the one is drawn toward
the north pole of the other. But if the north pole
of the one be presented to the north pole of the
other, they repel one another. The north pole of
the one that is free to move swings away. In like
manner, if the two south poles be placed near one
another, they mutually repel.
Thus we see : (1) that the magnetic forces at the
opposite poles are opposite in certain respects; and
(2) that like poles repel, unlike attract.
NEUTRAL LINE.-About half-way between the
north and south poles there is a neutral line, ex-
tending across the magnet. Along this line the
opposite magnetic forces neutralize each other.

If a piece of iron, or a magnetic needle, be suspended ex-
actly over this line, it will not be attracted at all. On either
side of it, however, a suspended needle is drawn toward one
or the other of the poles. The exact position of the neutral
line depends on the relative strength of the poles. As these
are seldom if ever of equal strength, the neutral line will
rarely or never be equidistant from both.








MAGNETISM OF THE EARTH. I


4. The Earth a M]agnet.-In some very
important respects the earth behaves like a magnet.
ATTRACTIVE PowEn.-In the first place it dis-
plays attractive power -r...;-. 1 similar to that of
the magnet. It is terrestrial magnetism which
causes magnets to point northward when suspended.

MAGNETIC PoLEs.-Secondly, like the magnet
the earth has magnetic poles. These are not ex-
actly at the north and south geographical poles,
but at some distance from them. They are the
points at which the needle stands vertical. The
north magnetic pole is in North America. It is
situated in Boothia, latitude 70 north, longitude
97 west. The discovery of this pole was made
by Sir James Ross in 1830.
The position of the south magnetic pole has not been so
accurately determined. Sir James Ross reached a point in
the Antarctic Ocean where the inclination was 88 37', from
which its situation has been computed. It is not, however,
diametrically opposite the north magnetic pole, but far to
one side. It lies in the vicinity of lat. 75 S., long. 134 E.
The position of both these poles is constantly changing.

'NEUTRAL LirNE.-Thirdly, the earth, like a mag-
net, has a neutral line. This line encircles the
globe about midway between the north and south
magnetic poles. Along it the opposite polar forces
counteract each other. It is called the ... '.
equator. Its course is traced upon the chart.

5. Inclination or Dip of the Needle.-
As you go northward from the magnetic equator,
the north end of the needle is drawn downward
from a horizontal position until you reach the mag-
netic pole, and there the needle, as already said,
points vertically. As you go southward from the
magnetic equator, the south pole, in like manner,
is drawn down, until at the south magnetic pole
the needle would again become vertical.
The amount of deviation from the horizontal
position is called the Inclination or Dip of the
needle. Only upon the magnetic equator or neu-
tral line is there no dip.

6. Declination of the Needle.-While
magnets free to move assume a north and south
direction, they do not point exactly to the true
geographical north, but a little to the west or the
east of it. The deviation from the true northerly
position is called the declination of the needle.
Declination differs in different places, both in
direction and amount.
The direction in some places is east, in others west. It
will be seen from the map that over about one half of the
globe it is easterly, over the other half, westerly. The
amount of declination is greater in some places than others.
In Liverpool, Edinburgh and Glasgow, it is about two de-
grees greater than at London.


VARIATIONs.-The intensity and position of the
forces which cause the needle to deviate from the
true north and south direction are constantly
changing. Hence there arise, (1) secular varia-
tions ; (2) diurnal variations.
Secular Variations extend over long periods. The decli-
nation at London waseast in 1580, and amounted to 11 36';
in 1663 it was zero ; in 1818 it attained its maximum, 24
41', and was west. In 1877 it had decreased to 19' 3' west.
It is therefore decreasing at the rate of about 5'annually;
so that in 200 years it will probably be east again.
In diurnal variations the needle moves from east to west,
from 8 A.M. till noon, and back again in the afternoon. In
Washington City the variation is about 14'.

LINE OF NO VARIATION.*-Just as there is a
magnetic equator along which there is no dip or
horizontal deviation, so there are lines on which
there is no declination. Such lines are commonly
known as '' lines of no variation." t
There are two such lines, one in the eastern
hemisphere, and one in the western. Their posi-
tion is constantly changing. In the time of Co-
Iambus the western line was about 20 west of the
Azores. It now passes through the West Indies.

7. magnetic Storms.-Unusual and violent
fluctuations of the needle indicate the prevalence
of magnetic storms. Such storms take place dur-
ing displays of lightning, but more particularly
during the occurrence of the Aurora Boroalis. One
of the most violent on record occurred N.. il" r.
17th, 1882. It prevailed throughout the United
'Si I.-, and even extended to Europe. ('1, .,.
seems to have been the focus of the disturbance.
Here operating keys were in some cases melted.
Telegraphic communication was practically sus-
pended throughout the country, and even the
ocean telegraphs were disabled for many hours.

8. Sn.-Spots and Terrestrial J1a{-
netism,.-It is believed that there is a relation
between the spots observed upon the sun and the
magnetism of the earth.
The sun-spots are periodical, both as to number and fre-
quency. They attain their maxima and minima in from
ten to twelve years. The magnetism of time earth seems to
follow the same law of variation, Auroras and magnetic
disturbances appear to be most frequent when the sun-
spots are most numerous. IHence it is argued that some in-
timate relation probably exists between these phenomena.

The interest attaching to this line is great. Spain and Portugal
quarreled about the possession of the lands discovered by their navi-
gators in the l5th century. The pope dir( eted that I lhe "line of no varia-
tion" should be the boundary between them. All landsdiscoveredto the
eastward of this line were to belong to Portugal, ill to the westward to
Spain. Spain was determined to possess herself of some of the East
India Spice islands, but she could claim them rinly by making it appear
that they were to the westward of the 20th meridian. Hence Magellan
proposed, in the interest of the King of Spain, to reach the Moluccas by
sailing westward. lHis voyage resulted in the circumnavigation of the
globe, t Variation here means declination.





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1n"rJH1 .:M.rL. 1.UlM~ i j ~ <,M *~ /i. f;, ,L


lr-,m- ,,.g AN k.









INTERNAL HEAT OF THE EARTH.


NOTE UPON THE MAP.-The buff color indicates easterly dec-
lination, the blue westerly. The lines which diverge from
the magnetic poles have numbers affixed to them which show
the amount of declination. A curious oval is observed upon
the buff space. It embraces part of China and the Japanese
Islands. Within its limits the declination is abnormal. It
is westerly. From this it is inferred that there probably
exists another, though subordinate, north magnetic pole in
Northern Asia.



9. Causes of Terrestrial Magnetism.
-If a current of electricity is made to pass round a
piece of soft iron, the latter acquires magnetic prop-
erties, and retains them so long as the current
lasts. If vast currents of electricity passed round
and round the earth, they would convert it into a
gigantic magnet. This, it is believed, actually
occurs.
The sun's rays, resting successively on different
portions of the earth's surface as it rotates, pro-
duce thermo-electric currents ; i.e. electric currents
produced by heat. These follow the apparent
course of the sunlight from east to west round the
globe, and convert the earth into a magnet.
The above-noted relation between magnetism
and sun-spots seems to corroborate this theory.

10. Uses of Terrestrial Magnetism.-
It might seem that the magnetism of the earth is
only a curious and interesting fact. But its bear-
ing upon the welfare of the human family is mar-
vellous. To it we owe the compass, and to the
compass the possibility of modern navigation.
Without his magnetic needle ever pointing north-
ward, how could the mariner find a pathway
over the trackless waters, and steer unerringly for
"the haven where he would be ?"


TOPICAL ANALYSIS.

III. MAGNETISM OF THE EARTH.

1. How demonstrated.
2. Magnets.
Natural. Origin of name. Artificial. Modes of
making. Kinds.


3. Properties of the Magnet.
Attraction. Magnetic Poles.
traction. Neutral line.


Law of magnetic at-


4. The Earth a Magnet.
Attractive power. Magnetic Poles. Neutral line.
5. Inclination or Dip of the Needle.
Effect upon the needle of approaching the magnetic
pole.
6. Declination of the Needle.
Definition. Variations in declination. Secular.
Diurnal. Line of no variation.


7. Magnetic Storms.
Indications. Times of occurrence.
8. Sun-spots and Terrestrial Magnetism.
Supposed relation between.
9. Cause of Terrestrial Magnetism.
Influence of electric currents.
10. Uses of Terrestrial Magnetism.

NOTE.-In connection with this subject the teacher might advert to
the disturbing effects of iron vessels upon compasses ; the less of
vessels from this cause, and the means adopted to counteract the attrac-
tion of the iron used in the construction of vessels.


IV. INTERNAL HEAT OF THE EARTH.

1. Evidences of Internal leat.-While
the crust of the earth is generally of a moderate
temperature, there are various reasons for believing
that its interior is in a state of intense heat. Three
sources of proof may be mentioned : (1) mines;
(2) hot springs, geysers, and artesian wells; (3)
volcanoes.
MINES.-As we descend through mines into the
interior of the earth, we find the temperature to
increase at the rate of about 1 Fahrenheit
for every 50 feet of perpendicular descent. In very
deep mines it is impossible for miners to exist with-
out a constant current of fresh air to reduce the
temperature. A limit is soon reached, beyond
which, owing to the increase of heat, mining is
impracticable.
The greatest depths at which miners have found
it possible to work are about 2,500 feet below the
surface.
In the Consolidated Virginia and California Mine in Vir-
ginia City, which has a depth of 2,000 feet, the temperature
is 115 Fahrenheit. The miners are divided into gangs,
each gang working twenty minutes and resting forty. They
drink ice water freely, and apply ice to their wrists to cool
the circulation.
At Monderf, in Luxemburg, a mine has been sunk to the
depth of 2,920 feet, and one at New Salzwerk, in Prussia,
is 2,280 feet deep.
ARTESIAN WELLS bear testimony to the same
rapid increase of heat. These have been sunk in
various parts of Europe and America to a depth
varying from 1,000 to 4,000 feet.
In Europe the average increase of temperature
is 1 Fahrenheit for about 55 feet ; in America,
1 for about 70 feet. The temperature of the well
at Grenelle, near Paris, is 81.7 Fahrenheit. Its
depth is 1,798 feet. That at Buda-P.esth is 3,160
feet deep. Its temperature is 178 Fahrenheit.
It supplies a large part of the city with warm
water.
Experience shows that by boring artesian wells,
jets of warm water may be obtained in almost every
region of the earth.








INTERNAL HEAT OF THE EARTH.


IHOT SPRINGS are found in countless numbers in occur. There are certain premonitions when these are
various parts of the world. They arc most abun- about to take place. At intervals of a few hours under-
dant in volcanic regions; but they are not con- ground rumblings are heard : the water in the basin boils
furiously, and jets of hot water with clouds of steam are
fined to the vicinity of volcanoes. Those of Bath, thrown up to the height of several feet.
in England, arc more than 1,000 miles from either Several of these intermittent discharges occur, and then
Etna or Vesuvius. 31..r than 1,500 exist in succeeds a grand eruption. With a rumbling that shakes the
Europe. The cut below shows those of St. Michael, ground, a huge column of boiling water 150 or 200 feet high
one of the Azores. is forced up into the air with loud explosions and amid
clouds of steam. The basin and pipe are thus emptied of
... '-, water. But at once they begin to fill up, only to be emptied
again by another grand explosion.


BOILING SPRINGS OF ST. MICHAEL (AZORES).


The temperature of these springs seems to indi-
cate that everywhere, not far below the surface of
the ground, some source of high heat exists. The
Arkansas hot springs vary from 110 to 150 Fah-
renheit. One of those in Iceland is 49 above the
boiling point.
GEYSERS are intermittent hot springs. The
temperature of their waters rapidly rises with
every few feet of descent. The surface water of
the Great Geyser of Iceland Bunsen found to have
an average temperature of about 180. At the
depth of 72 feet the temperature was upwards of
250. This high temperature is probably due to
the same causes as produce the heat of volcanoes.
Geysers occur in volcanic regions, and within
limited areas. The most noted are those of Ice-
land, the Yellowstone National Park, and New
Zealand.
The region wheie they are chiefly found in Iceland is
about two miles square. Within this space are nearly one
hundred openings or geyser mouths piercing the ground.
Description. -The mouths of geysers are surrounded with
rims of variously colored incrustations. These rims vary
in size from a few inches to many feet in diameter. That
of the Great Geyser is fifteen feet in height, and fifty-six
feet in diameter. In the centre of this monstrous basin is a
pipe or funnel eight feet wide. Out of this funnel boil-
ing water constantly issues. Eruptive discharges also


Of the Yellowstone Geysers an observer says :
Of all the geysers whose eruptions we witnessed, the
Grand was, I think, the most interesting. It played each
evening at a regular hour. Suddenly, with a single prefa-
tory spurt, it shot a vast stream of water over two hundred
feet into the air. This was maintained for a few minutes
with unabated vigor; then it suddenly ceased, and the
waters shrank back out of sight into the cavernous hollow
below. Meanwhile subterranean thunder shook the ground.
After a minute's cessation, the geyser again burst forth with
even greater violence. This continued until nine successive
pulsations had occurred.

VOLCANOES are the most striking of all mani-
festations of the earth's internal heat. They are
so important that they will be considered in de-
tail in a subsequent lesson. Here, however, it is
proper to observe what strong confirmation they
afford to the theory of central heat. Streams of
lava, white-hot, like molten iron, issue through their
craters from the interior of the earth.

2. Condition of the Interior of the
Eardth.-The phenomena above noticed have sug-
gested the conclusion that the interior of the earth
is in a fluid condition, and that, consequently, only
to the depth of about thirty or forty miles is the
crust of the earth solid.
It is argued that if the heat goes on increasing
as the centre of the earth is approached, at the
same rate as it does in mines, then at a comparatively
shallow depth even the most refractory substances
must necessarily be in a state of fusion.
Many philosophers, however, doubt the fluidity
of the central mass, and admit the existence of only
local seas and lakes of molten rock. They contend
that, instead of being fluid, the interior of the
earth, though intensely hot, is pasty, or even solid.

In justification of this view they argue that the enormous
pressure exerted upon the interior of the earth would nullify
the effect of its internal heat, because, if a substance is sub-
jected to pressure, it cannot melt as readily as under ordinary
circumstances. A body, therefore, may remain solid at a
very high temperature, if it be under pressure. Of course,
the condition of the successive layers that constitute the
substance of the earth is, that while they are subjected to a
heat which increases enormously as the centre is approached,
they are at the same time subjected to a pressure which also
increases enormously as the centre is approached.








VOLCANOES.


Whether, however, we adopt the view that the central
mass is fluid or solid, it does not affect the conclusion that
it is in an intensely heated condition.

TOPICAL ANALYSIS.
IV. INTERNAL HEAT OF THE EARTH.

1. Evidences of Internal Heat.
Mines. Increase of heat with depth. MIeans of
mitigating the heat. Depth of mines.
Artesian Wells. Depth reached. Increase of tem-
perature with depth. Distribution of such wells.
Hot Springs. Number and distribution. Tempera-
ture.
Geysers. Location. Most noted geysers. Geyser
basins. Action of the geyser. Geysers of the
Yellowstone.
Volcanoes. How they indicate internal heat.
2. Condition of the Interior of the Earth.
Two views held. Arguments in favor of them.
General conclusion.

TEST QUESTIONs.-Why can miners not work deeper below the sur-
face than about 2,500 feet ? Why should artesian wells be colder thau
mines, at the same depth? Why are rims formed round geyser basins?
What force is it that drives out the water to such a height? What do
we infer from the existence of geysers in any region ?


V. VOLCANOES.

1. A J7olcanto is usually a mound, hill, or
mountain, formed of materials thrown up from
the interior of the earth. Its most important
feature is the crater, a depression or hollow,
shaped, as the name implies, like a vast bowl or
basin. It is either upon the summit or upon the
slopes of the volcanic mountain. Through a hole,
or holes, in the bottom or the sides of the crater,
the materials ejected find their way.
Example.-The crater of Kilauea, in Hawaii, is one of the
most remarkable in the world. It is a vast oval basin about
1,000 feet deep, one mile wide, and three in length. Its
floor is partly occupied by two lakes of molten matter in a
state of violent ebullition. Fiery jets are sometimes thrown
from the surface to the height of seventy feet.

2. Formation of a Volcano.-At the be-
ginning of its existence, a volcano is simply a hole
in the crust of the earth. Materials are ejected.
These naturally fall around the sides of the vent,
and form a circular mound. Successive eruptions
occur. The mound becomes larger and loftier with
each eruption, until in the course of centuries a
mountain is formed. The vent remains low while
the matter ejected is thus built up about it, and in
this way the crater assumes its basin-like shape.
RAPIDITY.-The process of formation is some-
times very rapid. Jorullo, in Mexico, was thrown
up in a single night to thle height of 1,695 feet
above the plain in which it stands. MouiL, Nuovo,


a volcanic hill near Naples, was formed ij' hlie
course of a few days.
SUBMARINE VOLCANOES.-The formation of a
volcano may begin at considerable depths below the
level of the sea. -In proof of this it may be said
that vast numbers of oceanic islands owe their ex-
istence to volcanic action, and recent deep-sea
soundings show that many of the deepest parts of
the ocean are covered with volcanic debris.
In 1881 a mass of matter rose from lihe sea near the coast
of Sicily, and attained in a few weeks the height of 170 feeA
above the water. It was named Graham Island. In a few
months it disappeared, because the materials composing it
were so loosely held together. If the matter ejected by sub-
marine volcanoes is compact, a permanent island is formed.
In the year 1790 a volume of steam was seen to arise from
the sea about thirty miles north of Unalaska, one of the
Aleutian Islands. E I. i-i I.1m, ik, ; I.-: gradually accumulated.
The mass grew higher and higher, until now it is several
thousand feet above the sea level, and has a circumference
of two or three miles.


5


COTOPAXI.


THE FORIt OF VOLCANIC MOUNTAINS is gener-
ally more or less conical. If the materials ejected
are in a fluid state, the elevation is comparatively
small. The volcanoes of the Sandwich Islands
present the form of exceedingly flattened cones.
This is because the matter which they emit is very
liquid. When the materials are less fluid, the
slopes are steeper, and the form of the mountain
approaches that of a pointed cone.
A notable example is Cotopaxi. It is the most
symmetrical of volcanoes.
THE HEIGHT or VOLCANOES.-The highest vol-
cano in the Old World is Klintchevskaia, in Kanit-
chatka. It is 16,512 feet high. There are sonte
in South America higher than this. Several among
the Andes have an altitude of more thIan 20,000
feet.

3. The inate'ifals ejected, from volcanoes








VOLCANOES.


are steam, gases, mud, lava, or molten rock, stones,
ashes, sand, and dust.
LAVA is a mixture of various rocky substances.
The most important of its elements is silica, which
is familiar to us in the forms of white sand, quartz,
and flint. Issuing from the volcano lava closely
resembles the slag of a smelting furnace.
Formation of Lava.-It may be asked how we account
for its fluid condition, if we suppose that the materials in
the interior of the earth, though intensely hot, are still
solid. The explanation is, that these solid but intensely
heated materials, on being driven upward, are relieved from
pressure, and assume the fluid state, even before reaching
the surface.
When steam bubbles are imprisoned in molten
lava in the act of cooling, the lava is converted
into a light porous mass, which is the well-known
substance called umnice.
Often the lava is completely reduced to powder,
and it is then called volcanic ashes, or, if coarser,
volcanic sand. Sometimes the wind blows the
molten lava into delicate fibres like those of spun
glass.* The Sandwich Islanders gave the name of
"Pele's Hair" to this substance, Pele being the
name of the goddess of the volcano of Kilauea.


VOLCANO OF SANTORINI (in Grecian Archipelago, active in 1866).

4. Quantity of ]latter E-jected.-The
quantity of lava and other matter emitted by vol-
canoes is immense. The lava that issued from
Hiecla in 1783 was computed by Sir Charles Lyell
to be equal in volume to the water discharged by
the Mississippi in three months.


In the eruption of Vesuvius, A.D. 79, the mat-
ter vomited forth far exceeded the entire bulk
of the mountain ; while in 1660 Etna disgorged
twenty times its own mass.
In 1878 such quantities of pumice were thrown
out of the volcanoes of the Solomon Isles into the
surrounding sea that it took ships three days to
force their way through them. Sometimes one
may even walk upon t'ie floating pumice as upon
a vast raft.

5. Volcanoes Classified.-Volcanoes may
be classified as active, dormant, or extinct. Active
volcanoes ejectvarious substances. When no signs
of activity are given for a considerable time, the
volcano is said to be dormant. When a volcano
has been dormant for centuries, and it seems prob-
able that its activity is lost forever, it is said to be
extinct.
The frequency of volcanic discharges is varied.
Some volcanoes are continuously active. Stromboli
has been for 2,000 years in a state of constant, but
not dangerous activity. It is visible at night to a
distance of more than 100 miles all round. A red
glow is seen from time to time above the summit
of the mountain. This becomes gradually more
and more brilliant, and then as gradually dies away.
It is this phenomenon which has given to Strom-
bolif the name, "Lighthouse of the Mediterra-
nean. "
On the other hand, Cotopaxi and Tunguragua
in the Andes have had eruptions only once in 100
years.
Vesuvius exhibits great irregularity. It had been long
dormant before the eruption of A.D. 79. Its crater was
nearly filled up, and was occupied by an abundant forest-
growth. Cities and villages graced its slopes. After this
eruption, none of great moment occurred until 1631. At
that time, one of the most destructive on record took place.
It continued for three months, and destroyed a number of
cities and villages. The last eruption occurred in 1872.
From these and similar facts, it is evident that we have
no knowledge of any law which governs the frequency of
volcanic eruptions.

6. Eruptions.-There is no definite order in
which the phenomena of an eruption succeed one
another. They are usually preceded by subterra-
nean rumblings and tremors. Before the great
eruption of 1872, Vesuvius gave indications of un-
usual activity for a whole year. In many cases,
however, the eruption follows the warning imme-
diately. An eye-witness, writing of Stromboli,
says that he had observed numerous light, curling
wreaths of vapor ascending from the crater; then


A similar substance is artificially produced by directing a blast of -I This fire, it should be observed, is really the reflcclion upon the
air or steam into the slag of a smelting furnace. It is known in corn- vapor-cloud from the seething surface of the red-hot lava within the
merce as mineral wool. crater.








VOLCANOES.


suddenly, without the slightest warning, a sound
was heard like that of a locomotive giving off
steam ; and the eruption at once occurred.
IEMISSION OF STEA-M.-In general, after the pre-
liminary rumblings and tremors, dense columns
and globular masses of watery vapor mingled with
a variety of gaseous substances issue from the
crater. According to the state of the atmosphere,
and the existence of winds and air currents, the
vapor assumes a variety of forms.
In the case of Mount Vesuvius it not unfre-
quently expands after attaining a certain height,
and becomes like a vast "umbrella," as the Ital-
ians call it, having a top many miles in circumfer-
ence. The lurid glare of the boiling lava in the
crater below is reflected upon the under-surface of


tricity. A machine has been constructed to generate elec
tricityin this way. From it torrents of sparks as much as
fourteen inches in length have been obtained. The crater,
with its immense volume of uprising vapor, may be compared
to a gigantic machine of this description.

EnISSION OF SOLID MATERIALS.-Often with the
vapor are mingled immense quantities of volcanic
ashes and sand, which descend and cover the sur-
rounding country, sometimes to the depth of many
feet.
Eighteen hundred years ago (A.D. 79), the cities
of Herculaneum and Pompeii in Italy were cov-
ered with a deluge of ashes from an eruption of
Vesuvius. They were buried from 70 to 120 feet,
and lost to view for nearly seventeen centuries. In
1711, a well-digger turned up a bit of statuary,


VESUVIUS IN ERUPTION, AS SEEN FROM NAPLES, APRIL 26, 1872.


the umbrella, and gives the appearance of a vast
conflagration. This spectacle is indescribably im-
pressive at night. During the eruption of Vesu-
vius in 1872, instantaneous photographs were
obtained of the umbrella. The above cut is a copy
of one. From this, recollecting that Vesuvius is
4,000 feet high, we see that the vapor rose to the
height of 20,000 feet, or nearly four miles.
The vapor emitted, being condensed, falls as rain.
The rainfall is excessive and long continued, and
often gives rise to destructive floods. Around the
vapory column vivid lightning constantly plays.


which led to the discovery of the two cities. The
work of exhuming them is still going on.
The distance to which the ashes of a volcano may be car-
ried is almost incredible. In 1845, the ashes of Heela were
carried to the Orkney Islands, a distance of nearly 700 miles,
and in 1813, those of Tomboro, in the island of Sumbawa,
fell at Bencoolen, 1,100 miles away.
Rocks and stones are sometimes vomited forth
with fearful noise, and hurled with prodigious
force. A mass of rock, measuring 300 cubic feet,
was on one occasion thrown from Cotopaxi to a
distance of about eight miles.


Jets of steam under high pressure, if allowed to issue from THE EMISSION OF rLAVA in the toolten state is the
an orifice, give rise, in doing so, to large quantities of delec- most imposing of volcanic phenonmena. The ac-








l8 VOLCANOES.


tion which goes on has been compared to that which
occurs in a pot of boiling porridge.
Explanation.-As the mass of porridge gets hot, steam is
generated in it at the bottom. This rises through the por-
ridge. In doing so it forces a portion upward. More and
more steam being generated, bubbles of porridge rise to the
surface, and mimic explosions occur, or the porridge is
thrown in little jets above the surface of the boiling mate-
rial. The process may increase in violence until the phe-
nomenon of boiling-over takes place. Quite similarly the
boiling lava is forced upward higher and higher in its crater
by vast volumes of steam that are seeking to escape. Ex-
plosions occur on the boiling surface, and often jets are
thrown far up into the air.
Finally, the rising lava overflows the rim of the crater, or
quite as often bursts through the sides of the mountain, and
pours down its slopes in rivers of fire.
So numerous were the fissures which rent Vesuvius in the
eruption of 1872 that liquid lava seemed to ooze from every
portion of it, and, as an eyewitness expressed it, "Vesuvius
sweated fire."
LAYA STREAMS vary in magnitude. The larg-
est recorded were those of Skaptar Jikul, in Ice-
land, in the years 1783-5. Torrents of molten
rock deluged the island. River-courses, ravines,
and lakes were filled, and the surface of the coun-
try for hundreds of square miles was completely
devastated. Some of the streams were about fifty
miles in length, and in certain places fifteen miles
in breadth, and 100 feet deep. In some of the
narrow valleys the depth was 600 feet.
The velocity of the streams, and the distance to
which they reach, depend on the fluidity of the
lava, and the slope of the land. One thousand
feet per hour is a rapid rate ; the extreme of
ten thousand feet per hour has been observed,
though rarely.
The retention of its heat by a lava-stream is very
remarkable. When the surface of the stream has
cooled, it becomes a hard crust which prevents the
escape of the heat.
A mass of lava 500 feet thick, ejected from Jorullo in 1759,
was seen smoking by Alexander von Humboldt forty-five
years after. The Indians lit cigars at its crevices. The lava
thrown from Vesuvius in 1858 continued as late as 1873 to
give out steam, and remained so hot that one's hand could
not be held in some of the fissures for more than a few
seconds.
END Or ERUPrIoN.-The flow of the lava is the
beginning of the end, After its occurrence the
showers of ashes gradually cease, the explosions
become less and less frequent, and at length no
evidence of volcanic activity remains, save perhaps
a vapor-cloud veiling the summit of the mountain.

r. Distribution of Volcanoes.- Two
significant facts are to be observed regarding the
distribution of volcanoes.
First : the active volcanoes of the globe are, as a


rule, situated upon areas which are undergoing
upheaval. Those portions of the surface of the
earth which are subsiding are without volcanic
activity.
Second : almost all volcanoes are near the sea.
Those upon the continents are close to the shores.
The only well-authenticated examples of volca-
noes situated far inland, are the active volcanoes of
Boschan and Turfan, or Hot-Schen, and the Sol-
fatara of Urumtsi, all in Central Asia.
The most striking exemplification of this law of volcanic
distribution is presented by the Pacific Ocean. It is literally
encircled with active volcanoes.
THE GREAT VoLCANic BELTs.-There are three
great belts traversing the globe, within which
nearly all the volcanoes of the world are situated.
These may be called the Pacific Insular Belt, the
Atlantic Insular Belt, and the American Conti-
nental Belt. [See map on opposite page.]
The Pacific Insular Belt extends all along the
northern and western shores of the Pacific Ocean.
Beginning with the Aleutian Islands it embraces
Kamtchatka, the Kurile, Japanese and Philippine
Islands, Sumatra, Java, New Guinea, the Friendly
Islands, and New Zealand.
One extension of this belt embraces the Society, Marquesas
and Sandwich Islands ; another is the volcanic region of
Victoria Land.
The Atlantic Insular Belt comprises extinct and
active volcanoes and volcanic islands which trav-
erse the Atlantic from north to south. The Isl-
ands of Jan Mayen, Iceland, the Azores, Cape
Verd Islands, St. Helena, and Tristan d'Acunha,
are points which mark this volcanic band.
The American Continental Belt.-The third
great volcanic belt is continental. It extends from
Cape Horn in South America, to Alaska in North
America, a distance of more than 10,000 miles.
All along this line volcanoes, singly or in groups,
are found. An outlying spur of it includes the
West Indies.
A minor, yet very important volcanic belt is that of the
Mediterranean region. It comprises Etna, Vesuvius,
Stromboli, and Vulcano in the Lipari Islands, and Santorini
and Nisyros in the .Egean Sea.
Outside of the three great belts there are many
volcanoes irregularly distributed. In the Pacific
all islands not of coral origin are composed of vol,
canic rocks. In the Indian Ocean there are vol-
canoes upon Madagascar and the adjacent islands.
In Central France, in Spain, and generally
throughout Europe, there are numberless proofs
of volcanic action. Africa contains about ten
active volcanoes. The most remarkable for
the irregularity of their situation are those in
Central Asia already mentioned.
































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VOLCANOES.


THE NUMBER OF ACTIVE VOLCANOES on the sur-
face of the globe is estimated at from 300 to 350.
Of dormant and extinct about 700 are reckoned.

8. The iost active Volcanic Region in
the world, at present, consists of the islands in the
Malay Archipelago. Java is the centre of it. No
region is so thickly studded with burning moun-
tains as this island. It has twenty-one volcanic
cones.
In 1772 one of them was in violent eruption. Its immense
cone actually disappeared. It carried down with it ninety
square miles of land, and forty villages were swallowed up.
In 1815, Tomboro, on the island of Sumbawa, 300 miles
from Java, burst forth with such violence, that the explo-
sions were heard at the distance of 970 miles.

9. Causes of Volcanoes.-The fundamen-
tal cause of volcanic action is undoubtedly the ex-
pansive force of compressed steam and other gases.
Two cases are conceivable: (1) the compressed
steam and gases may be free, i. e. not blended
with the lava; or, (2) they may be imprisoned
within the substance of the lava. The force
developed will be the same in both these cases, but
the mode of action will be somewhat different. Let
us consider the first case.
ACTION OF FREE GASEs.-Bear in mind that at
a comparatively shallow depth the earth is intense-
ly hot. Then observe that water may readily find
its way through crevices or between the strata of
rocks, and come in contact with the heated mat-
ter.. The effect will be to convert a portion.of the
inflowing water into steam. This may be done
with great suddenness.
The same conditions will occur as those which
often cause the explosion of a steam boiler. The
water in the boiler gets low, the fire is kept up,
and the walls of the boiler become intensely heated.
If now there be a sudden influx of water, some of
it is converted into steam with such rapidity and
in such quantity that it cannot possibly escape.
The boiler is unable to resist the pressure, and an
explosion takes place.
Similarly the water that finds its way into the
intensely heated interior of the earth may be sud-
denly converted into steam. The expansive force
of the steam increases under the two influences of
enormous heat and enormous pressure.
Suppose the water to enter some subterranean cavity
partly filled with molten lava. Steam is suddenly gen-
erated and an explosion occurs. By the concussion, the fis-
sure which admitted the water is closed, and the remaining
water completely pent up. It is converted into steam.
Heavy pressure and intense heat give to it enormous expan-
sive power. We can imagine how such superheated steam
might drive upward lava, or stones and sand. It would act
on exactly the same principle as that of the compressed air
in the air-chamber of a force pump or a water-ram.


ACTION OF ABSORBED GASES.-The second case
in all probability occurs more commonly than the
first, and in fact, it seems-to contain the explana-
tion of nearly all the phenomena of volcanic erup-
tions. A number of substances, solid and liquid,
absorb, under pressure, and at high temperatures,
many times their own volume of steam and other
gases. If the temperature be reduced, or the
pressure be relieved, these gases can no longer be
retained in absorption. They escape with explosive
violence. Lava, intensely heated and under press-
ure, absorbs many times its volume of steam and
other gases. Imagine it thus charged to be forced
upward through the crust of the earth. Its capac-
ity for retaining gases in absorption is diminished.
The liberated gas expands and forces the lava in
whatever may be the direction of least resistance,
precisely as the volume of gases liberated from
gunpowder and similar substances expands and
forces obstacles before it with explosive violence.
Among other things this satisfactorily explains
the pulverization of lava and the production of
volcanic sand. The gases absorbed by the lava
being relieved from pressure blow it into atoms, as
wood is blown to pulp in a well known process for
making paper.
The above theory that volcanic action is mainly due to the
expansive force of steam derives confirmation from the fact
that volcanoes are in general situated close to the sea.

TOPICAL ANALYSIS.
V. VOLCANOES.

1. Description.
Principal feature. Crater of Kilauea.
2. Formation.
Mode. Rapidity of formation. Submarine vol-
canoes. Form of volcanic mountains. Height of
volcanoes.


3. Materials ejected.
Lava. Formation of.
and sand. Peie's hair.


Pumice. Volcanic ashes


4. Quantity of matter ejected.
Examples.
5. Volcanoes classified.
Frequency of discharge. Examples.
6. Eruptions.
Phenomena of. Appearance of flame, how pro-
duced. Cause of lightning. Emission of solid
materials. Emission of lava, how produced. Lava-
streams, magnitude and velocity of. Retention
of heat by. End of eruption.
7. Distribution of volcanoes.
In relation to change of level of sur-onnding area.
In relation to the sea. Great volcanic belts. Pacific
Insular. Atlantic Insular. American Continental.
Minor belt. irregularity of distribution. Num-
ber of active volcanoes. ,








EARTHQT


8. Most active volcanic region.
Situation.


9. Cause of volcanoes.
Conceivable cases. Action of free gases. Action of
absorbed gases.
TEST QUESTIONS.-In what way would you suppose the number of
active volcanoes to be changing, and why ? What volcano is nearest to
the place where you live ?


VI. EARTHQUAKES.

1. A n Earthquake is a shalkcing or trem-
bling of some part of the crust of the earth. It is
a vibratory or wave-like motion resembling the
ground-swell or roll of the sea. It may be nothing
more than a slight tremor like that made by a
loaded wagon passing along a street, or it may be
such a violent movement as to destroy whole cities.
Usually, at the commencement of an earthquake,
a rumbling noise, like distant thunder, deep down
below the surface of the earth, is heard travelling
along, as if in search of some weak place through
which to burst. Then suddenly, without any
warning, the ground rises and falls, houses rock
to and fro, until they are rent from top to bottom,
or fall with a crash into ruins. In some cases the
earth opens with gaping cracks which either close
again or are permanent. In a few seconds a city
may be demolished, and hundreds or thousands of
its inhabitants may be dead or dying.

THE OiIGIN of the vibratory motion or earth-
wave is called the centre or focus. It is not a
point, but a fissure or space between great masses
of rock. It is believed that it is rarely more than
thirty miles below the surface.
A


*-*
'' ,


Diagram illustrating the propagation of an earth-wave from F, the focus.
V is a point where the shock is vertical; A, a town where the shock is felt.
If we know A V, the distance between A and V, and the direction of the
shock at A, we can compute V F, the depth of the focus.

From the focus the earth-wave is propagated in
all directions. While, however, this is generally
true, it must be observed that the transmission of
the vibration will necessarily depend on the nature
of the materials encountered. In some directions,
perhaps in many, the earth-wave will meet with
such obstacles that it will rebound, and practically
be nullified, like a wave of water dashing against
a rock.

THE VELOCITY of the earth-wave appears to be,
on an average, about twenty-five miles a minute.
It may attain the enormous speed of five or six
thousand miles an hour.


(


JAKES. 2I


2. Duration of Earthquakes.-Earth-
luakes may be momentary ; or they may consist
)f several successive shocks; and these may bo
repeated during long periods. After the earth-
quake, which, in 1766, destroyed the city of Cu.
nana, in Venezuela, shocks were felt nearly every
iour for fourteen months.
In St. Thomas, after the earthquake of 1867,
and at Charleston, after that of 1886, shocks
were felt for many weeks.

3. Area, of Disturbauice. The area
throughh which the disturbance extends may be
very large. The shock of the earthquake of Lis-
bon, in 1755, was definitely felt as far as Finland
n one direction, and as far as Madeira in another.
[See map, page 19.]
The disturbance affected the sea to a much
greater distance. The water rose among the West
India Islands so that Antigua, Martinique, Guade-
loupe and Barbadoes were overflowed. The area
disturbed was four times as great as that of Europe.
In 1783, all the towns within a radius of twenty miles
from the town of Oppido, in Calabria, wore destroyed.
The great earthquake of Guadeloupe, in 1842, extended
through the distance of 3,000 miles in a direct line. and sen-
sibly affected an area of not less than 3,000,000 square miles.

IN SHAPE, the area of disturbance is commonly
an irregular oval.

4. The Sea- Waves which are caused by
earthquakes that have their centre under the
ocean bed, are appalling phenomena.
The water at first recedes from the beach, and
exposes the sea-bed even beyond the usual limits
of low water. Then the sea-wave comes in with
a steep front or wall sometimes more than fifty
feet high. It drives back the receding water,
and deluges the shore, sometimes demolishing
whole towns. It often passes inland to the dis-
tance of several miles. The inhabitants rush to
the hills, and remain there until the wave sub-
sides.

Examnples.-The great wave of the Lisbon earthquake was
sixty feet high at Cadiz. It rose and fell eighteen times at
Tangier, in Africa.
In 1854, when Simoda, in Japan, was destroyed by an
earthquake, the sea-wave completely overwhelmed the place.
The receding wave actually crossed the Pacific, and made
the water rise on the coast of California.
In 1746, the town of old Callao, in Peru, was destroyed by
an earthquake. A wave 80 feet high tore from her anchors
a Spanish man-of-war, lifted her over the houses, and carried
her several miles inland. The receding wave left her high
and dry on the road to Lima.
Sea-waves are often perceptible throughout an entire ocean
basin. They travel across tihe Pacific at the rate of about
350 miles an hour.








EARTHQUAKES.


If the centre of the earthquake is on land, so near the
coast as to disturb the sea, the waves produced are thrown
out from the shore and are harmless. This explains why,
although the Charleston earthquake was felt at sea as far as
the Bermudas, no wave-damage was done in the harbor of
Charleston.

5. Destr active effects.-Earthquakes are
perhaps the most impressive manifestations of
power in the material world. The destruction of
human life occasioned by them is appalling.
On the 1st of November, 1755, Lisbon was
shaken by the "great earthquake," and in six min-
utes its palaces were in ruins, and 60,000 of its
inhabitants were dead.
In March, ] 812, Caracas, in Venezuela, was de-
stroyed, with 10,000 of its inhabitants.

6. Uplheavals and Depressions.-Geo-
logical changes of great importance often accom-
pany earthquakes.
In the year 1819 an earthquake occurred in the
region adjacent to the mouth of the Indus. It
completely destroyed the town of Bhooj, and was
felt within a radius of hundreds of miles. A tract
to which the natives gave the name of "Allah
Bund," or "Mound of God," was raised where,
before, there had been a level plain. The "Band"
was fifty miles long, sixteen miles wide, and about
ten feet high. At the same time the fort and vil-
lage of Sindree, with the neighboring region, sub-
sided ; the sea flowed into the sunk area, and an
inland sea was formed covering 2,000 square miles.

't. Distribution of Earthhquaakes.-No
part of the earth is entirely free from earth-
quakes. In certain parts of Japan tremors are
felt every day. Vessels not infrequently report
earthquake shocks at sea.
In the OLD WORLD they are most frequent in a
region which embraces the northern shores of the
Mediterranean Sea, and extends eastward into the
central portions of Asia.
In the NEW WORLD earthquakes are far more
common than in the Old. Both the eastern and
western mountain regions of North America are
subject to them, but the region of greatest fre-
quency is in South America. It comprises Ecua-
dor, Peru, and Chili.
In many places within this region the houses are built of
reeds and bamboo, lashed by thongs of bull's hide, and se-
cured in their places with cords instead of nails, that they
may yield to the shocks without being shaken to pieces.
The natives can feel the approach of an earthquake long
before the stranger can. Suddenly, in the midst of gayety,
the author has heard the cryv, accompanied by shrieks,
"Trembler !" earthquakek. Tlihen a rushl for the streets.
Sometimes, when these alarms take place in the dead of
night, the whole population may be seen out in their night-
clothes, kneeling' an,1 praying in an agony of terror.


8. Causes of Earthquakes. -Various
causes have been assigned to account for earth-
quakes. Many have referred them to volcanic
action; but they are probably due for the most
part to what is known as displacement."
(1) By this is meant the sliding of vast masses
of rock one upon another. When the millstones
in a grist mill are in motion, the whole building
is in a state of vibration or tremor. The vibra-
tions are more or less violent according to the
size and number of the stones. And in like man-
ner the noise or rumbling produced will vary.
Now imagine that, from any cause, masses of rock
millions of times the size of the millstones should
slide or grind upon one another. Clearly rum-
blings and tremors would be occasioned. We can
imagine the tremors produced by the sliding of
vast rock masses to be so violent as to produce
the destructive effects of earthquakes.
But can any cause be conceived for the displace-
ment supposed ? It is believed that the cooling
and contraction of the interior of the earth ac-
count for it. The inner strata or layers of rock,
as they cool and contract, shrink away from the
outer layers. Then some portions of the outer
layers are left without support. They may now
bend or they may break. Having broken, they
may slide and grind upon the rocks that lie under-
neath. The effects of such sliding may be faintly
illustrated by the jarring and noise produced by
millstones in motion, or by a heavy body of snow
when it slides upon the roof of a large church.
If reference be made to page 28, it will appear that the
same causes which are believed to occasion earthquakes are
considered to have been at work in the formation of the
grand mountain systems of the earth. If this view be correct,
then where mountain-making goes on, earthquakes should
abound. And this has always been, and is the case.
(2) While thus displacement is the direct cause
of earthquakes in general, it is probable that cer-
tain earthquakes, which have been termed "ex-
plosive," are due to volcanic action, as their indi-
rect cause. These are of minor importance and
are local in their effects.

9. Relation of Eaithquakes to Vol-
eanoes.-A close relation exists between earth-
quakes and volcanoes. Displacements are the
direct cause of earthquakes, and they are condi-
tions which at least contribute to the production
of volcanic action. Hence it is that earthquakes
are most frequent in volcanic regions.
Moreover, aside from what is noted above in paragraph (2),
volcanic action may aid in the production of earthquakes
by removing matter from the interior of tlhe earth, and de-
positing it upon strata already under strain. This would
contribute to displaceinment andl so to eartihqutakes.








TOPICAL ANALYSIS FOR REVIEW.


TOPICAL ANALYSIS.

AETHIQUAKES.

1. Description.
Characteristic phenomena. Origin of vibrator
motion of earth-wave. Velocity of.

2. Duration.
Examples.

3. Area of Disturbance.
Examples.


4. Sea-Waves.
Description. Examples.
5. Effects.
Destruction of human life.
6. Upheavals and depressions.
Examples.
7. Distribution.
In general. In thle Old World. In the New.
8. Causes of Earthquakes.
9. Relation to Volcanoes.
As to locality, cause and time of occurrence.


TOPICAL ANALYSIS FOR REVIEW.


The Earth as a Planet. .







The Planetary Movements.


Magnetism of the Earth .


Internal Heat of the Earth .






Volcanoes . .









Earthquakes .


What is the Earth ? Ancient Theory. Copernican.
The Solar System. The Sun. Planets. Nebular Hypothesis.
Actual size of the Earth.
Comparative 1i. -ii_ .


Effects of the Earth's Motions.
Rotation.
Revolution.
Inclination of Planetary Axes. Results.
Adaptation of the Earth for Human Habitation.


Ilow Demonstrated.
Magnets. Natural. Artificial. Properties of the Magnet.
The Earth a Magnet.
Inclination of the Needle.
Declination of the Needle.
Magnetic Storms.
Sun Spots and Terrestrial Magnetism.
Cause of Terrestrial Magnetism. Uses of.


Evidences of. Mines. Artesian Wells, Hot Springs, Geysers, Volcanoes,
Condition of the Interior of the Earth.


Description of. Formation of. Rapidity. Form.
Materials Ejected. Kinds. Quantity.
Eruptions. Most Common Phenomena. Lava-streams.
Distribution of Volcanoes. Two Laws. Volcanic Belts.
Most Active Region.
Causes of Volcanoes. Action of Gases.


Description. Duration of Earthquake.
Area of Disturbance.
Sea Waves.
Destructive Effects.
Upheavals and Depressions. Distribution of Earthquakes.
Causes of Earthquakes. Relation to Volcanoes.


VI. E









JjESTEPN HEMISPHERE


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PART II.


THE LAND.


I. ARRANGEIEMENT OF LAND MASSES.

1. Relations of land, water and air.
-In the preceding pages we have regarded the
Earth as a whole. In those which are to follow
we shall consider (1) the various constituents of
the earth, viz., the land, the water, and the air;
(2) the phenomena which belong to each of these;
and (3) the life which they support.
The land, the water, and the air are to be con-
sidered as parts of a grand and most perfect mech-
anism. They contribute in a variety of ways to
the maintenance of plant and animal life.
Without a knowledge of Physical Geography we look
upon the earth and its diverse agencies, as the young appren-
tice may be supposed, when he first enters the machine-shop,
to look at the various parts of the steam engine which he
sees there lying about, but ready to be put together. There
they are, all the different parts, fly-wheel and crank, piston,
valve and ratchet, steam-chest and boiler. Though they
have so little resemblance to each other, and look so little
like a compact and powerful machine, yet, when he comes
to see them put together, to have the fires lighted, steam
raised, and the engine started, he discovers at once that
each part is made to fit into another and work with its fel-
low; that the whole is according to design, and that every
piece has a special office to fulfil, failing in which the whole
machine would be thrown into confusion. So it is, as the
study of our science will show, with the terrestrial machin-
ery.
2. Distribution of Land.-Of the 197,-
000,000 of square miles which embrace the surface
of the earth, about 144,000,000 are covered by
water, and 53,000,000 by land. In other words,
there is nearly three times as much water as land.
The land is found in masses of irregular shape
and size, which are separated by intervening por-
tions of water. The six largest land-masses are
called Continents. The smaller divisions of land
are called Islands.
Most of the land is in the northern half of the
globe. It surrounds the North Pole in an almost
continuous ring, and from the polar regions it ex-
tends in long irregular masses towards the south.
We may consider these masses as forming three
pairs of continents. The division comprising
North America and South America affords the
most perfect example of this arrangement; that
consisting of Europe and Africa is less well de-


fined; while that is most irregular which com-
prises Asia and Australia.
In regard to shape the continents follow a gen-
eral law. They spread out broadly towards the
north, while towards the south they taper to
points, or throw out peninsulas. Thus, in general,
they approach the form of a triangle. This is
.1 ii; -,-v illustrated in the case of Africa and the
two Americas. Europe and Asia combined form
a vast triangle. Australia is the only marked ex-
ception to the rule.
Almost all the large peninsulas are southern
projections from the continents.

3. Northern and Southern Hemti-
spheres.-The globe is divided by the Equator
into a Northern and Southern Hemisphere.
North America, Europe, and Asia, two-thirds of
Africa, and a portion of South America are con-
tained in the Northern ; Australia, part of Africa
and the greater part of South America, in the
Southern. There is three times as much land in
the Northern as in the Southern Hemisphere.
The Northern Hemisphere is the seat of knowl-
edge, civilization and power. It is the commer-
cial hemisphere.
The Southern Hemisphere has never been the
seat of power. The Peruvians and the Javanese
were the only nations which attained a high degree
of civilization there. Only about one-fifteenth of
the population of the globe have their home with-
in this hemisphere.

4. Land and Water H1emispheres.-
The earth may be divided into two hemispheres,
one of which contains nearly all the land, and the
other nearly all the water. These hemispheres are
known as the Land Hemisphere and the Water
Hemisphere. London is nearly at the centre of
the Land Hemisphere ; New Zealand nearly at that
of the Water Hemisphere. Australia presents the
largest extent of land in the Water Hemisphere.

TOPICAL ANALYSIS.
I. ARRAINGEMENT OF LAND MASSES.


1. Relation of land, water and air.
Design in creation.









FORMS OF LAND.


2. Distribution of land.
Extent of land and water. Continents. Islands.
Location and arrangement of the land. General
form of the continents.
3. Northern and Southern Hemispheres.
Dividing line. Continents in each. Proportion of
land and population in the two hemispheres. Of
civilization and power.
4. Laud and Water Hemispheres.


QUESTIONS ON MAP OF THE WORLD.-How do Europe and
Asia compare in general direction with North and South
America ? Which of the Old World continents resembles
.he New in general direction ? What zones are traversed
wholly or in part by each of the continents ? What is the
general direction of the mountain ranges of the Eastern
Hemisphere ? Of those of the Western ? What islands are
near the centre of the land hemisphere ? What islands are
near the centre of the water hemisphere ?


I[. FORMS OF LAND.

1. Horizontal Forms.-In horizontal form
the various land-masses are very irregular. Every-
where the sea more or less deeply indents the shore.
The indentations form navigable seas or sounds,
harbors or roadsteads. The length and indenta-
tion of the shore line, therefore, are indications of
the commercial capabilities of a continent.
Comparing the several continents, we find that
the southern have far more regular outlines than
the northern. Their indentation is comparatively
limited, and their coast-line short. The contrast
is most marked between Europe and Africa.
Europe has six limes more coast-line in prop)or-
tion to its area than Africa. The effect of this
has been very important in the history of the two
continents. By the multitudinous seas, bays, and
gulfs of Europe inter-communication of one part
of the continent with another, and with other por-
tions of the world, has been facilitated, and thus
its several countries have been rendered accessible
to commerce and civilization. Europe has enjoyed
among the continents the leadership in commerce.
Africa, on the other hand, with its comparatively
unbroken coast-line and scanty harbors, has been
barred by nature from extensive intercourse with
the outside world.
North America, though in a less degree than
Europe, is pre-eminent for the indentation of its
sea-coast. This contributes to render it the com-
panion of Europe in commerce and civilization.

2. Vertical Forms.-By vertical forms we
mean the elevations of the land above the sea-level.
With very insignificant exceptions all the land is
more or less raised above the water.


THE AVERAGE ELEVATION of the earth's surface
is not great. It has been estimated that if all the
mountains were levelled, and all the valleys filled
up, the land of the globe, taken as a whole, would
not be raised, on an average, as much as 1,000
feet above the sea.
Although the mountains are so massive in size, and reach
so far into the blue ether that their highest peaks can never
be scaled ; yet, when compared with the size of the earth,
their huge proportions dwindle into insignificance.
A mountain five miles high, which is higher than any but
the loftiest peaks of the Himalaya or Karakorum, rises
above thesea-level but part of the earth's radius. Hence
upon a globe sixteen inches in diameter, it would be repre-
sented by an elevation of only I,,, of an inch, about the
thickness of two leaves of this book.
On a globe sixteen feet in diameter, the highest mountains
would rise above the surface less than the eighth of an inch.

3. Forms of Relief.-Aeeording to their
relief, the various forms of land are classified as
lowlands or highlands.
Lowlands are elevated less than 1,000 feet above
the sea. They are commonly called plains.
Highlands have an elevation of 1,000 feet or
more above the sea. They are called plateaus or
table-lands and mountains. There is no uniform-
ity in the use of the term hill. It commonly des-
ignates an elevation of less than 2,000 feet.

4. Plains are those portions of the earth's
surface which are level, or which, though diversi-
fied with hills, have only a moderate elevation
above the sea-level. About half the extent of the
continental surfaces consists of plains. If covered
with grass, but generally destitute of trees, they are
called prairies in our country, panmpas or llanos in
South America, and steppes in Asia. T'he densely
wooded plains of the Amazon are called selvas.
Plains are classified according to their origin as
marine or alluvial.
MARINE PLAINS are considered to have been,
at some remote period in the history of the globe,
portions of the floor of the sea. Upon them are
found sometimes saline deposits, sometimes the
remains of animals and plants that must have
lived in salt water. Our own Atlantic seaboard
and the Caspian region in Asia are noted examples
of marine plains.
ALLUVIAL PLAINS are those which have been
formed from materials washed down from the hills
and mountains by the rain and the rivers. The
Delta* and valley of the Nile, the Delta of the


The Ierm Delta was originally applied to the deposit formed ati the
month of the Nile, and enetlosed by its two main outlets. The area thus
formed was triangular like the Greek letter a (deltfa), and hence the
word has been applied in a general sense to alluvial lands at the mnouths
of rivers.








FORMS OF LAND.


Mississippi, the plains of the Indus and the Gan-
ges, and the Black Lands of Russia are alluvial.
Such plains are among the most productive por-
tions of the surface of the earth.
The Nile Valley and that of the Menam in Siam are an-
nually overflowed, and covered, when the flood subsides, with
a fine sedimentary deposit. This consists of rich fertilizing
materials brought down from distant mountain slopes. It
imparts perennial fertility. It has clothed the land of Egypt
with verdure since the days of the Pharaohs, 3,000 years
ago. It secures the great rice-crop of Siam.
Plains, centres of civilization.-Owing to their
fertility and case of cultivation, plains have been,
throughout the history of man, centres of popula-
tion, civilization, and power. The imperial glory
of Nineveh and Babylon, the culture of ancient
Egypt, the enduring prosperity of China, and the
unrivalled wealth of India, all owe their origin to the
treasures brought down from the everlasting hills.

5. Plateaus or Table-lands are broad
elevated areas which rise above the level of the
surrounding surface. The name suggests that
they are flat. And some, indeed, as the Llano
Estacado of Texas, are as level as the prairies.
Generally, however, they present a surface highly
diversified. Great mountains are often piled up
upon them.
The plateau of Thibet consists of grassy plains
and wide basins, often containing large lakes, en-
girdled by ranges of gigantic snow-clad mountains.
The aspect presented also by the great plateau
lying between the Rocky Mountains and the Si-
erra Nevada in our own country, is that of a vast
uplifted mass from which the mountains rise;
while the plateau of Titicaca, in South America,
with the towering peaks of the Andes embosoming
its upland lake, singularly resembles the plateau
of Thibet.
In elevation plateaus vary greatly. Low pla-
teaus, like the desert of Sahara, are from 1,000 to
3,000 feet in height. The loftiest in the world are
those of Thibet, 10,000 to 15,000 feet high, and
Titicaca, about 12,000.
Plateaus unproductive.-The plateau regions of
the world are for the most part unproductive.
Many of them are absolute deserts. Hence few
plateaus have ever become centres of popula-
tion and power. It is interesting, however, to ob-
serve that the table-lands of Mexico, Peru, Titicaca
and Thibet have each been the seat of a civiliza-
tion peculiarly its own.
The desert plateaus have undoubtedly their part to per-
form in the economy of nature. They are not wastes in the
sense of being wasted or useless areas. Their effect upon
the rainfall and its distribution is most imptort.it. It will
be more fully considered when we treat of the moisture of
the air. [See p. 8!)9.|


6. MJtountains are elevations rising above the
general level of the land to the height of 2,000
feet or more. Sometimes they stand singly, like
Etna or Vesuvius, but are generally joined one to
another and form a connected series. Such a series
is called a mountain chain or range. The top of
the chain is called the crest.
Mountain chains are seldom solitary. Usually
two or more are parallel, or nearly parallel, with
one another, forming what is called a mountain
system. The Andes, the Alps, and the Appa-
lachians are examples. In all of these there is
not simply one long line of mountains, but a num-
ber of associated and nearly parallel ranges.
THE FORMATION OF MOUNTAINS is a subject
which properly belongs to geology. It is gener-
ally considered that mountains have been formed
mainly by two processes: (1) what is commonly
called the crumpling of the surface of the earth ;
(2) the action of volcanic vents. The latter of
these has already been sufficiently discussed in
treating of the formation of volcanic cones. [Seep.
15.] The former requires some explanation, since
the great mountain systems of the world are
thought to be due to it.
The crumpling or folding process. -Suppose the
earth to have been at some period of its long past
history a heated mass. The heat subsides. The
outside, of course, cools before the interior, and
becomes a spherical crust, while the parts under-
neath are still heated and form a pasty sphere.
This in its turn cools. In doing so it contracts.
What is the consequence ? Some portions of the
solid crust fall in toward the centre of the earth.


STRATA FOLDED.

In this process the crust must obviously be crum-
pled or folded somewhat like the skin of a baked
apple, so as to be packed into the diminished space.
The diagram will perhaps serve to convey an idea
of this.
Two cases may occur : (1) if the strata, when depressed,
are in a plastic state, there will be a simple.flexure or curv-
ing at the points, a a; (2) if the strata are quite cooled, then
there may arise a fracture at the same points. The former
ease may be compared to the bending of a piece of whale-
bone or a steel spring, lhe latter to the bending of a piece
of wood or iron. It is obvious that the one process will give
rounded tops to the mountains, the other will give them
jaggeu peaks and sharp ridges








FORMS OF LAND.


V. Valleys are depressions through which usu-
ally water-courses run. Every mountain range is
intersected by valleys, and every mountain-system
has valleys separating its parallel ranges. The
valleys intersecting ranges are called transverse.
Those lying between parallel ranges, and having
therefore the same general direction, are called
longitudinal.
The formation of mountain valleys is due to the
upheavals and depressions which have disturbed
the surface of the earth in the manner indicated in
paragraph 6, previous page. The formation of val-
leys is really a part of the folding process by which
mountains are formed. The action of running
water has, of course, widened and deepened them.


BLACK CANON, COLORADO RIVER.

Valleys traversing plains and plateaus have been
formed by the erosive action of water. Of such
valleys the most extraordinary in the world are
the calions of our western rivers.
That of the Colorado is a gorge shut in by almost perpen-
dicular walls of rock. It is from 3,000 to 6,000 feet in depth,
and 300 miles long. The catons are among the most im-
pressive evidences of the age of our earth. Hundreds of
thousands of years would be a brief period for performing
the work of wearing away the solid rock by running water
to the depth of more than a mile.


Transverse valleys render it possible to cross the
lofty mountain ranges. Human ingenuity and in-
dustry have improved these natural courses of
travel, or passes, as they are called, and some of
them have been made marvels of engineering skill.
The Simplon, St. Bernard, and the St. Gothard,
crossing the Alps, are among the most noted. The
Alpine tunnels have, to a large extefit, taken the
place of the passes.

8. Causes ani Effects of Relief.-
Few topics connected with Physical Geography
have greater interest than the questions, how were
the elevations of the earth produced, and, of what.
use are they in the terrestrial machinery.

CAUsEs.-What precisely may have been the
causes of the general elevation of the continents,
we cannot with certainty tell. On the principle
that like effects are due to like causes, we should
conclude that similar forces produced the general
elevation as those to which we refer the formation
of mountains. Whatever maybe our conclusion on
this point, it is clear that there have been forces
at work for untold ages, silently and gently, but
steadily raising some portions of the earth's sur-
face, and depressing others.
In many cases it is evident that not only low-
lands such as the Mississippi Valley, but even
mountain tops, were once at the bottom of the sea.
Norwayand Sweden, with the Scandinavian moun-
tains, are rising at the rate of 2- to 5 feet in a cen-
tury. On one of the mountains of Wales is an
ancient sea-beach elevated 1,300 feet above the
present shore.
On the other hand many parts of what is now
the ocean floor were once dry land. Greenland is
gradually sinking.
There is reason to believe that all that part of
the Pacific Ocean, embracing an area of several
millions of square miles, which so abounds in coral
reefs, is gradually subsiding.

EFFECTS.-The elevations of the earth's surface,
though in one sense insignificant, are properly to
be regarded as important regulators of climate.
Not many hundred feet added to the relief of a
country would suffice to alter its physical aspects
entirely, converting vineyards into pasture lands,
or pasture lands into regions of perpetual snow.
Reverse changes would result from a corresponding
diminution in the average elevation. [See p. 74.]
Again: Relief is the great regulator of drainage.
If the surface of the earth had been a dead level,
without a hill to embellish the landscape, there
would have been no water-courses. The whole land
would have been one broad marsh incapable of
drainage, and unsuited for human occupation.








30 RELIEF FORMS OF THE CONTINENTS.


TOPICAL ANALYSIS.
U. FORMS OF LAND.
1. Horizontal Forms.
Irregularity of continental outlines. Difference be-
tween northern and southern continents. REela-
'tion of this difference to commerce.
2. Vertical Forms.
Average elevation of the land. Relative Insig-
nificance of the highest elevations.
8. Forms of Relief.
Lowlands. Highlands.
4. Plains.
Extent and varieties of plains. Marine. Alluvial.
Relation of plains to civilization.
5. Plateaus.
General character. Elevation. Productiveness.
6. Mountains.
Distribution, Formation. Crumpling and folding
process.
7. Valleys.
Transverse. Longitudinal. Formation of valleys.
Of western caions. Mountain passes.
8. Causes and Effects of Relief.

TEST QUESTIONS.-Can you name any region that is lower than the
sea-level ? What locality contains the highest mountains in the world?
Is the Mississippi Valley transverse or longitudinal ? The valley of the
Amazon ? Of the Potomac ? Relation of mountain passes to commerce.


III. RELIEF FORMS OF THE CONTI-
NENTS.

1. General Features of Continental
Relief.-There are certain features of relief which
belong to all the continents in general. (1) Each
continent is bordered by mountains. (2) Each con-
tinent is traversed in the direction of its greatest
length by a grand mountain-system. The line of
direction taken by the principal mountain-system
is termed the main or primary axis of elevation.
This axial line is not, however, in any ease
placed centrally, as the word axis might seem to
imply, but far to one side of the continent. It
thus. divides the continent into two unequal slopes.
(3) For the most part a subordinate system occurs
in each of the continents. This system follows a
secondary axis of elevation. (4) The central
portions of each continent are comparatively de-
pressed.

NOTE.-The relief maps and profile sections accompanying
them will be found very useful. Their examination in connec-
tion with the text will serve to impress upon the minds of the
pupils the conspicuous features of continental relief.
The heavy black lines upon the maps represent, in a general
way, the extent and direction of the mountain chains. The ele-
vations and depressions are shown in the profile sections. They
-are indicated also by the buff and green colors on the maps.
The buff, according to the depth of its tint, represents elevations
of greater or less altitude. The green indicates lowlands.


NORTH AMERICA.

1. North America conforms very
closely to the general principles of
continental relief. It has a pri-
mary highland, a secondary high-
land, and a great central depres-
sion.

2. Pacific Highland.-The
primary elevation of North Amer-
ica is the vast area known as the
Pacific Highland. It consists, in
general, of a high plateau from
which rise the Rocky Mountains
and the parallel Sierra Nevada and
Cascaderanges. The plateau varies
in breadth from 300 to 600 miles.
The general elevation increases
toward the south. On the Arctic
shores it is 800 feet above the sea;
in Mexico it is more than 8,000.
THE RocKY MOUNTAIN SYSTEM
is composed of several nearly paral-
lel ranges which form the main
axis of the continent. It embraces
also numerous intersecting cross
ranges. The system extends from


- .J .- '" .. 7... .


.- ** -* -... .-^ "_ I k .2 ,.
*_ L -. 1_



":" -u .' .:" ,
.. ,.
r ..... .. t -'
-***~~~ ~ --.^^ '... / p

- - .^ --
1: .7tV^r-...-'^ if*

^ -..- ,-.-- s^ 4'.'*-.


~ 'i *** i. -*t "7







RELIEF FORMS OF THE CONTINENTS.


the Arctic Ocean to the Isthmus of Panama, the
Sierra Madre range of Mexico being regarded as
the southern prolongation.
From the plateau upon which the mountains
stand they do not attain a height of more than
6,000 to 8,000 feet, but when it is remembered
that the plateau itself is 5,000 or 6,000 feet high,
it will be seen that their actual elevation above the
sea-level is as much as 12,000 or 14,000 feet. Their
loftiest peaks are about 15,000 feet high. I
-o00 Sierra Nevada nockyxts.
THESIERRANE- ., '
VADA AND CAS- r- ,..' "-.,.
CADE MOUNTAINS L'"--
follow, in general, SECTION OF NORTH ABB
the line of the Pacific coast. They form the west-
ward wall or buttress of the great plateau. In alti-
tude they resemble the Rocky Mountains. Their
loftiest peak is Mount St. Elias, 17,500 feet high.
The low Coast Range stretches along the shores of the
Pacific between Cape St. Lucas and Vancouver's Island.

3. The Secondary Highland of the con-
tinent comprises the Appalachian mountain-system
and the plateau of Labrador. These extend from
Labrador nearly to the
Gulf of Mexico. The .... .n
Appalachian Moun- ......
,ains in their north- .P
ern course consist of a -
number of disconnect- SECTION or SOUTH AMERI
ed groups. To the southward they are composed
of several well marked and nearly parallel ranges.
The general elevation is not more than about
3,000 feet above the sea, but the loftiest peaks are
nearly 7,000 feet.
From the Appalachian Mountains the land de-
scends gradually to a _______
low, narrow coast
plain known as the
"tide water" region. .


One slopes to the north and drains off the waters
into the Arctic Ocean and Hudson Bay, the other
inclines toward the south, and drains into the Gulf
of Mexico.

SOUTH AMERICA.

1. The general features of South America
are similar to those of North America. The pri-
mary elevation of the continent lies along its
western border.
Ar.aacan Secondary high-
Atpr, ral~lacha
^XMts. lands are found
,-:,,-,----------',-- toward the eastern
CA FROM EAST TO WEST. coast. Central
plains lie between the primary and secondary high-
lands.

2. The Primnary Highland of the conti-
nent is formed by the Andes, the grandest mountain
system of the western hemisphere. It stretches
from the Isthmus of Panama all along the western
edge of the continent down to Cape Horn, a dis-
tance equal to one-sixth the circumference of the
earth. The Rocky Mountains of North America
may be appropriately
regarded as its north-
ern prolongation.
.. "' -- "~'- THE ANDES are re-
CA FROM EAST TO WEST. markable for the con-
tinuity of their height, for their regularity of form,
and for their system of parallel chains. In the
southern portion they consist of a single chain ;
in the central part mainly of two nearly parallel
chains ; and in the north of three. Eight times
these parallel chains gather into mountain knots,


': ; -:3 ---_--. --- -_ --L-_ ------_' _- :. -,_,-" ,.-_ -_.. -=- --: -- .. ..^ '^^ ^ -t^ '-y -
4. The Central -.... ---
Region between the O -
primary and second-
ary highlands is called
the Great Central 7
Plain. It is a well
marked depression ex- _q
tending from the Arc-
tic Ocean to the Gulf
of Mexico.
The Height of
Land, a narrow ridge TOP OP THE ANDES.
-crossing it from east
to west, having an elevation of from 1,000 to and, again separating, enclose valleys and table.
2,000 feet, divides it into two distinct portions, lands wonderful in height and extent.


=.- -_ : : __.- -- --_... =-- -








RELIEF FORMS OF THE CONTINENTS.


Of these table-lands the broadest and highest is
that of Bolivia.
Passing northward we observe the lofty crest of
this imposing system crowned with hundreds of
snow-capped peaks, and studded with smoking vol-
canoes, all the way from the Desert of Atacama to
the centre of the United States of Colombia. In
the whole of this distance of nearly three thousand
miles, there is not a gap or a pass below the height
of 11,500 feet. Twenty peaks attain a height of
more than 19,000 feet, and the average elevation
is estimated by Humboldt at 11,840 feet.
Very important
in its bearing upon
the physical geog- .-.:. ..-.
raphy of the conti- r:.<. .
nent is the singular '- .-
proximity of the 'i :'..-
Andes to the west- .
ern coast. Their ..' -'"^
greatest distance os e 6- .,
from it is about 80 "
miles. X = -


3. The Second-
ary Highlands
of South America
are those of Brazil
and Guiana.
Thi e Brazilian
Highland is abroad
plateau region trav-
ersed by nearly
parallel ranges of
moderate elevation.
Their loftiest peaks
are from 5,000 to
10,000 feet high.
The Highland of
Guiana is a plateau
supporting several
closely-set ridges,
the most important
of which are the
Parime Mountains.


Maravaca, the culminating peak,
feet high.


is nearly 10,000


4. The Central Region of the continent,
.like that of North America, is a well-marked de-
pression lying between the primary and secondary
highlands. It is called the Great Central Plain.
It consists of the river-basins of the Orinoco, the
Amazon, and the La Plata. These are divided by
ridges so low and so narrow that the three together
may not unfairly be considered as forming one
great basin.


The following curious facts will show hw nearly alike
their level actually is. The Cassiquiare, which rises between
the Amazon and the Orinoco, forks, after running some dis-
tance, and sends off one branch to the south to unite with
the waters of the Amazon, the other to unite with those of
the Orinoco on the north; it thus connects these two river-
basins by a water-way that permits the Indians to pass in
their canoes from either of the two great rivers into the
other.
Furthermore, in the Brazilian provir.ce of Matto Grosso
there are two springs side by side, and within a few feet of
each other. From one the water flows into the Amazon,
from the other into the La Plata ; and so close are the nav-
igable waters of these rivers to each other, that, with a sin-
gle portage of a few
miles, the voyager, as-
cending the La Plata
from the sea. may re-
z turn to the ocean again,
S--_ either through the
,r~~- '. .- Amazon or the Orinoco.

-4/4 EUROPE.
P..,
'" _.. .: 1. Europe, like
North America and
/ j / )1 South America, has
\ a I <' .. -its primary and
secondary high-
-lands and its low
..) i, :i. plain ; but the ar-
.1 .. -"... .. rangement of these
?, } --- '._ features is different
/. ?' .7 from that which
"- prevails in the New
World. Two ob-
S. 1 vious differences
-"''" present themselves:
(1) the main axis of
v elevation extends
east and west, not
like the Andes and
Rocky Mountains,
tt TT north and south;
S 0F IT I H(2) the mountain
S A II E B I ( A chains have not tne
Same well-marked
parallelism as is
shown by those of the New World.

2. The Primary Highland of Europe
stretches all through the southern portion of the
continent, from the Atlantic to the Black Sea, and
we may say, regarding the Caucasus as its eastern
prolongation, that it reaches the shores of the
Caspian.
Beginning with the Pyrenees, as its western ter-
mination, it culminates in the Alps. Eastward of
the Alps it throws out two important branches, the
Carpathians to the north, and the Balkans to h\.


I







RELIEF FORMS OF THE CONTINENTS. 33

south. These, with the Dinaric Alps, enclose the Now and then a muttering like distant thunder may be
basin of the Danube. In addition to these ranges caught, as some loosened mass of snow or ice falls with
the Apennines of Italy and the mountains of Greece a crash into the valleys; or the wind brings up from below
the Apennines of Italy and the mountains of Greece in fitful gusts the murmur of the streams which wander
are included as parts of the primary system, down the distant valleys."
THE ALPS are the most celebrated of all the The highest peaks of the Alpine system are
mountain-systems in the world. Their historic Mont Blanc, 15,781 feet, Monte Rosa, 15,220 feet,
and poetical associations ; the grandeur and beauty and the Matterhorn, 14,780.
of their varied Alps The Alps are
scenery; the 15- 0A destitute of ac-
numberandex- ,. .',.. tive volcanoes.
tent of t h e i r The Pyrenees
glaciers, and I. .. .. ...-_-__.., ..,; p ,, present a much
their accessibil- .---- *r...--..------- - greater uni-
ityto travellers, SECTION OF EUROPE FROM NORTH TO SOUTH. forty of ar-
ity to travellers, formity of ar-


invest them with an interest unrivalled by the
loftiest summits of other lands.
Occupying a central position between France
and Germany on the north, and Italy on the south,
they can be reached in a few hours from any of
the great cities of Europe. Owing to their varied
attractions they are visited by so many thousands
annually, that they have been called, not inappro-
priately, "the play-ground of Europe."


As we climb the Alps, says a distinguished scientific writer,
"peak rises behind peak, crest above crest, with infinite
variety of outline, and with a wild grandeur which often
suggests the tossing and foaming breakers of a stormy
ocean. Over all the scene,'if the air be calm, there broods
a stillness which makes the majesty of the mountains yet
more impressive. No hum of bee or twitter of bird is heard
so high. No brook or waterfall exists amid those snowy
heights. The usual sounds of the lower ground have ceased.


rangement than the Alps. Their average height
(8,000 feet) is not greatly inferior to that of
the Alps (8,000 to 9,000 feet) ; but their highest
peak, Mount Maladetta, 11,167 feet, is far below
the towering masses of Mont Blanc and Monte
Rosa. The passes of the Pyrenees, however, are
higher and less practicable than those of the Alps.
The Carpatlians separate tlie plains of Hun-
gary from the great low plain of the continent.


sula on the west, the Italian in
the Grecian on the east.


Their greatest
elevation is
about 9,000
feet.
The Caucasus
range stretches
from the Sea of
Azov to the
Caspian. Two
of its peaks,
Mount Elburz,
18,572 feet, and
Kasbek, 16,545,
surpass in
height the lof-
tiest summits
of the Alps.

PENINSULAS.
-High Europe
throws out three
mountainous
projections to-
wards thesouth:
the Iberian or
Spanish Penin-
the centre, and


The Iberian or Spanish Peninsula is a great plateau sur-
mounted by several parallel ranges. The Pyrenees, which
are the principal of these, form the dividing line between
France and Spain.
In the Italian Peninsula we find the Apennines, an im
portant prolongation of the Alpine system. These are more








34 RELIEF FORMS OF THE CONTINENTS.


famed for their beauty than for their altitude. The volca-
noes of Vesuvius, Etna, and the Lipari Islands, are consid-
ered as belonging to this chain.
The Grecian Peninsula, like the Italian, boasts of no very
elevated ranges. Its mountains are famed less for their
height than for their historic and poetic associations. They
were the mythic homes of the gods of ancient Greece. 'he
throne of Jupiter rested on Mount Olympus. The Balkans
are the most important range. They have an average ele-
vation of about 5,000 feet.

3. The Secondary Highlands comprise
the ranges of Scandinavia and the -Ural mountains,
together with others of less importance.


CLIMBING THE ALPS.
The Scandinavian mountains consist, for the
most part, of a broad elevated region, intersected
by deep and gloomy valleys. Some of these


"fiords," as they are called, are thousands of feet
in depth, and penetrate far into the country. One
of them is 100 miles in length.
The Ural mountains form a natural boundary
between Europe and Asia. They extend south-
ward, 1,200 miles, from the Arctic Ocean nearly
to the Caspian Sea.

4. Low Europe consists of a vast plain lying
northeast of the primary highland. It is bordered
on the northwest by the mountains of Scandinavia,
and on the northeast by the Ural range. It ex-
tends from the Arctic Ocean to the Black Sea, and
westward as far as the Bay of Biscay.
The Valdai Hills, near the centre of the plain,
mark the highest point of a swell which separates
the rivers flowing into the Baltic and White Seas
from those which enter the Black and the Caspian.

ASIA.

1. Asia, like Europe, may be divided into two
grand sections, High Asia and Low Asia. As in
the case of Europe, the highlands lie to the south;
the great low region to the north.
2. The Primary Highland of the con-
tinent consists of two portions: (1) the various
mountain chains which radiate from the central
elevated region known as the Plateau of Pamir;
and (2), the Plateau of Thibet.
The Pamir is called by the Asiatics the "roof
of the world." In shape it may be regarded as an
irregular square. From three of its corners great
chains project. The southeast corner is the start-
ing point of the great ridges of the Himalaya, the
Karakorum, and Kuenlun. From the northeast*-
em corner the Thian Shan range takes its origin.
From the southwestern starts the line of the Hin-
doo Koosh.
The Plateau of Thibet lies between the Him-
alayas on the south, and the Kuenlun mountains
on the north. It is the loftiest table-land in the
world, having an extreme elevation of about 15,000
feet.
THE HIMALAYAN RANGE stretches eastward
from the Pamir in an unbroken course, for a dis-
tance of 1,500 miles. Its breadth varies from
150 to 350 miles, and its mean height has been
estimated at 6,000 feet higher tbhn that of the
Andes. Over forty of its peaks rise to an altitude
of 23,000 feet, and more than 120 reach 20,000
feet. Mount Everest, with an elevation of 29,000
feet, is, so far as known, the highest mountain on
the globe.
The Himalayas present the grandest possible mountain
scenery; deep gorges wrapt in perpetual twilight gloom,
frightful precipices; sombre forests of rhododendrons and







RELIEF FORMS OF THE CONTINENTS.


pine trees ; higher up, vast glaciers filling the ravines, and
ice and snow covering the ridges which rise one above an-
other to such sublime heights as must ever secure their sum-
mits immaculate from the footsteps of man. Everything is
colossal; but the Himalayas lack the smiling valleys and
sheltered lakes which impart such picturesque charm to the
Alps. They possess the grandeur without the amenity, the
magnificence with-
out the variety, 0oooo ya Mta
which mark the less A :'
elevated European ; V
p, J *y* ,/\Panu
system. iu-.*. / .i. .
The Passes of lae
Himalayas, instead SECTION 0
of leading through
low gaps and over gentle declivities, rise up into the regions
of perpetual snow and ice, and are so difficult as to be of
little avail for the purposes of commerce between the people
on the opposite sides. They are on an average 10,000 feet
higher than those of the Alps, and nearly 4,000 feet higher
than those of the Andes. We cannot be surprised that In-
dia and Siberia are practically farther removed from each
other than if they were separated by an ocean, nor even that
the opposite slopes of the Himalayas are occupied by men of
different races.


The Kuenlun range separates Thibet and East-
ern Turkestan, and is prolonged by the Chinese
range of the Peling mountains. The Thian Shan
range forms the northern boundary of the plateau
of Eastern Turkestan. Some of its peaks attain
the height of 20,000 feet.


Than Shan
\Mt. 0.
G \jV .4
. j A ,


Siberian Plain


F ASIA FROM NORTH TO SOUTH.

The Hindoo Koosh extends in broad, massive
ranges westward for 400 or 500 miles. A depression
then occurs. The range, however, is really con-
tinued in the Elburz mountains, which form the
northern boundary of Persia.
The general direction of the great mountain
chains of the primary highland region is east and
west.


The Karakorum range traverses the plateau of I 3. The Secondary Highlands comprise
the Altai moun-
~t c ; z c .2 --C' tains and their
"-,- '_.. ., northern con-
7 .., .; :. ..... .. [ ,- .L. ". .- "' f tinuations, to-
'~-.... *.. *-, -. .. ": .~ [ '-*, / i". gether with the
.......-*-'- '... ,^ ...-- I / Great Khingan
/ --' /-'- -- range, and the
S\ -. :J ], ranges of south-
-y7 '"' N '- '^ eastern Asia,
... ... ,.-.. --'- .' ) /\-,'( and, finally, the
.- .:~ i ( ... f / -. subordinate
s.. ... / .' / plateaus of the
.( -'.:" -*" -. /,"" Y continent.
The Altai
-R- r\Sa 0 / 0 _'-'--' mountains ex-
u\ i -t- i '' tendina north-
,,' \ "' ,. easterly direc-
-7.. tion, and termi-
,'I "-. '( r hateintheYab-
",* 'A, '- --.'. -" ( ]onoi and Stan-
l -' -' ^. ovoi ranges.
'-.. | L-'\' f) They separate
'.* . ", .- ,-' t_.- /.7 = the desert
~/-"^ '-. '.. ;;wastes of Mon-
S- golia from the
1. (plains of Sibe-
IA '.' s^ *ria. Some of
A I- A I ., '"CE- P their peaks are
/" ---' . .. ', - -S t" ,-, -'--
2,000feethigh.
Thibet, and is believed to have a greater average The Great Khingan mountains, with their
height than even the Himalayas. It contains southern offshoots, form the eastern barrier of the
Dapsang mountain (height, 28,300 feet), believed great Desert of Gobi.
to be the highest summit next to Mount Everest PLATEAUS are a prominent feature of the
in the world. Asiatic continent. A series of them extends from








RELIEF FORMS OF THE CONTINENTS.


the shores of the Red Sea nearly to the Pacific
Ocean. In general they are arid and rainless,
sandy, stony, and barren. In the spring the sur-
face is thinly sprinkled here and there with grass
and herbs, but in the summer and autumn it is, for
the most part, dry and sterile.
The sheltered valleys are, however, in many cases
exceedingly fertile. In such valleys there is a set-
tled population, but outside of them the plateau
region may be described as the home of roving
herdsmen and marauding Bedouin.
North of the Kuenlun mountains are two plateaus, Eastern
Turkestan and the Desert of Gobi. These are shut in on
the north by the Thian Shan and Altai mountains. The
average elevation of Eastern Turkestan is about 2,000 feet
above the sea-level; that of Gobi about 4,000 feet. Should
we enter Gobi from Thibet, we should make a descent of
nearly 9,000 feet.
The triangular plateau of the Deecan in India rises to
the average height of about 8,000 feet. The sides of the
triangle are the Eastern Ghauts, the Western Ghauts, and
on the north the Vindhya mountains.
The plateau of Iran or Persia, including large portions of
Afghanistan and Beloochistan, is shut in by the Elburz
and Hindoo Koosh mountains on the north, by the Zagros
chain on the south, and the Suleiman on the east. It rises
from 8,000 to 4,000 feet above the sea-level.
The plateau of Armenia,with Ararat (about 17,000 feet high)
for its culminating point, rises to the westward of Persia.
The plateau of Asia M.inor lies westward of that of Ar-
menia. It has an average elevation of 2,500 feet. The
Taurus ranges bound it on the south.


extends through Europe and Asia, from. the shores of the
North Sea to Behring Strait, a distance of more than 5,000
miles.
The Kirghiz Steppes are wide and monotonous
tracts, covered in spring with rough grass, desert
in summer, and bleak and desolate in winter.
The Siberian Plain consists of prairies, wood-
lands and tundras. The prairies and piny forests
are in the southern portions, the swampy tundras
on the northern edges.
Inferior in size to the Siberian Plain, but vastly
more important for their influence upon the his-
tory of the human race, are the plains of China and
India. They support nearly one-half the popula-
tion of the globe.
A remarkable depression is found on this conti-
nent. It is occupied by the Dead Sea, the surface
of which is 1,300 feet below the level of the ocean.

AFRICA.

1. The Continent of Africa obeys quite close-
ly the general law of continental structure. It has
mountain ranges along the coast, while a plateau
region of less elevation occupies the interior.

2. The Primary Highland is in the
east. It consists of an elevated region which ex-
tends all the way from the Isthmus of Suez to the
Cape of Good Hope. One important portion of it,


DESERT OF SAHARA.


The plateau of Arabia forms the southwestern projection
of the continent.
4. The Great Lowland of the Asiatic con-
tinent lies to the north. It extends from the shores
of the Arctic Ocean southward to the base of the
Altai mountains and the adjacent ranges, and com-
prises the Kirghiz Steppes and the Siberian Plain.
It is a part of the almost continuous depression which


the plateau of Abyssinia, attains an elevation of
7,000 to 8,000 feet. The culminating points,
however, are the snowy heights of Kenia, and
Kilima-Njaro (about 19,000 feet high), situated
near the equator. South of these elevations
occur the Livingstone mountains, walling in lake
Nyassa ; and nearly at the southern extremity of
the continent lie the Snow mountains, which may







RELIEF FORMS OF THE CONTINENTS.


be considered as vast terraces ascending from the which are below the sea-level. They are the
sea toward the interior, I marshy regions known as the chottes (shots).


3. The Secondary High-
lands include the ranges which
border the northern and western
coasts. The Atlas mountains on
the north consist of three or four
parallel ranges which ascend from
the Mediterranean stage by stage,
and increase in height to the
* westward.
The Kong and Cameroons
mountains are the principal
ranges on the west. The latter
are volcanic. They attain at some
points the height of 13,000 feet.

4. The Interior of the con-
tinent may be regarded as a vast
plateau bordered by the various
coast ranges. Low plains are to
be found only along the coast.
The plateau region may be
divided into two sections: (1) that
portion which consists of prairies
and fertile river basins; and (2)
the arid Sahara.
The SAHARA is considered to
have formed, in an older period of


the world's his-


tory, a portion of the bottom of the sea. It is not
an absolute level. Its average elevation is about
1,200 feet, but it contains areas which are 4,000
Sor 5,000 feet in height, and has a mountain


The surface of the desert consists, in some places,
of sharp stones, in others of gravel, in others again
of loose, shifting sand. This last is driven before
the winds, andarranged in long lines like billows of


^-?- L-*


J -~
.4-'


,/" ,. -



"I /
in1 ; / .
S( _..- .
- I / 7 ( J


USTRLIAC
AUSTRALIA


t L.


L. ~'

I,
-
~/,.


.I NV


" T AT r. iA


AUSTRALIA.

1. Australia resembles Africa in
conforming to the general law of
continental relief. It has an elevated
border and a depressed interior.
The Primary Highland lies along
the eastern and southeastern shores.
It culminates in the Australian Alps,
the loftiest peaks of which are about
7,000 feet high, and terminates in
York Peninsula.
The Secondary Highland, border-
ing the western and northwestern
edges of the continent, has an average
elevation of 2,000 to 3,000 feet.
Of the Central Lowland only
small portions, such as the basins
of the Darling and Murray rivers,
are well known. Large areas are
believed to be desert. A character-


range one of whose peaks is nearly 8,000 feet istic feature of the lowland is its inland salt lakes,
high. Southward of Tunis are found depressions several of which, are more than 100 miles in length.


.> -. ,- '



N, -, - -'

~t h
.. .. : "* i .' ,

-rL? '



Alld
'a=" i "-; .: %- L ** '.
-- ,.-- l y ,aai c r o ots
I, Ml ..^ i^ o


.. .\ .

.0 ,


'-N


z
II -


A F R I CA


1









38 ISLANDS.


TOPICAL ANALYSIS.

III. RELIEF FORMS OF THE CONTINENTS.

General Features of Continental Relief.
Location of axial line. Central depressions.
North America.
1. General Features.
2. Pacific Ilighland. Description. Rocky mountain
system. Sierra Nevada and Cascade mountains.
Coast range.
3. The Secondary Highland. Description. "Tide-
water" region.
4. Central Region. Description. Height of land.
South America.
1. Genrald Features.
2. Primary Highland. Location. The Andes. Re-
markable features. Elevation.
3. Secondary Iighlands. Brazilian Highland. Guiana
Highland.
4. Central Region. Consists of what ?
Europe.
1. General Features, as compared with those of the
American continents.
2. The Primary highland. Location. Principal
ranges. The Alps. Circumstances which make
them celebrated. The Pyrenees. Carpathians.
Caucasus range. Peninsulas; Iberian, Italian
and Grecian.
3. Secondary Highlands. Scandinavian mountains.
Ural.
4. Low Europe.
Asia.
1. General Features.
2. The Primary Highland. Divisions. Plateau of
Thibet. Himalayan range. Grandeur of its scen-
cry. Passes. Karakorum. Kuenlun. Than
Shan, and Hindoo Koosh ranges.
3. Secondary Iighlands. Corsistof what? Plateaus
of Asia, extent and barrenness of. Eastern Tur-
kestan. Desert of Gobi. Deccan. Iran. Armenia.
Asia Minor. Arabia.
4. The Great Lowland. Location. Kirghiz Steppes.
The Siberian plain. Plains of China and India.
Dead Sea region.
Africa.
1. Correspondence to the general law.
2. Primary Highland. Location. Extent.
3. Secondary litghland, include what?
4. The interior. Divisions. The Sahara.
Australia.
1. Conformity to the general law.
Primary Ilighland.
Secondary HIfighland.
Central Lowland.
TEST QUESTIONS.-Considering Europe and Asia as one continent,
where would be the central depression ? Do you know anything re-
markable about it ?


IV. ISLANDS.

1. Classification.-A portion of the dry land
consists of islands. These are divided into two
general classes, continental and oceanic islands.


2. Continental Islands, as the name im-
plies, are situated near the continents, and in
earlier periods of the world's history many of them
doubtless actually formed parts of the continents.
This conclusion is based upon the resemblances
that exist between the islands and continents in
their rocks and soils, and in their vegetable and
animal productions.
From the fact, for example, that in past geological peri-
ods the same animals lived in Great Britain as in Europe,
geologists are convinced that Great Britain and the adja-
cent islands were originally connected with the European
continent.

Continental islands are usually arranged either
in a line parallel to the coast of the continent,
or upon a line which may be fairly regarded as a
continuation of the continental coast line. The
Japanese Islands illustrate well the parallel ar-
rangement; the West Indies and Sunda Islands
are arranged upon lines which may properly be re-
garded as prolongations of the eastern shores of
North America and Asia respectively. [See map,
p. 24.]

3. Oceanic Islands are situated in mid-
ocean, far away from the continents. They are
arranged sometimes in lines, sometimes in groups
of irregular shape. They are strikingly unlike the
continental islands. These latter are made up of
the same rocks as the continents. The oceanic
islands are not. They are composed either of vol-
canic products or of coral. In regard to forma-
tion, oceanic islands are, therefore, of two kinds,
volcanic and coral.

4. Volcanic Islands are arranged, as a
rule, along the great bands or belts of volcanic ac-
tivity which traverse the globe.
Most of them are found within the volcanic
belts of the Pacific and the Atlantic. [See p. 18.]
There are, however, exceptions to this general rule,
many volcanic islands being situated quite irregu-
larly. It is curious that the volcanoes upon islands
in the Pacific belt are among the most active in
the world ; those in the Atlantic belt are either ex-
tinct, or are bordering on extinction.

FORMATIOMN.-Volcanic islands are formed by
the accumulation of materials thrown out by sub-
marine volcanoes. Sometimes such islands are
formed very suddenly, as in the case of Graham
Island, in 1831, and of one off the Island of San-
torini, in the Mediterranean, in 1866. [See p. 15.]
In elevation above the sea-level, volcanic islands,
owing to the method of their formation, are natu-
rally far higher than those of coral origin. Some,
like the Sandwich Islands, attain an altitude of
many thousand feet.








ISLANDS.


5. Coral Islands. Multi- -_ .. -
tudes of islands are mainly corn- ---- ... :---- -
posed of coral, and hence are called _- -
coral islands. They are formed -- "
chiefly by the agency of the coral i : ;-
polyp, but partly by the action of _-~ --
the waves.
THlE CORAL POLYP. -The polyps
themselves must first be described, 'o-
before we can rightly appreciate i
their work. There are many differ- t0e o
ent species, but we need to concern s O-
ourselves only about the reef-build- an ti at t
1 -------
ing polyps. Of these there are va- ... A-.e a, "-
rious kinds. The cut represents a cm s 7_ go ,,. rc u .. te -
II-- (. jj : = ii. . ., .
piece of coral crowned with a colony '-- =
of tiny laborers. .' iln.s











i -' ..... OK 0,S TH POY-, S
DESCRIPTION.-The numerous rays which '
project from the polyps are called tentacles. p I i
T'hey are so many little fans which the % myb cl (
polyp moves, so as to draw a current of ..f
water towards his mouth. The mouth is
represented in the cut by a slit in the con- -" i. o,
tre of the rays. The body of each polyp of-.. coin
is in a little pocket, or hole, in the sub- Tn_,'
stance of the coral. It consists of an outer t, ._.--ae..,_ateo
sack containing an inner sack, this latter reef a e. a
being the stomach. In the open space be- d__,,_ , ,
tween these two, the bony part of the skel- -nw .__,. ,_ .
eton of the polyp is formed. It is lime- __-_,_,_'__',_-_-'
stone, and is separated by the polyp from i',.,I ,,
the sea-water which is continuously sup- POLYPS BUILDING CORAL-(natural size),
plied by the movements of the tentacles.
Then again, although we may consider each polyp as an endures for ages. As rapidly as individuals die, others take
individual, like a single bee or ant, it is to be observed that their place. Young polyps actually shoot like buds out of
the members of such a colony as is shown in the cut are the substance of the older ones, and, besides this, addi-
not altogether independent. A common fleshy substance tional multitudes are hatched from eggs. One vast host of
extends from one to the other, and this acts as the individual workers then deposits its layer of limestone, and passes out
polyps do. Like them it separates limestone from the sea- of existence. Another and another succeeds, and thus coral
water, and makes out of it a sort of common skeleton. With grows and rocky columns rise through the waves to become
the supports of coral islands.
WORK OF THE POLYP.-Let us
now consider what we may term the
life-work of the polyp. It consists
in the building of reefs.
S Coral reefs may be classed as (1)
ToS
--. -fringing reefs; (2) barrier reefs;
/ r ~ '(3) atolls.
Fringing r-eefs are bands of coral
-, io. ,rising a few feet above the water,
and surrounding islands or skirting
....... the shores of continents. The bil-
lows dash themselves into spray on
-- these reefs, but leave the water on
CORAL REEFS OFF THE NORTH SHORE OF TAHITI. the inside as smooth as a mill-pond.

this the skeletons of all the polyps are united so that they Barrier reefs are the. same as
form one dense rock-like mass. This substance is known as fringing reefs, only that they are further removed
coral. from the land. Some of them are only a few miles
The life of the individual polyp is brief, but the colony in circumference, others are several hundred.








ISLANDS.


--W
. =2 "- . .. . .. .. . i


- -._ -- - _-_- - .

.- &- t- -: --ND-Y ISLAND.
r,-- ': --: '---- - .'-- .- .,



M HJIT S UNIIAY ISLAND,


The great barrier reef of Australia is 1,200 miles long.
The island of New Caledonia and many others are protected
from the sea by similar reefs.
An atoll is a reef from within which an island,
once encircled, has disappeared. It consists, there-
fore, of a belt or strip of coral enclosing an ex-
panse of water. The water thus enclosed is called
a lagoon.
Atolls are usually nearly oval or circular, but
in many cases they are quite irregular in shape.
Sometimes, as in the case of Whitsnnday Island,
they are complete rings; but most frequently, on




*' I

7.











REI ) CORAL,

the side not exposed to the prevailing winds, there
are one or more breaks.
The atolls are almost innumerable. There arc nearly a
hundred of them in the Dangerous Archipelago, which lies
to the westward of Tahiti. They are not more than half a
mile across, fromn the sea to the lagoon. In their highest
parts they are only a few feet above the waler; still they re-
sist the ut most foury olf Ilie waves. They are thickly covered
with vegetation.


WoRK OF THE WAVES.-When the polyps have
reared their wondrous structure up to the level of
low water, they have finished their part in the
formation of the coral island. Now follows the
work of the waves. They break off portions of
the coral growth. They next sweep these portions
into a ridge, just as the sand is swept up on the
sea-shore. The ridge, heaped up by successive
additions of broken coral, finally becomes so high
that it overtops the waves, and an island is formed.
The next stage is the appearance of vegetable life.
Floating wood lodges among the coral fragments.
It decays and forms mould. Seeds, such as cocoa-
nuts, not injured by salt water, are :, it. .I to the
new-born islet; others may be carried thither by
birds. Under the stimulus of a tropical sun they
grow, and in process of time deck the dead coral
mass with living green.
The bread-fruit and cocoa-palm are the most
important of the forms of plant-life that flourish
upon the coral islands. No large animals live
upon them, and of course neither metals nor coal
are found on them. They are not fitted to be the
abode of human beings at all advanced in the scale
of civilization.

6. Coral Groves" and Coral Seas.-
So singularly transparent is the water enclosed
by the atolls, that the ship, as she lies at her an-
chor, appears rather to be suspended over the bot-
tom than to be resting on the deep. I have seen
plainly coral-trees, standing in groves at the depth
of one hundred feet.
The coral groves of the ocean floor are decorated like the
gardens of the land, t lie flower-like polyps answering to our
pinks andt daisies, violets, and lilies. Some of them are of
tie brightest and softest tints, pink, pearl color, and blue,
green, purple and yellow. They strew th.lie bottom, which isF,








ISLANDS.


of the whitest and purest sand; or hang like leaves and
flowers, or cling like mosses and lichens to the branching
coral, and lend rare enchantment to the scene. Fishes of
many colors, with exquisite grace of movement, dart among
the branches. They are as multitudinous as bees over the
flower-beds, and, with their polished scales, vie in .ri, 11, ,,.-
with the feathered tribes of the land. To look down upon
such a scene in the great bosom of the ocean is like gazing
upon the splendors of fairyland itself.
The full beauty of the coral groves, however, cannot be
seen from above. Their admirer must dive to the bottom.
Yet not without risk does he venture. The fire coral (Mil-
lepora). and the Medusn swimming amid the treasures of the
deep, sting, when touched, like the worst of nettles. Black
sea urchins drive their long barbed stings into the flesh of the
foot, where they break off and remain, inflicting painful and
dangerous wounds. But the worst of all injuries to the skin
are inflicted by the coral rocks themselves, owing to their
myriads of hard points and sharp jagged edges.

7'. Distribution of Coral.- The reef-
building polyps are confined to tropical waters.
The central part of the Pacific Ocean is the scene
of their greatest activity. They are also found in
many portions of the Indian Ocean, in the Red
Sea and the Persian Gulf.
Except in the region of the West Indies, at the
Bermudas, and off the coast of Brazil, there are none
in the Atlantic.
The area within which they are at work is not
less than 25 millions of square miles.

8. Origim of Atolls.-Many of the reefs
and atolls rise from very great depths ; but the
polyps are most vigorous in water not deeper
than sixty feet; and in water that is more than
180 feet deep they cease to live. The question,
therefore, arises, how can the foundations have
been laid for certain reefs and atolls, which are
known to stand in water not less than a mile and
a half deep ?
This was a question that long puzzled Physical
Geographers. Finally, Darwin suggested an an-
swer. It enables us to understand not alone how
atolls in deep water may have originated ; but
also how atolls in general were formed. It is
well known to geologists that the level of the
ocean bed is subject to change. It may be up-
heaved, or, again, it may subside. Darwin con-
jectured that as fast as the coral reef, ages ago,
was being built up toward the surface, it was car-
ried down by the subsidence of the ocean bed.

EXPLANATION.-Let us notice the successive
steps of this process. There is reason to believe
that in those parts of the ocean where atolls now
abound, high mountains once towered. These
mountains were islands. The polyps built encir- i
cling reefs around them.
But in many cases, as they built up, a glraduidal


subsidence took place, until the island itself disap-
peared beneath the waves. This subsidence on the
one hand, and this building up on the other, may
have continued for ages, and to the extent of thou-
sands of feet, so that where the mountain then
was, may be now deep waters and low atolls. Thus







(L) Section of mountain rising above water. (R R) Sections
of fringing reef resting on slopes.

s R', ____ ___ f R _





(L) Section of same mountain submerged : (Ri R) Sections of
same fringing reef become an atoll.

the mountain-top was replaced by the lagoon, and
the encircling reef became the atoll.
Tahiti affords an illustration of this process. It is a vol-
canic island with a fringing reef, the foundations of which
rest upon the submarine slopes of the island. It exhibits the
appearance which must have been presented by existing
atolls before the subsidence of the ocean floor had carried
down beneath the surface of the sea the mountainous islands
formerly enclosed by them.


TOPICAL ANALYSIS
IV. ISLANDS.

1. Classification.
2. Continental Islands.
Situation, Character.
3. Oceanic Islands.
nHow distinguished from continental.
4. Volcanic Islands.
Location. Formation. Elevation.
5. Coral Islands.
How formed. The coral polyp. Description. Work.
Coral reefs. Kinds. Atolls. Work ofthe waves.
Origin of vegetation. Characteristic animal and
vegetable life. Minerals,
6. Coral Groves and Coral Seas.
Clearness of. Beauty or.
7. Distribution of Coral.
8. Origin of Atolls.
Difficulty connected with. Depth at which lthe coral
polyp can work. Darwin's theory. Illustration
in Tahliti.

TEST QUESTIONS -Woutld yon contidcr :; coral island a desirable, place
of rvsidence Wly y









TOPICAL ANALYSIS FOR REVIEW.


TOPICAL ANALYSIS FOR REVIEW.


Arrangement of Land Masses. .


Forms of Land


Vertical Forms . ..


Relief Forms of the Continents.


Islands.


Relations of air, water and land to each other.
Extent and distribution of the land and shape of the continents.
Northern and Southern Hemispheres compared as to extent. As to progress.
Land and Water Hemispheres.



Horizontal Forms,


f Lowlands. Plains. Various kinds.


\ Highlands.


SPlateaus.
Mountains. Formation of.
SValleys. Kinds. How formed.
SCauses and effects of relief.


General features of continental relief.
North America.
South America. Resemblance to North America.
Europe, general description. Alps. Peninsulas of High Europe.
Asia.
Africa. The Sahara.
Australia.


r Continental.


O i( Volcanic.

{Oceanic ....

Coral.


Coral Polyp.
Coral Reefs. Classes of.
Development of the reef into an island.
Distribution of Coral.
Origin of Atolls.














PART III.


THE WATER,


I. PROPERTIES OF WATER.

1. Composition.-Turning from the land
we come now to the consideration of the water.
Its offices are of the highest interest and impor-
tance.
Pure water is composed of two gases, hydrogen
and oxygen, united in the proportion of two vol-
umes of hydrogen to one of oxygen.

2. Physical Properties of Water.-
The properties of water that specially interest
the Physical Geographer are the following:
(1) water changes its forms with remarkable
readiness;
(2) it expands when passing into the solid state;
(3) it has extraordinary capacity for heat;
(4) it has great solvent power.
F''i If- OF WATEit.-The three forms of water
are the liquid, solid, and gaseous. Changes of
temperature that are of common occurrence cause
it to pass from one to another of these.
Now it becomes a solid. Falling gently as snow,
it muffles up the young plants as with a mantle,
screening them from the biting winds of winter ;
as ice, it covers the surface of the lakes and the
rivers, and protects the denizens of the water, as
snow does the insects and tender plants of the
land.
Now it becomes a gas, and carries off water from
the sea to supply the springs among the moun-
tains that give drink to man and beast; or, man-
tling the earth with an invisible screen, prevents
the too rapid escape of its warmth at one time ;
or, assuming the form of clouds in the sky, shields
it from the too great heat of the sun at another.
Having fulfilled these duties, it turns again into beauti-
ful, dancing, laughing water. Enduring as the mountains,
it is one of the few visible things on earth upon which time,
since the world began, has wrought no marring change.
Friction abrades it not, nor have all the keels that have
ploughed the ocean wasted so much as one single drop of
it. There it is. pure and bright, just as it came from the
hands of its Maker; its power is unimpaired and always
fresh; it is ever busy and never weary.
ExPANSION OF WATER, -Water expands when


passing from the liquid state to the solid. This
is probably due to the fact that its particles, when
crystallized, require more space than before. When
cooled, it follows the general law, and contracts un-
til it reaches the temperature of 39,- Fahr Be-
low this it disobeys the general law, and expands
till it reaches 32 Fahr., its freezing point. Then
suddenly it hardens into ice, and attains its maxi-
mum expansion.
Because ice is more expanded than water, it is
lighter than water, and, as we all know, it floats.
The law by which ice floats is one of the beautiful
and benign provisions of nature. Were ice heavier
than water, it would sink as fast as it was formed,
and our river-channels and shallow lakes would be
filled with solid ice from the bottom to the top.
Expansive Force.- Another important conse-
quence of the expansion of water when freezing is
that it exerts a force that is practically irresistible.
It sunders the solid rock from the foundations of
the mountains, and crumbles it into fragments.
One of the most interesting effects of the force exerted
by freezing water occurred in Norway in 1717. The snow
covering a rocky region had rapidly thawed, and filled
the crevices of an enormous mass of rock with water.
Suddenly the weather changed. The water enclosed in the
crevices of the rock was frozen. Expansion occurred, and
a mass of rock was rent away and precipitated into the
neighboring fiord. The waters of this being suddenly driven
from their channel engulfed a household, and submerged the
adjoining fields.


EFFECTS OF EXPANSION PRODUCED BY THE FREEZING OF WATER.
Two bombs having been filled with water, and the fusee holes firmly
closed with an iron stopper, were exposed to intense cold ; on freezing,
the stopper of one was projected to a distance of more than 150 yards,
while the other bomb was split open and a sheet of ice was forced
through the crack.








PROPERTIES OF WATER.


CAPACITY FOR HEAT.-Water, of all known
substances, has the greatest capacity for heat. The
heat of bodies exists in two forms ; as sensible
heat, or that which you can feel, and insensible, or
that which you cannot feel. The latter is conm-
monly called latent, or hidden heat.
In the process of evaporation a certain quantity
of sensible heat is absorbed and rendered latent ;
in the opposite process of condensation a certain
amount of latent heat is released and made sen-
sible.
Capacity for heat" means the power possessed
by a body of storing away heat, and rendering it
latent or unfelt.
Explanation.-Suppose you take a cubic foot of ice at 27,
for instance; put it in a vessel and set it over a steady lamp
which affords sufficient heat to raise the temperature of the
ice 1 a minute. At the end of five minutes the ice would
be at 32. The heat has warmed the ice. It is sensible,
that is, you can feel it. The ice will now begin to melt, but



A ^ ___.- .. .. _-_____ :._- _


'r ..-


~- -' ..


CIRCULATION OF WATER.


the heat, instead of warming the ice or the water, only
melts the ice. At the end of 143 minutes all the ice will be
melted; but the temperature of the water will still be 32',
and no more. Now what has become of all the heat received
from the lamp during these 143 minutes ? It has gone to
convert the solid into a fluid, and has been rendered latent;
that is, it has been stowed away and concealed in the water.
Now let the lamp burn, as before, with sufficient inten-
sity to raise the temperature of the water 1' a minute. In
180 minutes the temperature will be raised from 32 to 212,
which is the boiling-point; and the water will feel hot. This
again is sensible heat. The boiling water, however, now
ceases to become hotter, but if you let it stay over the lamp,
you will find that, at the end of 967 minutes more, it will
have boiled away. Now the vapor thus produced has iden-
tically the same temperature as the water, viz., 212, so that
967' of heat will have been rendered latent.
Evaporation exerts a cooling influence.-From
the above it is evident that ice or water becoming
vapor, Labsorbs heat, and renders it latent or
hidden.
Condensation of water, on the other hand, exerts
a warmiina "'/'..' You niust have frequently


noticed, how, as a general rule, the intense cold is
mitigated just before a snow-storm. This is due
to the condensation of vapor into water, and the
freezing of that water into snow.
It has been computed that from every cubic foot
of vapor condensed, and frozen into snow, heat
enough is set free to raise more than 100,000 cubic
feet of air from the temperature of melting ice to
summer heat.
Nature makes great use of these counter-proper-
ties, the evaporation and condensation of water.
She bottles away the heat of the torrid zone in
little vesicles of vapor, thus cooling the atmos-
phere. She then delivers these vesicles to the
winds to be by them transported to other regions.
There they are condensed into rain, and their heat
set free to warm the air and modify the climate.
[See p. 86.]
THE SOLVENT POWER of water is another prop-
erty of great importance. The forms of
plant and animal life are largely built up
of materials which enter them in solution.
-- -. Water acts as a vehicle for conveying these
materials into the living system. It is es-
sential therefore to the maintenance of the
.:-:. life of the world.

S! 3. Circulation of Water.-The
S readiness with which water changes its form
.;- and passes from the liquid state to that of
S.'-_ vapor, and from the vaporous to the liquid
state again, is the means whereby a con-
--" stant circulation is carried on from the sea
to the land, and from the land back to the
sea again.
Let us trace its course. Incessantly the
waters of the sea are converted by the sun's heat
into invisible vapor. This passes into the air, and
the winds transport it to the land. Condensed, it
falls as rain or snow. It fills the springs and replen-
ishes the rivers; it waters the thirsty lands. Por-
tions of it find their way back to their home in the
sea, through the river channels; others, evapo-
rated, rise on the wings of the wind, and again,
being cooled, descend as rain or snow.
And thus all the water of the globe comes out of
the sea, as from a reservoir, and it all finds its
way back there again.

TOPICAL ANALYSIS.

I. PROPERTIES OF WATER.

1. Composition.
2. Physical Properties.
Forms of water. Case of changes of forms. Uses
in the solid form. In the gaseous form, Illn.
diestrictllile taoture if water.








WATERS OF THE LAND.


Expansion in freezing. Important result.
Capacity for heat. Heat rendered latent in melting.
In evaporation.
Effect of evaporation and condensation of water on
temperature and climate.
Solvent power.
3. Circulation of Water.
The great reservoir.

TEST QUESTIONS. -Name some forms of water remarkable for their
beauty. At what temperature is water heaviest ? In the circulation
of water between land and sea what force carries the water down to the
sea ? What force carries it back to the land ?


II. WATERS OF THE LAND.

1. Springs.-A portion of the rain which
falls upon the land flows off to the sea through
brooks and rivers. The larger part of it, however,
does not flow off, but accumulates in swamps and
lakes, or enters the ground. The latter portion,
sinking into the earth under the influence of
gravity, finally encounters layers of rock which it
cannot penetrate. It then follows the incline of
these layers, and flows for a greater or less distance,
until it reaches a point where the land is depressed.
Here it finds egress as a surface spring. If the
area through which such water percolates be large,


water, they crop out upon the surface. Dipping down,
however, they are perhaps 1,000 feet below the surface at the
point H. Between them is KK, a layer of gravel through
which rain water can percolate, but from which it cannot
escape, being confined by AB and CD. Trickling down
through KK the water accumulates. The tube of an Arte-
sian well, I, sunk through AB, enables it to rise to the height
of its distant source.
When the source of supply is very much higher than lhe
surface where the well is sunk, the water shoots upward
with considerable force. The jet from such a spring near
St. Etienne, in France, rises to a height of about 25 feet.
The French colonists in Algeria have sunk a number of
Artesian wells on the margin of the Great Desert of Sahara,
and thus supplied themselves with an abundance of water.


INTElIrTTE'.NT dPItNI.


and if the slope along which it flows be gentle, INTERMITTENT SPRINGS.-The springs which
then the spring will be perennial or unfailing, have excited the greatest curiosity are those which,
The depth to which percolating water descends is sur- from their alternate subsidence and flow, are called
prising. From a deep well sunk in a certain district of intermittent. The cause of thigf peculiarity is
France, pieces of leaves were thrown up by the first gush of illustrated in the accompanying cut, and will be
water from a depth of about 400 feet. These leaves were readily understood by any one who has seen a
comparatively fresh. They were ascertained to have come i s
-, , ^,., siphon used.
from a distance of about 150 miles from the spring. A
similar phenomenon has been observed in other places. The passage front the reservoir to the surface of
From the percolation of water through the earth arises the ground is curved like a siphon and acts in the
ane of the greatest difficulties in mining operations. Before same manner. Water percolates through the fissures
the invention of steam-pumps many coal pits in England in the rock and accumulates in the reservoir. As
had to be abandoned owing to thefact that, in the expressive soon as it rises above the level of the bend of the
language of the miners, they were drowned. i i t de
siphon, b, it begins to flow, and does not
---,':., cease till it has fallen below the mouth of
the passage at a. Thuns the reservoir alter-
4.\ "'" .I ,. .-".". /. .." , nately fills and discharges itself.
\ "^ -*::= *- ,,' -" .^. .- :-; .^"^ '''-, -
\,':.i' -r-J ---'-- --- -,/'^ ..-- .' -_, ,; THERMAL or HOT SPRINGs and GE,'SEilS
", \ ,i~--.- i,,/ ,. have been already discussed. [See p. 14.
-,K _._ .- .. ......" It remains to be said ttibt the waters of such
', ,. .. ....... --. .- _-_ l springs may be ejected in two ways : (1) in
." '" "" .- ."---:---- -- -,' --- :.i--.-. .' nge manner above indicated, the water seek-
11 v -. .t..- water . ,
-y ........_ '.. -----. .. ... _.ing th ie level of its source; or (2) by ti) e
---=- : ;' --_-.--" -Z-.:- -- .-':-- S?" - - 1 1.... 41 .. ........ ....,+ ,l 1 ,,,


ARTEItAN WELL.

Action of ArtesianWell.-- Thlie action of "Artesian wells,"
so called from Artois in France, where they were first used,
very clearly illustrates that of natural springs.
Let us suppose that ABl and CD, in the illustration, are
layers of rock impervious to water, and that at a distance of
500 miles or more from a desert or region ill supplied with


-IUlL UJo sU lelll, Uo gasesUl Sup/L-llaltbbUU- U i e
internal heat of the earth.

MINERAL SPRIrNGS abound in many parts of the
world, chiefly ini mountainous and volcanic regions.
-Their waters are charged with various substances.
Iron, salt, sulphlur, and earbonie acid are the most
Conimlon ingredient s.


<



(
1








WATERS OF THE LAND.


2. .Rivers.-Rivers receive their supply of
water from springs, or melting snow-fields and
glaciers. From various springs in one vicinity
little streamlets pour their contributions. Influ-















'Jf I(' I,

11 i. '


















[ ,T I ,
WATER DOING ITS WORK-RAVINE OF OCOBAMIBA.

enced by gravity these seek the lowest level. They
unite and form a river. Again, just as the stream-
lets issuing from a number of springs make a
river, so a number of rivers, all seeking the chan-
nel of greatest depression, blend together and make
one mighty water-course. Such a water-course, with
its tributary streams, is called a river-system.
Not unfrequently on the way to the sea a river passes by
a very sudden descent from a higher to a lower level. This
gives rise to cataracts. .',.. -_1".1,- to the violence of the
descent they are classed as rapids or waterfalls. When the
descent is very abrupt, but still not perpendicular, the
term rapids is properly employed. The cataracts of the
Nile and the rapids of the St. Lawrence are noted illustra-
tions.
The term waterfall is used when the water drops per-
pendicularly. The loftiest waterfalls are those of the Yosem-
ite in California, 2,500 feet, and the Keelfoss in Norway,
2,000 feet high.
The grandest of all waterfalls are those of Niagara. Here


the water discharged by four of the Great Lakes of North
America plunges in a single leap of 160 feet from the terrace
of Lake Erie to the lower level of Ontario.
OFFICES OF RIvERS.-Rivers, viewed as parts
of the terrestrial machinery, have two main
offices: (1) they bring about vast changes in the
surface of the earth ; (2) they are channels by
which the drainage of the land is accomplished.

3. Hovw 'ivers Change the .iificr' of
the _Earth.-The process by which rivers bring
about changes in the surface of the earth has
three stages: erosion ; transportation ; deposit.

EROSION means the eating away of the solid
materials which form the channel of a river. It
is brought about: (1), by the solvent power of
water; and (2), by its mechanical force when in
motion. These two combined wear away the more
soluble and soft clays and rocks with ease ; but even
the hardest cannot withstand their action.
If the soluble particles of a rock are dissolved
by water, the surface of the rock becomes disinte-
grated, and crumbles. Now, when a stream inces-
santly runs over such a constantly dissolving and
disintegrating rock, it is clear that erosion will make
rapid progress. The rock will be worn away.
The fragments thus removed are whirled con-
tinuously against the water, against one another,
and against the sides and bottom of the channel.
And thus, as the river rolls on, the particles eroded
become smaller and smaller. In the upper course
of the river they may be of considerable size." IS
the lower course they are reduced to fine sand and
sediment.
Example.-The erosive action of rivers is most impres-
sively illustrated by the excavation of rocky gorges. That of
the Niagara and the caions of our western rivers are per.
haps the most striking examples that can be offered.
The Falls of Niagara, it is evident, were at one period
about seven miles lower down the stream than they now are.
The vast volume of water that passes over the falls erode[
the edge of the cliff over which the water pours. Falling
from the height of about 160 feet upon the rocks below, it
wears them away, and thus erosion occurs both above and
below.
It has been computed that the rate at which the falls eat
their way up the gorge is about one foot a year, and that
therefore it has taken them about 35,000 years to pass back-
ward from Qucenstown to their present point. At the same
rate they will have worked their way back to Lake Erie in
about 30,000 years from the present time.
TnRANSPORTATION. -The finer particles of eroded
matter are carried along by the river in suspension,
that is, simply mixed with the water. The coarser
portions are rolled onward by the force of the
current. This twofold action constitutes trans-
portation.
A river will transport eroded matter to a greater








WATERS OF THE LAND.


or less distance, and in greater or less quantity, in
proportion to the velocity and -oluhme of its cur-
rent. Water moving half a mile an hour will
carry along ordinary sand. If the velocity be in-
creased to three-quarters of a mile, it will roll fine
gravel, while a current having a speed of three
miles an hour, can sweep along pieces of stone as
large as eggs. In floods masses of rock as large as
a house have been moved.
As to the quantity of matter transported, it is
estimated that of visible sediment the Rhone
carries into the Mediterranean more than 600,-
000,000 tons annually, and of salts invisibly dis-
solved, more than 8,000,000 tons. The amount
of silt carried into the Gulf of Mexico by the
Mississippi in one year, would make a column one
mile square and 241 feet high.

The removal of this matter from the surface of the il.
reduces its average level one foot in 6,000 years. Could the
same rate of denudation be kept up continually over the
entire surface of North America, it would reduce the con-
tinent, which has an elevation of about 750 feet, to the level
of the sea inl half a million years.

DEPoSIT.-The materials borne or rolled along
by rivers are deposited at various points in the
channel. The finer portions called silt, familiar
to us as muddy slime, are carried down as far as
the mouth of the river. Farther up the stream
sandy particles come to rest ; still higher, gravel
is deposited ; and finally, in the upper course of
the river we find stones of greater or less size.
It is obvious that deposit will depend very largely
upon the slope of the river-bed and the rapidity


of the current. Any-
thing that cheeks the
latter favors deposit.
RESULTS OF DE-
POSIT.-The main re-
sults of deposit are
changes in river-
courses; and the for-
mation of bars and
deltas.
('. ... in river-
courses are frequent
effects of deposit.
They occur especially
in rivers that flow
through alluvial lands.
Very often the course
of such streams is
marked by what are
called sinuosities, or


sharp curves resembling the letter S. The lower
Mississippi presents a striking illustration of
this. [See diagram.] In some eases portions of


the land are carried from one side of the river to
the other, giving rise to the important question to
whom does the land so transferred belong.
Sometimes, as when a river is unusually high, itl
may make for itself a straight course instead of
following its old curves. The impetus of the
swollen waters forces them through the soft clay
banks. The portion of the old channel that is
abandoned is closed by silt at each end, and be-
comes a lake.
Bars.-But by far the most important cases ofl
deposition are those which occur at the mouths of
rivers. Here the current of the stream is checked
by the mass of the ocean waters, or by the in-
coming tide. Along the line of meeting, it is clear
that there will be comparatively little movement,
and in consequence there will be, in the case of.
large rivers, vast deposits of sediment. This is
the process by which bars at the entrance of
harbors are formed.
The Mississippi, and all the rivers of the United
lh, that flow directly into the Atlantic Ocean,
have bars.
So great is the amount of solid matter brought down by
the Mississippi that a bar no less than two and a quarter
miles in breadth was formed off one of its outlets called the
South Pass. Fleets of vessels more than fifty in number
might sometimes be seen, detained on the bar for weeks,
ii',- for a chance to go to sea, or enter the Pass. The
operation of towing a ship into the deep waters of the Gulf
occupied days, and in some cases weeks.
In 1875 Captain Eads, by the i..i .i, of Congress,
constructed jetties or long walls, which narrowed and con-
fined the current, and thus gave it greater velocity, and, or
course, greater power to scour out the channel and carry off
the sediment into deep water. A similar project has been
proposed for keeping the mouth of the Danube free from
obstructions.
Deltas.-Then again, when the river waters
encounter the waters of the sea, the check to their
velocity will extend some distance up the stream.
Hence deposits are likely to occur near the mouths,
and some distance above the mouths, of all silt-
bearing rivers. In this way are formed in the
course of ages what are termed the deltas of rivers.
The Mississippi, the Nile, the Ganges, the
Orinoco, the Danube, the Volga, and many other
rivers which flow into inland seas or gulfs protected
from the sweeps of the tides and ocean currents,
are famous for their deltas.
But where there is a very strong littoral current,
it sweeps off the sediment as fast as it enters the
sea, and there is no delta formed. This is the
case with the Amazon, the Rio do la Plata, and
with all the American rivers that empty into the
Pacific Ocean.
The area of deltas is often very large. That of
tile M'. .-IT.q is about 12,000 square miles. One


NUOSITIES OF THE MISSISSIPPI.
SIUaOSITIES OF TOlE MI~ISIS5PPI.









WATERS OF THE LAND.


third of it is still in process of formation, being as
yet only a sea marsh.
Branchiing of Rivers in Del'as.-Not alone is sediment
dileposited upon the bed of rivers, out also upon their banks.

.. . . : -, .:. .,.-. .. .

SECTION OP THE MISSISSIPPI.

This has the effect of raising the banks above the general
level of the neighboring country. In some portions of their
course both the Mississippi and the Po are above the adja-
cent fields. The land, therefore, slopes from the river on
either side. and one goes up to it instead of dow-n fo it


."" - r -


I,,,





DELTA OF lIISSI1Il'1.

Now if we bear this in mind, and remember, also, that
the natural bank of the river is only a mound of sediment,
we shall see how readily, in case of flood, the river may
divide into branches and make for itself new outlets. This
is to be observed iin all delta regions. It is admirably shown
in the case of the Mississippi delta in the accompanying
illustration.
This branching of rivers in passing through their deltas
serves to explain why many rivers, such as the Nile, the
Mississippi, the Ganges and others, have more than one
outlet.

4. Relation of Rivers to Ocean Life.-
When the rivers have discharged their waters into
the sea, they have not yet finished their task.
Sea-shells and coral-rocks are formed chiefly of the
limestone which is dissolved and gathered by the
rains and running waters from the mountains,
plains and valleys.
Of materials thus collected and brought from
Upper Egypt by the Nile, and from the mountains
of Asia by the great rivers of India and China, or


from the peaks of the Andes by the Amazon-of
such materials the great whale and all the fish of
the sea form their bones, the pearl oysters make
their jewels, the sea-conch its shell, and the coral
polyps their evergreen islands.
Water is thus seen to be one of the most wonderful and
benign agents in the terrestrial economy. It is as marvel-
lous in its properties, in its adaptations, and in the perpetual
development of the most beautiful phenomena, as is the fire
on the hearth. It not only performs the offices that are
familiar to us all, and which have almost ceased to be
observed, or, when observed, have ceased to surprise us,
but, ever in a thousand unfamiliar and hidden ways, it is
fulfilling the beneficent will of Him who created it.

5. Lakes.-The formation of lake-basins may
be ascribed to various causes. Of these the follow-
ing is, perhaps, the most frequeAnt. When the
surface of the earth was crumpled as described on
page 28, depressions of greater or less depth were
necessarily formed. Some of them, receiving the
rainfall drained from neighboring slopes, became
the basins of lakes.
FRESH-WATER LAKES.-In the case of lakes
situated in cool or damp regions precipitation is in
excess of evaporation, or, in other words, the
amount of rain falling in the vicinity of such
lakes, and carried into them by streams, is greater
than the amount of water taken up from the
surface by evaporation. They gain more than
they lose.
Clearly, therefore, there will come a time when
an overflow must occur. The waters that no
longer can be contained by the lake-basin, will
break through the rim at some weak point, and
form for themselves a channel to the sea. In
doing this they will sometimes cut pathways
through the densest rock, or burst through the
barriers of the everlasting hills. Hence rapids
and waterfalls, water-gaps, gorges and canons.
SALT LAKES.-In the case of lakes situated in
regions of great warmth and dryness, the amount
of water evaporated is sometimes equal to that
which is supplied, and sometimes greater. As
fast as the water is poured in by the rivers it is
carried away in the form of vapor and clouds.
Such lakes are never filled to overflowing, and,
consequently, have no outlets.
The water of lakes having no outlets is commonly
salt. The water of lalces having outlets to the
sea is fresh.
Expjlanation. -Rivers carry into lakes, in solution,
many saline materials, of which one of the most
abundant is chloride of sodium (common salt).
This is present in ordinary river water, although
it cannot be tasted ; but if a large quantity of such
water were evaporated, a small amount of


'". i I i








WATERS OF THE LAND.


YELLOWSTONE LAKE.


would be left behind. Thus it is clear that if a
lake have an outlet, not only is its superfluous
water removed, but the salts brought in are also
taken out.
On the other hand, if a lake have no outlet, then,
while the water brought in is removed by evapora-
tion, the salt introduced remains behind. Thus
lakes having no outlet may be compared to the
evaporating vats or troughs in which, as at many
points on the shores of the Mediterranean Sea,
water is boiled, or evaporated by solar heat in the
manufacture of salt. The water passes off, the
salt remains. Hence, year after year, salt lakes
become salter.
Conspicuous examples of salt lakes arc the Great Salt
Lake and the Dead Sea. Both of these are heavily charged
with saline ingredients. The water of the Dead Sea is
about one fifth heavier than that of the ocean, and sustains
the human body so that it cannot sink in it. From its
great salinity the Dead Sea is often called the Sea of Salt.
But the Jordan, which supplies it, is of course fresh.
The Dead Sea is situated in a depression remarkable for
its intense heat, and the region in which the Great Salt Lake
lies is very remarkable for the dryness of its atmosphere.
In the case of both these lakes, therefore, evaporation pro-
ceeds at an enormous rate.
INLAND SEAs.-Some inland bodies of salt
water, however, have evidently been at one time
parts of the ocean. These are properly designated
inland seas. The most remarkable of them are
the Caspian and Aral.
When the Arctic Ocean extended, as geologists
believe it did, southward as far as the mountains
of Persia, these two seas and many neighboring
bodies of salt water were included within its limits.
Seals and certain fish, which are inhabitants of
oceanic waters, are found even yet in the Caspian.
Like other salt lakes these inland seas have no
outlet. The Volga, the largest river in Europe,
and the Ural pour volumes of water into the


Caspian, yet its level does not rise. The Sea of
Aral receives the Oxus and the Jaxartes ; yet its
level seems actually to be lower than formerly.
%[ ,,, small salt lakes entirely evaporate duitring
the summer, and leave their beds covered with
saline incrustations. From the dry bed of Lake
Elton, in the Caspian region, i,'.n, tons of salt
are annually gathered.

6. Offices of Lakes.-Lakes are reservoirs
for the rivers. They hold the waters back in time of
flood, and give them out in time of drought. They
thus help to maintain a constant rate of discharge
and a uniform stage of water in the rivers. Hence
the Niagara, the St. Lawrence, the Nelson, Mac-
kenzie, and other rivers, that are fed by large lakes,
never overflow so as to devastate with floods tihe
country through which they run.
On the other hand the lower Mississippi is sub-
ject to frequent inundations, because it is swelled
by the floods of its principal tributaries, and there
are no lakes to hold back the surplus waters.
Lakes again are sources from which supplies of
vapor are obtained, to be gathered into clouds, and
in the form of dew or rain to water the hland.

'7. Geographical Distibution of L La(lkes.
-In North America are found the vast bodies of
fresh water which are called the "Great Lakes."
The northern part of the Great Central Plain of
the continent abounds in lakes, of greater or less
magnitude. In the Basin between the Rocky
Mountains and the Sierra Nevada there is a region
of saline lakes.
In Europe, the great lake region lies in Northern
Russia and Scandinavia. Ladoga and Onega,
Wener and Wetter are the largest lalkes of the
continent. Those of the Alps, Como, \i.*,_..!.
Geneva and others are comparatively small, but
famed for their beauty.








o50 DRA]


Asia is noted for the size and number of its salt
lakes. The Caspian, Aral and Dead seas are
examples. Of fresh water lakes Asia has few.
Lake 3Baikal, however, 400 miles in length, may be
compared with our own Lake Superior.
Africa rivals North America in the magnitude
of her great lakes. Victoria and Albert Nyanza,
Tanganyika and Nyassa are the largest.
South America has two lakes of importance,
Titicaca and Maracaybo. Australia is nearly
destitute of lakes.


TOPICAL ANALYSIS.
f. WATERS OF THE LAND.


1. Springs.
How caused. Artesian wells.
Intermittent springs. now caused.
IHot springs and Geysers. Forces by which tlhe
water is ejected. Mineral springs. Common in-
gredients.
2. Rivers.
How formed. River-systems. Cataracts. Rapids.
Waterfalls. Noted falls.
Oltces of rivers.
3. How Rivers change the surface of the Earth.
Erosion. ITow brought about. Effects on eroded
material. Gorges and caflons.
Transportation. Transporting power, how in-
creased. Quantity of matter carried down by the
Rlihone and the 2Mississippi. Deposit of eroded
material, by what occasioned.
Resunits of deposit. Changes in river-courses,
how caused. Bars, how formed. Deltas, how
formed. lRemnarkable deltas. Formation of, lhow
prevented in some cases. Branching of rivers.
4. Relation of Rivers to Ocean Life.
5. Lakes.
Formation of. Cause of overflow. Salt lakes.
Cause of saltness. Examples. Inland seas.
6. Offices of Lakes.
7. Distribution of Lakes.
In each of the continents.

TEST QnUEsIoxs.-If the soil were everywhere equally permeable to
water, how would that affect the springs ? What kind of springs may
rise higher titan their source, and why? Why are mineral springs so
called I HIow can the water supplied by rivers make tlie ocean saltecr ?
Why is tlhe St. Lawrence not subject to floods? Largest inland sea in
the world ? Largest body of fresh water ?


III. DRAINAGE.

1. Adi,, r ,.i ifq i.. of Drainage,--The sec-
ond great office of rivers is to effect the drainage
of the land.
Any portion of thle globe, to be well adapted for
human occupation, requires to be drained. As a
rule crops do not flourish in a cold, damp soil; and


INAGE.


precisely so human health and strength cannot in
general be maintained where the ground is always
wet. The vicinity of swamps is unhealthy.
For this reason a very large area of the sunny
peninsula of Italy, called the Campagna, is almost
uninhabited. From the days of ancient Rome
until now it has remained, owing to the level
nature of the land and the consequent absence of
any stream into which the waters might be
directed, a vast swamp and a breeding ground of
pestilence.

2. Htowv Drainage is Effected.-Drainage
is accomplished by two combined causes : (1) un-
evenness of the land ; (2) the flow of rivers.
The mountains and slopes of every country
determine in a large measure the number of its
water-courses, their length and direction, and the
velocity of their currents-in a word, their capacity
for carrying off -""". i1,....1 rain-water.
The rivers are the channels through which the
water carried from the sea in the form of vapor
and rained upon the land finds its way back to
the sea. Every running stream may therefore be
regarded as a kind of rain-gauge, which measures,
in a general way, the quantity of rain that falls
upon the valley which it drains.
The region drained by a river-system is called
the river-basin. The basins of large streams are
hundreds of thousands of square miles in area.
That of the Mississippi contains nearly 1,250,000
square miles.
The limits of a river basin are defined by what
are termed water-sheds, i.e., water-divides, shed
being from a German word meaning to divide. A
water-shed is a line of elevation, sometimes lofty
and sometimes low, which, like the ridge of a roof,
divides the rain as it falls, and causes one portion
to descend one slope of a country or continent, and
the other portion another.
If on a map of North America you trace a pencil line
round the sources of all the rivers that pour into the Mis-
sissippi from the Appalachian slope on the one side, and from
the Rocky Mountain slope on the other, you will have
marked out the water-sheds which define the eastern and
western limits of the Mississippi basin.
The '- -, t.- amount of water discharged into
thle ocean by all the rivers of the world is com-
puted at more than two and a half million cubic
yards per second. All this volume of water, too
vast for us to conceive of, is being incessantly
removed from the surface of the earth, so as to
render and keep it suitable to be the abode of man.
This shows how busily and grandly the terrestrial
machinery works.
TNUNDA-TIONS.-The inundations which occa-
sionally submerge large areas of land, and are so








CONTINENTAL DRAINAGE.


destructive to life and property, occur where the
quantity of water to be removed exceeds the capac-
ity of the draining rivers. Many rivers, as the
Nile, the Orinoco and the Mississippi, are subject
to periodical overflow. So extensive are the inun-
dations of the Po that the Italian engineers have
actually proposed a scheme for cutting an artificial
channel to be used in case of emergency.

TOPICAL ANALYSIS.
III. DRAINAGE.

1. Advantages of drainage.
2. How drainage is Effected.
River-basins. Water-sheds. Quantity of water de-
livered by rivers. Cause of inundations.
TEST QUESTIoNS.-Which of the oceans receives the greatest amount
of drainage ? What ocean is without a single river flowing into it, so
far as known ?


IV. CONTINENTAL DRAINAGE.

1. 2Vorth America.-The four bounding
waters of North America are the Arctic, Atlantic,
and Pacific Oceans, and the Gulf of Mexico. These
receive the drainage of the continent.
Thli6 great water-shed is the Rocky fountain
system. It acts like the ridge-pole to the roof of
a house, shedding the water to the east and the
west. All the region lying westward of it is
drained into the Pacific and into Behring Sea by
the Colorado, the Columbia, the Frazer, the Yukon
and other rivers of less importance.
East of the Rocky Mountains the continent is di-
vided by the Height of Land and the Appalachian
Mountains into three slopes : a northern inclining
toward the Arctic Ocean ; an eastern toward the
Atlantic; and a southern toward the Gulf of
Mexico.
The region lying north of the Height of Land
is drained by the Mackenzie, the Saskatchewan,
and certain other streams which enter Hudson
Bay. Southward of the Height of Land we have
the great basin of the Mississippi, the drainage of
which is poured into the Gulf. This basin em-
braces all that enormous area which lies between
the Rocky Mountains on the west, and the Appa-
lachians on the east.
The amount of water carried by the Mississippi from this
region into the Gulf of Mexico every second is 675,000 cubic
feet, enough, in other words, to cover about 18 acres of
ground to the depth of a foot. We can see from this how
soon the Mississippi basin would become a desolate swamp,
if it were a dead level untrenched by its mighty system of
rivers.
The eastern slope of the continent, including
the terraced plateau occupied by the Great Lakes,


is drained by the St. Lawrence and by :t series ol'
rivers large and small which l.. from th' Appal-
lachians to the Atlantic.

2. South Ante-ica.-The drainage of Souli
America, like that of North America, is mainly
effected by one river system. fThe crest qf the
Andes is the great wvater-shed. It lies along tihe
western edge of the continent. Silence the drain-
age has in general an easterly flow.
The eastern slope embraces nearly the whole of
the continent. It is naturally divided into three
great river basins, those of the Orinoco, the La
Plata and the Amazon. The last contains the
,.,. '" river system on the globe.
The Amazon 1,. i .1 -. six times as much water as the
Mississippi. In respect to volume it is the largest river in
the world. It rises in the beautiful little lake of Lauricochia,
high up among the Andes. Descending ., ,I II, I rapids,
it reaches the alluvial country below, and then becomes a
stream navigable for large steamers from the foot of tlh
mountains to the sea, a distance of about 2,200 miles.
So great is the force of its current that its fresh waters
are carried a distance of about 200 miles into the sea. An
ocean current passes near its mouth, and sweeps away
sediment as fast as the river brings it down. Thus tlih
river's own current andl the ocean current prevent tihe
formation of a bar.
The western slope of the continent is steep and
narrow. There is no room for long, and no water
for large rivers. The Pacific receives only a few
small mountain torrents, fed by the melting snows
of the Andes.

3. Europe.-From a point in the Ural Moun-
tainis at about latitude 61 north, to the Yaldai
Hills, thence in a south-westward direction through
Central Europe down to the southern shores of
Spain, an irregular line may be traced which will
separate Europe into two great slopes. The one
inclines to the northwest, the other to the south-
easit.
All the rivers have one or the other of these two
general directions; and the continent is drained
into the Mediterranean, thle Adriatic, the Black
and Caspian Seas on the one side; or into the
Atlantic and Arctic Oceans, and the North,
Baltic and White Seas on the other.
The region of the Alps is drained by four
streams, the beautiful Rhine of the Germans, the
Rhone, the Danube and the Pc ; the 1I i ;,,-... of
the Low Plains is accomplished by a number of
rivers, among which the Volga, the Don, tle
Dnieper and the Dniestcr are conspicuous.

4. Asia.-The continent of Asia, like that of
Europe, may be regarded as consisting of two
great slopes, one having a general incline toward
thle north, the other toward the south and cast.









CONTINENTAL DRAINAGE.


Beginning on the western shore of Asia Minor,
a line may be drawn to Mount Ararat, thence
along the crests of the Elburz and IHindoo Koosh
Mountains, thence north-eastwardly to the Sea of
Okhotsk, which will represent the great water-shed
of the continent.
Southeast of this line the Euphrates and Tigris,
the Indus, Ganges, the Yang-tse-Kiang, the
Hoang-Ho and Amoor carry the drainage to the
southward and eastward into the seas and bays of
the Pacific and Indian Oceans.
On the northern side of the line nearly every
important river flows in a northerly direction into
the Arctic Ocean.

5. Afriea.-The drainage of Africa is accom-
plished in the main by the four great river systems
of the Nile, the Niger, the Congo and the Zambesi.
IMuch of the surplus water of the continent, how-
ever, is removed by evaporation.


6. Australia.-Australia is scantily supplied
with rivers. The Murray and its tributaries are
the only water-courses of importance, and they are
often reduced in the dry season to a mere chain of
ponds and creeks.

TOPICAL ANALYSIS.
IV. CONTINENTAL DRAINAGE.


North America.
South America.
Europe.
Asia.
Africa.
Australia.


Physical divisions of the surface
and resulting drainage.


TEST QUESTIONS.-Largest river that flows into the Atlantic ?
Pacific ? Into the Indian Ocean ? Largest river in the world that does
not reach an ocean ? What river of North America corresponds in
magnitude and location to the Orinoco of South America ? To the La
Plata ? Besides rivers, and rain or snow, do you know of anything
else that supplies fresh water to the Ocean ?


THE SEA.


The most interesting feature in the drainage system of
Africa is the river Nile. But for it Egypt would be as
barren as the Great Desert of Sahara. The river is formed
by the junction of two streams called the White and the
Blue Nile. The former issues from the Equatorial Lakes.
The latter rises among the hills and the table-lands of
Abyssinia.
During June, July, and August the rains pour down in
torrents upon the regions drained by these streams. Each
is flooded. Uniting at Khartoom the descending torrents
reach Cairo by the middle of June, and during the latter
part of summer and in the autumn the whole of Egypt is
under water.
As the flood subsides a layer of fertilizing sediment is
deposited upon the land. Most of it has been washed down
from the Abyssinian hills by the Blue Nile, which takes its
name from the color which the sediment imparts to its waters.


V. THE SEA.


1. Extent of the Sea.-Nearly three-
fourths of the earth's surface are covered by water.
This surface comprises, in round numbers, an
area of 197,000,000 square miles, of which about
53,000,000 are land, and 144,000,000 water. All
of the land, except 13,000,000 square miles, is on
the north side of the equator. The northern
hemisphere therefore contains three-fourths of all
the known land, and two-fifths only of the water-
surface, of the world.

The extent of water that is visible to the eye at one time
is not great. If we stand on the shore and look seaward,









THE SEA. 53

our view is closed in by a line in which sea and sky appear In certain parts of the Indian Ocean the waters,
to meet. To this line we give the name horizon, i.e., bound- as seen from a distance, are black.
ing line. Its distance from us depends on our elevation. a s f d, bp,
If we occupy a position which is elevated six feet above the In the Mediterranean, in the, Gulf Stream, and
sea-level our horizon will be three miles off. If we ascend between the tropics generally, the sea waters are
a bluff or lighthouse, and so gain a point about 100 feet dark blue ; along the shores and near the mouths
high, our horizon will be twelve miles distant, of great rivers and in coral seas they arc green.
Thus the sea assumes here and there various
2. Saltness of the Sea.-Various solid shades of color; yet its waters, when taken by hlie
ingredients are found dissolved in sea water. Of tumblerful, are as clear as the purest crystal.
these the most abundant is what we
call common salt. Others are cer- --- - - - - _-__-
tain compounds of lime, magnesium, .-_.--" -----
potassium and iodine. The solid 57'\a-. -'
ingredients may be estimated on ans
average as about one-thirtieth part
of the whole by weight.
Though there is little variation from the .
average, yet it seems to be well ascertained ,a
that within the regions of the trade winds // =0 I-
(see p. 70.) the proportion of saline ingre- ----'--.. .-. i I
dients is greater than elsewhere. This is ," "
natural, since in that region evaporation* 'I
is at its maximum. North and southof of -- .
the trade-wind region there appears to 5 "'
be a progressive diminution of saline mat-. .---_----
ter as the poles are approached. -=__--_


3. Origin of Saltness.-Sup-
posing the water of the sea to have .
been originally all fresh, it is easy ..
to see how in the lapse of time it
can have become salt. The case of
the sea may be compared to that of
a lake with no outlet. All the rivers
run into the sea and carry into it im-
mense quantities of saline matter.
The amount thus contributed during the past ages
of the world's history would be simply inconceiv-
able-amply sufficient to account for the present
saltness and density of the waters of the sea.
Another theory is, that when the vapory materials consti-
tuting the earth were originally condensed (see p. 7), the
saline substances were among the last to be condensed and
deposited. Following soon after these watery vapor was
condensed, and falling as rain washed the saline deposits
into the ocean-basin. According to this view the sea was
salt from the beginning.

4. Color of the Sea.-The sea is green, or
blue; it is sometimes colored here and there by
reddish, or whitish, yellowish, or crimson patches,
according to the tints imparted by the color of the
bottom, by the shadow of the clouds, by the ingre-
dients of its waters, or by its myriads of organisms.

Evaporate a small portion of sea water until it is very much concen-
trated. Then take a drop of this concentrated fluid and put it on a piece
of thin glass under a microscope. You will see the saline substances
which have given the sea water its peculiar taste crystallizing in regular
shapes as the water gradually dries from the glass.


PHOSPHORESCENT SEA.


5. Phosphorescence.-In most parts of
the sea the water is phosphorescent. The phos-
phorescence is caused by certain animalcules,
which, like glow-worms and fire-flies on the land,
have the power of emitting light, some in flashes,
and some in a steady glow. These little creatures
are invisible to the naked eye, but they are as
multitudinous as the sand, and as beautiful as the
stars.
In tropical seas and in certain waters they tip
the waves with flame, and cover the sea after dark
with sheets of light. As the ship ploughs these
waters, she leaves a bright streak far behind in her
wake.
Though we cannot see the dolphin and other fish, as they
sport in the depths of these phosphorescent seas, yet, by the
streaks they leave behind, we can often track them through
the water, as we do rockets through the air. As they chase
each other in the mazes of their sport, these threads of light
are, to those who are fortunate enough to see them, among
the most pleasing wonders of the deep. They are particu-
larly beautiful in the harbor of Callao.

6. The Temperature of the Sea is in









THE OCEANS.


general highest near the surface. In the equato-
rial waters the average surface temperature is about
80 Fahlir., sometimes rising in the Indian Ocean to
90 Fahr., and in the Red Sea to 94. Towards
the bottom the temperature is depressed. Indeed,
near the bottom all over the globe deep-sea water
seems to be about as cold as that of the Polar seas.
The variations at the same place between the win-
ter and summer temperature of the sea rarely ex-
ceed 10. Thus, in Polar seas, the surface-water is
seldom above 42, nor in equatorial below 68.

'. Offices of the Sea.-(1) The sea receives
the drainage of the land; (2) it wears away or
builds up the land ; (3) it supplies the atmosphere
with moisture ; (4) it is one of the great regulators
of climate ; (5) it is the highway of the nations.
Commerce, civilization and Christianity have been
. ir .i on its bosom to the ends of the earth.

TOPICAL ANALYSIS.
V. THE SEA.
1. Extent.
Comparative sea area in northern and southern
hemispheres. Extent of water visible at one
time.
2. Saltness.
Due to what ingredients. Quantity of saline matter.
Variation of saltness with distance from the
Equator.
3. Origin of Saltness.
4. Color of the Sea.
5. Phosphorescence.
Cause. Beautiful effects.
6. Temperature.
Surface temperature in Equatorial regions. Deep
bottom temperature. Variation with the season.
7. Offices of the Sea.
TEST QUEsTIONs.-Why should the sea be saltest where evaporation
is greatest ? Why should it be coldest at the bottom, while the land
grows warmer as we descend ? Why should the Red Sea be warmer
Chan the Indian Ocean ? Why does not a glass of sea water show the
0ame color as the sea itself ?

VI. THE OCEANS.

1. The Oceans.-The sea is one immense
body of water encircling the globe. It is, how-
ever, divided by the intervening land masses, or
continents, into smaller bodies, called oceans. Of
these the Pacific is the largest. It contains more
ihan half the water of the sea. Next in size, but
only about half as large as the Pacific, is the At-
lantic. The Indian is the third in area. The
Arctic is properly only an extension of the Atlan-
tic, while the Antarctic hardly deserves to be re-
garded as distinct from the main body of the sea.


OCEAN BASINS.-The form of each ocean basin
depends naturally upon the shape of the enclosing
continents. The Pacific approaches the oval; the
Atlantic has been compared to a long trough ; the
Indian is triangular, while the Polar oceans cannot
be said to have any describable shape.
Of all the oceans the Atlantic is the most marked
by indentations of its shores. The Asiatic edges
of the Pacific and Indian oceans are also well sup-
plied with bays and border-seas.

2. _Depth of the Oceans.-Two questions
connected with the subject of ocean basins have
been within a few years made matter of accurate
investigation-their depth and the nature of their
bottom.
The average depth of the Atlantic is about
15,000 feet. It seldom exceeds 18,000 feet, or 3
miles. The deepest sounding was near the island
of St. Thomas. It was 23,250 feet, or rather less
than 4- miles.
The average depth of the Pacific seems to be
about the same as that of the Atlantic. It has,
however, deeper abysses. Soundings of 41 and 5
miles have been obtained. These are the very
deepest that have been accurately measured.

3. The Pvolbf,,. of the Ocean is, like the
land, diversified with hill and dale. Vast plateaus,
banks, and shoals spread themselves out; and
mountains rise from the ocean depths far more
abruptly than they do on the land.
San Domingo and many other islands of the sea
rise from the bottom to the surface almost per-
pendicularly. The Silla de Caracas, on the other
hand, which is the steepest mountain in the world,
rises at an angle of 53.
BED OF THE ATLANTIC.-The bed of the Atlan-
tic has been more thoroughly examined than any
other. It seems to consist of two nearly parallel
valleys extending north and south and separated
by a lofty dividing ridge. The islands which are
scattered along its length are the summits of this
ridge. That portion of the Atlantic bed to which
the name of T ... ,.. Plateau has long been
given is of special interest. This plateau stretches
entirely across from Newfoundland to Ireland, at
an average depth of somewhat less than two miles.
If we imagine ourselves walking across it from Newfound-


NOTE.-The practical value of the information derived from the
Atlantic deep-sea soundings was early appreciated by the author of this
book. Almost as soon as the results of the soundings were made known
to him, he saw that the laying of a telegraphic cable was a practicable
project. le was the first to suggest and urge the carrying out of this
scheme, the accomplishment of which has been one of the grandest
achievementsof modern science. To Alaurybelongs the glory of having
pointed out a highway under the waters, whereby the ends of the world
have been brought into instantaneous communication.-THE REVISER.








'n7 ANT TFO A ITTC XT mTor.


Vt ~t~X V Jjn.7 .51.1


N


05 Longitudte 30


klp l I i 55


rom 0 Greenwich i0 West 0 'F:.t



S_. .,__ '.'-


j-. ----
/ i -- : j; :-.: --,- : .___ ].


VERTICAL SECTION OF THE ATLANTIC OCEAN AT 52 NORTH LATITUDE. Sca. -1 lOeucslngth lO00ft. heilt


land to Ireland, we shall first descend by an easy slope to ocean. When however, we have performed half our
the Grand Banks. Dere the depth is about 1,000 feet. journey, we shall ascend again, first, ranipidl'- and then
Leaving the Grand Banks we shall pass quite rapidly to the gently, until we reach the neighborhood of t1he British Isles.
depth of about 13,800 feet. From this point there is not For a distance of about 23:0 miles westward of Ireland the
much variation in the depth for about half way across the upward slope is very gradual until we gain the dry land.


50 Longitude West 40 from Greenwich 30


, ,. ,,M

' :' - --- .'.. :'. "


VERTICAL SECTION OF THE ATLANTIC OCEAN AT 1448 NORTH LATITUDE, Scale-10 Oiles lcngjhI 1000J'l. h ijlt


BED OF THE INDIAN OCEAN.-The soundings TEST QUESTIoNs.- low does the average depth of the ocean compare
with the average height of the rand 9 Fsee p. 07.] hy should iI]ands
thus far taken in the Indian Ocean seem to indicate rise more perpendicularly under the water than mountains d.o tn the
that the configuration of its bed is not unlike that land?
of the Atlantic.


It is believed that two valleys similar to those
of the Atlantic traverse this ocean. As in the
Atlantic they are nearly parallel and extend in a
north and south direction, while a ridge indicated
by the Laccadive, Maldive and ('ih ..- Islands
separates them.

BED OF THE PACoIFIC.-Of the bed of the ',. ii
we have little accurate knowledge. Judging from
the multitude of islands, great and small, which
diversify its surface, we know that a corresponding
number of rock masses, miles in height, and
shaped like gigantic columns, must rise abruptly
from its floor.
The cruise of the ship Challenger revealed the
fact that in the bed of this ocean are the greatest
depths hitherto measured. One sounding gave a
depth of more than 5 miles; another about 42-.
No complete survey has, however, been made as
yet.

TOPICAL ANALYSIS.
VI. THE OCEANS.
1. The Oceans.
Number and relative size. Form of basins.
Indentation of shores.
2. Depth.
Of the Atlantic. Of the Pacific.
3. Bottom.
General form as compared with the surface of the
land. Bed of the Atlantic. Of the Indian Ocean.
Of the Pacific. Practical value of deep-sea
sonndings upon the intercourse of nations.


VII. WAVES AND TIDES.

1. TVa ves,.-" The troubled sea t]hat cannot
rest" has ever been the enibledm of unending
movement. laves, tides, aind currents incessantly
disturb it.
Tarves (oe causf(d l t1ihe wind. -Thle wind
strikes with more or less force upon tihe surface of
the sea, and thus produces an alternateli upwardly
and downward movement of its waters. A mass
of water moved in this way is called a wav.n
The elevated portion of the water is called the
crest of the wave ; the distance from one crest to
another is the breadth.
WA-V-MOVENLENT.-The rolling in of waves
upon the beach produces tHle impression that the
entire body of water is minoving toward the land.
As we shall see, however, when we come to con-
sider the subject of tides, it may actually be reced-
ing. We minst, therefore, distinguish between
the motion of the wave-movement and the motion
of the water.
To illustrate: If w e produce a ripple upon the
surface of water in a basin, bath, or pond, the
ripple will travel from end to end of tihe water,
and communineate an lundulatintg or wave-move-
ment to each portion t of tle surface. Butl tho
water itself has n)o p)rogressivo ml)ovetlelnlt.
The action of a breeze upon a ,i. I.I of wheat,


i60


V-a--.
.1;~ I --
~' ~4"Tts-r-~-,-t_'~r~;j2_______ ,,, - .- -








WAVES AND TIDES.


or tall grass, illustrates the matter very forcibly.
The wind passes over the field, and each stalk and
blade bends alternately down and up, thus forming
depressions and wave-crests. Yet there is no
onward movement of the stalks. It is only the
motion that travels.
Those portions of the water, however, which
actually reach the shore, do possess an onward
movement. Instead of being driven against an
adjoining mass of water, they encounter the solid
bottom. Thus the lower part of their mass is


-.z -

WEARING AWAY OF THE ROCKS.

retarded, while the upper part moves onward,
curls over, and dashes as a breaker upon the
beach.
THE HEIGHT OF WAVES depends mainly upon
the force of the wind, and the depth of the water.
In general they are not more than 8 or 10 feet
high. The highest known are those off the Cape
of Good Hope, where they are said to attain the
height of more than 40 feet.
THE VELOCITY OF WAVE-MOVEMENTS depends
(1) on the velocity and force of the wind ; and (2)
upon the depth of the water, and its freedom from
obstructions. In the open sea the advance of a
wave-movement is more rapid than in one ob-
structed with islands. The rate of wave-travel is
estimated at from 15 to upwards of 150 miles an
hour.
EFFECT orF WAVE-MOVEMENTS.- The wave-move-
ments of the ocean are incessant. Even where a
perfect calm prevails, there is a ceaseless move
ment of the water, which, like a great pulse, keeps
the surface constantly rising and falling. This


heaving is commonly known as the ground swell
of the ocean.
Waves .. : the surface .'/. The highest
waves in a storm have no appreciable effect in
water more than a quarter of a mile in depth. A
wave 40 feet high and a quarter of a mile in
breadth would not, in all probability, disturb the
smallest grain of sand lying on the sea-bed at
a depth of 200 fathoms.

2. Force and Work of Waves.-The
heaviest billows beat against
i--: t~he rocks on the shore with a
--_:-r v force varying from 600 to 6,000
". ~-l-- ]bs. to the square foot. They
.- t .... dash the rocks to pieces, and
.- .:. grind them into sand, which is
transported by the currents of
the sea to other parts of the
;-* .: _ world.
_-_. _--__.All the sand, many of the
stratified rocks, much of the
^ ^ ^p clay and soil, with which the
rocky skeleton of the earth is
:- clothed, have at one time or an-
other been broken or pulver-
ized by the action of water.
-- '-- The waves have in many places
_- modified the features of the shore by
? erecting dunes, or shifting hills of
: -- ----- -- sand. In some cases harbors have
been filled up. Many fishing vil-
lages on the shores of the Bay of
Biscay have been overwhelmed.


3. The Tides are ,..: ',' wave-movements
which ,fa. the entire mass of the sea. In a gen-
eral way it may be said that two vast waves,
each having its crest and its depression, to-
gether encircle the globe from north to south.
These two ceaselessly chase one another over the
broad expanse of the sea, occasioning two ele-
vations and two depressions of its waters in the
course of about twenty-five hours.* From the
fact that these elevations and depressions occur
with regularity about one hour later each day, and
thus rudely mark the time, they are called tides,
from the Anglo-Saxon lid, time.
The elevation or rising of the water is called
high or flood-tide ; the depression or falling of the
water, low or ebb-tide.

4. Theory of Tides.-The tides are mainly
due to the influence of the moon. The sun also has
a tide-producing power, but it is insignificant com-
pared to that of the moon, owing to the fact that
*The exact time is twenty-four hours, fifty minutes. or what is
known as a lunar day, i.e., the lime between thle cro-sing of the merid-
ian of a place by the moon and her being on the same meridian again.


.. ;..= -_'-
: :-_%4-







WAVES AND TIDES.


the sun is 400 times farther off from the earth than
the moon is.
The moon is comparatively near to the earth.
Let us see then how, in consequence of this, she af-
fects its waters.
High Tides.-As represented in the illustration,
the opposite sides of the earth have high tide at
the same time, and low tide at the same time.
High tide occurs at A, on the side of the earth
toward the moon, for this reason; the moon is
nearer to the water on that side of the earth than
it is to the centre of the earth. Hence the moon
attracts the water more powerfully than it does the
earth, and the water bulges forward as a high tide.
But why is it high tide also at B, on the opposite
side of the earth ? In this case the general mass
of the earth is more powerfully attracted by the
moon than the water is, and the effect is as though
the earth were drawn away from the water; so that
here also the water bulges forward as a high tide.


tide-producing forces. Hence we have walt are
known as the spring tides. I)uring these I he low
is at its maximum. When, on the other hand, the
moon enters her first and last quarters, the two
forces do not act in harmony, and we have in con-
sequence the neop tides, in which the li....' is greatly
less than in the spring tides.

5. Orifiin of the Tidal- IVa(ve.-In pursu-
ance of regulations established some years ago by
the authority of the British government, observa-
tions were made upon the tides, night and day, for
a whole month, in all parts of the world. These
observations led to the conclusion that the tidal-
wave has its cradle in that great erpanzse of ocean
that surrounds the Antarctic region.

6. irb'i'., Ut of Tidal-Wauve.- Starting
at the point of its origin, let us observe the progress
of the tidal-wave as it passes from ocean to ocean
round the globe.


i'PRING TIDES.


Low Tides.-Half-way between the tidal wave-
crests or high tides, there are depressions, as rep-
resented in the illustration. These occur where
the water is drawn away to form the high tides.
They create the low tides. Like the high tides
they take place twice in a lunar day, at intervals
of a little more than twelve hours.
Evidence.-Evidence that the moon chiefly is
concerned in causing the tides is to be found inthe
facts (1) that high tide occurs at any place nearly at
the time when the moon is over the meridian of
the place; and (2) that, at full moon and new
moon, the tides are higher than usual.
SPRING AND NEAP TIDEs.-A marked phe-
nomenon of the tides is that the intensity of the
movement varies. Three days after full and new
moon the flow or rise of the water is far greater
than usual. This is explained by the fact that
when the moon is new, as in the illustration, and
when she is full, the sun and moon combine their


The "chart of co-tidal lines" on page 59 will
be found useful in doing this. These lines con-
nect places which have high tide at the same time.
They represent the crest of the tidal-wave. In the
waters about New Zealand, the birth-place of the
tides, and to the northward as far as the Tropic
of Cancer, they show that the tidal-wave extends
nearly north and south. As it advances, portions
of it are retarded, or deflected or even repelled by
reefs, islands, or continental shores.
The deeper thie water, the more rapid is the rate
of the tidal-wave. This is indicated by the bulg-
ing of the co-tidal lines. The distance between
any two lines is the distance traversed in an hour.
With our eye upon the chart, let us now follow
the movements of thIe tidal-wave in thie three great
oceans, the Pacific, the Indian, and tihe Atlantic,
PAxcIFIC OC.AN.-In the Pacific Ocean the tidal
movement is more regular than in either the In-
dian or the Atlantic. The general course of the







WAVES AND TIDES.


wave, however, instead of being due west, is north-
westward. The long crest extends across the ex-
panse of the ocean, and advances toward the shore
of Asia. In three hours after it has broken upon
the coast of New Zealand, it reaches Sydney and
Tokio.
The islands and continental masses on either
side of the Pacific basin retard its movement,
whereas in mid-ocean, as indicated by the bulging
of the curves, it advances with vastly greater
rapidity. When, for instance, its northern ex-
tremity has reached San Francisco, its centre has
bulged 4,000 miles to the westward.
It will be seen that one portion of the wave is reflected or
repelled in a south-easterly direction to the shores of South
America. The cause of this is not understood.

INDIAN OCEAN.-In the Indian Ocean we ob-
serve the same general phenomena as in the Pacific.
The tidal-wave advances to the north-westward.
Its centre crosses the main body of the Indian
Ocean with rapidity. Its extremities are retarded
by the shores and islands which it encounters.

ATLANTIC OCEAN.-In the Atlantic, as in the
Pacific and Indian Oceans, the tidal-wave has a
north-westward direction. It traverses the length
of the ocean from south to north in about twelve
hours. It travels, therefore, at the rate of about
500 miles an hour.
Owing to the narrowness of the Atlantic basin
and the irregular contour of its shores, the tidal-
wave encounters many retarding and deflecting
obstacles.
North of the Equator a portion of the wave, fol-
lowing the narrow channel between the shores of
Europe and Africa on one side and those of Green-
land on the other, assumes a north-easterly direc-
tion.
On the western side of the North Atlantic, the
tidal-wave travels faster than on the eastern, be-
cause, as is supposed, this portion of the ocean is
deeper than the other. It reaches Newfoundland
on the west in latitude 48 north, when it is no
farther on the east than Cape Blanco, in latitude
21 north, on the African shore.

7. Speed of Tidal-Wave.-Since the tides
follow the moon, they have to travel round the
earth from east to west in the same time that she
does, viz., twenty-four hours and fifty minutes.
The tidal-wave, therefore, in equatorial seas,
would, if it were unobstructed, and could pursue
a direct course, travel at the rate of 1,000 miles an
hour. As a matter of fact, however, its speed is
about 500.
When, however, it comes near the shores where
the water is shallow, a change occurs. The undu-


lation is retarded, but the motion of the water is
vastly increased, and it sweeps as a current along
the continental shores and up the bays and rivers.
The current gains in speed as the tidal-wave loses.
The current often attains unusual speed in pass-
ing headlands; and then the term race is com-
monly applied to it.
,, Such an accelerated cur-
r , c rent moves from six to
\o. eleven miles an hour.
1 ..2,o' In order that the imagina-
i tion may not be bewildered
~ ,("~ by the attempt to conceive
of water travelling with the
1 high velocity of the tidal-
wave, it should be borne in
z mind that the water in mid-
o
5 ,%', ocean has only an impercept-
.i. ai %+- ible progressive motion; it
Jis simply the motion or un-
y.'' dulation that travels at this
*t2p high rate of speed.
f The waving grain, as it
,. + bends to the breeze, causes
l an undulation that travels
hhdp Iacross the field faster than
Syou can run; but the stalks
S4 \ are rooted ; they only sway
S backward and forward to the
breeze. So it is with the sea
i, N and its swell.
8. Heightof Tides.
o -In the middle of the
j 2" Pacific Ocean the rise of
w.'Wagthe tide is sometimes less
S than a foot; in the At-
-lantie, near St. Helena,
% about three feet. On the
+ other hand, between the
SA converging shores of
.8 narrow seas and bays
o 1.6 the water is sometimes
heaped up to the height
of from twenty-five to
forty, and in the Bay of
S Fundy from fifty to sev-
enty feet.
ATLANTIC COAST TIDES.
(Mean height, in feet.) The Mediterranean and the
Red Seas, however, with their
narrow and shallow entrances, almost cut off the tidal-wave
of the ocean, so that neither in the eastern part of the
Mediterranean, nor at the head of the Red Sea, is there any
regular ebb and flow of tides.
In the Caribbean Sea and Gulf of Mexico, likewise, the
tides are quite feeble, owing probably to the fact that these
sheets of water are protected from the tidal-wave by the
West Indies.
DIFFERENCES ON THE SAME COAST.-Very great
differences exist between the tides at various points
of the same coast. On the shores of Florida the


* 58










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CHART.


I Ni I .


. 7T


i,' 7 '" / 4


, F_
- 'i *F I I VI"


I


ENGRAVED ,--,- .. - .


il ,


II








WAVES AND TIDES.


rise is not more than about three feet. It increases as
we go northward, until we reach the Bay of Fundy,
where it attains its maximum. [See Chart, p. 58.]
" At some points on the shores of Great Britain
there are tides of great height and strength, while
at others close by the rise and fall are barely per-
ceptible.
The rise and fall at Liverpool are 28 feet ; in the
Bristol Channel, 40 feet; at Wicklow, on the oppo-
site Irish coast, only two or three.
Causes. -To account for these differences various
causes may be o.- _--t,:,1 : the form of the bottom,
the projection of headlands, the narrowing of


ordinary velocity. People crossing the dry bed of
the river Dee, in England, are often overtaken
and drowned by the inrushing water.
The case of the Amazon is of special interest.

The tides ascend this river to a greater distance from the
sea than any other in the world. Tide-water extends in it
700 miles up the current ; and the singular phenomenon is
presented of there being several tides (Sir John Herschel says
eight *) in the river at the same time; for before the flood
of one has reached the end of its 700 miles' journey, several
other tidal waves, each in succession bringing high tide with
it, have had time to enter.

BoRns.-A tidal-wave of great height sometimes
enters the mouth of river
-== ~...... -- and ascends its channel
: as a perpendicular wall
of water. Such a tidal-
.. l wave is known as a bore.

-= , i". ; able are those of the

/",' iI i'1,,""",' Hoogly at Calcutta, the
'""" ','' '' Garonne in France, the
... ,i ','f i,!".*i'i ''
', Tsien-tsang in China,
','i,'.,' and the Amazon.


THE "BORE" OF THE TSIEN-TSANG lIVER.


channels along which the tidal current is forced,
and the position of those channels with reference
to the direction of the tidal wave.
A glance at the map shows, for example, that
were the tidal-wave propagated from the northeast
instead of the southwest, the Bay of Fundy would
cease to be celebrated for the height of its tides.
The peculiarities of a shore are sometimes such as to cause
a complete sundering or division of the tidal waters. Two
currents are thus formed. In some cases these meet again
after their division and give rise to a whirlpool 1 ,, yi, .
in the Straits of Messina, and the Maelstrom among the
Lofoden Isles, are illustrations of this phenomenon.

9. 1Tides of Hivers.-The tides of some
rivers present interesting peculiarities.
They enter certain river channels with extra-


At certain times bores 12
to 15 feet high come rushing
into the channel of the Am-
azon on the top of the tide.
Sometimes as many as five,
30 or 40 miles apart, dash up
the river, capsizing small
craft as they go and spread-
ing consternation among the
watermen.
The bore of the Tsien-tsang
is even greater than that of
the Amazon. It spans the
river with a feather-white and
roaring wall of water, 30 feet
high, and travels at the rate
of 25 miles an hour.


TOPICAL ANALYSIS.
VII. WAVES AND TIDES.
1. Waves.
Howcaused. Crest of thewave. Breadth. Nature
of wave-motion. Height and velocity of ocean
waves. Circumstances affecting velocity. Effect
of wavc-movements. Depth to which the motion
extends.
2. Force and Work of the Waves.
Force per square foot. Effect in pulverizing rocks.
In causing encroachment of sea lands.
3. The Tides.
General description. Origin of the name. Flood
and ebb tides.


*"Physical Geography," by Sir John Herschel.


- -.! ,4








CURRENTS OF THE SEA.


4.



5.
6.


Theory of Tides.
Cause of high tides. Low tides. Evidence. Spring
and neap tides.
Origin of Tidal-Wave.
Movement of Tidal-Wave.
Co-tidal lines. Curving of the lines, how caused.
Movement of the wave in the Pacific. In tile
Indian Ocean. In the Atlantic.


7. Speed of Tidal-Wave.
Of the current.
8. Height of Tides.
Cause of feeble tides in certain waters. Difference
In tides on the sane coast. Causes. Whirlpools.
9. Tides of Rivers.
Tides of the Dee. The Amazon. Bores.
TEST QUrESTIONS.-How is the expression "waves running mountains
high" to be regarded? What is the general effect of wave-action along
the coasts on the relative area of land and sea? Why do the tides occur
a little later every day?


VIII. CURRENTS OF THE SEA.

1. The Cuirrents of the Sea.-There are
rivers in the sea. They are of such magnitude
that the mightiest streams of the land are rivulets
compared to them. They are either of warm or
cold water, while their banks and beds are water
of the opposite temperature. For thousands of
miles they move through their liquid channels uin-
mixed with the confining waters. They are the
horizontal movements called currents.
The mariner can sometimes detect them by the
different color of their stream, while, if they give
no such visible sign of their existence, he can trace
them by testing their temperature with his ther-
nomieter.
CLASSIFICATION.-The chart on pages 62 and 63
exhibits a general view of the oceanic currents. It
presents these facts :
(1) there is an equatorial current sweeping from
east to west all along on either side of the equa-
tor, and well nigh encircling the globe ;
(2) there are polar currents setting from the
polar regions toward the equator ;
(3) there are counter currents setting from the
equator toward the poles.
COURSES OF CURRENTS MIODIFIED.-The chart
shows that as in the case of the tidal-wave, so in
the case of oceanic currents, the shores of conti-
nents and islands have marked effect in modifying
their normal courses. These are also i..-I I,.l by
the rotation of the earth.
Effect of Rotation.-Let us see what the effect of rotation
is. If two trains are moving on parallel tracks in thle same
direction and with the same speed, an object thrown or a
ball shot point blank from one to the other may strike
the point aimed at. But if the train from which the ball is


shot be going 35 miles an hour, and the other only 15, tlhe
ball from the first will strike in advance of the point aimed
at. If the direction of the trains be eastward, then the ball
will fall a certain distance to the east of the slower train.
This is what occurs when water starts from the equator
toward the poles. It rotates toward the east at the speed of
1,000 miles an hour. Passing to either role it is at the same
time moving with a higher speed of rotation than belongs to
the latitudes which it reaches, ind hence it has an eastward
movement.
If now we suppose the ball to be discharged from the
slower train, it will obviously fall behind, or to the westward
of the point aimed at. This is what occurs when water
starts from either pole to the equator. It has the slower ro-
tary motion of the pole, and as it approaches the equator it
constantly enters latitudes which have a higher speed of
rotation. They, as it were, pass it by, and it lags to the
westward.
Ience currents moving to the poles derive from rotation an
eastward trend; those moving to the equator a westioard.
NoTE.-Ifn of oceanic currents it is important to ob-
serve the method of naming them. A northlieast wind comes
from Lhe northeast, a northeast current goes totnrd the north.
east. In other words, while the winds are named ....... to
the points from which they blow, currents are named accord-
ing to the quarter toward which they flow.

2. Currents of the Atlantic.-Wc will
now consider the currents as they present them-
selves in the several oceans. For convenience we
begin with the Atlantic.
THE EQUATORIAL CURRENT crossing this ocean
between the shores of Africa and South Amnierica
strikes the latter continent at Cape St. Roque.
Here it divides. One portion passes southward,
following the coast line of South America. It is
named the Brazil Current. Its waters, reaching
the Antarctic regions, are carried back with the
return polar current which sets along the west
coast of Africa toward the equator.
The other portion of the Equatorial Current, on
leaving Cape St. Roque, flows northwestwardly.
It is divided by the West Indies. Its main section
enters the Caribbean Sea and the Gulf of Mexico,
from which it issues through the Straits of Florida
as the well-known Gulf ,'...
THEm GULF STREAr.-Among the counter cur-
rents which carry the ocean waters from the equta-
tor to the poles, the Gulf ',I ... i. is the most re-
markable. Issuing from the Gulf this ocean river
crosses the Atlantic in a northeasterly direction.
On leaving the Straits of Florida, it takes a course
nearly parallel to our Atlantic seaboard. Reaching
the latitude of Newfoundland, it turns more
directly eastward. (See Recent Facts, p. 1.)
North of the Azores it divides. One branch
passes southward, skirts the western shores of
southern Europe and Africa, and finds its way
back into the Equatorial Current. The other
branch passes on to the northeast, bathes the shores















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SWhat current bathes the south-eastern shores of South Describe the course of the Equatorial Current. Where Indian Ocean.-Where do the two currents that
QUEsTIONs ON THE CUiRRENTS OP THE SEA. America ? Where does it originate ? Into what ocean does it divide ? Name of the southern branch ? Of the enter the Indian Ocean come from ? What current issues
does it pass ? What current brings into the Atlantic the northern ? Trace the Japan Current. What name has from this ocean ? What is its course ?
Atlantic Ocean.-What two currents carry the water of the Antarctic ? Name the warm currents of the it in its eastern half ? Would the current west of South Where do you find the Sargasso Seas ? How many ?
Arctic waters into the Atlantic ? Trace the course of Atlantic. The cold currents. America make the neighboring shores warmer or cooler?
the Equatorial Current in this ocean. What does it be- America make the neighboring shores warmer or cooler ? Examine carefully the drainage of each continent and
come east of the United States ? Describe the course of Pacific Ocean.-What two currents form the Equa- Why? Show how the Pacific system of currents resem- tell into what ocean it passes. How is this indicated on
the Gulf Stream. torial Current of the Pacific ? Where do they blend ? bles that of the Atlantic. the chart ? What regions have no ocean drainage?


DRAINAGE or THE LAND.


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a









CURRENTS OF THE SEA.


of the British Isles and northern Europe, and
enters the Arctic basin, possibly to emerge through
Behring Strait into the Pacific.
Dimensions.-The length of the Gulf Stream,
from the Gulf to the Azores, is about 3,000 miles.
Its breadth in the si i of Florida is about 32
miles. In its progress it constantly increases in
breadth, till in the middle of the Atlantic it is 120
miles across. The depth is about 2,400 feet near
the straits. This naturally diminishes as the width
increases. Off C'i 1i. ,i. it is reduced to 1,800
feet.
In volume the Gulf -r i, exceeds the Missis-
sippi more than 1,000 times.
S temperature of the surface waters of the
Gulf Stream, as they pass the Straits of Florida,
is sometimes as high as Fahr. It is a river of
warm water, and retains its warmth in a remarka-
ble manner. Off Cape Hatteras, and even as far
as the Grand Banks, its temperature is 15, 20 or
even 30 higher than that of the atmosphere.
The storing up of heat begins, no doubt, while
the Gulf Stream is a part of the Equatorial Cur-
rent, and continues all the time that its waters are
exposed to the tropical sun, whether in the Atlan-
tic, the Caribbean Sea, or the Gulf of Mexico.
Color.-From the Gulf up to the Carolina
coasts the waters of the Gulf Stream are of an
indigo blue ; and the line which marks the di-
vision between them and the edge of the inshore
waters is sometimes so sharp that you can dis-
tinguish when one-half the vessel is in the Gulf
Stream and the other is in the cool littoral waters.
The line of demarcation is so .'-i. i.. '; that
navigators in the olden times, when both instru-
ments and methods for determining longitude at
sea were rude, used to judge by it of their
longitude.
G-... -.-The ..i... of the Gulf Sh ..1... are two :
(1) it carries the warm waters of the torrid zone
into the Arctic Ocean ; (2) it is the great heat-
carrier of the North Atlantic Ocean.
Such immense volumes of heat are conveyed by
this benignant stream to northern latitudes, ihat
the winter climate of thie whole western face of
Europe, as far north as Lapland, is softened and
tempered with genial warmth.
The ponds of the Orkney Isles, though bordering
on the parallel of 60 north, owing to this mod-
erating i,1,1., h ,. never freeze ; and the harbor of
I-Iamnerfes, in latitude 70 40', the most nor-
therly seaport in the world, is always open.
POLAR C'i i i i -.-On either side of Green-
land cold, ice-bearing currents come down from
the Arctic Ocean to replace the warm water
carried northward by the Gulf Stream. Off the


southern point of Greenland these currents unite
and advance as far as the Grand Banks.
Here one portion of the united stream sinks
below the warmer and lighter waters of the Gulf
Stream, and pursues its course to the tropics as an
undercurrent. The other portion turns southwest
and follows closely the eastern coast of North
America, keeping between the shores and the Gulf
Stream, as far south as Cape Hatteras, where it
passes under the Gulf Si' i. 11 and continues its way
toward the equatorial regions as an undercurrent.


ii,


.I-, ,I




I. *



";",', '"-" "--" ''t j- -


- ,' J I
__ - ----,


BIRTIIIPLACE OF THE ARCTIC ICEBERGS.

This current supplies the markets of New Eng-
land with the choicest fish of the sea, and gives to
the coast of Maine its singularly cool summer
temperature.
At the Grand Banks the Arctic Current meets the Gull
Stream, and, chilling the vapor which rises from its surface,
produces the dense fogs which render this part of the ocean
so dangerous to navigation. (See p. 87.)
From the Antarctic, as from the Arctic Ocean,
there is a constant flow of icy waters into the
Atlantic basin. The South Atlantic Current,
issuing from the Antarctic Ocean, follows the
western shore of Africa, passes northwestwardly,
and contributes to form the Equatorial Current of
the Atlantic.
3. C(]rents of the Pit ;fi,.-Turning
now to tha Pacific, we find its currents presenting


_ ;,:'i








CURRENTS OF THE SEA.


in general similar features to those of the At-
lantic.
AN EQUATORIAL CURRENT starts westward
from that portion of the ocean lying to the south-
west of Mexico. Like the corresponding current
of the Atlantic it divides. One branch passes to
the southward. Bathing the shores of Australia,
it is called the Australian Current. It loses itself
in the Antarctic waters.
The northern branch of the Equatorial Current
pursues a course not unlike that of the northern
branch of the Equatorial Current of the Atlantic.
Passing through the Archipelago off the south-
eastern coast of Asia, it turns northward and
eastward, and, sweeping past the Japanese Islands,
receives front them its name, Japan Current.
The natives of Japan call it, from the dark blue
color of its waters, EKuro Siwo, i.e., Blackc . -.
The Japan Current is the Gulf Stream of the
Pacific. Like that stream, it has the twofold
office of water-carrier and heat-bearer. It transfers
the water of the central and western Pacific to its
northern and eastern portions ; and with its warm
waters it softens the climate of the Aleutian
Islands, and the northwest coast of America, just
as the Gulf Stream does the climate of western
Europe and the British Isles.
Passing the Aleutian Islands the main volume of the
Japan Current receives the name of the Aleutian Current,
takes a southeastwardly course, and becomes again a portion
of the Equatorial Current.
A small branch of the Japan Current enters the Arctic
Ocean through Behring Strait.

POLAR CURRENTS.-A small surface current
issues from the Arctic Ocean through Behring
Strait. It flows between the Japan Current and
the eastern shores of Asia, like the polar current
which flows between the Gulf Stream and the
shores of America, and, like the corresponding
current of the Atlantic, it teems with excellent
fish, -whereby the capacity of China and Japan to
sustain population is greatly increased. It brings
down field-ice from the seas of Okhotsk and
Behring.
From the Antarctic a broad Drift flows toward
the equator. Off Cape Horn it divides. One
branch passes into the South Atlantic ; the other,
known as the Humboldt Current, enters the Pacific.
The Humboldt Current carries its cool Antarctic
waters all along the west coast of South America
from Patagonia to the Galapagos Islands. These
waters, when they touch the equator, are still too
cold for the coral insects to inhabit. Hence the
whole western coast of South America is without
coral reefs or coral formations of any kind ; though
in the same latitudes, at a distance from the coast,


where the waters are warm, the ocean is alive with
them.
After crossing the equator the IIumnboldt Cur-
rent is .-.: .,. ,1 1 to the westward and becomes part
of the Equatorial Current of the I', ;..

4. Currents of the Ind(lian Ocean.-
The Indian Ocean has no such well-defined system
of currents as the Atlantic and Pacific. A branch
of the Equatorial Current of the Pacific, sweeping
to the westward, enters this ocean, and washes the
southern shores of Asia. Passing Cape Comorin
it is deflected to the south-west, and flows along the
eastern coast of Africa as the -It .. .' ." current.
This is a warm current. It is sharp and well-de-
fined until it clears the Mozambique Channel, when,
passing southward, it loses itself in the Antarctic
waters.
From the Antarctic a current setting north-
westward passes to the southward of Australia and
pours its icy flow into the Indian Ocean.

5. Oceanic Circulatioit.-From this gen-
eral survey of the currents of the sea it appears
that there is a complete system oq/ circulation by1
which the waters of the equatorial and polar regions
are incessantly changing place and blending to-
gether.

6. Causes of Oceanic Circulation.-
Two main causes of oceanic circulation have been
4. -.- 1... They are (1) difference of specific
gravity* in the waters of various parts of the ocean;
(2) the influence of the winds.
DIFFERENCE OF SPECIFIC GRAVITY between sea
water at one place and sea water at another is the
chief cause of oceanic circulation.
Whenever and wherever the waters in one part
of the sea differ in specific gravity from the waters
in another part, no matter from what cause this
difference may arise, or how great may be the dis-
tance between two such parts of the sea, the heavier
water will flow, by the shortest and easiest route,
toward the lighter ; and the lighter, in its turn,
will seek the place whence the heavier came.
In other words, front whatever part of the sea a
current runs, back to that part a current of equal
volume must flow.
CHANGES IN SPECIFIC GRAVITY are mainly
brought about by (1) heat and cold; (2) evapo-
ration and precipitation.
Effects of Heat and Cold.-Sea-water when

Two bodies are said to differ in specific gravity when equal voluimes
or measures of the two differ in weight. A gallon of salt water, for
example, weighs more than a gallon of fresh water. A pint of water
weighs about a pound; a pint of quicksilver weighs about thirteen
pounds.









66 CURRENTS OF THE SEA.


heated expands. A given volume of such heated
water, if it contain the same proportion of salts as
an equal volume of colder salt-water, will weigh
less. On thle other hand, when sea-water is chilled,
it contracts and becomes heavier.
The average temperature of sea-water is for
polar seas about 30, for equatorial about 70. This
difference of temperature is permanent, and the
difference in specific gravity of sea-water at 30,
and sea-water at 70, is very great.
The cold of the polar regions, therefore, and the heat of
the tropics are two powerful and ever-acting causes which
produce constant disturbance of equilibrium in the waters
of the ocean. Necessarily there will result from this dis-
turbance a never-ceasing movement of the cold waters toward
the warm, and of the warm toward the cold.

T.: of Evaporation.-If you evaporate a quan-
tity of sea-water completely, you have solid saline
matter remaining. In proportion therefore to the
amount of evaporation going on upon its surface,
a body of sea-water will be more or less dense, and
consequently more or less heavy.

Effect of Precipitation. -Precipitation, or the
process by which moisture is returned to the earth
in the shape of rain, snow or hail, also changes the
specific gravity of sea-water.
If upon any part of the ocean a large amount of
rain falls, or if rivers flow into it, the sea-water
becomes less salt and therefore lighter.

Illustrations.-Striking illustrations of the effect of
evaporation and precipitation in producing currents are
furnished by the Red, Mediterranean and Baltic Seas.
The Red Sea lies under a burning sun. It is riverless and
almost rainless, while the evaporation from it is enormous.
To supply the waste created thereby, a constant current
from the Indian Ocean is drawn into it through the Straits
of Babelmandeb.
In the Mediterranean also evaporation is very great. Into
this sea rains fall and rivers flow. Nevertheless, the sup-
ply from them is not sufficient to make up for the loss by
evaporation. The deficiency, therefore, comes in through the
Straits of Gibraltar as a surface-current from the Atlantic.
The water of these two seas, after it has supplied the
winds with vapor, becomes salter and heavier than it was
before; it sinks and escapes back into the ocean as an under-
current.
With the Baltic the case is reversed. There the water
which is received from the rivers and the rains, is more than
sufficient to balance the loss by evaporation. Here, there-
fore, we have the diluted and lighter sea-water escaping from
the Baltic as a surface-current, while an undercurrent of
salter water enters from the North Sea.

We can now appreciate what must be the effect
of evaporation and precipitation upon the general
circulation of the ocean.
Between the equator and the parallels of 25
north and south there is an area of 112,000,000
square miles. Here there is more evaporation than


precipitation. The case is similar to that of the
Red Sea.
On the polar side of latitude 50 north and 50
south there is an area of 45,000,000 square miles.
Here precipitation is in excess of evaporation.
The case is parallel to that of the Baltic.
Now try to estimate the total quantity of water
that is taken up by evaporation from the one of
these parts of thie globe and poured down upon
the other, and the disturbance created thereby in
the equilibrium of the ocean.
The effort to restore this equilibrium is seen in the
currents of the sea and the circulation of its waters.
A more accurate measure of the work done by
evaporation is the entire annual rainfall upon the
surface of the globe. This is estimated at 186,240
cubic miles, or more than 510 cubic miles a day.
Reflect, then, that every day on the average this
immense volume of water is being uplifted by the
agency of evaporation from the surface of the
ocean, and you will be better able to estimate the
prodigious influence which evaporation must exert
in disturbing oceanic equilibrium and producing
currents.

T7. Salts.-The solid matter of sea-water lends
indispensable aid in producing the currents of the
ocean, since the vast and ready changes of specific
gravity upon which these movements depend could
not occur in a sea of fresh water.
For if two portions of fresh water be evaporated,
one more than the other, the specific gravity of
both will at the close of the operation be the same.
But mix with the fresh water a certain amount of
common salt; then evaporate one portion more
than the other, and a difference in the specific
gravity of the two portions at once results.
Just so any diminution of or addition to the
saltnessof any portion of the sea produces a change
in its specific gravity and a disturbance of its equi-
librinmn. Hence currents result.
And thus evaporation really owes its power as a
cause of oceanic circulation to the salts of the sea.
The very separation from the sea-water of solid
matter for sea-'shells and coral reefs is a continuous
cause of difference in the specific gravity of the
waters of the ocean.
It seems more like a vagary of the fancy than the stub-
bornness of fact, to say, that so great a matter as the circu-
lation of the water in the sea should depend, even in the
slightest degree, upon such minute creatures as the little
coral reef-builder and his tribe. Yet, look at the great
Barrier-reef of Australia, the coral rocks, reefs, and islands
of the Pacific Ocean. Contemplate the quantity of matter
which is required to build these structures, and say if the
taking of it out of solution be not sufficient to disturb the
whole ocean, and put it in motion from the equator to the
poles.









CURRENTS OF THE SEA.


8. Winds a Cause of Cua-rents.-The
Trade Winds are considered to be the producing
cause of the Equatorial Current and its off-
shoots,
Blowing incessantly to the westward and meet-
ing over the equatorial regions, they impart to the
waters beneath them a gentle but continuous
westerly movement. Hlence the Equatorial Cur-
rent.
Other winds produce irregular currents. You
may yourselves have observed the effect of the
wind upon rivers, ponds, or canals, in piling the
water up on one side, or at one end, and blowing
it away from the other.
In great storms at sea the winds drive the water
before them, and they sometimes pile it up many
feet above its usual level.

Our nautical works tell us of a storm which forced the
Gulf Stream back into the Gulf, and piled up the water to
the height of 30 feet. The Ledbury attempted to ride it
out. When it abated, she found herself high up on dry
land, and discovered that she had let go her anchor among
the tree-tops on Elliott's Key.
The Florida i,, were inundated many feet, and it is
said the scene presented in the Gulf Stream, on that occa-
sion, was never surpassed in awful sublimity.
The water dammed up rushed out with wonderful velocity
against the fury of the gale, producing a sea that beggared
description.

9. Office of Ocean Currents.-The great
office of ocean currents in general is to modify cli-
mate. Those from equatorial regions are carriers
of warmth those from polar regions are reducers
of heat.


GULP WEED.


different oceans which arc most free from the in-
fluence of currents.
If bits of cork or chips, or any floating substance,
be put into a basin, and a circular motion be given
to the water, all the light substances will be found
crowding together near the centre of the pool
where there is the least motion. Like such a basin
is the Atlantic Ocean, with its Equatorial Current,
and its Gulf Stream. The Sargasso Sea is the
centre of the whirl.

The Sargasso Sea of the Atlantic embraces an area of
several hundred thousand square miles ; and though the
weeds are all afloat and held by nothing, yet the Sargasso
remains where it was nearly 400 years ago, when Columbus
passed through it on his first voyage to America.
During the author's researches connected with the Phys-
ical Geography of the Sea," the existence of four other
Sargassos was established, viz.: one in the Indian Ocean,
two in the Pacific, and another in the Atlantic. [See
Chart, pp. 62, 63.]


TOPICAL ANALYSIS.

Vi1. CURIErNTS OF TIE SEA.

1. Currents of the Sea.
Magnitude. Temperature. Classification. Direc-
tion, how modified. Trend of polar and counter
currents. Mode of naminJg Culrrcnts.
2. Currents of the Atlantic.
The Equatorial Current. Point of division. Brazil
Current. The Gulf Stream. Dimensions. Tem-
perature. Color. Olliccs. Polar currents, north
and south.
3. Currents of the Pacific.
General character. Australian Currelnt. KuroSiwo
or Black Stream. Polar currents. humboldt Cur-
rent.
4. Currents of the Indian Ocean.
5. Oceanic Circulation.
6. Causes of Oceanic Circulation.
Chief cause. General law. Causes of changes in
specific gravity. Effects of heat and cold. Of
evaporation. Of precipitation. Ill iustrations from
- the Red, Mediterranean and Baltic Seas.
," .. 7. Effect of Salts on Circulation.
Their effect In promoting changes of specific grav-
ity. Effect of formation of coral-reefs.
8. Winds a Cause of Currents.
Effect of Trade Winds. Of storms.
9. Office of Ocean Currents.
10. Sargasso Seas.


alu. ouI-rif.u r _10 Sa r* ss Ses. A .*erstn evidence j Description. Cause. Number and location.
of the circulation of the oceanic waters is to be Decrition. Cause. Number and location.
found in what are known as Sargasso Seis, so- TEST QUESTIONS.-Whieh of the currents of the sea exerts the most
called from sargazo, the Spanish name for sea- important influence oni climate ? Why ? General effect of oceanic cur-
weed. These are vast collections of drifting reuts oni climnle. Effect on saitncss of thile sea. influence on coin
en rce. Are tlie curr'nts of tle sea of iany linelfit to marine animals I
sea-weed, which gather in those portions of the Who discovered the first Sargasso Sea ?



















Properties of Water.


TOPICAL ANALYSIS FOR REVIEW.




Composition.
Changes of form. Uses in the solid and gaseous forms.
Expansion in freezing. Important result.
Capacity for heat. J Heat rendered latent in melting. In evaporation.
SEffect on climate.
Solvent power.
Circulation between sea and land.


Springs. How caused. Remarkable kinds.
How formed. River-systems. Cataracts. Offices of rivers.



Erosion. Ci

Transportati
Rivers. How rivers change surface of the earth.

Deposit.



Relation to ocean life.
Formation. Cause of overflow. Salt lakes. Inland seas.
Lakes. Offices.
SDistribution.


cause. Effects.
on. 1 Power.
Quantity of matter.


Causes.

Results.


Deflection of current.
Bars.
Deltas.
Branching of rivers.


Drainage. . .


Continental Drainage.


The Sea. . . .


The Oceans. . .


Advantages.
How effected . ... I. Quantity of water delivered by rivers.
Cause of inundations. Examples.

North America.
South America.
Europe.
Asia.
Africa.
Australia.

Extent. Relative area in northern and southern hemispheres.

Saltness . . . Saline ingredients. Quantity.
Variation with distance from equator.

Origin of saltness.
Color.
Phosphorescence.
Temperature. Variation with depth, place and season.
Offices.


The oceans .

Depth ..

Bottom .


Number.
Form of basin.
The Atlantic.
The Pacific.


General form.
I Beds of explored oceans.


Waves.




Tides .


Currents in general . .

Currents of the Atlantic. .

Pacific currents . .

Currents of the Indian Ocean.

Causes of oceanic circulation.


The Sargasso seas.


How caused.
Nature of wave-motion. Height. Velocity.
Force and work of waves.
General description.
Theory of tides. High. Low. Spring and neap.
Origin of tidal wave. Movement in different oceans. Co-tidal lines.
Speed of tidal-wave.
Height of tides in different localities. Charybdis and the Maelstrom.
Tides of rivers. Bores.

Magnitude. Temperature. Classification.
Direction. How modified. Rotation.
Mode of naming.
Equatorial Current. Brazil Current.
Gulf Stream. Polar currents.
General character. Australian Current.
Japan Current. Polar currents.

Chief cause. General law.
Causes of changes in specific gravity.
Effect of salts on circulation.
Winds a case of currents. Office of ocean currents.


Waters of the Land.


Waves and Tides


Currents of the Sea.















PART IV.


THE ATMOSPHERE.


I. PHYSICAL PROPERTIES OF THE He filled a tube, about three feet in length,withmcr
ATMOSPHERE. cury. He then inverted the tube and placed the open
mouth in a vessel of mercury. The mercuryin the
1. The Atmosplhere.-Wherever we go on tube then fell, until it was about thirty inches in
the surface of the earth we perceive that air is height. This column of mercury was sustained by
present. If we ascend above the mountain tops, the weight of the air. Torricelli thus discovered
or pierce the loftiest clouds, it is still with us. It what is known as the barometer or weight-nmeasure,
envelops the earth. (from the Greek baros, weight, and mei/ron,
The entire mass of the air is commonly spoken measure).
of as the atmosphere. Its upper portion, which on
a clear day is blue, we call the sky.
COMPOSITIoN.-The first question which natu- : .- -'
rally occurs to us regarding the air is, What is it ? .. .'
It was long thought to be an element, i.e., some- '7 I'
thing unmixed with anything else. About one "..- i
hundred years ago it was found to consist mainly L:- I
of two gases. Names had to be invented for them. I
They were called Oxygen and Nitrogen. In every -. ,.
one hundred gallons of air there are about seventy- i I
eight of nitrogen and about twenty of oxygen. i I
Vapor of water and carbonic acid gas are also pres-
ent in the atmosphere. The latter consists of
carbon combined with oxygen.
Thp. vsanor, 1"ipc i(^pc n+ n+hp nfflnft Ttirn tQC!n+1-ii -fho flo- !iL'_


ness of the solar rays by day, and prevents radiation into
space, or the escape by night of certain portions of the heat
that the earth receives from the sun during the day.
The plants, by means of their leaves, appropriate carbon
from the carbonic acid. From it, and the water obtained
through their roots, they elaborate fibre, fruits and flowers,
returning the oxygen again to the air for the use of "every-
thing that hath breath."

2. Weight of the Air.-As we do not feel
ourselves pressed down by the air, it may seem
surprising that it has weight. Yet, in truth, it is
very heavy. The famous Galileo was the first to
point this out. A pump-maker wished to know
from him why a pump would not raise water from
a well which was more than thirty-two feet deep.
Galileo concluded that it was because a column of
water thirty-two feet high is as much as the weight
of the air can balance.
BAROMETBR.-Torricelli, a celebrated pupil of
Galileo, 'confirmed the conclusion of his master.


I,

.1


I, 11

'. i ', ,
,, , ,, ,1,," ,,,
S,. L';lilfrL'l


TORRICELLI'S EXPERIMENT.


B



.IjIT

IIALIOMETER.


Pascal, a French philosopher, completed the
work of Galileo and Torricelli. He argued that if
the atmosphere has weight, that weight must be
less on the top of a mountain than down at the
base, and that, consequently, a less column will be
sustained above than below. The experiment was
tried upon the Puy de D6me, a lofty mountain in
France. It established the fact that the air has
weight; for the mercury fell about ,- inch for
every ascent of about ninety feet,








PHYSICAL PROPERTIES OF THE ATMOSPHERE.


The weight of the atmosphere is ,.i... ." called
its pressure.
AMOUNT OF PiEssuRs.-At the level of the
sea the atmosphere presses with the weight of
fifteen pounds* upon every square inch. Although
its pressure upon the body of each one of us is
several thousand pounds, yet, in consequence of
the simple law of nature, that the atmosphere
presses equally in all directions, we do not feel it.
An interesting consequence of the weight of the atmos-
phere is the fact that the boiling point is lowered at high
elevations. At about the level of the sea, water boils at
212 Fahr. At Quito, 11,000 feet high, the boiling point
is 194 Fahr. On the top of Mont Blanc, nearly 10,000
feet high, it is 180.
This arises from the diminished pressure to which water
is subjected at great elevations. It has the inconvenient
effect of making it impossible in such situations to cook by
boiling.
VARIATIONS IN PRESSURE.-Variations in at-
mospheric pressure are occasioned (1) by change of
level; (2) by changes in the weight of the air.
Effect of Change of Level.-As you ascend
a mountain, you pass through a certain proportion
of the atmosphere, and are, of course, relieved
from a portion of its pressure. For the first 10,000
feet of ascent the barometer falls ten inches ; an
average of one inch to every 1,000 feet of ascent.
For the second 10,000 feet the barometer would
fall about 6.7 inches, the amount of its fall con-
stantly decreasing as you ascend. Mr. Glaisher
in his balloon reached a height of 37,000 feet,
and then the barometer went down to seven inches.
The lowest reading of the barometer ever ob-
served upon a mountain was 13.3 inches, at an
elevation of 22,079 feet, on the summit of Ibi-
Gamin, in Thibet. It is easy to see that the
amount of fall furnishes a means of measuring
heights of mountains, and altitudes to which
balloons ascend.
Effect of Changes in 'Weight of the Atmos-
phere.-A fall of barometer occurs, also, when
the column of air above any area becomes lighter
than usual. This takes place when there is more
than the ordinary amount of vapor in the air:
because vapor is lighter than dry air. Conse-
quently, the greater the proportion of vapor in tht
air, the lighter that air will be. A low baromete7
therefore usually indicates a moist, rainy atmos-
phere. A high barometer indicates that the atmos.
phere is heavy ; either because it is dry, or because
it is dense.
HEIGHT OF ATMOSPHERE.-The main body o:

This may be verified by the simple experiment of employing
barometric tube one square inch in bore. A column of mercury thirt
uches high in such a tube weighs fifteen pounds.


the atmosphere is about forty miles high. It
probably extends in a state of extreme attenuation
to the height of several hundred miles.
THE DENSITY, or compactness of the air, of
course diminishes with thle height. On lofty
mountains it is highly rarefied, which means that
its particles, being relieved from pressure, are
more widely separated from one another than at
lower levels.
Persons ascending to great elevations sometimes expe-
rience a singular difficulty. The walls of the blood-vessels
burst, and there is a flow of blood from the nose and ears.
This mal de montagne is seldcm felt at a lower level than
16,000 feet, and balloon ascents have been made to a height
of 29,000 feet before any serious inconvenience has arisen
from this cause.

TOPICAL ANALYSIS.
I. PHYSICAL PROPERTIES OF THE ATMOSPHERE.

1. The Atmosphere.
Composition. Uses of the vapor of water and car
bonic acid.
2. Weight of the Air.
Evidence that the air has weight from the action of
the common pump. From Torricell i's experiment.
From Pascal's experiment.
Amount of pressure. Effect of pressure on the
boiling point. Variations in pressure, to what
due. Effect of change of level. Lowest baromet-
ric readings observed. Effect of change in the
weight of the air. Meaning of high and low
barometer. Height of the atmosphere. Variation
of density with height. Physiological effect.
TEST QUESTIONS.-What is the color of tlie atmosphere ? Of what
use is this to us ? A cubic yard of air weighs about 2.2 Ibs: what is the
weight of the air in a room 15 feet square and 12 feet high? Iiave you
ever observed anything to indicate that the air has weight ? How long
ago did Galileo live ? Above the mercury in the barometer is a
vacant space called the Torricellian vacuum : why should it be so
called?

II. CLIMATE.

1. Main, Elements.-The temperature and
moisture of the air arc the two main elements of
climate. Obviously the more important of these
is temperature.
The principal causes which modify temperature
are, distance from the Equator ; distance from the
sea; prevailing winds and ocean currents; and
height above the sea-level.
2. Distance from the Equator.-The
e first and most apparent cause of difference of cli-
mate is distance from the Equator. This has two
results : (1) as the distance increases, the average
annual temperature falls ; and (2) there are greater
and greater contrasts of summer heat and winter
cold.
EFFECT ON ANNUAL TEMPERATURE.-The area








CLIMATE.


within the tropics receives the vertical rays of tlhe
sun, and is therefore the region of greatest heat.
Between the tropics and the polar circles the
sun's rays fall slantingly, and exert therefore a
feebler power.
Within the polar circles the slant of the sun's
rays is at its greatest, and hence, except during a
brief period of a few weeks, excessive cold pre-
vails.
The reason why less heat is received where the sun's rays
are oblique may be readily understood from the accompany-
ing diagram.
If the beam of heat, HH', fall vertically, it will be dis-
tributed over a smaller space (CB) than if it falls obliquely.
The amount of heat, therefore, received at any point along







a"
SUN'S RAYS.
AB is diminished in the same ratio as the surface is increased.
The intensity, therefore, of the heat upon the surface AB is
to its intensity upon CB, inversely as the surfaces, or as CB
is to AB.
CLIMATIC CONTRASTS.-The contrasts between
summer heat and winter cold are mainly due to
variations in the length of the day, and these de-
pend on distance from the Equator.
Within the tropics there is comparatively little
difference between the two periods of day and
night all through the year.
Only twice in the year, at the equinoxes, are they
equal for other parts of the globe.
As the sun passes northward from the Equator,
the day lengthens all over the northern hemi-
sphere, until, within the Arctic circle, the sun does
not set at midsummer at all. The same thing
occurs for the southern hemisphere, after the sun
passes southward of the Equator.
Now it is because there is very little difference
between day and night at the Equator that we
find within the tropics a nearly uniform tempera-
ture throughout the year.
And it is because north and south of the tropics
there are important differences between day and
night, that in all regions outside of the tropics cli-
matic contrasts are found.
At the poles these contrasts are at their maxi-
mum. The summer of the polar regions, strange to
say, is exceedingly hot.* It is marked by a ra-
pidity of vegetable growth that is marvellous. In

At Yakutsk, about 300 miles south of the Arctic circle, the tempera-
ture varies from-585 Fahr. in winter to 99 In summer.


a few weeks crops mature which require twice
that length of time in latitudes much nearer the
Equator. But, on the other hand, the winter cold
is correspondingly excessive.
Explanation.--We shall better understand the climatic
effects of variations in the length of day and night, if we
know something about the absorption and radiation of heat.
If two bodies are of different temperatures, heat will pass
through the space between them from the warmer to the
cooler. The giving off of heat by the warmer body is called
radiation. The receiving of it by the cooler is called ab-
sorption.
If a red-hot cannon-ball be placed near a mass of ice, heat
will be radiated from the cannon-ball to the ice. The ice will
absorb the heat from the ball. So wherever the sun is shin-
ing, the earth is absorbing heat. Wherever it is night-time,
the earth is radiating heat into the cooler regions of space.
It is clear that when the day-time of northern regions is
lengthened, the quantity of heat absorbed is greater; and,
at the same time, since the nights are shorter, the loss of
heat by radiation is less. Hence, there is every day an ac-
cumulation of heat.
It is for this reason that our own hottest weather occurs
subsequently to the longest day, and that in places like St.
Petersburg and Yakutsk, where the sun is below the hori-
zon at midsummer only for about three hours, the summer
heat is intense.

3. Distance froimn the Sea.-In certain
countries climate is affected more by distance from
the sea than by distance from the Equator.
The climate of a region adjacent to the sea is
called an insular or maritime climate. The cli-
mate of a region remote from the sea is called an
inland or continental climate.
INSULAR CLIMATEs.-Certain causes moderate
insular climates.
(1) Water absorbs heat much more slowly than
the land, and therefore remains, in hot weather,
comparatively cooler. Hence the summer tempera-
ture of a country bordering on the sea is lowered.
(2) On the other hand, water parts with its heat
by radiation much more slowly than the land, and
therefore remains in cold weather comparatively
warmer. Hence the winter of a maritime country
is moderated.
(3) Vapor is incessantly rising from the sea, and,
being condensed, falls as rain or snow upon the
land, and, as you have learned, this liberates latent
heat.
(4) The vapor in the atmosphere of a maritime
climate prevents the escape of heat. It acts like a
warm blanket. A familiar illustration of this is
the fact that we rarely have frost on cloudy nights.
(5) But again, since the process of evaporation
goes on more rapidly in hot weather than in cold,
it has the effect of moderating the summer heat of
a maritime country.
For the above reasons, insular or maritime cli-
mates are equable, or free from extremes.








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,"'-' ,* _-I---,-"-.-,--"SOTHERMAL LINES ri
,-_ I --....... "I H I U:
:'' '"' .-----___-------'.t.-" ' ^^^---------------- Z: ij :" ... _- ... ,i" E'7 ,-M- hE .-TJ1='L ---- -- ---.__'*
-I X:_ -" "L '---_- ' -'- .. ; "
!r, 7 -I IX',. --.-_ ._ ., -,.- _........ ... .. .. .....
!~~ .X.i







-- - -E -I E - - --




t\^ ^s^ .^r^_, isothermrm passes near New York and London ; how much tries of each continent does the isotherm of 82 pass ? annual temperature as Italy and Spain ? What parts of
__- -. -. - -







QosrI~ N H IOHRMLCHRdifference is there in the latitude of these two cities ? North of this line what is the condition of the ground ? Europe have the same annual temperature as Alaska ?
"What are isothermal lines ? Why should the isotherms Trace the course of the Thermal Equator. What is In which continent is the limit of constantly frozen What should you judge from the chart to be the annual
be so irregular and differ so much from the parallels of the average annual temperature of places through ground" farthest to the north ? On which side of our con- mean temperature of Mobile ? Of Rio de Janeiro ? Of St.
latitude ? which it passes ? What isotherms bound the zones of tineut is it farther north ? What difference between the Louls ? Of Charleston ? Of Buenos Ayres ? Of Paris ?
New York sand Romne are in about the same latitude ; Tropical temperature ? What isotherms bound the annual temperature of Labrador and the British Isles ? Where are the two poles of greatest cold in the north-
how do their mean temperatures compare ? The same Temperate zones ? The Polar ? Through what coun- What parts of North and South America have the same em hemisphere ?
%~ i ...14.,- -- -
0 C' ... ,- X.




to ~ql' II, SOTB HERr] gM. MAL.A NE.



difference is there in the latitude of these two cities ? North of this line what is the condition of the ground ? Europe have the same annual temperature as Alaska
What are isothermal lines ? Wrhy should the isotherms Trace the course of the Thermal Equator. What is In which continent is the I Ilimit of constantly frozen What should -you judge from the chart to be the annual
be so irregular and differ so much from the parallels of the average annual temperature of places through ground frtshest to t~he north ? On which side of our con- mean temperature of Mobile ? Of Rio do Janeiro ? Olt St.
latitude ? which it passes ? What isotherms bound the zones of tineut is it farther north? What difference between the Louis ? Of Charleston ? Of Buenos Ayres ? Of Paris ?
New York and Rome are in about the same latitude ; Tropical temperature ? What isotherms bound the annual temperature of Labrador and the British Isles ? Where are the two poles of greatest cold iii the north-
how do their mean temperatures compare ? The same Temperate zones ? The Polar.? Through what eoun- What parts of Nforth and South America have the same ern hemisphere ?








CLIMATE.


INLAItD CLIMATES.-Inland or continental cli-
mates are the opposite of maritime. They are sub-
ject to great extremes, intense heat in summer and
excessive cold in winter.
Two reasons may be assigned for this:
(1) Countries far from the sea are without its
cooling influence upon their summer heat, and
they have no reservoir of warmth to compensate
for their rapid radiation of heat in winter.
The interior of Asia affords the most striking instances
of the excessive character of inland climates. The Russian
army advancing towards Khiva in 1839-10 experienced
vicissitudes of temperature from a heat of over 100 Fahr.
to a cold of 45 below zero.
At Yakutsk, in Eastern Siberia, the culminating point of
excessive climate in all the world is reached. The tempera-
ture there sinks to the lowest known point, many degrees be-
low the average of the polar ocean to the northward of it,
and the soil is permanently frozen to the depth of 380 feet.
In the month of June the Lena is free from ice; the surface
soil has thawed for 3 or 4 feet; and the warmth of the
short summer is such that grain will ripen in the shallow
stratum of soil above the frozen mass. The mean tempera-
ture of July is 69 Fahr., or as high as that of Paris.

(2) The comparative dryness of the air of an
inland region contributes to create extremes. This
is strikingly illustrated by the climate of the Sa-
hara. The air there is perfectly dry. No vapor
hinders the reception of heat by day or its loss by
night. By day the sand is as fire and the wind
like flame ; and yet the temperature often falls
from 200 Fahr. during the day to freezing-point
during the night.
Travellers have been known to find the water in
their canteens turned into ice before morning.

4. Prevailing Winds acnd Ocean Cur-
rents.-The climate of a country is also greatly
modified by the prevailing winds and the neighbor-
ing ocean currents. If the prevailing winds come
from the sea, they temper the extremes of heat
and cold. If a cold current bathes any portion of
the shore, it lowers the temperature ; a warm cur-
rent raises it.
Examples.-The British Isles and the province
of Labrador are the same distance from the Equa-
tor, and in many parts the same height above the
sea. Yet such is the difference of climate be-
tween them, that Labrador is covered with snow
for nine or ten months every year, and is so cold
as to be almost uninhabitable ; while in England
the ground is rarely covered with snow, and the
pastures are green all the winter.
Both countries are in the regions of westerly
winds; but in Labrador they come from the land,
and are dry and cold ; in England they come from
the sea, and are laden with moisture and warmth.
The shores of Labrador are washed by a cold Arc-


tic current ; those of Great Britain by the warm
waters of the Gulf Stream.
The climates of Western Europe, from North
Cape all the way down to the Straits of Gibraltar,
are modified by the sea-winds and the influence of
the Gulf Stream.
Norway stretches up beyond the 70th degree of north lati-
tude ; yet the westerly winds are so richly laden with
warmth and moisture from the waters of the Gulf Stream
that the harbor of Hammerfest, lat. 7040', is never frozen,
even in the severest winters. But cross the Scandinavian
mountains, and you encounter at once, if it be winter, the
severest cold. In this short distance from the warm waters
and the west winds of the Atlantic, you find the Russian
lakes and rivers, the gulfs and bays of the Baltic, closed
against navigation every year from November till May.

Climatic conditions similar to those which affect
the western shores of Europe are found upon the
western slopes of Oregon, British Columbia, and
Alaska. Westerly winds prevail, and they are
laden with moisture from the Pacific Ocean. The
result is that here, as in Norway, open harbors and
evergreen hills are found in the high latitudes of
Alaska and other parts of our northwest coast.

5. Height above the Sea-Level.-Among
other circumstances, climate depends upon height
above the sea. A change of elevation of a few
thousand feet at the Equator produces a change of
temperature as great as would be experienced in
sailing 6,000 miles to the frozen regions of the
poles. [See small map p. 105.]
The Island of Cuba and the Mexican mountain
of Orizaba are in the same latitude. The summit
of the mountain is covered with snow all the year;
the island with fruits, flowers, and evergreens.
The reason wlhy elevation above the sea-level
causes reduction of temperature is that the radia-
tion of heat goes on from elevated parts of the
earth's surface more freely than from its lower
portions. Two causes may be assigned for this:
(1) elevations are comparatively small, and there-
fore lose heat with rapidity; (2) the air and
vapor upon elevations are rarefied, and hence little
hindrance to radiation is presented.
The general rule as to the effect of elevation is
this : for every one hundred yards of perpendicu-
lar ascent there is a decrease of one degree in the
temperature; so that, even at the Equator, you
may, by ascending t6 the height of about sixteen
thousand feet above the sea, reach the snow-line,
where the cold is extreme and the winter eternal.

6. Isothermal Lines.-From thermomet-
ric observations made in all parts of the world, the
actual distribution of temperature over the globe
has been ascertained. To show this, Humboldt
I constructed a series of lines called isothermals or








WINDS AND CIRCULATION OF THE AIR.


lines of equal heat. These are drawn round the
globe so as to connect all places which have the
same mean temperature during the year or any
given part of the year.
Isothermal lines are far from coinciding with
the parallels of latitude. Let us take by way of
illustration the line in the Northern Hemisphere
indicating the mean ano ual temperature of 50
Fahr. [See chart pp. 72, 73.] It passes through
Oregon on the Pacific shores, and leaves our
Atlantic coast between New York and New
Haven. It bends northward in crossing the At-
lantic, and in Europe passes through Liverpool,
Vienna, and Odessa, and in Asia, near Peking.
We are not to conclude, however, that because
the same isothermnial line passes through two places,
they have a climate identically the same. Of two
such places one may have an extremely hot sum-
mer and a correspondingly cold winter. The other
may have a climate free from extremes. Yet both
may have the same average yearly temperature.
Thus San Francisco and Washington have the same
mean annual temperature, while their climates are very
different.
Again, the same isothermal line passes through New
York and Dublin. Yet the climates of these places have
no resemblance. The mean winter temperature of Dublin
is six degrees above that of New York ; while the summers
of the two places are so unlike, that whereas grapes and In-
dian corn are successfully cultivated in the vicinity of New
York, they will not ripen in the open air, at Dublin.
ZONES OF TEM3PERATURE.-By means of iso-
therms we define the zones of temperature. They
are indicated by the colors on the chart. The true
Torrid Zone is bounded by the isotherms of 70 on
either side of the Equator. The true Temperate
Zones extend from the isotherms of 70 to those
of 32-. The F., ,. Zones extend from these to
the poles.

TOPICAL ANALYSIS.
U. CLIMATE.

1. Main Elements.
Causes which modify climate.
2. Distance from the Equator.
Results of distance from the Equator. Effect on
annual temperature. Climatic contrasts. Ex-
planation.
3. Distance from the Sea.
Insular and inland climates. Causes which moder-
ate insular climates. Reasons for the extremes
of inland climates.
4. Prevailing Winds and Ocean Currents.
Illustrations.
5. Height above the Sea-level.
Effect of elevation. Cause of increase of eoel with
elevation. Gnpral] rule


6. Isothermal lines.
Represent what. Relation to parallels. Zones of
tcnperature.
TEST QUESTIONS.- HiOW do( the regions deficient in nmoliktre colm-
pare in extent with those deficient inll temperature '? How would in-
crease of moistnre affect tleo temperature of desert region, ? How call
ocean currents affect climates as far inland as they do ? In what cli-
mates have nations been most proierolus ? If the climate of0 England
should become a very dry one, how would that affect the temperature ?


III. WINDS AND CIRCULATION OF THIE
AIR.

1. Ai, in Jfotionw.-The ocean of air, like
the ocean of water, is never at rest. It lihas its
waves and its currents.


L


Ii)


ANEMOMETER.

A 7.. of air in motion is called wind.* As we
all know very well, the wind travels at various
rates and in many different directions. By means
of an instrument called the anemometer, it has
been ascertained that the velocity of a light wind
is five miles an hour; of a "stiff breeze," 25
miles ; of a storm, 50, and of a hurricane from 80
to 100, or even 150.
Again: the direction in which a wind blows is
so constantly changing that we often speak of tlhe
winds as fickle, inconstant and uncertain. There
is, however, order in the movements of Mie altmos-
phere. The fickle winds are obedient to laws.
There are causes which make them blow with
greater or less rapidity. There are reasons why
they blow now north, now south, east, or west.

2. Causes of Winds.-The main causes of
winds are two (1) the unequal distribution of

Winds are named according to the quarter from which they blow.
A iiws/ wind comes from the west. anll east wind from the cast.







76 WINDS AND CIRCULATION OF THE AIR.


heat in the atmosphere; and (2) the unequal dis-
tribution of vapor in the atmosphere.
EFFECT OF HEAT.-Let us consider the effect
of the unequal distribution of heat in the atmos-
phere. If a fire be lighted on the hearth, the air
in the chimney will be heated and forced up the
chimney by an indraught of cooler and heavier air
from all parts of the room. This continues as
long as the fire burns.
The same thing occurs when a bonfire is lit, or
a house is on fire. Every child knows that the
sparks fly upward to the sky." They are carried
up by the hot ascending current. The air above
the fire is expanded, rendered lighter, and driven
upward by currents of cool air that come rushing
in from all sides. These, when heated, ascend
with such force as to carry up clouds of smoke
and sparks.
This unequal distribution of heat, the warming
of the air in the chimney or above the burning
house, while that in the room or in the space
about the burning house is comparatively cold,
establishes a system of air currents.
If there are no obstacles in the way of these currents,
and if they are not chilled or heated in their course, they
will go straight toward the mouth of the chimney. Chairs
and tables and other objects in the room will deflect them
and cause more or less irregularity in their direction.
To prove that such currents really do flow, place a lighted
candle in the doorway of a room in which a fire is burning.
You will see the flame drawn inward by the inflowing cur-
rent.

Now what occurs in the air of a room when a
fire is kindled on the hearth takes place in the at,
mnosphere. Some portions of it are always more
heated than others; and the unequal distribution
of heat establishes a system of currents. The
heated surface of the earth warms the air above it.
This air, forced up by the surrounding cool air,
ascends as a current; and streams of cooler, heavier
air flow in. Just in proportion to the size of the
area heated, the volume of the inflowing currents
will be greater or less, and in proportion to the
difference of temperature between the heated air
and the inflowing currents, the rapidity of their
flow will be greater or less.
EFFECT OF MOISTURE.-The effect of unequal
distribution of moisture is similar to that of un-
equal distribution of heat. Vapor of water is only
about half as heavy as dry air at the same tempera-
ture. Evidently, therefore, if there is much vapor
in any part of the atmosphere, that part will be-
come lighter than the neighboring portions. Like
the air heated by the fire, it will be forced upward
as an ascending current, and there will be an in-
rush of drier, heavier air to supply its place.


In general, the two causes above mentioned
operate together, for it is natural that where there
is most heat, there is also most vapor present in
the atmosphere. For this reason, and because the
effect of the two is so similar, it will not be neces-
sary to consider in detail the effect of vapor as a
cause of air-currents.
3. General Circulation of the Atmos-
ph ere.-Let us now turn our attention from
these simple illustrations to what is going on in'
the atmosphere at large.
Within the tropics there is perpetual summer.
The veA' ,al rays of the sun are incessantly heat-
ing the to-'rid zone and its atmosphere, and filling
the air whih vapor, while the air on either side of
that zone is comparatively dry and cold. What
must be the effect of this unequal distribution of
heat and vapor ? It creates a general circulation
of the atmosphere.
In the first place, as in the case of the fire upon
the hearth, thlie heated, moist air of the tropics is
pressed upon by thle heavier air on either side. It
is forced upward, and there is an indraught both
from the north and the south to supply its place.
Now, if the earth were at rest, and if its sur-
face were covered with water, the inflowing cur-
rents would go straight from the polar to the
equatorial regions. There would then be a simple
circulation of light air from the equator to the
poles, and of heavy air from the poles to the equa-
tor. The winds would be steady and unvarying.
MODIFYING CAUSES.-But the earth is not at
rest, and its surface, instead of being uniformly
covered with water, is varied by land masses of
greater or less magnitude and elevation. The ro-
tation of the earth and the influence of its land
masses are two causes which largely affect the cir-
culation of the air, and render it exceedingly com-
plicated.
WINDS ARE CLASSIFIED, according to the regu.
clarity with which they blow, as constant, variable,
and periodical.

4. Constant or Trade Winds.-Certain
of the winds blow without interruption in the
same direction, and at nearly the same rate. So
constant are they that vessels often sail in them for
days and days without, as the sailors say, chang-
ing a stitch of canvas." It was the steady blowing
of these winds which so alarmed the crew of Co-
lumbus on his first voyage to America, and led
them to fear that they should never get back to
Europe.
From their importance to the navigator these
winds have been called the trade winds or trades.
They are currents of air which are ceaselessly







WINDS AND CIRCULATION OF THE AIR.


winging their flight from the polar and temperate
regions toward the equator.
DIEECTION.-If the earth had no daily motion,
these winds would blow on one side of the equator
from the north, on the other from the south, di-
rectly into the equatorial regions. But in conse-
quence of diurnal rotation, the air, when it arrives
at the equator, is in a region which is moving
toward the east, 120 miles an hour faster than the
region in latitude 30, where it began to blow as
a trade wind.
During its whole journey to the equator the wind
lags a little behind, and the earth, which is revolv-
ing from west to east, is slipping from under it all
the time, so that
the wind appears
to come from the s -
east. Thus an ad- POLAR
ditional motion is North EasterI
imparted to it- //
viz., a motion to- ALTERNATE POLAR AN
ward the west; Ws--el
/ CA LM S 0OF
and so it is made ,/ ./ ---------m-
to come from the / /EAST
northward and d /
eastward on the BEL EQUA
S UATOR BELT OF EQUA
n ort h sid e, in stead V ... .. .. .. .. ..
of directly from
the north; and \ SOUTH EAST
from the south- \ \\
ward and eastward -CAM O
on the south side, cAL-- O
instead of directly \ ALTERNATE POLAR AN
instead of directly Westerly
from the south.
Thus we haveP POLAR
the two systems of South E aste r
trades,; the north-
east andthe south- ". -
east. The north- CIRCULATION o0
east trades blow Diagram showing course of cure
from about the poles and back. Let the pupils all di
parallel of 30


COUNTER TRADEs.-Referring to the chart, you
see that on the polar side of the trade winds, thel
arrows show that the prevailing direction of the
winds is counter or opposite to that of the trades
-that is, from the southward and westward in the
northern, and from the northward and westward
in the southern hemisphere. For this reason these
westerly winds are called the counter trades.
Origin.-The origin of these winds is interest-
ing. It is thus explained. While the trades blow
steadily from the poles, there must be return-cur-
rents from the equator to the poles, otherwise the
polar regions in time would be destitute of air.
When the upward current at the equator has risen


-- - - - -^------ ---
W I N D S

y Prevailing NIk i,

D EQUATORIAL WINDS ', \
Srevai I i n g \
u CANCER.
..t .. of -ar -frm ----eqao to t\
TRADE WINDS i \

TORIAL CALMS y
----------------- -

TRADE WINDS ]
//

CAPRIC-R--"

D EQUATORIAL WINDS // /
Prevailing // /
-- // /

ly P re v Iin -'



THE ATMOSPHEIBE.
nts of air from the equator to the
raw from memory similar diagrams.


north, to the equator; the southeast trades from earth, probably for the reason
about the parallel of 30 south, to the equator, ture has fallen below that of t
Both extend entirely round the world, ing from the poles. They i
winds and constitute the coun
5. Variable Winds.-North and south of
the trades are the zones of the variable winds. Proofs.-That the upper currents
and out northward and southward from
They extend from the parallels of 30' north and bu antly proved. Sometimes v
abundantly proved. Sometimes v
south, to the polar circles. Within these limits ready learned, eject vast quantitic
the winds blow without regularity. Two systems quently this passes into very elevat
contend, and sometimes the one prevails, some- phere; and instances are on reco
times the other. These contending winds are the sometimes for hundreds of miles in
counter trades, which blow from the equator, and that of the surface winds.
,, _, n i rm oseguina, in Guatemala, is in1
the polar winds, which blow from the poles. The Coseguina, in Guatemala, is in
east trades. During the eruption
variable winds are designated on the chart, p. 79, carried to tihe island of Jamaica.
as polar and equatorial winds, northeastward of Coseguina. No c


to a considerable
elevation above
the surface of tlhe
earth, it divides
and flows toward
the poles, one
volume going to-
ward the north,
the other toward
the south pole.
These two
streams of air re-
main upper cur-
rents as far as
the northern and
southern limits of
the trade winds-
i. e., about as far
as the parallels of
30 north and
south.
When,howcver,
they have gone so
far on their north-
ward and south-
ward journey, they
descend to the
surface of the
that their tempera-


lie air which is flow-
low flow as surface
ter trades.
above alluded to do flow
the equatorial regions is
olcanoes, as we have alr
s of dust. Not unfre-
ed regions of the atmos-
rd of its being carried
a direction opposite to

lhe region of the north-
Sof 1<35, its ashes were
Jamaica is 800 miles
their explanation of this







WINDS AND CIRCULATION OF THE AIR.


is possible, except that an upper current was blowing above
the surface winds, in a direction opposite to theirs.
Again, in 1815, ashes from a volcano in the island of Sum-
bawa, near Java, were borne to the island of Amniboyna, 800
miles to the eastward, although the southeast wind was then
at its height. This again proves that there must have been
a powerful current toward the northeast, above the southeast
surface-wind. It is clear, therefore, that return currents
flow from the equator to the poles, as indicated on the chart.
We shall see in the following paragraphs what becomes of
these return currents.
Direction.-Were it not for the earth's rota-
tion, the counter trades would move straight to the
poles. But rotation has upon them a similar ef-
fect to that which it has upon the trades. It
changes their direction, and it gives them motion
from the westward. This is explained as follows:
while in the equatorial regions, these winds have
acquired the rapid rotary motion toward the east
which belongs to those regions. Hence, when they
reach latitudes nearer the poles, they are blowing
to the eastward with a velocity far more rapid than
that which belongs to the latitudes which they have
reached, and thus they become westerly winds.
THE POLAR WINDS are currents of cold air
making their way from the poles toward the equa-
tor. Their direction is similar to that of the trade
winds, northeast in the northern hemisphere, and
southeast in the southern hemisphere. Coming
from the equator, the counter trades bring moist-
ure and warmth; the polar winds are dry and cold.
The trades, counter trades and polar winds,
though treated separately, are really only parts of
the same great atmospheric current which is cease-
lessly accomplishing its unending circuit from the
equator to the poles, and from the poles back to
the equator, as shown in diagram on p. 77.

6. The Calm Belts.-When two equal cur-
rents of air meet, a calm is produced. Over the
equator, where the northeast and southeast trade
winds meet, there is a belt of calms encircling the
earth. It is called the Equatorial Calm Belt.
This name is not altogether a good one, because
throughout the belt a vast current of air is inces-
santly ascending. The belt is calm in the sense of
being comparatively free from horizontal move-
ments of the atmosphere.
The most difficult part of the ocean for sailing-
vessels to cross is this calm belt. Ships are some-
times detained here for many days.
As where the northeast and southeast trade
winds meet, so where the trades and counter trades
meet and cross, there is, in each hemisphere, a belt
of atmosphere marked by the prevalence of calms.
In the northern hemisphere we have the Calms of
Cancer; and in the southern the Calms of Capri-
corn.


The position of all the calm and wind belts
above described is not invariably fixed. They all
move northward and southward, following the ap-
parent march of the sun. They reach their farthest
northward limit in autumn, their farthest south-
ern limit in spring.

T. The PCi/-lvI-dit. Winds are those which
blow for a certain time in one direction, and then
for an equal, or nearly equal time, in the opposite
direction. They are the land and sea breezes, and
the monsoons.

LAND AND SEA BREEZES.-All along the sea-
shore of warm countries, there is a breeze from
the sea by day, and one from the land by night.
The rays of the sun heat the land more readily
than they do the water. This makes the land
warm in the day, leaving the sea cool; the warm
rocks, sand, and soil, heat and expand the air in
contact with them and render it light. Pressed
upward by the cooler air of the sea, it rises. Cur-
rents then come rushing in from the sea to supply
the place of the ascending columns, precisely as
the indraught to a furnace supplies the rush up
the chimney : thus we have the sea-breeze.
By night the opposite effect occurs. The land
has the property of radiating-that is, of throwing
off-its heat more rapidly than the water can.
HIence the land by night grows cooler than the
sea. It then cools and makes heavier the air
above it. The air above the sea remains compara-
tively warm and light. Hence it is pressed up-
ward by the cooler air of the land, and currents
rush from the land to the sea. This is the land-
breeze.


QUESTIONS ON CHART OF WrNDS.-(The red color on the
chart indicates the constant or trade winds ; green, the
variable winds, or those which blow alternately from the
equator and the pole ; blue, the northeasterly winds blow-
ing from the pole ; yellow, the monsoons.)
Define the region of the trades. What do we find along
their line of meeting ? Where else do calms prevail ? What
special names are applied to the calms ? Are the calms at
all seasons exactly where shown on the chart ? Why not ?
Where do the great monsoons blow ? Within the region
of what winds ? Point out other monsoon regions.
How many regions of typhoons and hurricanes do you
find on the chart ? Where are they ? Describe the course
of the West India hurricanes. Of the Australian.
What is the direction of storms in the regions north of
the equator ? In those south ol the equator ?
What winds occasionally prevail in Northern Africa ? In
the countries of Southern Europe ? Where do these latter
some from ? Where does the Harmattan of Guinea come
from ?
Trace the circulation of a volume of air, supposing it to
start northward from the equator. Supposing it to start
southward. (See diagram p. 77.)










; .I.I 1 A .. .H J l i -j-, ,R . . .... -1-
'. '- s., i' '^' t
E, r- I-, -,,
,,, t ,2',; ," r;.
j- .--- ,. ''-/ ", , '" ." 2i .,, .",i
, ." ; ---;- ,. --X V,---. iT L i L 'ti, .X- .|
. : ,,-, ':> ... ",*v v .*.,.-- .,.- ).-> i, 7 *.*T, < ', L: L, r I

. , .-' ") IX .'' / ,- *,' '. V t-- -* ,- "- " 3 .5 -* -.', .' y i'^ .-,."5.A1: ,-, .
I I i -* - V - 11.- -, ./ -t"I,.... .-- \"" < "


C 1 7" ...... ........ .K-. _
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-








WINDS AND CIRCULATION OF THE AIR.


Were it not for these refreshing breezes, many
countries along the sea-shore, that are now the
abodes of health, prosperity and happiness, would
be uninhabitable.
MoNsooxs.--Mi... ... -are winds that blow
from a certain direction for part of the year, and
for the rest of the year from quite another quarter.
They are land and sea breezes on a grand scale. In-
stead of alternating with day and night, and blow-
ing a few hours at a time, they alternate with
summer and winter.
The most famous monsoons are those of South-
ern Asia. In India they blow from the northeast
for six months of the year, and from the south-
west for six months.
Cause. -During the summer the sun plays upon
the great deserts and inland basins of Central
Asia. Those dry and barren wastes glow like
furnaces, and the heated air ascends from them
in immense columns. A disturbance is created
which is felt to the distance of 2,000 or 3,000
miles from its centre. Cooler air rushes in from
the sea on three sides of the continent. Along
the coasts of Siberia it comes from the north.
From China round the south of the continent to
the Red Sea, it comes from the Pacific and Indian
Oceans-that is, from the southeast, south, or
southwest.
In this region, which is largely in the zone of
"trades," the effect is so great as actually to re-
verse the trade wind and cause it to blow in the
contrary direction.
In the winter the centre of Asia is a region of
low temperature. Its atmosphere is dry, cold,
and heavy. That of the seas surrounding the
continent is moist, warm, and light. The light air
is pressed upward by the heavy, and ascends into
the upper regions of the atmosphere. Currents then
blow from the land toward the sea. In conse-
quence of this we have, during the winter in
India, the northeast monsoons, which are really
the northeast trades, blowing with augmented
force and velocity ; on the Chinese coast we have
the northwest monsoons.
'T,1 '..-The summer or the southeast and
southwest monsoons having passed over the sea,
are laden with moisture, and are the wet monsoons.
They give its wet season to Southern Asia. The
northeast and northwest monsoons are for the
most part dry, because they come from the land.
During their prevalence it is the dry season. The
changing from the dry winds to the wet is com-
monly called in India the "bursting" of the
monsoon.
Bursting of the Monsoon.-The southwest monsoon sets
in generally toward the end of April, a steady wind sweep-


ing up from the Indian Ocean and carrying with it dense
volumes of vapor. The atmosphere becomes close and op-
pressive. Flashes of lightning play from cloud to cloud.
The wind suddenly springs up into a tempest. Then a few
great heavy drops of rain fall ; the forked lightning is
changed to sheets of light, and suddenly the flood-gates of
heaven are opened, and not rain, but sheets of water are
poured forth, refreshing the parched earth, carrying fer-
tility over the surface of the country, filling the wells and
reservoirs, and replenishing the dwindling rivers and streams.
The whole land from Cape Comorin to Bombay seems sud-
denly recalled to life. Vegetation may almost be seen to
grow, and from the baked mud of the river-banks emerge
countless fishes, which for weeks or months have lain in
torpor.
MINOR MoNsooNs.-Certain other winds that
resemble the monsoons are those of Australia, the
Gulf of Guinea, and the Mediterranean.
The winds of Australia blow landward in the hot months;
seaward in the cold season.
Over the Gulf of Guinea and the Mediterranean periodi-
cal winds blow in summer in opposite directions; the winds
of the Gulf of Guinea come from the southwest, those of the
Mediterranean known as the Etesian winds-are from
the northeast. Both are due to one cause, viz., the intense
heating of the Sahara. This produces an upward current of
heated air and an inrush of cooler air from the Gulf of
Guinea on the one side and from the Mediterranean on the
other.
The periodical winds of Mexico, Central America, and
the Brazilian waters, and those known in Texas as "North-
ers," are due to causes similar to those of the monsoons.
OTHER PERIODIC WINDS of less importance are
what we may call the return currents from the
deserts. These are laden with heat and sand and
dust.
From the Sahara currents flow northward and southward.
Those from the south enter Egypt, and blow for a few days
at a time during a period of fifty days. Hence they are
called khamsin, an Arabic word meaning fifty. During
their prevalence the air is filled with blinding dust and the
midday sun is darkened. By such a wind of unusual vio-
lence, the army of Cambyses, 50,000 in number, is said to
have been destroyed, when on its way to attack the oasis and
temple of Jupiter Ammon.
Crossing the Mediterranean, the desert wind scorches the
vegetation of Southern Europe. It is known as the sirocco.
From the deserts of Syria and Arabia comes the dreaded
simoom, a suffocating wind which often heaps up vast
mounds of sand, and completely buries whole caravans of
travellers.
Mountain Winds.-The tops of mountains chill
the surrounding air. This sometimes descends as
a cold wind into the warmer regions below. Thus
from the snowy heights of the Andes the cold
pamperos sweep over the Pampas of the Rio
Plata, and the icy puna descends upon the table-
land of Peru.

8. Offices of Winds.-Three offices of winds
may be mentioned: (1) they keep the elements
of the atmosphere uniformly mixed by maintain-








STORMS.


ing a constant circulation; (2) they bear vapor
from the sea to the land, and thus water the earth ;
(3) they carry heat imprisoned in the particles of
vapor, from the overheated regions of the earth to
the colder ones, and in this way make the torrid
regions cooler, and the temperate and polar
warmer than they would otherwise be. Discharg-
ing these various offices, they verify the Psalmist's
words, God maketh the winds his messengers."

TOPICAL ANALYSIS.
IlL WINDS AND CIRCULATION OF THE AIR.


1. Air in Motion.
Wind. Velocity of different winds.
winds.


Order in the


2. Causes of Winds.
Effect of heat. Of moisture.
3. General Circulation of the Atmosphere.
Location of constant ascending currents. Causes
which complicate the circulation. Classification
of winds.
4. Constant or Trade Winds.
General character. Direction. Cause of their west-
ward trend.
5. Variable Winds,
Locality. Countertrades. Origin. Proofs. Direc-
tion. Polar winds.
6. The Calm Belts.
Equatorial. Calms of Cancer. Of Capricorn. An-
nual movement of calms and winds.
7. Periodical Winds.
Land and sea breezes. Benefits of. Monsoons.
Cause. Effect. Bursting of monsoon. Minor mon-
soons. Other periodic winds. Mountain winds.
8. Offices of Winds.

TEST QUESTIONs.-What is in general the circuit" of the winds ?
Their general effect upon climate ? What force is the primary cause of
winds ? What other force acts as auxiliary ? Can you give any reason
why the ocean of air is so much disturbed at the bottom, while the
ocean of water is disturbed chiefly at or near the surface ? Should the
solar heat diminish, what would be the effect on the winds


IV. STORMS.

1. General Description.-Storms or tem-
pests are sudden and violent commotions of the
atmosphere. Especially at sea they are among the
most grand and terribly sublime spectacles in nat-
ure. A wind becomes a storm when it attains the
velocity of fifty miles or more an hour.
The great storms of the West Indies and of the
Indian Ocean are called hurricanes and tornadoes;
those of the China Sea, ', ,,. .. [See Chart of
the Winds. ] These are alike in cause and charac-
ter, and may best be considered under the general
name of cyclone. This name, derived from the


Greek kculos, circle, refers to the fact that they
consist of columns of air revolving round a perpen-
dicular axis. At the same time they have a pro-
gressive motion of greater or less rapidity over a
certain portion of the surface of the earth.
llustration.-You have noticed, especially in autumn, lit-
tle whirlwinds travelling along the roads or through the
fields, and raising eddying or whirling columns of leaves
and dust to a great height. These are miniature cyclones.
They have both a revolving motion and a progressive one.

2. Cause of Storns.-The general cause of
all such atmospheric disturbances is the same in
principle as that of ordinary winds. It is a differ-
ence or inequality of pressure or weight, in different
regions of the atmosphere. The principle may he
thuns stated : into an area of low barometer a wind
must always blow from an area of .7 barometer.
When from any cause the weight of the atmos-
phere in a locality is diminished, an ascending
current results. Currents of colder and heavier
air rush in to supply the deficiency. The force
and velocity of the currents thus created will be
greater or less according to the difference of atmos-
pheric pressure, or the gradient," as meteorolo-
gists call this difference. The larger the gradient,
the more violent will be the resulting wind.


COURSES OP CYCLONES.

Now suppose there is one area of low barometer
and one of high ; the result will he a simple wind


COURSE OF CYCLONE
Northern Hemisphere -






- - -


K-~s-


EQUATOR 5--








STORMS.


having one direction. But if the one area of low
barometer have areas of high barometer on all
sides of it, it is clear that from every one of these
a current will flow in upon the area of low barom-
eter. Such in-coming currents of air do not pass
in straight lines to the centre of the area of low
barometer, but circle round it in an ever-narrow-
ing spiral, gradually ascending as they approach
the centre. They constitute


the cyclone.


Illustration.-The curves de-
scribed by the air-currents of a cy-
clone may be readily illustrated.
Fill a basin having a stopper in
the bottom with water. Remove
the stopper and observe how the
water-currents take descending
spiral courses. They move round
the centre, but they also move to-
ward the centre. They are like
the air-currents of a cyclone turned
upside down.
The belief is gaining ground
that cyclones are largely due to
electrical disturbances. Some
very interesting experiments seem
to corroborate this view.

3. Lawivs of Storms.-
Cyclones obey the following
well ascertained laws:
(1) The wind revolves in
opposite directions according
as the cyclone is in the nor-
thern or southern hemisphere.
In the northern the direction
of revolution is from right to
left, or against the hands of
a watch. In the southern it
is from left to right, or with
the hands of a watch. This
is shown in the diagram, page
81.
The direction of the whirl
seems to be due to the influ-
ence of the rotation of the
earth upon the air-currents,
which press from all adjacent
quarters into the areas of low


(2) The storm, while revolving, travels forward.
The direction of this progressive motion is in gen-
eral northwest and southwest within the zones of
the trades, and northeast and southeast in those
of the counter-trades.
The course of land cyclones is not necessarily horizontal
or parallel to the surface of the earth. The revolving
column appears frequently to dip down at certain points in
the line of its progress, and, again


NORTHERN HEMISPHERE
Wind East


SOUTHERN HEMISPHERE


Wind
STORM
(Showing direction of wh


barometer, and to the action of these currents one
upon another.
As the wind revolves in a spiral, it constantly changes its
direction at any given place in the storm-track, in the same
way as the various parts of a moving carriage-wheel do. On
opposite sides of the centre it has opposite directions. Hence
we see why the wind changes as soon as the storm-centre
passes. This is shown by the "storm cards on this page.
The rate of revolution, or velocity of the wind," is from
50 to 150 miles an hour,


rising, leaves long distances un-
touched.
The starting point of cy-
clones is in the tropics.
North of the equator they
move northwestwardly up to
about latitude 30 N. Here
They turn to the northeast
South of the equator they
pursue the reverse course ;
starting near the tropics they
advance toward the south-
west, and near the parallel
of 27 they turn to the south-
east. From this it will be
seen that the pathway of cy-
clones somewhat resembles
- the curve called a parabola.
[See diagram, p. 81.]
The rate of travel is from one to
forty-five miles an hour, though
S storms are sometimes stationary
for a considerable time.


(3) The storm-centre is
an area of calm, and also of
S\\\ low barometer. The arrival
~', \of the storm-centre at any
S point is indicated by the
rR barometer. The descent of
th/ e mercury in tropical
storms often amounts to two
inches. It is sometimes so
S : rapid that it can be detected
by the eye.
East Let us see why this fall of
CARDs. the barometer should occur
irl in both hemispheres.) at the storm-centre. For
reasons not well understood
the atmosphere at this point of the storm area
is most largely charged with vapor, and here the
rainfall is usually heaviest. Now moist air is light,
because vapor of water is only about half as heavy
as dry air. Therefore the greater the proportion
of vapor which the air contains, the lower will be
the barometer.
Furthermore, the rainfall itself contributes to
depress the barometer by the condensation of








STORMS.


STORM AT ST. THOMAS, OCTOBER, 1867.


aqueous vapor into rain-drops, and by thle conse-
quent liberation of latent heat.
Such appear to be some of the reasons why the
storm-centre is an area of low barometer.
If from a series of observations we know what has been
the position of the storm-centre for every day during the
continuance of the storm, we may readily map down the
track of the cyclone.

Irregularity of Land Storms.-The above laws
apply with more exactness to storms at sea than
to those on land. The comparative irregularity of
land storms is mainly due to two causes: (1) on
land, such obstacles as mountains and hills change
the direction of storms and the wind currents of
which they consist; (2) the air on the land is
more irregularly heated than over the sea, and
areas of heated air and low barometer must attract
storms out of their normal course.
STORM AT ST. THoMAS.-On the 29th of October, 1867,
the island of St. Thomas was visited by a cyclone of marked
violence. [See diagram above.]
In the morning there was nothing unusual in the appear-
ance of the weather. The barometer stood at 30. At 11
o'clock, and without any warning from the barometer, a
gale sprang up from the northwest. It blew for an hour.
Then there was a great calm, which lasted 13 minutes.
The barometer now fell more than two inches.
This showed that the centre of the storm, the area of
quick and copious condensation and rainfall, had reached
the island. So dense was the body of rain and spray which
now filled the streets that objects 20 yards away were
rendered invisible, and persons seeking their homes held on
to lamp-posts, door-handles, or whatever promised tempo-
rary security uncertain which way to turn in the darkness
and the flood.
The 13 minutes of calm were the time during which the
stormi-centre was travelling over the island. When it had


passed, there was a change in the wind. It had blown from
the northwest; it now came from the sou theast. The storm
at this time reached its height.
The bark was blown from the trees, and the masts of
ships were literally whipped out of them. Every vessel in
the harbor was wrecked, stranded, or dismasted. Large
blocks of stone were lifted from the earth and blown ahout
the streets, Houses were unroofed or carried along by the
wind; and in the short space of four hours thousands of
persons had been rendered houseless, 75 vessels had been
wrecked or crippled, and 114 lost.
The little island of Tortola happened to lie in the track of
this storm. Entire villages were blown away; scarcely a
hut was left standing.
This storm continued its course to the westward, passing
over Porto Rico, and reaching the Island of Ilayti the next
day, where again it was very destructive.

4. Value of Storm Laws.-A knowledge
of the laws of storms is of the utmost value to the
navigator. By observing the direction of the wind
he may learn in what direction the storm-centre is
from him. The rule for this is : turn your bacl to
the wind, tnd the low barometer is always to your
left in the northern hemiisphere, and in the sou/h-
ern hemisphere to your right. This will readily ap-
pear by examining the diagram on page 81, and
imagining yourself with your back to the arrow
heads. If the sailor knows whereabouts tihe
storm-centre is, he knows how to steer away
from it.
Again : suppose he finds his barometer sinking
rapidly, an inch or even two inches below its
usual height. He now knows that he is in the
storm-centre. Obviously it will be well to trim
the sails and prepare for a gale. The centre of
calm will soon pass beyond him and a tempest wilj
strike him.







STORMS.


5. The Areas of .lh,ti.g differ in size and
shape. Though in general circular, they are fre-
quently elliptical ; as, for example, in the United
States, where their shape is a very elongated oval.
As to size, they are seldom less than six hundred
miles in diameter, and usually average twice that
amount.

6. Vhirlwinds anld Tornadoes differ
from hurricanes and typhoons, (1) in duration;
(2) extent of area; and (3), sometimes at least,
in direction of the whirl. They seldom last long ;
often not more than a minute. Their breadth
varies from a few hundred yards to a mile or two,
and their course is ordinarily not more than
twenty-five miles in length. The direction of
their whirl depends on the direction of the
stronger of the two currents which produce them.
Whirlwinds and tornadoes not infrequently visit


WATER-SPOUT AT -EA.


large areas of the Mississippi Valley. They sweep
everything before them. Houses are lifted up
bodily, and lanes, called "wind-roads," are made
through the forests. Large trees are uprooted ;
they are whirled about in the air like stubble, and
often left with their tops pointing toward the place
from which their roots have been torn.
Dust Whirlwinds.-Passing over desert regions
they give rise to the phenomena known as dust
whirlwinds. Those of India are the most singular.
They consist of a single column of sand, or of a


multitude of such columns, each revolving upon
its axis. These sometimes range themselves to-
gether side by side and rapidly advance, envelop-
ing everything in midnight darkness, and covering
the unwary spectator with a deluge of sand.
WATERSPOUTS.-At sea whirlwinds sometimes
produce waterspouts. They correspond to the
dust whirlwinds of the desert. The air-current,
revolving like that of a cyclone, in an upward
spiral, takes np the spray of the waves, and a tall
column may be seen revolving on its axis and
moving over the waters with extraordinary speed.

7. Distribution of Storms.-[See Chart
of the Winds.] The most violent storms occur in
the vicinity of mountainous islands.
The Pacific is the most tranquil of the oceans.
In those portions of its trade-wind regions where
there are no islands, and where monsoons do not
prevail, storms are unknown. The typhoons are
confined to the southeast coasts of Asia and the
East India Archipelago.
The South Atlantic, along the coast of inter-
tropical Brazil, is almost storniless, whereas, in
nearly corresponding latitudes in the North At-
lantic, as on the coast of Florida, Central America,
M[exico, and the West Indies, terrific hurricanes
occur.
The portions of the Indian Ocean specially sub-
ject to hurricanes are the Bay of Bengal and the
neighborhood of Mauritius.

8. tVeather _For.eca(sts.*-During the last
thirty years growing attention has been paid by
scientific men to the subject of the weather. Ob-
servations, more or less systematic, have been made
upon the force and direction of the wind, the course
and character of storms, the pressure of the at-
mosphere, the amount of rainfall, the temperature
and moisture of the air, and meteorological phe-
nomena in general. The multitudinous observa-
tions made have disclosed to meteorologists cer-
tain general principles which may perhaps be
called laws of thIe weather.
Knowing these laws, and knowing by tele-
graphic reports the weather-conditions prevailing

Thirty years ago the author of this wvork urged upon the attention
of the government of the United States, and those of European nations,
the desirability of having systematic meteorological observations car-
ried on by all nations at sea. As the result of his efforts the United
States government invited all the maritime States of Christendom to a
conference, which took place in Brussels, 1853, and which adopted the
suggestions made. But the ideas of Lt. Maury were not limited to the
ocean.
In the preface to the second edition of his "Physical Geography of
the Sea," published in 1855, he says it is a pity that the system of
observations recommended by the conference should relate only to the
sea. The plan should include the iand also, and be universal." Only
a short time before his death lie delivered a lecture on this topic in
Boston, and another in St. Louis.







STORMS.


throughout the country, we are enabled to predict
from day to day, with considerable accuracy, the
approach of storms, or of cold or hot weather.
We shall now briefly consider the way in which this
is done by the Signal Service of the United -i If.. .
GREAT STORMS OF THE UNITED STATES.-Most
of our great storms consist of northeasterly winds,
and travel in a northeasterly direction. They
may be conveniently classed as those which conime
to us from the Pacific Ocean, and those which
come from the Atlantic.
The storms of the Pacific penetrate to a greater
or less distance into the country, and often cross
it entirely. Their general direction is from west
to east.
The storms of the Atlantic are first felt either
at some southerly point on the Atlantic seaboard,
or on the shores of the Gulf. Generally they
come in from sea by the way of the Gulf, pass
northward on the west side of the Mississippi Val-
ley, or the western slope of the Appalachians, and
then turn to the northeast.
Those which make their appearance first on the Atlantic
seaboard are the western halves of cyclones, which, pursuing
their parabolic course, first northwestwardly and then north-
eastwardly, happen partially to embrace our shores within
their area. These western half-cyclones consist of northeast
and northwest gales. The eastern halves of the same storms,
consisting of gales from the southwest and southeast, are at
sea. The storm-centre pursues a course nearly coinciding
with our shore line.
PREDICTION OF STORMS.-The transient and
altogether uncertain character of the tornadoes
which occur in many parts of our country renders
it impossible to make any predictions regarding
them. Lasting often for only a few minutes, they
come and go almost before we are aware of their
existence. Of their cause and their course it may
not unfairly be said that nothing is known.
The behavior of ordinary storms, however, is so
far regular, that, in a large proportion of cases,
their course, after they have once manifested
themselves, may be foretold with some degree of
accuracy.
Simultaneous observations are made at 100 Sig-
nal Service stations scattered over the country,
at 7 A.M., 3 P.M., and 11 P.M. every day. These
observations are telegraphed to the central office
at Washington. There they are examined, and it
is ascertained what they indicate.
A storm begins, as we know, within or near an
area of low barometer. Suppose on a certain day
the 7 o'clock observations indicate a rapid fall of
the mercury at Omaha, St. Louis, and Keokuk;
while to the eastward and westward of those points
the barometer stands comparatively high. We
know that a storm, from the Pacific or from Ihe


Gulf, has entered the Mississippi Valley ; we also
know that it is likely to make its way to the east-
ward. Moreover, the later observations of the
same day at points to the eastward will reveal the
direction in which the area of low barometer is
travelling, and the rate of its movement. Hence
it can be predicted where the storm is likely to
strike, and when.
This illustrates the way in which storms are
foretold. On the approach of one, cautionary sig-
nals are displayed at the lake ports and at those of
the Atlantic coast. The annual saving of life
and property due to these warnings is immense.
Changes of temnperature are foretold on the same
principle as storms. The Signal Service Bureau
telegraphs daily information as to weather proba
abilities all over the country, and by its maps and
bulletins forewarns us of approaching wind and
rain, frost and snow, waves of heat and cold.

TOPICAL ANALYSIS.

IV. STORMS.
1. General Description.
Hurricanes and tornadoes. Typhoons. Cyclones,
2. Cause of Storms.
Cause of spiral movement. Illustration.
3. Laws of Storms.
Direction of the whirl. ForwNard motion of Ilie
storm. C(ailm at the centre. Causes of low ba-
rometer at centre. Irregularity of land storms.
Storm at St. Thomas.
4. Value of Storm Laws.
5. Area of Storms.
6. Whirlwinds and Tornadoes.
Points of difference between these and hurricanes
and typhoons. Destructive effects. Dust whirl-
winds. VW aterspouts.
7. Distribution of Storms.
8. Weather Forecasts.
Great storms of the United States. Prediction oif.
TEST QUESTIONS. -Is there any relation between the frequency and
power of storms and the temperature of lthe places where t hey occur?
Why do they formn more sublime spectacles at sea than on land ?
When the earth was much hotter than niowi, what must have been the
character of the storms ? Why ?

V. MOISTURE OF THE AIR.

1. Aimount.-More or less moisture is always
present in the air. It exists in the form of vapor.
Although this vapor is invisible, we can form
some estimate of its amount.
The rivers measure it for us. For the same
amount of water that they discharge lihts been
taken up from the sea in the form of vapor.
The general law regarding tlhe ainount o' mnoist-







MOISTURE' OF THE AIR.


Lre in the atmosphere is, that the warmer the air,
the more moisture it can contain.

2. Evaporation.-One of the most wonder-
ful of the many wonderful properties of water is
the readiness with which it passes from one of its
forms to another. The assuming of the condition
of vapor is termed evaporation.
ETvaporation goes on at all temperatures and
under all circumstances.
]llustrations.-You may have observed water drying in
our streets and roads after a rain, or clothes hanging on
the line frozen stiff, and yet becoming dry; or you may have
seen a light fall of snow disappear in freezing weather.
These were all cases of evaporation.
Evaporation is accelerated and augmented (1)
by high temperature ; (2) by diminution of press-
ure ; (3) by a dry condition of the atmosphere ;
(4) by wind.
EFFECT OF TEMPERATURE. The higher the
temperature, the greater and more rapid will evap-
oration be. Hence we find the maximum of
evaporation within the tropics; the minimum at
the poles. Evaporation takes place chiefly through
the day, and in the warmest part of the day.
EFFECT OF PRESSURE.-The less the atmospheric
pressure, the more rapid will evaporation be. In
a vacuum there is almost no pressure, and theie
evaporation takes place almost instantaneously.
Hence on the tops of high mountains, where the
pressure of the atmosphere is very much dimin-
ished, evaporation goes on much more rapidly than
it does at the sea-level, where the full pressure of
the entire atmosphere is felt.
Indeed mountain peaks may be so high as to be
entirely free from snow, while a belt of snow gir-
dles the lower part of the mountain. The reason
of this appears to be that at certain altitudes
snow evaporates so rapidly that it cannot accu-
muilate.
Aconcagua in Chili sometimes appears with its
bare and bleak top peering above a girdle of snow.
EFFECT OF DRYNEsS.-Atmospheric air can
absorb or take up a certain amount of moisture.
Warm and dry air will absorb far more than cool
and damp. When air has absorbed all the moist-
ure that it can retain, it is said to be saturated.
Now if the air be near the point of saturation, it
is clear that evaporation will be retarded, while
again if the air is dry, it will be encouraged.
In a damp foggy atmosphere you see every
breath that you discharge. The air has all the
moisture that it can contain, and has no absorptive
capacity. In a dry warm air your breath is invis-
ible. It is absorbed as soon as it leaves your
mouth.


EFFECT oF WIND.-If a wind blow upon the
surface of water, evaporation is accelerated. This
is because as fast as one portion of the air becomes
charged with vapor, it is removed, and a fresh por-
tion takes its place.

3. Condensation and Precipitation.
-Vapor returns to the liquid or solid state and is
deposited upon the earth by the processes called
condensation and precipitation.
When condensed, it assumes the form of dew,
white or hoar-frost, fog or cloud, hail or snow.
The great cause of precipitation, or the removal
of moisture from the atmosphere, is loss of heat.
The atmosphere can contain more or less vapor in
a state of absorption in proportion to its tempera-
ture. If the temperature be 50 Fahr. a cubic
foot of air can absorb about 2 grains' weight of
vapor. At the temperature of 70 Fahr., i.e., with
an increase of only 20 of heat, the proportion of
vapor is about twice as great.
From this it is easy to see why reduction of
temperature causes precipitation. Suppose a cubic
foot of air saturated with moisture to be reduced
in temperature, even very slightly; it is obvious
that its capacity for moisture will be at once re-
duced, and a certain portion of its vapor must be
precipitated. The temperature at which the
deposit in such cases begins to take place, is called
the dew-point.

4. How Dew is Fornmed.-On clear and
calm nights, the grass, the leaves, and other ob-
jects rapidly radiate their heat and grow cool.
They chill the surrounding air. It can no longer
contain the same amount of moisture as when it
was warm. Hence a portion of it is condensed
and deposited upon the leaves in the shape of fine
drops of water. We often say "the dew begins to
fall," though, strictly speaking, it does not fall.
It is deposited upon the grass precisely as, on a
hot summer's day, the moisture is deposited on
the outside of a pitcher of ice water.
Clouds check radiation, and hence on cloudy
nights less dew, or perhaps none at all, is
deposited.
You must have noticed that dew, and hoar-
frost, which is only frozen dew, are deposited on
some objects more copiously than others. This is
because some radiate heat more rapidly, and there-
fore chill and condense more quickly the vapor of
the air that rests above them.

5. Fog.-Vapor coming in contact with cool
air, if chilled below the dew-point, becomes vis-
ible. It assumes the form of fine watery parti-
cles which we call mist orfoff.








MOISTURE OF THE AIR.


lllustrations.-The condensation of
into mist, as it passes from your mo
cold air, is a familiar illustration of tl
You may also have observed that
calm, and frosty morning the spri
and rivers "smoke." This is the
nomenon that is exhibited by the
issues from the tea-kettle, the locomol
steamboat.
Very often, too, fogs are seen upoi
of rivers in the early morning. Towa
vanish. The morning air, because
retain so much moisture in absorptio
the rays of the sun have warmed it, a


its capacity for
the fog disap-
pears.
The most foggy
sea in the world
is that part of
the North At-
lantic Ocean
that lies on the
polar side of lat-
itude 40; and
the most foggy
place is on the
Grand Banks of
Newfoundland.
Vapor rises
rapidly from the
warmn water of
the Gulf Stream
near the Grand
Banks. It is met
there by the cold
current from the
north. Owing to
the chilling in-
fluence of this
current the va-
por is condensed
into fog as fast
as it rises.


moisture, it absorbs th


2 e
-- --:: - -
,-- .--, :-;^^:: ^ i:_


]_. -f =- w j ^ *-: .
... ..-- S. __= " "

: -'*' : -.s ^ -- .:_ f- --.


1. Cirr
2. Cun


Though fogs are most frequent in summ
on the Grand Banks at all seasons, producing
exquisitely beautiful silver fogs of Newfoun
garnish the forests of that island with frostw

6. Clouds.-A cloud is simply a
or fog floating high in the air instead
ground.
Clouds present a very great variety
ance, and hence are divided into soy
three simple, cirrus, cumulus, and sti
compound, cirro-cumnulus, cirro-strat
stratus, and cumulo-cirro-stratus or n
CIRRUS.-The cirrus or curl clou6
white wavy lines or curled bands. It
est of all cloud-forms, and attains the
nations, floating four or five miles ab


Your breath
uth into the
is.
in a clear,
ngs, ponds,
same phle-
steam which
tive, and the


face of the earth in regions of perpetual frost. It
is supposed to consist of minute crystals of ice
such as we see in the 'I. il i-, and may be de-
fined as frozen fog.
Cirrus clouds are often heralds of the cyclone. Only re-
cently these nimble forerunners were observed 800 miles in
advance of a storm that swept over England. They some-
times caution the mariner, ere his barometer gives any in-
timation of the approaching tempest.


n the surface CUMULUS clouds derive their name from the fact
rd noon they that they are heaped up, like vast mountains tower-
cool, cannot ing one upon another. They are often of glisten-
n, but when ing whiteness. They abound in the tropics, and
nd increased frequently appear in the sky of temperate latitudes
e vapor, and during the summer, when evaporation is rapid.
Of all cloud-
-... _--- ...-_ -_..-- -- formstheyare
. __=___ -::. .. ..-- __ -- perhaps the c
grandest. Out
of them darts
.. .? the lightning
-..-- which makes
.... __.-- .- our thunder-
-.. .. .:- :." ." storm s so
.... "^- .- ?- magnificent.

4 clouds appear


SC_.-. ....or ribbons.
They arc seen
_-- :.:-7 --:_7 -- --- "- -m ost fro-

quently in the
evening, antd,
when tinged
___.___ __.__ ____5__ by the rays of
the setting
FORMS Or CLOUDS.
sun, they form
US. 3. Stratus. .
uluts. 4. Nimbus. those islets of
gol d which
er, they occur render the sunset sky so beautiful.
gin winter the
ndland, which The compound clouds combine the features of
ork. the simple ones from which they are named.
THE CIRRO-CUMULUS is made up of fleecy masses
nass of mist of cirrus which roll themselves up into rounded
l of near the i ,,n ,-
of near th shapes. These cause the mottled appearance com-

y of appear only known as a "mackerel sky."
y of appear-
-en classes : TiHE CIRRO-STRATUS consists of layers of cirrus
ralus ; four clouds. They are often so arranged as to resem-
us, cumulo- ble a shoal of fishes, all swimming parallel to one
imibuiis. another. This cloud, like the cirrus, is often the
Consists of precursor of storms.
is the light- THu CUMULO-STRuATUS is fo(rmed of heaped
highest ele- clouds resting on layer clouds. Like tlihe cumulus,
ove the sur- its general mass is often quite dark and threaten-








MOISTURE OF THE AIR.


ing, while its edges are bright with sunshine that
is behind the clouds.
THE CuXuLO-CIRRO-STRATUS, or nimbus, is
simply a cloud of any kind from which rain falls.
Heaped clouds, and curls and layers blend to-
gether, lose their characteristic features, and form
one dense leaden mass. It often overspreads the
whole heavens.
VELocITY.-The velocity of cloud movement,
when accurately estimated by observers, is found
to be far more rapid than we should suppose from
the apparent rate of the "passing cloud." It has
been found that cumulus clouds which seem to be
moving at a leisurely rate are often travelling 75 to
100 miles an hour.
This is of very great interest, for it indicates to
us the velocity of the upper currents of the at-
mosphere.
HEIGHT OF CLOUDs.-When clouds rest on the
tops of mountains, they are actually in contact
with the earth ; often indeed they are below the
summit of the mountain. Their average eleva-
tion, however, is about half a mile. At times they
cannot be less than four or five miles high.
WHY THE CLOUDS DO NOT FALL. -Clouds are not vapor;
they consist either of minute vesicles-that is, tiny hollow
globes of water-or of fine ice-crystals. In either case they
are much heavier than air. Why, then, do they not fall ?
So far as we know, they are falling constantly. But the
lower part of the cloud, as it comes into warmer air, is dis-
solved again to vapor, and disappears, while a new portion
may at the same time be formed above. Thus the cloud,
though constantly sinking, retains its place.
A different view is proposed in a recent theory. It is
that clouds consist of minute watery particles which have
attached themselves to motes floating in the atmosphere,
and that these buoy them up.
OFFICES OF CLOUDS.-The main offices of clouds
are two : (1) they screen the earth from excessive
heat in summer, while in winter they are a mantle
to keep it warm by checking radiation.
Plants and animals are distressed by the intense heat of
the noonday sun. But the more powerful the ray, the more
rapid is evaporation. Soon vapor enough is lifted from the
earth to form the mitigating clouds. They overshadow the
land, and both plants and animals are protected from the
fierce and scorching sun.
(2) they enhance the beauty of the natural
world. A pure blue sky, unvaried day after day
by a cloud, is not to be compared with one in
which azure and white are contrasted. Nothing
is more missed by the traveller in Egypt than the
grandeur of our storm clouds and the varied
beauty of our evening skies.


of cloud.* If, however, the process of condensa-
tion continue, and vapor exist in abundance, it is
easy to see that the tiny water particles which
make up the cloud will increase in size, until they
are too heavy to float, and will fall as raindrops to
the earth.
The general cause of rainfall is that a certain
volume of vapor-laden air has been chilled below
the dew-point, so that it has'no longer the same
capacity for moisture as before. This may be
brought about in several ways: (1) the moist air
may be driven up a lofty mountain slope into the
higher and colder regions of the atmosphere ; (2)
it may be carried thither as an ascending current
of heated air; (3) it may be chilled by being
mixed with a mass of colder air ; (4) a change in
the electrical condition of the air appears, in some
unknown way, to reduce the capacity of the at-
mosphere for moisture. This last is often ob-
served in a thunder-storm, when vivid discharges
of lightning are followed by an immediate increase
in the downfall of rain.

8. Distribution of ain.--Rain is very
unequally distributed over the earth.
(1) The rainfall is greater on land than at sea.
(2) It is greater in mountainous than in level
regions.
The reason of both these facts is, that elevations
have the effect of directing vapor-laden air into
the higher, cooler regions of the atmosphere.
(3) The rainfall is greater in the torrid than in
any other zone. The average annual quantity at
the equator is eight feet. It diminishes as we ap-
proach the poles. This follows from the fact that
the torrid zone, being the hottest, is that of the
greatest evaporation.
While, however, these are the general facts re-
garding the distribution of rain, there are modify-
ing causes which exert a very important influence.

9. Regulators of 1ainfall.-The great
regulators of the rainfall are the mountain chains,
the deserts, and the winds. Each of these has an
important part to perform in distributing the rain
over the surface of the earth.

INFLUENCE OF MOUNTAINS.-The mountains
are the great condensers of vapor. If mountain
chains face the winds that come from the sea, they
render the region between themselves and the sea
a well-watered one. They riot unfrequently make
rainless the region beyond them. They rob the
winds of their moisture.


R at .-- 'lihe first form assnilled 1y the l Ra in smltimens falls from a cloudless sky. In such cases vapor is
~Il O tU 1pe 11 r Mien 10111 ondenj-ed dire tly into wvltter, willolitl passing Illugli thle inlterveuing
noisture of the upper air whien condensed is that stage of cloud.







MOISTURE OF THE AIR.


In India.-Thus the Himalayas face the
southwest monsoon, as it comes freighted --
with vapor from the Indian Ocean. They I
make India one of the most productive
countries in the world; but the plateaus ::
lying to the north of them are almost rain- .=
less. On a smaller scale the Western --
Ghauts act in the same way. They, too, -
lie in the pathway of the monsoons, and -
intercept and condense their vapors. The _
annual rainfall upon their tops amounts to -
about 260 inches, while the country on the .
east of them receives comparatively little
rain. I
But perhaps the most striking illustra- -'--
tion of the influence of mountains upon -
rainfall is to be found in the case of the
Khasia hills, on the northern shores of the ,---1
Bay of Bengal. They intercept the south- I_-?
west monsoons, as they come burdened with
vapor from the bay. The result is that the Fz-
winds, as they slant up the hills into the -
higher and cooler air, have their moisture
at once precipitated as rain, of which
nearly 600 inches fall there in the year.
In South America the influence of the
Andes is familiar. The northeast and
southeast trades come from the sea satu- .,
rated with vapor, and so go into the inte -'"-?
rior, rising, and cooling, and dispensing iC''
showers as they go, until they reach the .
crest of the Andes. Here the cold is suf-
ficient to squeeze almost all the remaining '-
moisture from them. Thus the eastern
side of these mountains, within the trade- .....
wind region [see Chart of the Winds], is
abundantly watered, while the western is
dry. Hence it is that Peru is a rainless I
country.
South of the mouth of the La Plata, the
reverse takes place. There the prevailing
winds are from the west. They come from
the Pacific, reeking with moisture, and
water the western slopes of the Andes,
causing the excessive rains of Southern
Chili. The eastern slopes are comparatively dry.

In our own country the Cascade Range and the
Sierra Nevada have a similar influence. They lie
in the pathway of the westerly winds which come
loaded with moisture from the Pacific. They act
as condensers, and bring down the copious show-
ers which give fertility to the Pacific slope.

INFLUENCE OF DESERTS.-In many cases the
deserts are the directors of the winds, and thus
become regulators of the rainfall.


Iy j
^\" ,I
-i i i" ri ,'
-.,X !


. : - - - - _.-- .--'--_ '_ - .

'-- .






.-- -' -- --'-
---._ -- --- - ------- -.
7^^ 2-z3.^ y^\


VIEW OF THE ATMOSPHERE DURING A RAIN-STORM.


India is in a region in which the northeast
trade winds blow over the land, and are rainless.
Were it not for the deserts of Central Asia, which
have the effect of drawing in the southwest mon-
soons [see p. 80], India would be as arid as Gobi.
In Africa the Sahara produces the monsoons
which blow from the Indian Ocean upon that con-
tinent. By the month of June, the desert is
heated up sufficiently to bring in the sea winds.
The rainy season then begins, and lasts till late
in autumn.









6o 14o Loisit th 12o 0Wrest fm ioo Gromeiids 0, oGo


40) 60 B


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.~ to.scn.o ,.' .m '

P I F 4' A "Y41"f' ;" dA. ,
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f-V/a ,1
51~*'


ENC-RAVED ORMA JURY'S' PHYSICAL GEQGR I-Y
Trace the northern and southern limits within which What. parts bf North America have the greatest Where autumnal and winter rains ? Summer rains ?
Qussrlo~s oN TH RAIN CHAnT.
snow does not fall at the level of the sea. (The two red annual, rainfall ? What countries of South America ? What parts of what countries are embraced within the
How is the larger or smaller amount of annual rainfall lines crossing the chart indicate the northern and south- What countries on the east and west shores of Africa ? range of the Equatorial Calms and Cloud-ring ?
indicated on the chart? How are monsoons indicated? ern boundaries of the periodical rains.) Within these What portions of Asia? Of Australia ? What rainless districts are indicated ? Can you ex-
Where is the district of the great monsoons? What boundaries how is the year divided? At what seasons are the rains of Europe most frequent ? plain why these districts are rainless ?
portion of the earth's surface has the greatest annual Where is the belt of constant rains ? By what phe- In what parts of North America do spring and sum- What places in the United States have the heaviest
rainfall ? What winds bring the rains to this region ? nomenon are these rains usually accompanied ? mer rains prevail ? Where do all-the-year rains prevail ? rainfall ? (See Table on last page of the book.)


100 Longitude 1i20 East -ron l-O Greenwich 161






tjl I
1 ]
fit





-, 1 .I


t 160













" "-" i
" ( ;". -< S:

..... -^ -, ---_.


'f :: -,,:

S'* ** ,, i .....- .. .,';-"
: .. .-


I


r i.,


* \








MOISTURE OF THE AIR.


The periodical overflow of the Nile is due to the nature of the supplying winds, the rainfall in
the rains into which the vapor is condensed which any given region is Constant, Periodical, or Varin-
the African monsoons bring with them from the able.
sea. Thus Egypt owes its fertility in some degree CONSTANT RAINs.-The constant rains are
to the burning sands of Sahara. confined to a belt near the equator, about 5 wide.
North America has its deserts and its monsoons, In this belt there are almost daily showers. The
though they are far less marked than those of the cause is clear.
Old World. The northeast and southeast trades meet near
The table-lands of Mexico, Arizona, the dry plains of the equator. They are so completely saturated
Texas, New Mexico, and the neighboring regions, are with moisture that the sailor, hanging out his
heated by the summer sun to such a degree, that the air clothes in the ,., .... is often surprised to find
resting upon them becomes rarefied, and ascends, the cooler in the evening that they have not dried in the
air from far and near coming in to restore the equilibrium. y
Thus a southeast monsoon is created in the Gulf of Mexico, least. Under the vertical rays of the sun an as-
and a southwest one in the Pacific. sending current is produced which carries the
Both of these winds blow toward the lana, and bring the vapor-laden air into the higher regions of the
rains to Mexico, so that one side of that country is watered atmosphere. Here the vapor is cooled and con-
from the Pacific, the other from the Atlantic Ocean. densed ; and hence the frequent thunder showers
INFLUENCE OF THE WINDS.-As a general rule of this region of constant precipitation.
w inds are dry, if they have traversed the land, or if PERIODICAL RAINS.-Within the tropics, to the
they are journeying toward the equator. Winds north and to the south of the narrow belt of Con-
are wet, if they have traversed the sea, or if they stant Rains, lie the belts of Periodical Rains.
are journeying from the equator. 1n the New World the periodical rainfall is
Dry WVinds.-Land winds are dry for the sim- closely connected with the annual movement of
ple reason that they have so little opportunity to the Equatorial Calm Belt and its accompanying
take up moisture. Thus the northeast monsoons Cloud Ring.
which sweep over the inland regions of Asia are The Calm Belt travels northward and south-
the dry monsoons. The westerly winds of our ward, following the annual movement of the sun
own country, all the way from the Sierra Nevada in the heavens. It is farthest south in March,
to the Atlantic, are dry winds. They bring our and farthest north in September.
fair weather. During the time that it is passing over a place,
Again: a wind that is blowing toward the it gives to that place its rainy season. After it
equator is dry, because, entering warmer latitudes, has passed, there is scarcely a drop of rain until it
it is gaining capacity for moisture with every de- comes again.
agree of its progress. The trade winds, for ex- Let us follow the cloud ring in its journey from south to
ample, blow toward the equator. You perceive, north, and you will readily understand its movements, and
therefore, that they are going from cooler to the rainy seasons that depend upon them.
warmer latitudes. Their temperature is increased The time is February; it is then over Guayaquil (lat. 3'
by the way, and with increase of temperature S.), and then the rainy season there is at its height. It corn-
there is increase of capacity for moisture. The mences its movement for the north in March. Quitting the
trade winds, therefore, take up more water from skies of Guayaquil soon after, it leaves them bright and
clear with the commencement of the dry season. In a little
the sea than they return to it. They are evapo- while it has travelled as far as latitude 4' N. It then over-
rating winds, shadows Bogotd, where the rains begin in April or May.
Wet Winds.-Sea winds and winds blowing In June it is over Panama, and hence a rainy season pre-
0 vails there; and so the cloud ring continues on to Mexico,
toward the poles are rainy. The counter trades reaching Mazatlan, just under the tropic, about September,
go toward the poles. They are travelling from when it commences its march toward the south, so as to be
warmer to cooler latitudes. Their temperature is again at Guayaquil by February or March.
decreased by the way, and, therefore, there is a It is clear that on its return from north to south the
decrease in their capacity for moisture ; they de- cloud ring must give to certain places a second rainy season,
posit more than they take up. They are, there- because, in coming and going, it passes over them twice.
fore, rain winds. In the Old World the periodical rains are occa-
sioned by the monsoons or reversed trades. For
10. Rains Classified.-The winds are about six months, in Southern Asia and Central
classified according to the regularity with which Africa, copious rains fall. When the monsoons
they blow, as constant, variable, and periodical, change, the dry season sets in, and scarcely any
It is proper, therefore, to classify the rains which rain falls until after six months, when the wet
they bring in the same way. Hence, according to monsoon begins to blow again.









MOISTURE OF THE AIR.


Rainy and Dry Seasons.-Within the belt of snows of the Andes; while the peasant of Egypt, like hi.
the Periodical Rains the year is divided into rainy ancient forefathers, supplies his fields and his gardens from
seasons and dry. the sacred waters of the Nile.
seasons and dry.


In general terms, the rainy season in the northern belt
may be said to begin with April, and last till October, while
the dry season extends from October till April. In the
southern belt this order is reversed-the dry season lasting
from April till October, and the season of rain from Octo-
ber till April.
It is not to be supposed that during the rainy season
there is an incessant fall of rain. In Mexico, for instance,
the rainy season is the most delightful portion of the year.
As a rule, the nights and mornings are clear and beautiful,
and the weather fine, with a few hours of rain after three
or four o'clock P.M.

VARIABLE RAINS.-North and south of the
belts of Periodical Rains, the rains become Varia-
ble ; i.e., they are irregularly distributed through
the year. In some countries they occur mainly
during the summer, in others during the winter;
in others, again, during the spring and autumn.
This condition of things prevails throughout the
temperate regions.

11. Excessive and Deficient Rain-
fall.-Owing to the influence of local causes,
there are regions of excessive and deficient rain-
fall. Let the pupil, now familiar with the influ-
ence of the winds, the mountains, and the deserts,
refer either the excess or the deficiency in the
cases about to be mentioned to its appropriate
cause. [See Rain Chart.]

REGIONS OF ExcEss.-Naturally the regions of
excessive rainfall, with few exceptions, lie within
or near the tropics. Cherrapunjee, in the vicinity
of the Khasia hills in India, receives annually
about 600 inches-or a depth of fifty feet-a greater
amount, so far as we know, than any other place
on the globe.

Parts of the British Isles, the coasts of Guinea and Sene-
gambia, Eastern Africa and India, are all remarkable for
their heavy rainfall.
In the New World, Brazil, Guiana, Venezuela, the West
India Islands, Central America, Patagonia and the Pacific
shores of Alaska are all regions of excessive rainfall.

REGIONS OF DEFICIENCY.-Rainless or almost
rainless regions are the great belt of deserts ex-
tending across Africa and Asia, from the Atlantic
nearly to the Pacific ; the Great Basin in North
America, lying eastward of the Sierra Nevada;
Peru, together with the northern part of Chili,
and portions of the Argentine Republic lying
eastward of the Andes.

Cultivation in all dry countries is carried on by means of
irrigation. For this purpose tanks have been constructed
in India at vast expense. The Peruvian farmers avail
themselves of the miounlain-slreams that are fed by the


TOPICAL ANALYSIS.

V. MOISTURE 01' THE AIR.

1. Amount.
Ihow measured.

2. Evaporation.
Conditions under which it takes place. Causes
which increase it. Effect of tenprait nre, Con-
sequent place and time of imaximunnm evaporation.
Effect of pressure. Effect of dryness. Effect of
winds.

3. Condensation and Precipitation.
Cause of precipitation. Dew-point. Forms or
water derived from vapor.

4. How Dew is Formed.
Effect of clouds. Difference in quantity of dew or
frost formed on various substances.

5. Fog.
now formed. Illustrations. Fog's. of the Grand
Banks.

6. Clouds.
Various forms. Cirrus. Cumunlus. Stralil,. Cirro-
cuimuilus. Cirro-stratus. Cuimuiilo-strat us. (ii-
mulo -cirro-stratus. Velocity of cloud movement.
Height of clouds. Why thle clouds do not fall.
Offices of clouds.

7. Rain.
General cause. How brought about.

8. Distribution of Rain.
How caused.
9. Regulators of Rainfall.
Inflluence of mountains. The Ilimalayas. Westernl
Ghauts. Khasia hills. The Andes. The Cas-
cade Range and Sierra Nevada. Influence of
deserts. Deserts of Central Asia. The Sahara.
Table-lands and dry plains of Mexico and the ad-
joining regions of the United States. The influ-
ience of the winds. Dry winds. Wet winds.

10. Rains Classified.
Constant rains. Theirlocality. Cause. Pcriodical
rains. Their locality. Annual movement of lie
Equatorial Calhin Belt. Periodical rains in lhei
Old World. Cause. Rainy and dry seasons.
Variable rains, locality of.

11. Excessive and Deficient Rainfall.
Regions of excess. Of deficiency. Causes. Irri-
gation in dry regions.

TEST QUESi'ONis,-Dews are liheavier it) the fall lihan in spring,
why c Why are they heavier on low grounds than on the adjacent
hills ? You have noticed that the clouds in spring lake on a different
appearance from w hat hey have in winter ; can you think of any rea-
sonI for it ? To \vhiih class do tlluider-cloudls lelonig ? How is it talui
clods cha:glela Iheii. rlinis so iollslantly ? Why should there bec IOi't.L
riaih OIt l]a li thaln 1, siai








HAIL, SNOW, AND GLACIERS.


VI. HAIL, SNOW, AND GLACIERS.

1. Hail.-Moisture, descending through the
cold upper regions of the atmosphere, is some-
times frozen, and becomes hail or snow.
When examined carefully, hail has been found
to consist of concentric layers of ice, encasing
one another like the layers of an onion.
In size, hailstones vary. Occasionally they are
as large as marbles, or even hens' eggs, so that
severe hailstorms occasion very great damage to
crops.
The formation of hail is not well understood.
It usually falls in the heat of summer, and it is
difficult to account for a temperature at that sea-
son so low as to freeze the moisture of the atmos-
phere. The sudden ascent of moist air into the
cold upper regions of the atmosphere is, probably,
the most common cause of this phenomenon.


SNOW CRYSTALS.


2. Snoiv.-The moisture that falls from the
clouds, frozen in flakes, is called snow. When ex-
amined, it is usually found to consist of exquisitely
formed crystals, which are generally in the shape
of a six-pointed star. [See illustration.]
Snow rarely occurs within the limits of about
30 north and south latitude, except on high
mountain tops. It is naturally more abundant as
we approach the poles. It is also in general more
abundant where the climate is inland, than where
it is maritime. Paris has, on an average, 12
snowy days in the year ; St. P .-, ..1I.,,r_ 170.
Snow is perpetual, however, even at the equa-
tor, upon all heights greater than about 3 miles
above the sea-level. The line above which snow is
always found is called the snow-line. [See small
map on p. 105.] It varies in altitude from many
causes.
Whatever tends to elevate the temperature of
any locality, tends also to elevate the snow-line.
Hence a low snow-line means a cold climate.
While at the equator the snow-line is 16,000 feet
high, at the Straits of Magellan it is only about
4,000.


THE OFFICES OF SNow are two-fold: (1) it
protects the earth and the crops planted in late
autumn from the intense cold and the injurious
effects of frost. Sometimes there is a difference
of 40 between the temperature of the ground a
little below the surface, and that of the snow that
covers it ; (2) the vast quantities of snow that fall
on the great mountain ranges, as the Himalayas,
the Alps, and the Rocky Mountains, serve as per-
petual feeders of the rivers.

The .. ; ,.:- of snow that falls on an extensive range of
mountains, such as the Alps, is very great. Agassiz ob-
served a fall of fifty-seven feet in six months at the Hospice
of Grimsel, and observations during twelve years near the
Pass of the Great St. Bernard showed an annual snow-fall
varying from twelve to forty-four feet. It has been esti-
mated that the average annual snow-fall on the Alps
amounts to sixty feet, which is equivalent to six feet of
water.

AVALANCHES.-A large part of the snow,
as already stated, gradually melts and flows
through the river-courses to the sea. Other,
although much smaller portions, descend the
mountain slopes into the valleys as avalanches.
The snow is loosened from its bed by the warmth
of the advancing season, and plunges down the
steep declivities with frightful velocity. Some-
times the very echo of a loud word is enough
to disturb the overhanging mass and hurl it
into the valley below.
Many instances are on record of the appalling destruc-
tion wrought by this scourge of the Alps, whole villages
having been overwhelmed, and hundreds of lives destroyed
by a single avalanche. Thick forests are the best protection
against danger from this source, and in former times the
penalty of death has been adjudged against any who should
destroy a single tree of the protecting barrier.

3. Glaciers (from the French glace, ice,) are
vast masses of ice filling mountain valleys. Im-
agine a river descending a ravine to be dammed
up so as to fill the ravine completely, and then to
be frozen solid. This will give you some concep-
tion of a glacier.
FORAMATION.-The process by which glaciers
are formed appears to be as follows: the snow
that falls in elevated ravines gradually becomes
compacted in structure, owing to its partial melt-
ing by the sun's rays, and from the pressure of its
own weight.
If we should follow one of these ravines down-
ward, we should find the snow growing more and
more solid under our feet, until we reached the
snow line. Below this line we should find the
compacted snow turned to ice. Following the
course of the ravine we should observe that the
ice mass filled it from side to side and terminated







HAIL, SNOW, AND GLACIERS.


at length among the gardens and pastures of the
lower valleys, a stream of watteY gushing forth
from its cavernous extremity. This is a ,hlior' of
the first rankc. Others again, smaller in extent,
and containing comparatively little ice, never
reach the lower valleys. These are .''.. *. ...of the
second rank.













C__. ,









TE LEC-flE-GLACE. ('From a Photograph.)
The compacted snow reaches about to the snow-
line, and is called the *nev (nd-Nd). The nev' is
in general about half the density of ice, or more
than three times that of snow.
MOTIoW OF THE GLACIERS.-Solid and immov-
able as these mighty seas of ice appear, they arc
really in motion. Long before glacier motion
was suspected by scientific men, it had been ]known
to the mountaineers thiat blocks of stone lying
.. - V. ...`


























upon01 the surface of glaciers moved slow ly down-
ward.
A large number of carefnlly conducted observa-
tions have been niade, which prove not only that
the glacier as motion, but tat its motion closely.








resembles that of a river. It is -'i in the
centre, and slower, owing to the friction, neart the
sides and bottom. Not' ithstanding this nov e-








ment, the termination of the glacier retains amort
the same position fron year to year, because it is
melted away as fast as it mO es downward.








'ate of Motion. -The rapidity of the motion of
a glacier depends pn the season of the year, the









size of the glacier, and the inclination of its bed.
Tile motion is more rapid in summer than in win-
ter, in the day time than at night, and in a large
tond deep glacier than in a small one.
The average rate per year, for glaciers of the
tin hav,. enmaewhch.roe.otony ha
resemble that of- a rier It is----d-I- -1i



centre, pactd slowe r eahe about to the frci nonart-
sides and is taied Nt withstanding v0 this iov6 i
iu entteterminationt of the glacityroretaesorbour
the shree pstions fratom yernow.vibcas ti
melted:, awa as: f Jast~ s-Soi and itmovesdwnad
aglaer deens uhese tihy season of the year, they r
Trealy motion. isn more rapdaciumer thanion w
ter, suspetheday scetifie than, tnigt, ad ien a larg
o deep mounaciners than inabmlolk one. oeyn
upnthe average raepryer o glaciers oedsofl towe


first rank in the Alps, is not far from 100 yards :
for glaciers of the second rank, not more Ihan
one quarter of the same amount.
The middle of the Mer-de-Ghlce was found bv
Tyndall to move thirty inches a day in sumiiner,
and half as much in winter.
The following figures express in yards the motion, during
one year, of a row of poles set in a straight line across ihe
glacier of the Aar, by Prof. Agassiz:
5. 20. 48. 55. (2. 64. 67. 69. 79. 68. 64. 54. 47. 39. 21.
11. 1.
The central part, it will be observed, moved about eighty
yards a year.

Some glaciers, notably that of thle Rhone, tell
their own tale of their movement down the valley.
On their surface concentric curves may be ob-
served bulging toward the lower end of the glacier.
These show, as clearly as a line of stakes, the more
rapid movement of the central portion of the
glacier.
Owing to the slowness of the glacier motion,
what is now the upper end of the glacier may be
a century or more before it gets to thie foot of tlhe
mountain.

THEORY 01o GLACIER MOTIo.-VYarious theo-
ries, none of which is in all respects satisfac-
tory, have been advanced to account for glacier
motion and the accompanying phenomena. The
first thing to be accounted for is the motion itself.
Two causes for this may be given : (1) gravitation ;
(2) expansion within the glacier. It is probable
that both these take part in producing the motion.
Gravitation, or the weight of the glacier, would
naturally draw the mass down the slopes of tihe
valley.
Expansion within the glacier needs explanation.
When the water from the melted surface of the
glacier percolates downward into the interior of
the mass, it encounters a temperature of 32 Fahr.
It freezes and of course expands. Its expansion
must necessarily take place in thle direction of
least resistance, i.e., toward the lower end of the
valley. When we recollect that freezing water
will burst a plugged bombshell [see p. 43], we can
readily see that a force will be developed by the
water freezing in the glacier-mass quite sufficient
to aid materially in urging forward its enormous
weight.
J,. .. '*...-The facts must now be considered,
first, that the ice of a glacier accommodates itself
to the shape of its enclosing valley very much as
a river does to its channel ; and, second, that i!i ,
fracture its parts reunite. These phenomena are
explained by what is known as -_ ].,i Gio, or second
freezing. If we pound a mass of ice into frag-
ments and then moisten the broken surfaces, the








HAIL, SNOW, AND GLACIERS.


fragments will readily freeze compactly together
again.
This is what occurs in a glacier. In passing
through narrow gorges it is crushed and broken,
and in gliding over steep irregularities in its bed it
is cracked and splintered. The lower parts break
away from the upper, and fissures of great depth
called crevasses are formed, as shown in the fol-
lowing illustration.
But after the ice has been thus broken and
splintered or sundered by crevasses, it reunites and
forms one compact mass. The crevasses admit
warm air, and their walls are perhaps slightly
thawed, or, the ice on the top of the glacier being
melted, water trickles down and moistens the
fractured surfaces. In this condition the mass of
fragments is compressed by its confining valley-
walls, the sundered portions are brought together
again, and regulation occurs.
Effect of pressure on melting point of ice.-It appears from
recent experiments that under pressure ice melts at a lower
temperature than 3"' Fahr. If a wire weighted at each end
be caused to cut through a block of ice, water will be seen
flowing round the wire, while, in the cut behind or above
the wire, it is found to be frozen. This experiment has an
important bearing upon the phenomena of glacier motion.
Pressure is obviously exerted by certain portions of the
glacier upon others, especially when the glacier is squeezed
within gorges. If this pressure develop heat enough to
bring the melting point of ice to 28 instead of 32, it is
easy to see how the onward movement of the glacier would
be facilitated by reason of its partial liquefaction.
MORAIXES. The rocks and debris brought
down from the slopes of the ravine by the action
of the frost and by avalanches, accumulate along
the sides of the glacier. Hence a dark band of
earth and stones may be seen upon each side, va-
rying according to the character of the rock en-
countered. These bands are called moraines.
Occurring at the sides they are called lateral mo-
raines.
At the ..,ii.-! ... of two glaciers, the moraines




-_: _- _:---:--=:
---- --: -_-2 -.-
---~~-_ _-"^ T i 1-.




CREVASSES,

which skirt the two sides that join are united,
and form a medial moraine. If another glacier
unites with this again, a second medial moraine is
formed in the same manner.


NOTE.-In the accompanying cut it will be seen that the
Glacier du G(ant unites first with the Glacier des Pdriades, and
from their junction the dotted line shows the medial moraine
formed from the right moraine of the Gdant glacier and the
left moraine of the Pdriades. Where the glacier thus rein-
forced receives the Glacier de Ldchaud, another medial moraine
is formed ; and a third where the Talefre adds its tributary
stream. By the junction of these is formed the Mcr-de-Glace,






1 2
-.

I ^ "





/ -' 0
\,' -A/ i ? .
' .-" ,:" *' 'f- ^
1. -- : \ i o,,- "* _-
,\ -- \ ---,- .-' -
-^-.^k I ,- ./. ;* -* --,. "-=-- "
..- '- .'... y / ,\ .*' .. ..

--. ^ '.'- *
j-\ i f
I,, IJ/L' //
i -
i /' --
,,,,, '\ i //-- -,; -=

Si .'. .-

\. \,
** \ 'y i:


MiORAINES (a, b, c, d, e) OF TIIE MER-DEE-GLACE.


The earth, stone and boulders brought down on
the glaciers form, at the lower end of the glacier,
where the ice melts and leaves them, immense de-
posits, called terminal moraines.
TRANSPORTING POWER o' GLACIERS.-The ex-
istence of what are known as boulders" and
rocking stones," or erratics" as they are
also called, is explained by the transporting power
of glaciers. Such stones have been portions of
ancient moraines. And therefore, from the pres-
ence of boulders, we argue that in former ages
glaciers moved over certain regions where they
are now unknown. A belt of country extend-
ing from the Baltic to the Black Sea has been
strewn, by glaciers and drift-ice of a former period,

"Rocking stones are large blocks of stone which are so balanced
that they may be rocked by a push. They are called erraticcs" 1. e.
i wanderers, because found at a distance from their original site.








HAIL, SNOW, AND) GLACIERS.


with boulders that were rent from the Scandina- It is estimated that the total number of glaciers
vian M..i ,l i'-. in the Alps is about .', and that the surface con-
A similar process is still going on in the trans- stantly covered by snow, acme, and ice is more than
portation of boulders southwardly from the Arctic 1,000 square miles. Thie thickness of the Alpine
cliffs. They are borne by the glaciers of Green- glaciers is believed to vary from 200 feet to 2,000.
land to the shores of Baffin Bay, and thence to the i The Pyrenees and the Scandinavian mountains
____ ___ contain glaciers of the second rank. Large ones
i - v- -- - . -- -- : exist in the Caucasus.
In the New World, Greenland and Alaska have
... .. glaciers far surpassing in magnitude those of the
."."-" '.....--' '.....Old World. The Hnumboldt Glacier, in Green-
land, is more than sixty miles in breadth, three
hundred feet deep, and of unknown length.
-" Glaciers of large size are found upon Mi. Shasta,
eeand upon Mts. Rainier and Tacoma. lf he Am les,
. . -: ':- t/' ,I e x c e p t in P at aqg o n ia a re d e s titu te o f th e mn .


ICE ANTI) BOiLDEI.S.


Banks of Newfoundland, where, meeting with the
Gulf Stream, they are dropped by the ice, and de-
posited on the bottom. Thus these banks are
formed.
GLACIERS AS RIVER SOURCES.-The glacier, as
it imperceptibly glides down the mountain, is
melting all the time, and the traveller upon its
rugged surface may hear, far down in its creviced
depths, the sound of running water, which gathers
volume from a thousand trickling streamlets, and
at last issues forth, the never-failing source of
some noble river.
The Rhine, the Rhone, and many tributaries of
the Danube and Po, spring from glaciers in the
region around the St. Gothard ; and every one of
the hundreds of glaciers found among the Alps
nourishes some stream, that it may fertilize the
land and cheer the heart of the husbandman. The
Ganges, in India, leaps out from under a glacier, a
torrent forty yards in width.
DISTRIBUTION AND SIZE OF GLACIERS.-Gla-
ciers of enormous size are found in the Arctic re-
gions. Probably most of the valleys in Greenland
and Spitzbergen are occupied by them.
Ti7e grandest glacier .-'.. of the temperate zone
is that of the Himalayas. The glacier of Bepho,
in one of the valleys of the Karakorumn range, is
36 miles in length-about four times as long as the
Mer-de-Glace-and covers hundreds of square miles
in area. Many others in the same region are of
nearly equal extent.


4. Iceber'gs.-The glaciers of thie polar re-
gions are not melted into rivers like those of temn-
perate latitudes. Their lower extremity there-
fore, is pushed out into the sea, and mounltain-like
masses are broken off from time to time and borne
away by ocean currents. These are called ir'cb( ./.
DISTRIBUTION.-On lhe polar side of 55 south, the sea, all
the way round the earth, is studded more or less thickly
with icebergs. [See Isothermal Chart, pp. 72, 73.]
During his Antarctic voyage in 1841, Sir James Ross
sailed 450 miles along an unbroken barrier of ice. It stood
180 feet out of the water, and was aground in waler 1,500
feet deep.
Admiral D'Urville fell in with one off the Cape of Good
Rope 13 miles long and 100 feet high. I have mnet with
them myself as near the equator as 37' south latitude. In-
deed, icebergs enough come from the unexplored Antarctic
regions to stud an area as large as the continent of Asia;
for navigation is endangered there by ice throughout an
area of not less than 15,000,000 square miles.
On the north side of the equator icebergs are found only
in the Atlantic; never in the Pacific Ocean. They drift
out from their nurseries in the polar regions with the cold
currents which bear them southwardly until they disappear
in the warm waters of the Gulf Stream. They f,.-.-. iil
lodge on the Banks of Newfoundland, where they greatly
imperil navigation.

TOPICAL ANALYSIS.

VI. HAIL, SNOW, AND GLACIERS.

1. Hail.
Size of hail.tiiones, Formation.
2. Snow.
Limits of snow-fall. Of perpetual snow. Offircs of
Siow. Amount of snow-fall illn inountain regions.
Avalanches-. Cause. Destrulctive effects.
3. Glaciers.
Formation. Glaciers of the first rank. Second
rank. .re. Motion. Resemblanilce to that of a
river. Circumstances affecting rapidly of mino-
fion. Rate of motion. How determined. Indi-
cations of motion oil the surllface. Theory of
motion. Causes of motion. Regelation, cre-









ELECTRICAL AND OPTICAL PHENOMENA.


vasses. Moraines. Origin. Lateral, medial and
terminal moraines. Transporting power of gla-
ciers. Former glacier regions. Glaciers as river
sources. Distribution and size of glaciers.
Himnalayan region. The New World.
4. Icebergs.
Origin and character. Distribution.


TEST QUESTIONS.-How can So cold a substance as snow be a pro-
tector from cold ? Why should the snow-fall be so much greater on
mountains than elsewhere ? Do you know of any other phenomenon
similar to avalanches in character and destructive effects ? At the rate
of 100 yards per year, how long would it take ice to move from the
upper to the lower end of a valley six miles long ? If there are four
moraines on a glacier how many smaller glaciers have united to form
it ? Icebergs project about 1-9 out of the water ; how deep will one ex-
tend which projects 100 feet, the size being the same above and below
the water ?


VII. ELECTRICAL AND OPTICAL PHE-
NOMENA.

1. Atmospheric Electricity.-The at-
mosphere is almost invariably in a positively
electrified condition ; the surface of the earth, in
relation to the air, appears to be always negative.
In other words, the air seems always to contain
more electricity than the earth. At the same
time, it is to be remembered that the conducting
power of the earth may render very difficult the
detection of its true electrical condition.
The electricity of the atmosphere manifests
itself chiefly in lightning and auroras.
LIGHTNING is of three kinds-zig-zag, sheet-
lightning and ball-lightning.
Zig-zag lightning consists of flashes passing
between two bodies of air or clouds, or between a
cloud and the earth, which are in opposite electri-
cal conditions. The electricity takes the path of
least resistance, and since different portions of the
air have different conducting powers, the pathway
of the lightning naturally becomes zig-zag.
Sometimes the flash divides and presents a forked
appearance.
., -' ,',;'.'..' ,, ,frequently called heat-lightning,
appears as a glow of light illuminating vast clouds
and even large areas of the sky. It is probable
that this kind of lightning is the reflection of the
lightning of some distant storm.
Ball-lightning appears in the shape of globular
masses of fire, which explode with violence. It is
of rare occurrence.
Thunder is considered to be occasioned by the sudden
rushing together of the portions of the atmosphere that have
been divided by a flash of lightning. It is not heard at a
greater distance than fourteen miles.
The flash is seen instantaneously. The sound requires
about five seconds to travel one mile. Hence, if after see-
ing the lightning, we count the number of seconds, or pulse
beats, until we hear the thunder, it is easy to ascertain how
Bear the flash has been to us.


AURORA IN ARCTIC REGIONS.


The form of the aurora varies greatly. Some-
times it is simply an arch of light spanning the
sky near the horizon, with quivering streamers of
white, green, or crimson light, shooting fitfully to
the zenith. Sometimes mere masses of colored
light are observed. At times the whole heavens
are flashed.


THUNDEli-STORIMS are usually very local, but this
is not always the case. That which accompanied
the "bursting" of the May monsoon in 1848 ex-
tended over an area of 600 miles in length and
fifty in breadth.
In general the electricity does not pass from the
air to the earth, but only from one portion of the
atmosphere to another. When a discharge to the
earth does occur, the effects are often very destruc-
tive. The strongest trees, if struck, are rent and
stripped of their branches, the sap being suddenly
converted into steam, and an explosion actually
taking place. Animals and men who are struck
are almost always killed.
Distribulion.-Thunder-storms are much more frequent
in warm than in coo] climates. They occur in that section
of the torrid zone known as the belt of Constant Precipita-
tion almost every day in the year.
THE AURORA BOREALIS, or Northern Lights,
is a luminous appearance often observed, as the
name implies, in the northern heavens. In the
southern hemispehre the same phenomenon is
called Aurora Australia.








ELECTRICAL AND OPTICAL PHENOMENA.


Nature.-The aurora is simply an electrical
phenomenon. The following facts establish the
probability of this.

(1) The delicate shades of rose, and purple, and violet,
which characterize the more brilliant auroras, can be pro-
duced by passing the spark from an electrical machine
through a partial vacuum, as has been remarkably illustrated
by some experiments of Mr. Crookes, of England.
It has been computed from observations of a large num-
ber of auroras, that the beams never approach nearer to the
earth's surface than forty-five miles, and sometimes extend
from it to the distance of more than 500. Hence the at-
mosphere in which the auroral light is displayed is very
attenuated, like that through which the electricity is passed
in the experiments alluded to.
(2) Positive evidence of the electric origin of the aurora
is found in the effect produced upon the telegraph wires
during an auroral display. The aurora sometimes has actu-
ally rendered unnecessary the use of a battery in telegraph-
ing. The effect is similar to that occasioned during a
thunder-storm, but usually of less intensity.


ST. ELMIO'S F iRE.


(3) The magnetic needle, also, is disturbed during auroras
in a degree corresponding to the brilliancy of the display.
During the splendid aurora of September 2d, 1859, the dec-
lination of the needle, at Toronto, changed nearly 4 in
half an hour. This aurora extended round the globe, for it
was seen in Europe and North America, and in the Sand-
wich Islands, and it indicated its presence in Northern Asia,
where the sky was cloudy, by magnetic disturbances.
Distribution.-Auroras are more frequent as we
approach the poles. Within the tropics they are
almost unknown. Thus their law of distribution
is just the reverse of that which governs the dis-
tribution of lightning.
In North America the zone of greatest frequency
lies between 50 and 62 north latitude. Here
the displays are of almost daily occurrence. North
and south of this belt the annual number rapidly
decreases, being on the average about ten in lati-
tude 40, and the same in latitude 78. In Europe
the zone of greatest frequency lies between 66
and 75 north latitude.
ST. ELMO'S FIRE.-In storms at sea the masts


and yards of the ship are sometimes tipped with
balls of electric light. The superstitions sailor
trembles with awe at the sight of them, believing
them to be the souls of the dead.
They are due to electricity passing without noise,
when the clouds are low, between the clouds and
the tips of the spars of the ship.

2. Optical Phenomena.-The most im-
portant of all the optical phenomena connected
with the atmosphere is also the most common.
It is the diffusion of light. This is '",. .. 7.' about
by reflection and refraction. By the former, light
is propagated from particle to particle of the at-
mosphere. By the latter, it is retained above the
horizon when the sun has actually gone down, and
it is bent into the atmosphere before he has actually
risen above the horizon.
Refraction and reflection give rise to the ex-
quisite variety of colors which deck the morning
and evening sky. They also occasion the less fre-
quent phenomena of rainbows, halos and mirage.
The Rainbow is an arch of colored light which spans tim'
heavens during a storm. It is seen only when the sun is
shining at the same time that rain is falling. Thie descending
drops separate the white sunlight into its elementary colors.
H.alos are rings of prismatic colors round the sun or moon.
They are really circular rainbows, and are probably due to
the refracting power of the small ice-crystals composing
cirrus clouds.
-I .... Another effect of refraction and reflection is
commonly called mirage. It is often observed in the desert.
Distant villages seem under its influence to be near to thie
spectator, or to be suspended in the heavens above. Some-
times the traveller thinks he is approaching a pool of spark-
ling water, and hastens to quench his thirst, when hlie finds
that he has been pursuing a mirage.
Mirage is also observed at sea, distant ships being seen ele-
vated above their true position, or even inverted in tlihe air.

TOPICAL ANALYSIS.

VII. ELECTRICAL AND OPTICAL PHENOMENA.
1. Atmospheric Electricity.
Electrical condition of air and earth compared.
Character. Hlow manifested.
Kinds of lightning. Zig-zag lightning. Cause of
its broken and forked course. Sheet-lightning.
Ball-lightning. Cause of thunder. At what distance
audible. Distance of the flash. HIow computed.
Area and distribution of thnnder-storms. Destruc-
tire effects of lightning.
Aurora Borealis and Australis. Form and appear
ance. Nature. Reasons for considering it an elec-
trical phenomenon. Distribution. St. Elmo's tire.
2. Optical Phenomena.
Diffusion of light. How caused. Other effects.
Description of the rainbow, halos and mirage.

TEST QUESTIONS.-If the thunder is heard in three seconds after thoe
flash, what is the distance of the discharge ? Why does the rainbow
show seven colors ?









TOPICAL ANALYSIS FOR REVIEW.



FThe Atmosphere. Composition. Uses of ingredients.
Physical Properties of the Atmosphere, Evidences that the air 1' ..... iahf
physical Properties of the Atmosphere Amunt of pressure. : .., ... .. boiling point.
E. effect of changes of level.
The weight of the air. j Causes of variation in pressure. Effect of changes in weight of ai.
:T. ;J. of the atmosphere.
.,, of density with height.


Climate . . . ..











Winds and Circulation of the Air.












Storms. . .















Moisture of the Air . . ..

















Hail, Snow and Glaciers ....












Electrical and Optical Phenomena,


Climate. . i .ain Elements.
Climate . . u] ..,; f ;,. ,- .. .
Distance from the equator. ........ I icmpcraturc.
) Climatic contrasts.
Distance from the sea. i Insular climates. Causes which moderate them.
) Inland climates. Reasons for their extremes.
S, ,ni;,,. ,.i .... *Iocean currents.
1i . t .-level. Reasolls for effect of elevation. General rule.
Isothermal lines. . ( Relation to parallels.
SZones of temperature.

SCa.uses of winds. Heat. Moisture.
( Location of constant ascending currents.
General Circulation. Causes which complicate circulation.
SClassification of winds.
Trade w inds. General character. Direction.
Cause of westward trend.
Locality.
Variable Winds.. Counter trades. Origin. Proofs. Direction.
Po lar winds.
Tile calm belts. Equatorial. Calms of Cancer. Capricorn.
f Land and sea breezes. Benefits of.
Periodical winds. Monsoolns. Cause. Effect. Minor tmonsoons.
SOther periodic wind Desert winds.
1 Mountain winds.
Oflice of winds.

General Description. Cyclones. Classes.
Cause of storms. Cause of spiral inoveenent.
[ Direction of the whirl.
Laos of stores ...... Forward motion of tile storm.
LwsoftorCs. almn at the centre. Causes of low barometer at tihe centre.
'g Irregularity of lInd storms.
SValle of storm laws. Areas of storms.
( Difference between these and hurricanes and typhoonls.
Whirlwinds and Trornadoes. Destructive effects.
SDust whirlwinds. Waterspouts.
Distribution.
Weather forecasts. Great storms in the United States.

Evp,>oration......... Conditions under which it takes place.
Causes which increase it. Temperature. Pn sure.
WOW liclass Dryness. Wilunds
Condensation and Precipitation. Fursm of water derived fromt vapor.
SCause of precipitationl. Den Ifoint.
Formation tof de.w .... I Effect of clouds.
N" o * Difference in quantity on various substances.
Fog . . . .. How formed. Illustrations.
S( Cirrus. Cumulus. Stratus.
SVarious forms.- Cirro-cumulus. Cirro-stratus. Ciniunlo-stratu.
Clouds. . ...... ( Cumulo-cirro-stratius.
S|Velocity of cloud movement.
I Height. Offices.
Cause of rainfall. Distribution.
M Mountains. Various examples.
Regulators ofrainfall. Deserts. Examples.
( Winds. Dry and wet winds.
Rain ... .r Constant. Locality. Cause.
Classificatio. Periodieal 11 Rainy d dry seasons i
i J. sd O Worlds.
1 Variable. Where found.
Excessive and dolicient rainfall. ,, r .1I, uises.
Caues


Hail. Size. Formation.
SLimiits of snow-fall. Of perpetual snow.
Siiow. Offices. Amount of snow-fall i n intinll regions.
A Cause.
Avalanches. Des'tructive effects.
Formation. Glaciers of the first rank. Second rank.
( iteiriniimst n(s'ff-ti'"- '--ipidity of motion. Average rate.
Motion, ) o .i ..
I't ecry ol M...oto. j Regelation. Crevasses. Effect of pressure.
Glaciers. 4 Moraines. Origin. Kinds.
Trasportig Power. J Origin of boulders.
TransportingPower. Foirer glacier regions.
Glaciers as river sources.
1 Distribution and size.
Icebergs. Origin. Distribution.

f Character. How manifested.
Atmospheric Electricity.. Kinds of i- -,,,,
1 Cause of -,1,.. Distance of the flash.
L Distribution of storms. Destructive effects.
Aurora Borealis and Australis a Form and appearance.
. -Nature. Distribution.
St. Elmo's Fire.
( Difusin of^. it ii)w caused.
Optical Phenomena. Diffusion of ;, .. ofi clouds. The rainbow.
Other effects. IHalos. Mirage.