YALE UNIVERSITY
LIBRARY

Friee Five. ShiUing.s,
AN ATLAS OF
PHYSICAL & HISTORICAL GEOGRAPHY,
TO .\CCOMPANT THE
Manual of Geographical Science.
ENGRAVED BY J. W. L O W R Y,
UNDEK THE DIKECTION OP
D. T. ANSTED, M.A., F.R.S.,
PHOFESSOK OF GEOtOGY IN KING'S COLLEGE, LONDON ;
AND
THE REV. C. G. NICOLAY, F.R.G.S.,
LIBRARIAN OF KING'S COLLEGE, LONDON.

CONTENTS.
I. Reference Map : The World on Mercator's projection.
II. Meteorological Map of the World.
in. Eelief Map of the World, shewing the Elevations of the Earth's
Surface.
rv. Phytographical Map, shewing the Distribution of Plants in various
Parts ofthe World.
Vertical Distribution of Plants and Animals.
V. Zoological Map, shewing the Distribution of Animals in various
Parts ofthe World.
Ethnographical Map, shewing the Distribution of the Principal
Races of Men.
VI. Comparative Chart of Ancient and Modern Geography and Geo
graphical Discovery.
The World according to Eratosthenes and Strabo.
The World according to Herodotus.
The World according to Ptolemy.

LONDON: JOHN ^'. PARKER AND SON, -WEST STRAND.

MANUAL

or

GEOGEAPHICAL SCIENCE,

MATHEMATICAL,
PHYSICAL, HISTORICAL,
AND
DESCRIPTIVE.

LONDON:
JOHN W. PARKER AND SON, WEST STRAND.
MDCCC LIT.

LONDON :
SAVILL AND EDWARDS, PRINTERS, 4, CHANDOS STREET,
rOVF.NT GARDEN.

MANUAL OF GEOGRAPHICAL SCIENCE.

PART THE FIRST,.
CONTAINING
MATHEMATICAL GEOGRAPHY,
By rev. M. O'BRIEN, M.A., F.R.S.
PE0FES8OB OF NATUfiAL PHILOSOPHY AND ASTRONOMY IN KING'S COLLEGE, LONDON.
PHYSICAL GEOGRAPHY,
Bt D. T. ANSTED, M.A., F.R.S.
PROFESSOR OF GEOLOGY IN KlNO's COLLEGE, LONDON.
CHARTOGRAPHY, By j. R. JACKSON, F.R.S.
LATE SECRETARY OF THE ROYAL GEOGRAPHICAL SOCIETT.

THEOEY OF DESCEIPTION AND GEOGEAPHICAL
TEEMINOLOGT, *
By rev. C. G. NICOLAY, F.R.G.S.
LIBRARIAN OF KING'S COLLEGE, LONDON.

PREFACE.

A T the present time, when so many works on the subject are
before the public, a Manual of Geography may seem to
require more than ordinary preface; nevertheless, a short one may
explain the object of its publication.
Hitherto, those intended to be used in education have been
rather compendious works of reference, than introductions to the
study of a science, and are often overloaded with details, while
general principles are omitted.
In the present work, an attempt has been made to avoid these
evils, and so to classify, arrange, and systematize the information
contained in it, that it may be immediately available both to the
teacher and to the scholar; and by the omission of all non-essential
details, whether political, statistical, or topographical, to confine
the attention to the principal subject. How far the attempt has
been successful, those must decide for whose benefit it has been
made. Although the First Part may appear to be composed of distinct
and separate treatises, it is presumed that, on consideration, they
will be found to form a consistent whole, — each part being, not
withstanding, complete in itself ;— that Professor O'Brien's mode of
working astronomical problems by construction, the explanation of

VI PREFACE.
the form and use of the more simple instruments, and other things
not usually found in the mathematical portions of geographical
works, will be readily accepted, by the unscientific reader, in the
place of the barren outlines of astronomy and paradoxical problems
in the use of the globes, which made this science so unpalatable in
our youthful days. In the portion devoted to Physical Geography,
Professor Ansted's classification of great leading facts may well
compensate for the absence of minute details; while in the chapter
on Chartography, Colonel Jackson's intimate acquaintance with the
various modes adopted to portray the varying features of the surface
of the globe, will enable the reader to peruse in a condensed form,
information not easily accessible elsewhere; and in those on the
Theory of Description and Geographical Terminology, the effort
which has been made, on the one hand, to develop a system, and on
the other, to pursue inquiries hitherto comparatively neglected, will,
it may be hoped, not only facilitate the attainment of knowledge
now, but lead to its extension hereafter.
The geographical knowledge of the ancients, the principal use
of which is to illustrate ancient history, being limited in its extent,
and derived from those who were, for the most part, entirely
ignorant of geography, in the more enlarged acceptation of the
term; " The world as known to the ancients" must of necessity be
considered topographically; but the world as known at the present
time, will be considered first as a whole, then in its larger divisions
and minuter sub-divisions, whether natural or ci^dl. In this, which
forms the Second Part of the work, the less essential details have
been omitted, as generally accessible in Geographical Gazetteers.
Normal figures and sections have been introduced, in the belief
that their general adoption, in the study of Geography, will much
facilitate the acquirement of accurate knowledge.

preface. vu
In the Atla.s attached to this work, all the principal facts of
Physical Geography will be found compressed within less than
ordinary limits, but, it is believed, well defined and without con
fusion, and fully sufficient for the purposes of elementary study.
The compilers have freely availed themselves of the labours of their
predecessors, yet the work has features peculiar to itself; among
these may be mentioned the omission of names of places in the
maps generally, and confining them to a Reference Map, so that
the attention may not be distracted from the more immediate
object; a comparative Chart of ancient and modern Geography
and geographical discovery, and an attempt to express by reversed
shading the vertical contour of the surface of the land, from which,
at a glance, a general idea, not only of extent but of elevation,
may be obtained.
C. G. N.

CONTENTS.

Mathematical Geography,

INTEODUCTION

p.l

Chapter I.

General Statement of the Celestial
Motions .... p. 3—19
I. Of the Firmament.
II. Of the Circumpolar Motion of
the Heavens.
III. The Earth's Rotation the Cause
of the Apparent Circumpolar
Motion of the Heavens.
IT. Globular Form of the Earth.
T. Proper Motion of the Sun, Moon,
and Planets.
TI. Proper Motion of the Sun.
TII. Proper Motion of the Moon and
Planets.
Tin. The Complicated Motions of the
Planets are Explained by sup
posing that they and the Earth
move about the Sun as Centre.
Chaptee II.
The Celestial Sphere & its Circles.
The Constellations . p. 19—48
I. Importance of a Knowledge of the
Constellations.

II . Preliminary Observations respect
ing the Celestial Sphere and its
Circles.
III. Classification of the Stars with
respect to Brightness.
IV. Of the North Circumpolar Region
of the HeaTens.
T. Region of the HeaTens along the
Vernal Colure.
TI. Region of the HeaTens along the
Summer Colure.
TII. Eegion of the Heavens along the
Autumnal Colure.
Tin. Region of the Heavens along the
Winter Colure.
IX. Constellations Visible on the
Meridian at different Hours of
the Night, and at different
Seasons of the Year.
X. Signs of the Zodiac.
* Chaptee III.
Astronomical Terms Exf)lained.
Measurement of Time, p. 49 — 58
I. Terms relating to Vertical and
Horizon.
II. Terms relating to Pole and
Equator.
III. Of Time, Sideral and Solar.

contents.

Chapter IV.
Method of Solving Astronomical
Problems by Construction on
Paper .... p. 58—72
I. Instruments necessary.
II. Of Spherical Triangles.
III. Method of Representing the Dif
ferent Parts of a Spherical
Triangle on flat paper.
IT. Solution of Various Astronomical
Problems.
Chaptee V.
Optical Principles requisite in
Astronom'if . . p. 73—89
I. Ofthe Transmission of Light from
Luminous Bodies.
II. Inflection & Difiraction of Light.
III. Reflection & Refraction of Light.
IT. Dispersion of Light.
T. Passage of Light through Plates,
Prisms, and Lenses.
Chapter VI.
Formation of Images. — Vision. —
The Telescoj)e, Microscope,
and Micrometer. — The Ver
nier . . . . p. 89—108
I. Formation of Images by a Hole
or a Lens.
II. Of Vision.
III. Of the Telescope as a Means of
ascertaining Direction.
IT. Of the Bye Piece, or Microscope.
V. Of the Astronomical Telescope.
VI. The Micrometer.
TII. The Diagonal Eye Piece.
Tin. Of the Astronomical or Reading
Microscope.
IX. Ofthe Vernier.

Chapter VII.
The Transit Instrument, p. 109— 123
I. Description ofthe Transit Instru
ment.
II. Examination and Adjustment of
the Transit Instrument.
III. Adjustments of the Transit In
stmment.
IT. Method ofFinding the True Time
of Transit of a Star across the
Meridian with a Transit Instru
ment not exactly in the Meri
dian Plane.
T. Method of Observing Transits
across the Prime Vertical.

Chapter VIII.
The Geographical Uses of the
Transit Instrument , p. 124 — 131
I. Determination of the Position of
the Meridian.
II. Determination ofthe Latitude.
III. Determination of the Longitude.
Chaptee IX.
The Altitude and Azimuth Instru
ment. — Hadley s Se.vtant. —
Refraction aud Paralla.i; p. 131—142
I. The Altitude and Azimuth Instru
ment.
II. Adjustments, and Method of Ob
serving with the Altitude and
Azimuth Instrument.
III. Uses of the Altitude and Azimuth
Insti'ument.
IT. Hadley 's Sextant.
V. Uses of Hadley's Sextant.

contents.

XI

Chartography,
p. 143 — 184.

Terrestrial Globe.
Projection of Maps.
Choice of Projections.
Different Kinds of Maps.
Reduction of Maps.
Topographical Maps.
Chorographical Maps.
Geographical Maps.
Construction of Maps from Various
Materials.

Mapping from the Information of Tra-
TeUers.
A Correct Map not always a Good
One.
Scale of Maps.
Gtraduation of Maps.
ConTersion of Longitudes.
Details of Maps.
Geographical Orthography.

Physical Geography,
Part I. — Of the Earth's Surface.

Chaptee I.
Introduction

p. 185—189

§ I G-eneral Outline of the Subject.
2 DiTisions of the Subject.
3 Planetary Condition of the
Earth.
4 Elemental Conditions of Matter.
5 Mechanical Conditions of Matter,
and DiTisions of Science thence
resulting.
6 AdTantage arising from the study
of Physical Geography.
Chapter II.
Forms and Modifications of In
organic Matter . p. 189—197
§ 7 Limits of our Knowledge with
regard to the Earth's Structure,
and importance of Heat as an
Agent of Change.

§ 8 Forms of Matter.
9 Forces affecting Matter, and effect
of Change of Temperature.
to Sources and Causes of Heat.
1 1 Chemical Action.
12 Polarity.
13 Material Substances usually in
combination at the Earth's Sur
face.
14 Elementary Substances.
Ig Oxygen Gas, and its important
Combinations.
16 Coinbustion.
17 Nitrogen, Hydrogen, and Chlo
rine, with their Combinations.
18 Non-Metallic Solid Elements.
19 Metallic Elements the Bases of
Earths.
20 Metals.
2 1 Mutual Action of various Forms
of Matter.
22 Terrestrial Magnetism.

Xll

contents.

Chapter III.
Meteorology ... p. 198 — 215
§ 23 Constitution ofthe Atmosphere.
24 Its Chemical Condition.
25 Its chief Importance in Physical
Geography.
26 Its Relation to Light generally.
27 Twilight.
28 Mirage.
29 Colour.
30 Atmospheric Meteors exhibiting
Colour.
31 The Phenomena of Sound.
32 Motion of the Air — Winds.
33 Land and Sea Breezes.
34 Trade Winds.
35 Monsoons.
36 Hurricanes.
37 Relations of the Atmosphere to
Water.
38 Dew.
39 Mists and Fogs.
40 Clouds.
41 Rain.
42 Distribution of Rain.
43 Snow.
44 Glaciers.
45 Hail.
46 Climate, and Distribution of Heat.
47 Conclusions.
Chapter IV.
On tlie Form aud Distributiou of
the Land ... p. 216— 228
§ 48 What is meant by 'land.'
49 Distribution of land.
go Continents.
51 Islands.
52 Inequalities ofthe surface of limd.
53 Low plains and stcppos.

§ 54 Deserts.
5S SilTas.
56 Llanos.
57 Pampas.
58 SaTannahs, or prairies.
59 High plains, table lands, or pla
teaux of the Old World.
60 Table lands of America.
61 Mountain systems of the earth.
62 General connexion of the moun
tains of the Old World.
63 Mountain chains of the New
World.
64 Mountains of Australia.

Chapter V.

Hydrology

p. 229 — 248

§ 65 General phenomena of the ocean.
66 Action ofthe wind on the ocean.
67 The Tides.
68 The Atlantic Ocean.
d^ The Pacific Ocean.
70 The Indian Ocean.
7 1 The Arctic Ocean.
72 Marine currents.
73 Whirlpools — Calms.
74 Inland salt seas — Bays, and Gulls .
75 Springs.
76 EiTcr basins.
77 BiTcr systems of the Atlantic
group.
78 Eiver systems of inland seas of
the Atlantic.
79 Eivers of the Asiatic syst€m.
80 EiTer systems of the Pacific
Ocean.
81 EiTer systems of the Indian
Ocean.
8j EiTcrs not communicating with
tho Ocean.

contents.

xm

Chapter VI.
Atmospheric aud Aqueous Action,
p. 249—262
§ 83 General Nature of Atmospheric
and Aqueous Action.
84 Changes produced by Atmo
spheric Action.
8g Changes directly effected by Al
terations of Temperature and
Exposure to Cold.

§ 86 Glaciers and Icebergs.
87 Changes produced by the Erod
ing Action of MoTing Water.
88 The Transporting and Distribut
ing Action of MoTing Water.
89 Changes produced by Water act
ing by the Aid of Substances
held in Solution.
90 Indirect Effects produced by
Water.

Part IL — The Structure of the Earth.

Chapter VII.
The Condition of the Interior of
the Earth and the Reaction
of the Interior on the Ex
ternal Surface p. 263—283
§ 91 Means of Obtaining a Knowledge
of the Earth's Interior.
92 InternalTemperatureoftheEarth as determinedbyDeep Sinkings.
93 Thermal Springs.
94 Volcanoes.
95 Volcanic Products.
96 Distribution of Volcanoes.
97 Subterranean Connexion of Dis
tant Volcanoes.
98 Connexion of Volcanoes with
Earthquake Action.
99 Nature of Earthquake MoTe-
ments.
100 Frequent Repetition and Wide
Eange of Earthquake Action.
loi Permanent Change of LctcI ac-
companyingEarthquakeAction.
102 Origin of Earthquakes.
103 Partial, butPermanent EleTation,
at a Distance from Volcanoes.
104 Depression OTcr Large Areas.

Chapter VIII.
Structural Phenomena of the
Earth indicating Igneous
Action . . p. 284—295
§ 105 Nature of Igneous Eocks in ge
neral
106 Extinct Volcanic Regions.
107 Ancient LaTa Currents, and
other Products of Extinct
Volcanoes.
108 Other Igneous Eocks not Vol
canic.
109 Metamorphism.
no Dykes and Miaeral Veins.
Chapter IX.
Structural Phenomena connected
with Aqueous Action, p. 296—317
§ III Stratification.
112 Mechanical Disturbances of
Beds.
1 13 Order of Superposition of Euro
pean Strata,
114 Lower Palfeozoic Eocks.
115 Middle PalEcozoic Eocks.
n6 Carboniferous System.

XIV

§ 117 Magnesian Limestone, or Per
mian System.
1 18 Upper New Eed Sandstone, or
Triassic System.
119 Liassic Group.
120 Oolitic System.
121 Wealden Group.
122 Cretaceous System.

CONTENTS. § 123 OlderTertiaryEocksofEngland, France, and Belgium.
124 Middle and Newer Tertiary
Formations of Europe.
125 Tertiary Deposits of Asia and
America.
126 Newest Deposits of Gravel and
DUuTium.

Part IIL — Organization.

Chapter X.
The Distribution of Vegetables iu
Space . . p. 318—338
§ 127 The Meaning and Nature of Or
ganization, and especiaUy of
Vegetable Life.
128 Natural Arrangement and Clas
sification of Plants.
129 Influence of Climate on Vege
tation.
130 Influence of Soil on Vegetation.
131 General Eange of Plants in Ta-
rious Countries at moderate
EleTation s.
132 The Botanical Eegions.
133 Distribution of Plants iu Ver
tical Space.
134 Range of CultiTated Plants.
135 General Considerations of the
Distribution of Plants in dis
tant Botanical Centres.
Chapter XI.
The Distributiou of Animals in
Space . p. 339-371
§ T36 Organization of Animals.
137 Classification of Animals.
138 Statistics of Animals.

§ 139

140
141 142
143144 145
146 147 148149150
151 1531.54155

Nature and Degrees of resem
blance amongst Animals, and
Comparison of their Structure.
Natural grouping of Animals in
a Fauna.
Distribution of the Faunas.
Arctic Fauna.
Temperate Faunas.
Tropical Faunas.
Special Distribution of Q,uadru-
7nana.
Distribution of Carnivora.
Distribution of Sodentia.
Distribution of Suminantia.
Distribution of Paehydermatu.
Distribution of the Edentata
and Mhrsapialia.
Distribution of Birds.
Distribution of Reptiles.
Distribution of the Marine Ter-
tehrata.
Distribution of the Articulata.
Distribution of the Mollusca and
Sadiata.

Chapter XII.
Distribution of Organic Beings iu
Time . . p. 372—337
§ 156 Nature of Organic Remains,
and Proof of the Existence

CONTENTS.

XV

in the Earth's Crust of Frag
ments of Plants and Animals
belonging to Species now
extinct.
§157 Distribution of extinct Mam
malia in time.
158 Distribution of extinct Birds.
159 Distribution of extinct Eeptiles.
160 Distribution of extinct Fishes.
161 Distribution of extinct Mollusca.
162 Distribution of extinct Articu
lata.
163 Distribution of extinct Eadiata.
164 Distribution of extinct Plants.
Chapter XIII.
Ethnology ... p. 388—413
§ 165 General Nature and Meaning of
the Science of Ethnology.
166 On Specific Character.

167 Divisions and Mode of Treat
ment of the Subject.
168 External Structural Peculiarities
of the Human Eace.
169 IntemalStructuralPeculiarities.
170 Principal Varieties of theHuman
Race, and their Arrangement
into distinct Groups.
1 7 1 Natural Geographical Limits of
Distribution.
172 Language.
173 ModiflcationoftheEacesofMan.
174 Mixture of Eaces.
175 Influence of Man on other
Animals.
1 76 Influence of Man on Inorganic
Nature and on the Vegetable
Kingdom.
177 Effect of Inorganic Nature on
Man.
178 Statistics ofthe Human Eace.
179 General Conclusion.

Theory of Description and Geographical
Terminology,

Chapter I.
p. 414—433.
I Nature and DiTisions of the
Subject.
2 Of PositiTe Position.
3 Of EelatiTe Position.
4 Of Land and Water in Extent.
5 Of Land in EleTation.
6 Of Water not in Motion.
7 Of Water in Motion.
8 Of the Natural Productions of the
Surface of the Earth.

Chapter II.
p. 433—445.
I Of Political Geography.
2 Of Historical Antecedents.
3 Of the Distribution of the Human
Race.
4 Of Geographical Statistics.
5 Of the Order to be obserTed.
6 OftheCiTU DiTisions of the World.
7 Ofthe Civil DiTisions of Countries.
8 Of Eeligious DiTisions.
9 Of the Dominant Religion.

XVI

CONTENTS.

IO Of Eeligious Sects.
1 1 Of Eeligious Statistics.
12 Of the Industrial Geography of
Countries.
13 Of Industrial DiTisions.

14 Of Occupation.
15 Of the Pastoral.
16 Of the Agricultural.
1 7 Of the Manufacturing.
18 Of the Commercial.

MATHEMATICAL GEOGRAPHY.

INTRODUCTION.
THE importance of Astronomical and Optical knowledge to the practical
Geographer is so obvious, that it will not be necessary to say anything
on the subject here ; and we shall therefore, without further preface,
proceed to state briefly the nature and extent of the information which we
propose to give the reader on the subjects of Astronomy and Optics.
In the first place, then, we must observe, that the space allotted to
Astronomy in the present Geographical Treatise is, of necessity, very
limited, and therefore we must follow one of two courses in treating of
the subject; we must either give a general outline of the whole science,
without entering into particulars, or we must select some portion of it of
special importance to the Geographer, and develop that at some length, so
as to make it practically useful.
We prefer taking the latter course, for two reasons : First, because the
space to which we are restricted would only allow us to give a very un
satisfactory outline of Astronomy in general; and, secondly, because,
though the greater part of Astronomy has some bearing, directly or in
directly, on Geography, there is one topic of paramount importance —
namely, the means which Astronomy affords of determining position on the
ewrtKs sm-face; the great practical problem which the Geographer has to
solve by means of his Astronomical information being — to determine the
relative positions of the various places he may happen to visit.
We shall therefore devote the space here allowed us to the explanation
of Astronomical Principles, so far as they have immediate reference to this
important problem, and no farther. We shall suppose that the reader is a
traveller who is anxious to know just enough of Astronomy to enable him
to determine the Meridia/n, the Latitude, and the Longitude of any place,
and that he has little or no acquaintance with the technicalities of mathe
matics. We shall, with this view, explain generally the apparent motions
of the heavenly bodies, dwelling but little upon the real motions. We
shall describe at some length the positions and appearances of the different
groups of stars or constellations, this being a most essential part of the
subject practically. As regards Optical science, we shall explain as much
as is necessary, in order to understand the construction and use of
the Astronomical Telescope, as employed to determine direction, and of
the Astronomical Microscope, as employed to subdivide space; we shall
show how the Portable Transit Telescope is to be adjusted, and how it may
be made use of in determining everything the Geographer requires to
know. We shall not have space to say much respecting other Astro
nomical instraments ; but this will not signify, as the Transit instrument
is capable of being used with the greatest advantage for every purpose
B

2 INTRODUCTION.
the Geographer has in view, ahd requires, on his part, no knowledge oi
what are called the Astronomical corrections. It is on this account that
we shall dwell more on the Transit Telescope, and say but little respecting
other instruments.
The following is a brief outline of the subject, as we shall here treat
of it :—
Chapter I. contains a preliminary statement of the more obvious
celestial phenomena^— The Fixity and Permanency of the Stars and Con
stellations—The Circumpolar Rotation — The Proper Motions of the Sun,
Moon, and Planets.
Chapter II. — The Celestial Sphere and its Circles. The Constella
tions described, in order that the reader may make himself familiar with
the localities and appearances of the principal stars. In this and the
previous chapter we have thought it advisable to introduce a certain
amount of information respecting the numerous allusions in ancient
writers to the celestial phenomena, and especially the constellations ; for a
dry description of the stars, without something of this kind, would be
scarcely readable, and our object, of course, must be to make the subject
not only useful, but, as far as we can, interesting also.
Chapter III. — Astronomical Terms explained — Measures of Time.
Chapter IV. — A Method of solving Astronomical Problems by Geo
metrical Construction with Rule and Compass. This method consists of
the Dissection, if we may so speak, of a solid angle or spherical triangle,
so as to represent its six parts on flat paper by construction. All pro
blems usually given in what is called the ' use of the globe-s,' may be solved
by this method with considerable accuracy. It has also the advantage of
requiring no mathematical knowledge on the part of the reader; at the
same time it leads very simply to all the mathematical formulse used in
Astronomy. Chapters V. & VI. — The Telescope and Microscope, as used in Astro
nomy, with the optical principles upon which their constraction depends,
explained. The Micrometer and Vernier. In Chapter V. some account
is given of the optical phenomena which have immediate connexion with
Astronomy, such as reflection, refraction, stellar aberration.
Chapter VII. — The Transit instrument, its adjustments, and the
method of observing with it.
Chapter VIIL— The Geographical Uses of the Transit instrument.
Chapter IX.— Hadley's Sextant, Altitude Instrument.
In Chapters V. & VI. we have introduced a little more optical matter
than is usual in a treatise on Geography; because our object is, not to
write a formal treatise on Astronomy, but to give such information to a
person, ignorant of Astronomy and Optics, as will enable him to under
stand the instruments and principles by which the relative positions of
places on the earth's surface are determined.

CHAPTER I.
GENEEAL STATEMENT OF THE CELESTIAL MOTIONS.

I. Of the Firmament.
THE first fact that is noticed by any one watching the heaTens at night
is, perhaps, the fixity and permanency of the different groups of stars
(or constellations as they are called), notwithstanding the gradual change
of position which they all appear to undergo from hour to hour during the
night. These constellations always exhibit the same form and appearance,
though they are ever on the move. For instance, if the obserTer fix his
attention upon the seTen weU-known stars, commonly caUed the Wain, the
Plough, or the Great Bear, he wiU perceiTC that they always preserve the

r •
I*
I -I'lg- <•¦
• I
• I
• I
Fig. rf II Fig. 6
• 1I *
I •
Fig. a ]
• • •! '

same distances from each other, though the whole group is continuaUy
changing its position in the heaTens. If he joins each of these stars with its
neighbour by drawing imaginary lines, the figure he so forms wiU be always
the same, though he wUl sometimes see it as is represented in fig. a, some
times as in flg. h, sometimes as in fig. c, and sometimes as in fig. d.
2 If he continues to watch this or any other of the consteUations for
years, he wUl ncTcr perceive any change of form ; and we may extend this
statement to many centuries of past time, for we have evidence, from astro
nomical records, and the aUusions of ancient writers, that the arrangement
and grouping of the stars on the celestial Tault has CTer been the same, with
a few remarkable exceptions hereafter to be noticed.
b2

4 MATHEMATICAL GEOGRAPHY.
o In ancient times, before calendars were known, the rising and setting
ofthe consteUations were the chief gmdes of the ^J^^P^^rd, anj the tiUer of
the ground, in determining the progress of the seasons, andthos made men
in etneral much more famfliar with tie appearances of the stars than they are
Low We therefore find continual mention of the consteUations in the works
oflntiquity, and especially in the poets. To giye a few examples we find
the foWng lines In Eesiod, Opera et IHes. which we shall quote atlength,
on account of their astronomical interest:— !,„„„„„„
' But when Orion and Sirius have come mto the middle ofthe heavens,
and the rosy-fingered Aurora has beheld Arcturus, then O Perses, gather aU
the^^apes^jme^^ length the Pleiades and the Hyades and the mighty Orion
have set, then be mindful of ploughing in time.'t .
' But if the desire of dangerous navigation has taken possession ot you,
when the Pleiades, flying the fierce strength of Onon, haTe atlength set mthe
dark sea, then surely storms of wind wilTblow on eTery side .'J
Another remarkable passage is found at the begmning of the Second
Book, Une 381 :— „ . , , • .^ i. x
' At the rising of the Pleiades the daughters of Atlas, begm to reap, but
when they set, to plough. These stars become iuTisible for forty days and
nights ; but they appear again, as the year roUs round, when first the scythe
4 The Fasti of Ovid, which is a poetical calendar, aUudes to almost aU
the consteUations of the heavens, makmg use of their risings and settings as
marks and signs, not only of the four great divisions of the year, the seasons,
but also of months and subdivisions of months. In fact, there is scarcely a
week which is not marked in the Fasti by some particular astronomical note.
Thus, in the month of May, we have, among several others, the foUowing
allusions to consteUations : —
VI No. (2na of May.) I
Pars Hyadom toto de gregc nulla latet.
Ora micant Tauri septem radiantia flammis,
Navita quas Hyadas Graius al) imbre vocat.
V No. (3rd of May.)
Nocte minus quarta promet sua sidera Chiron
Semivir. II No. (eth of May.)
Scorpius in coelo, cum eras lucescere Nonas
Dicimus, a media parte notandus erit.
5 We have stUl remaining a formal account of aU the consteUations, in a
philosophical poem, formerly held in great repute, caUed the Pheenomena of
Aratus, the same quoted by St. Paul in his address to the Athenians. This
poem was founded upon a description of the celestial sphere by Eudoxus, a
work of much celebrity in ancient times, and probably compUed ftwm earlier
astronomical writers. The description of the constellations by Aratus is not
very accurate, owing, not only to the imperfections of the work from which
he drew his niaterialB, but also probably from the fact that he either over
looked, or very imperfectly aUowed for, the changes in the rising and setting
of the consteUations caused by a change in the observer's latitude. This
poem was comcmented upon by many celebrated astronomers, and among the

nid. (14th of May.)
Pleiadas adspicias omnes, totumqne sororum
Agmen ; nbi ante Idus nox erit una super
Tum mihi non dubiis auctoribus incipit lestas ;
Et tepidi finem tempora veris habent.
VI Kal. (27th of May.)
Auferat ex oculis veniens Aurora Booten :
Continuaque die Sidus Hyantis erit.

' EvT ay y ^ilpiiav Kai Tejpior if MtVov gXtfj;
oypayov, 'ApKToCpow d' eaidrt pododdxTi/Xor 'Htir,
cJ n^ptrri. Tire ndvTat (!i7rodpe7re oiKade ySoTpvc.
HXriia'der 0''Y«3ec t« t«S t« aQivo^-ilpmvot
dvvuatv, t6t' ^ttcit' upoTov fxenvnfiivot elvai
&paiov.

i Et i^ ae vauTtXi'nt fiviTvetitp^\ov 7/iepor aipflT,
et'T* ov nXn'«d«f ffC^vof S^ptfxov -Qpiaii/ov
^ev-jovaat vinToitrtv h hcpoeid^a novrov,
6i] TOTe navTOiiav ULV^fiunt Ovova.v ikitTai.
§ n\)|t(^dt.)v -AT\a-teveei>v ivtTe\\ofieva<av
&pxeat>' u>i»;tou" iipoToto ii dtxrujuevduv.
al 6' firoi vvKTar T« Kai ^/ioTa recirapaKovra
KCKfiviparat, airip ii irepinXofxivov ^MauTOl/
0aivovTal Tii irpSra xa/xxraofiiroio (rti/ipov.

THE CELESTIAL MOTIONS. 5
rest, by Erastosthenes and Hipparchus. It was partiaUy translated into
Latin by Cicero, when a Tery young man, and this translation is stiU extant.
Eudoxus died about 370 B.C. This work, though rough and imperfect, is a
Taluable relic of the ancient Greek astronomy.
6 But it is to Ptolemy, the Alexandrian astronomer and geographer,
that we are indebted for nearly aU the accurate information we possess re
specting the state of astronomy before the Christian era. He was himself
an obserTer, and, considering the imperfection of his instrumental means,
his optical measurements deserve great praise. But the great service he did
to astronomy was by compiling with accuracy the obserTations of preTious
astronomers, and especiaUy of Hipparchus. In the 7th and Sth Books ofhis cele
brated work, th.Q Meg ale Syntaxis — or, aa itwas eaU^eAhj the Axaha, Almagest — ¦
we haTe the apparent places of the stars on the celestial sphere accurately put
down from his own observations, compared with those of the great astronomer,
Hipparchus. The catalogue of the stars by Hipparchus, who flourished about
150 years B.C., is lost, but its substance is preserved in Ptolemy's Syntaxis.
Ptolemy flourished about a.d. 130. The Chaldeans made great advances in
astronomy in early times, and Ptolemy often quotes their observations,
though none earher than B.c. 720.
7 From aU these numerous sources of information as to the appearance
of the heaTens in early times, we derive ample evidence that the various
groups of stars which we now see in the heavens have always exhibited the
same appearances and configurations, that they occupy the same relative
positions now as in olden time, and that no changes have taken place in the
general arrangement of the stars, at least none but minute changes, which
are not sensible to the eye unaided by instruments. Minute changes have
- indeed occurred in the places of the stars, but it requires the most perfect
and dehcate instruments to perceive them.
8 It is, in a great measure, this permanency and fixity of the stars in the
heavens that renders astronomy of such importance in practice. When
astronomers have once made accurate observations on any particular star, and
entered its position in their catalogues, there it remains for centuries, an un
changeable mark in the heavens, for the use of future observers — a mark
both of time and place, by which the sailor can guide his ship with perfect
safety over the ocean, and. the geographer construct his maps aud charts with
unerring fidehty. A star thus determined is a celestial time-piece, that
knows no error or variation, not only marking minutes and hours, but years
and centuries ; serving, at the same time, to regulate a watch, and to guide
the chronologer through the darkness of past ages.
9 It is not surprising that the fixity and permanency of the consteUations
should have led men to form the opinion that the expanse in which the stars
appear to be placed is no empty space, but a vault of durable and firm struc
ture. Hence the meaning of the Latin -woTd, firmamentu7n, which has passed
into our own language as firmament ; and of the Greek word, a-Tepea/ia,
stereoma, which is derived from a-Tepcas, firmus, or firm. Stereoma is the
word in the Septuagint which is translated firmament in our version of
the book of Genesis. The corresponding Hebrew word, however, contains
no aUusion to any firmness, but simply signifies space, or expansion. The
word star (coming, as it does, from aariip) is not derived from the same root
as stereoma, but from the negative, signifying unsteady, no doubt in aUusion
to the twinkling hght of the stars.
lo The opinions of ancient phUosophers as to the nature of the stars
were very Tarious. {See Plutarch's Moralia de Placitis Philosophorurri,
hb. II.) Many supposed them to be nothing but bright ornaments,^ or, as it
were, naUs fixed in the crystaUine sphere, or firmament. [ifKav SUriv koto-
¦neirrf/evai t& Kpoa-TaWoeiSei.) Anaxagoras said that they were stones flung up
from the earth, and kindled by the rapid whirling motion of the aether,
(tJ S' evTOvta t^s wepiSivria-eas avapwaCovra werpos in TrjS -^s, Kal KaraipXe^avra
Tovros rjorepiKevai.) Herachdes and the Pythagoreans said that each star was

6

MATHEMATICAL GEOGRAPHY.

a worid, lUte the earth ; and the same view was held by the foUowers of
Orpheus. A great variety of opinions prevaUed respecting the nature, dis
tance, and magnitude of the heaTenly bodies, most of which are stated in
the work of Plutarch already referred to.
IL Crf the Ci/rcwmpola/r Motion of the Heavens.
1 1 At the same tune that an ordinary observer notices the permanency
of form and relative position of the various groups of stars, he perceives that
eTery star is moving slowly and steadUy ; an hour is sufficient to convince him
of this. Let him fix his eye on any particular star — say, for instance, one of
the seven, in the Great Bear — and let him mark its position with reference to
some terrestrial object, (not too near him,) such, for instance, as the top of a
tree or chimney, or the ridge of a roof, and he wUl soon perceiTe that the star
does not continue in the same place. A look at the Great Bear at fiTe or six
o'clock of a winter's eTening, and again at elcTen or twelTe o'clock, wUl show
the motion of the heaTens in a striking manner ; at the fitrst time it wUl be
seen in the position represented by fig. a; at the second time, in that repre
sented by fig. b. At five or six in the moming the figure wUl be inverted, as
in fig. e. At 12 o'clock in the day, if the stars were seen, (as they can be
through a telescope,) they would appear as in fig. d. At the same hour in
the eTening, the stars will come agam into the same position.
12 With a little care, three facts may be noticed respecting the motion
of the heaTenly bodies : — First, That they all describe paraUel circles about
one point of the heavens, caUed the North Pole, (supposing the observer to
be in the northem hemisphere of the earth.) Secondly, That they all com
plete their motion in the same time, coming back to the same positions every
twenty-four hours. Thirdly, That this circular motion is perfectly uniform,
each circle — i. e., each 360°, being described at the rate of 15° per hour, or 1°
ia eTery four minutes of time.
13 To observe the truth of these facts, some simple instrument will be
necessary, as, for instance, a little telescope mounted in the foUowing way: —
E D (fig. e) is the telescope, the ,

eye-hole being at D; C is a joint to
which the telescope is fixed ; B C,
a short hollow cyhnder, or tube, to
the extremity of which the telescope
is jointed by the joint C. By means
ofthis joint we may set the telescope
at different angles to the tube B C.
The two holes in the joint are for
the purpose of tightening or loosen
ing it, as may be necessary.
The tube B C fits on a piece
shown in fig./ round which it may
be moTed; and it is secured by
little screws B B. The piece on
which the tube fits is jointed at A
to the upright stem G A, by a
joint similar to that at C ; and the
stem has a heaTv base, G, so that it
may stand steadUy upon a table.
14 Supposmg A P to be the
direction of^ the axis about which
the tube B C (carrying the telescope
with it) may be turned, and D S
the direction in which
the telescope looks,
then by making the
line AP point to the

Rg.e

r

/

./

./p

THE CELESTIATi MOTIONS.

pole, and the Une D S to any particular
star, it wUl be found, that by turning the
tube B C round, without altering the in
clination of the line D S to the line A P,
we may always make the telescope point
to the star. This evidently shows that
the line D S, drawn in the direction of the
star, always makes the same angle with the
line A P drawn in the direction ofthe pole —
i. e., that the star always preserves the same
distance from the pole, and therefore that
it describes a circle about the pole; and
this being true, as wUl be found, for all the
stars, it foUows that they aU describe pa
raUel circles about the pole.
15 By pointing the telescope towards
a star, leaving it in that position for twenty-
four hours, and then looking again through
it, it wiU be found that the star comes back to its original position in twenty-
four hours.
16 This wUl be found true at aU hours, and therefore it foUows that the
motion of the star is uniform — i. e., that it always moves at the same rate.
17 To use this instrument as above described, the position of the Pole in
the heavens must be known in order to direct the line A P towards it.
The method of finding the Pole by means ofa star which is near it, caUed tho
Pole Star, wiU be explained in the next chapter. The Pole is about a degree
and a half from the Pole Star. We shall show in the next chapter how
the instrument is to be set, by means of the Pole Star aiid certain other stars
of the consteUation called the Little Bear, so that the line A P may point to
the Pole — at least, sufficiently near the Pole for our purpose.
18 This instrument need not be made very accurately, as it is not capable
of being used with any great nicety, but only in a rough way, to obserTe the
general motions of the heaTenly bodies, such as the diurnal rotation of tho
Stars, the annual motion of the Sun, the motions of the Moon and Planets. If
a better instrument cannot be procured, such an instrument as this wUl be
found very useful to the beginner, as the observation of celestial phenomena,
CTen in a rough way, is not only highly interesting, but Tery instructiTe as
far as regards practical astronomy.
19 Two graduated circles, whioh
may be made of pasteboard or paper
pasted on wood, ought to be added to
the instrument as above deseribed —
one at C, to measure the angle which
the line S D makes with the line P A,
and the other at B, to measure the
number of degrees through which we
tum the tube B C about the polar axis
A P. It wiU be sufficient to have these
circles graduated to degrees, as they
could not be expected to give smaUer
measures with any degree of accuracy.
20 Instead of the telescope, a rod
with a pair of ordinary sights may be
substituted, as is shown m fig. a, M
and N being the sights. The sight M
which is supposed to be next the eye,
is a smaU fiat piece of brass with a hole
in it, as is shown in fig. i. The other
sight is a simUar piece of brass, only

8 MATHEMATICAL GEOGRAPHY.
it has two pieces of thin wire drawn across the hole at right angles, as is
shown in fig. li, in order to mark the centre ofthe hole. The eye being placed
near M, sees these cross wires, and it should look in such a manner as to
make the wires appear to divide the hole M into four equal parts — ^i. e., the
point where the wires cross each other, or as it is called, the centre of the
cross wires, should appear to coincide with the centre of the hole M.
When this is done, any object, such as a star, which is seen at the centre
of the cross wires, is in the direction in which the sights point — i. e., tiie line
joining the centre of the hole M, and the centre of the cross wires points to
21 The Une joining the centre of the hole M, and the centre of the cross
wires, is called the line of Direction of the Sights, and more frequently, the
Line of Collimation. CoUimation is derived from the Latin word collineo, or
eollimo, (from con and lineo,) which signifies, to direct one thing in a straight
line towards another — i. e., to aim at. This is a hne of great importance in
astronomy, and we shaU speak more of it presently.
22 The telescope (if the instrument haTe a telescope instead of sights)
should be fumished with cross wires in the focus, to mark its line of direction
or collimation. The magnifying power of the telescope may be Tery small.
A single object-glass of three or four inches focus, and a single eye-glass of one
or two inches focus, wUl form a sufficiently good telescope.
With an instrument of this kind, any person may satisfy himself respecting
the uniform circumpolar motion of the heavenly bodies : first of aU, that
each heavenly body always keeps at the same distance from the pole, or, in
other words, that it describes a circle about the pole ; secondly, that it com
pletes this circular motion in twenty-four hours ; thirdly, that it always
moves at the same rate, namely, 15° per hour, or 1° in four minutes.
23 To prove these facts with accuracy, it is necessary to employ much
more perfect and deUcate instruments than the above. Astronomers employ
what IS caUed a Transit instrument, which we shaU presentiy describe at
some length, to observe the time at which each heavenly body comes on a
particular line called the Meridian, and for this purpose it is necessary to
nave a first-rate clock to subdivide time with accuracy to a fraction of a
second. To determine how far any heavenly body is "from the pole, astro
nomers use another instrument, caUed a Mural Circle, or an Altitude Instru
ment. Both these instruments are extremely simple as regards their motions,
and are capable of wonderful accuracy when weU made. A third instrument,
caUed an Fquatorial, is made use of for measuring smaU spaces and distances
in the heavens. These three instruments, fixed in a convenient buUding,
together with the clock, and some minor instruments, make an Astronomical
Observatory. The rude instrument above described may be made to repre
sent any one of these three great, or, as they are caUed, capital astronomical
instruments. If the line A P be made vertical, and the tube B C fixed in such
a position that the Une D S may be in what is caUed the meridian plane — i. e., in
the vertical plane which contains the pole, then the instrument represents a
Transit telescope. If, in addition to placing the instrument thus, a gra
duated circle be fixed at C, to measure the inclination of the Une D S to the
line A P, it represents a Mm-al Circle. If A P be fixed so as to pomt to the
pole, as originaUy supposed, then the instrument represents an Equatorial.
III. The Earth's Rotation the Cause ofthe Apparent Circtmpolar
Motion, ofthe Heavens.
24 The ch-oumpolar motion of the heavenlv bodies may be eitiier an
actual and real motion, or it may be only apparent," being caused bv an onnosite
motion of the spectator. If we^ suppose tfie Ea;tii to^e a rou7d body a^i?
may be proved to be by observation and mcasMement, and to revolve from
west to east once m twenty-fom- hours, about an axis passing through the tX
poles, this wdl sufficientiy account for the apparent motion of thi heavenly

THE CELESTIAL MOTIONS. 9
bodies from east to west about the pole ; for a motion of the earth round its
axis from west to east would evidentiy make the stars appear, to any obserrer
on the Earth's surface, to move about the same axis in the contrary direction,
from west to east. The natural impression, on perceiving the circumpolar
motion of the heaTens, is, of course, that it is a real motion ; and this was the
opinion oi mankind, with a few exceptions, for many ages. The inquisition
compeUed GalUeo to abjure the Copernican doctrine, (which taught both the
annual motion of the Earth about the Sun and its diurnal motion about its
axis,) and decreed, ' that the proposition, that the Earth is not the centre of the
world, nor immoTeable, but that it moTes, and also with a diurnal motion, is_
absurd, phUosophicaUy false, and theologicaUy at least erroneous in faith.''
The story that G^ilUeo, on rising from his knees after the abjuration,
whispered, ' E pur se muoTe' — ' It moves nevertheless' — ^is weU known.
25 The doctrine, that the Earth was the immoveable centre of the
universe, whieh was the basis of the Ptolemaic system, was universaUy
received until the time of Copernicus, who published his celebrated work,
De Revolutionihus Orbium Coelestium, in 1543, in which he refutes, but in a
cautious and hypothetical manner, the complex system of Ptolemy, which
taught that the stars were carried round the Earth daUy by an enormous
crystaUine sphere, and that the motions of the Sun, Moon, and planets, were
produced in the same manner. Considering the enormous distances and
magnitudes ofthe heavenly bodies, and the unnatural machinery of cycles and
epicycles by which the planetary motions were accounted for, Copernicus felt
that some other hypothesis respecting the celestial revolutions was necessary
to satisfy his mind. He found that some ancient phUosophers had taught the
motion of the Earth about ita axis and its annual motion about the Sun.
CarefuUy and cautiously considering these views, he at length came to the
conclusion that the Sun is the centre of the universe, and that the Earth revolves
not only about the Sun, but also about its own axis, whereby the apparent
diurnal motion of the stars is produced. These views he published in the work
above aUuded to, which was dedicated to the pope, Pauilll. After the time
of Gahleo, the Copernican system prevaUed, and the Ptolemaic was neglected,
though the works of both astronomers were stiU condemned as heretical by
the Eomish church. Mr, Drinkwater, in the Library of Useful Knowledge,
states, that both were in the Index Expurgatorms for 1828, with the words
'Nisi corrigatur.' But on this point see LyeU's Geology, p. 58 (7th ed.)
26 The proof of the Earth's rotation about its axis la, m a great measure,
derived from the fact that it simply, naturally, and reasonably accounts for
the apparent diurnal motion of the heavens, which the Ptolemaic system
does not. In addition to this, the pecuUar figure of the Earth, which is found
to be nearly spherical, but somewhat flattened at the poles and protuberant
at the equator, indicates the existence of a centrinigal force, caused by
rotation about an axis. Experiments onpendulums afford clear evidence of
the existence of this centrifugal force. Experiments on falling bodies, which
must be considered accurate and satisfactory, have been made, and it appears
from them that a body let faU from a considerable Height always falls a little
to the east of the vertical ; this can only be accounted for by the Earth's
rotation. Observation shows that the Sun, Moon, and planets, revolve from
west to east about their axes, and it is not unreasonable to conclude that the
Earth is not an exception to what appears to be the rule of the planetary
motions. 27 There is another proof that the Earth is not fixed, of the most con
vincing kind, derived from the phenomenon of the aberration of Ught, of which
we shaU presently speak. By this curious displacement, the Earth's motion is
made visible in every star, as it were in miniature, each star describing an
apparent orbit, similar to the motion of the Earth. Thia, however, apphes to
the motion of the Earth about the Sun.
28 One other consideration tends to confirm the truth of the opinion that
the Earth revolves about ita axis. It is this, that a most important end is

10 MATHEMATICAL GEOGRAPHY.
gained by the Earth's rotation— namely, the axis is thereby kept steady in
one position. But for its rotation, the Earth's axis would be contmuaUy
changing from one direction to another, and the effect of this would be extra
ordinary vicissitudes of seasons ; we should be at one time in the polar
regions — at another, m the tropics, subject to rapid and irregular changesof
cUmate, and to violent disturbances of the atmosphere and the ocean. The
example of a common spinning-top or hoop is sufficient to show the effect of
rotation in keeping a body in one position. It would be a practical inipossi-
bUity to balance a top by placing it with its point on the grotmd, without
having first communicated to it a motion of rotation ; but once make it spin
rapidly about its axis, and it wiU stand steadUy on its point— so steadUy that
it wiU require a considerable blow to upset it. The same thing is trae of
trundling a hoop ; the rotation communicated to it keeps it so steady that the
pressure of the stick upon it sideways does not upset it, but merely causes it
to tum shghtly out of its course.
29 It is, then, by a rapid motion of rotation that the 'round world is
made so fast that it cannot be moved,' not absolutely fixed, it is true, but
fixed with its axis in one position, by which means the changes from night to
day, and from aeason to season, become uniform and regular. And no doubt
the same important end is gained by the rotation of the Sun, and Moon, and
planets, each about its axis, and by the revolutions of the planets about the
Sun. It is by a wonderful combmation of motion and attraction that the
solar system is preserved imchanged, and each planet kept at its proper
distance from the Sun. And the rotations and proper motions of the stars,
now so clearly made out by astronomers, indicate that the same system per
vades the uniTerse. It is, most probably, by their motions and attractions
that the stars are preserved, each in its place. Without that perpetual revo
lution and rotation, and that bond of attraction which unites the remotest
systems, the whole uniTerse, as far as we may presume to judge, would drift
in confusion in the boundless ocean of space, and become a formless chaos.
IV. Globular Form ofthe Earth.
30 It is not necessary to say much on this point here ; that the Earth
is a globe may be, and has been, continuaUy proved by actual observation
and measurement. The most commonplace observation is sufficient to
make the fact evident. In every part of the ocean, the horizon is visibly cir
cular, this proves that the ocean, which covers a considerable portion of the
Earth's surface, is globular. The same is true of the great inland lakes which
are found in various parts of the world. The appearance of a ship approaching
land — the masts first becoming Tisible, and then the huU, is a famihar proof ot
the Earth's rotundity. So also is the circular shadow of the Earth, cast by
the Sun on the Moon, in an eoUpse. The circumnavigation of the Earth,
which is no imcommon occurrence, may also be adduced. The best proof is
actual measurement ; but we could not say anything satisfactory on this point
without introducing mathematical technicalities.
V. Proper Motion ofthe Sun, Moon, and Planets.
31 We have stated above, that, «!i<Aay%TOej-c(^<»o»«, the heavenly bodies
always preserve their relatiTe places unchanged, and appear to describe
circles about the pole, at the invariable rate of 15° per hour, so completing
the whole cu-cuit of 360° in twenty-four hours. We shall now briefly
explain what the exceptions are, commencing with the Sun, whose motion in
tne Heavens is the cause of so many important changes to us: those changes
from hght to darkness, and from heat to cold, which give rise to day and
nigiit, and brmg about in order the various seasons of the year. We shall then
briefly consider the motion of the Moon, and tiie apparentiy u-reaular and
anomalous wandermgs of the planets which were so satisfactorilv miraveUed
by Copernicus. The annual motion of the Sun, and the monthfy revolution

I I

THE CELESTIAL MOTIONS. 11
of the Moon, are simple enough at least to ordinary obaerTers, being always
from west to east ; but the motions of the planets seem to be goTerned by
some comphcated law — they sometimes move eastward, sometimes westward,
and they sometimes remam stationary. They were supposed in ancient
times to wander irregularly over the heavens, and hence they were caUed
jrXai/^Toi, or wanderers, by the Greeks, and 'errantes' by the Latins, and
sometimes ' vagse.'
32 These motions and appearances of the Sun, Moon, and planets are
beautifuUy described by Cicero, in the second book De Natura Deorum, which
is so much to the point, that we cannot do better than transcribe it here : —
' There remains, last of all, and at the greatest altitude above our habita
tion, surrounding and keeping in aU things, the expanse of heaven, which
is also caUed the sether, the extreme region and boundary of the universe ;
in which, in the most wonderful manner, bodies of fire perform their ap
pointed motions ; among which the Sun, though much exceeding the Earth
in magnitude, revolves about it. And he by nis rising and setting makes
day and night; and at one time approachmg (towards the pole), and at
another receding, he tums back twice every year, at opposite points of his
course — (i. e., at the solstices at midsummer and midwinter) ; between whioh,
during one period he chills the Earth, as it were, with sadness, and during
another gladdens it so that it seems to rejoice with the heavens. The Moon
also, which, aa mathematicians show, is more than half the magnitude of the
Earth, wanders over the same part of the heavens that the Sun does ; at one
time being in the same quarter with the Sun, and at another time in the op
posite, she transmits to the Earth the hght she receives from the Sun, and
she undergoes various changes of brightness ; also, at one time, she comes
between ua and the Sun, and obacures his Ught, and at another time, falhng
into the shadow of theEarth, which comes between her and the Sun, she becomes
suddenly eclipsed. In the same part of the heavens also those stars, which
we caU wanderers, are caused to revolve about the Earth, rising and setting
Uke the Sun and Moon ; and the motions of these stars are sometimes direct
and sometimes retrograde, and sometimes also they become stationary ; and
nothing is more wonderful, nothing more beautiftU, than this spectacle. After
these, comes an immense host of fixed stars,' &c. &c.*
He then goes on to describe the different consteUations, and in so doing,
he quotes a considerable portion ofthe astronomical poem of Aratus,
33 The motions of the Sun, Moon, and planets are twofold -.—first, they
partake of the same apparent circumpolar motion as the fixed stars, which,
as we have explained, is caused by the Earth's rotation about its axis; secondly,
they have other motions which the stars have not, and which are therefore
called Proper (or pecuhar) Motions. These motions we shaU now describe.

* ' Bestat ultimus, et a domiciliis nostris altiasimus, omnia cingens et coercens, coeli com-
plexus, qui idem aether vocatur, extrema ora et determinatio mundi : in quo cum admirabilitate
maxima ignese fornue cursus ordinatos definiunt. E quibus Sol, cujus magnitudine multis
partibus terra superatur, circum earn ipsam volvitur. Isque oriens et occidens, diem uoc-
temque conficit, et modo accedens, tum autem recedens, binas in singulis annis reveraiones ab
extremo contrarias facit : quorum intervallo tum quasi tristitia quodam contrahit terram, tum
vicissim lastificet, ut cum coelo hilarata videatur. Luna autem, quse est, ut ostendunt mathe-
matici, m^or quam dimidia pars terrae, iisdem spaliis vagatur quibus Sol ; sed tum congrediens
cum Sole, tum digrediens, et eam lucem quam a Sole accepit mittit in terras, et varias ipsa
mntationes lucis habet : atque etiam tum subjecta atque opposita Soli radios ejus et lumen
obscurat, tum ipsa incidens in umbram terra, quum e regione Solis, interpositu inteijectuque
terrae, repente deficit. Iisdem spaliis hae stellae, quas vagas dioimus, circum terra femntur,
eodemque modo oriunter et oooidunt : quarum motus tum incitantur, tum retardantur ; saepe
etiam insistunt. Quo spectaculo nihil potest admirabilins esse nihil pulchrius. Sequitur stel
larum inerrantium maxima multitudo,' &c. &c.

12

MATHEMATICAL GEOGRAPHY.

VI. Proper Motion ofthe Swn.
34 The proper motion of the Sun may be easUy observed and made out,

by means ofthe instrument above described, in the foUowing manner
the " 

Let

the axis A P be directed to the pole, and fixed in that position ; then, at
diOferent times of the year, let the fine D S be pointed to the Sim. It wUl be
eaay to aee when the teleacope, or the rod with sights, points to the Sun, by
the shadow it casts on a piece of card fixed at the extremity D, at right
angles to the telescope or rod. We may, then, by means of the graduated
circle, which we have stated should be fixed at C, measure the angle which
the Une D S makes with the line A P, and so find how far the Sun appears to
be from the pole ; i. e., if the angle is 80°, then the Sun is 80° from the pole,
if 90°, the Sun is 90° from the pole, if 100°— 100°, and so on. We may here
observe, that when a heavenly body is 90° from the pole it is said to be in the
equator, because, if it be 90° from the North pole, it must also be 90° from the
South pole — i. e., it is half way between the two poles, its distances from each
are equal, and it is said to be in the equator. The equator is, in fact, that
circle eTery point of which is at equal distances — i. e., 90° from each pole.
35 Now, if we obserre the Sun, as we have just stated, we shaU find,
about the third week in March, that the Sun is 90° from the North pole; and
at the corresponding periods of the foUowing months, we shall find that the
Sun's distance from the pole wiU be exhibited, in round numbers, by the
foUowing table : —

Sun's dis

Sun's

Sun's dis- Sun's

Month.

tance from

distance from

Month.

tance &om distance f^m

North pole.

Equator.

North pole.i Equator.
March . .
90°
0°
October .
102°
12° South.
AprU . .
May. . .
78°
12° Noriih.
November.
110°
20° South.
70°
20° North.
December .
113F
23i° South.
June . .
66i°
23i° North.
January .
110°
20° South.
July. . .
70°
20° North.
Pebruary .
102°
12° South.
August . .
78°
12° North.
March . ,
90°
0°
September
90°
0°
36 The Sun's distance from the pole in this table may be obtained by using
the instrument as above stated ; hia diatance from the equator is of course
immediately obtained by taking the difference between his polar distance and
90°. Thus, if the Sun is 70° from the pole, he is 20° above— i. e., north, of
the equator, because 20° added to 70° make 90°, and 90° is the distance of
the equator from the pole. In like manner, if the Sun is 110° from the
pole, he is 20° below — i. e., south, of the equator, for 20° added to 90°
make 110°.
37 By inspecting the above table, the Sun's motion towards and from the
pole wUl be immediately evident. About the third week in March he crosses
the equator ; after this, he moves continuaUynorthward, untU the corresponding
period in June, when he attains his greatest altitude above the equator, about
23^°. After this he begins to move southward, and continues to do so, tiU
about the third week in September, when he again crosses the equator. He
continues his motion southward tUl the third week iu December, when he is
at the most southerly point of his course, ahout 23i° below the equator.
After this, he returns again, and moves northwai-ds, tiU he comes back to the
equator, about the third week in March,
38 It is to this motion of the Sun towai-ds and from the pole that Cicero
alludes, m the words above quoted— ' Et modo accedens, turn autem recedens,
bmaa m singuha annis revorsioucs ab extremo contrarias facit.'
39 The Sun's motion towards or from the pole is quickeat t\ hon he crosses
THE CELESTIAL MOTIONS.

13

the equator, and slowest when he is at the greatest diatance from the equator ;
in fact, about the third week in June, and the corresponding period in
December, he is sensibly stationary for some days — i. e., nis motion towards
or from the pole is scarcely perceptible. This wiU be easUy seen from the
following table, in which his motions in March and June, 1849, are compared.
A simUar table woxdd show his comparative motions in September and
December.

Day ofthe

Sun's distance

Day of the

Sun's distance from

Month.

from Equator.

Month.

Equator.

March 15

2° 4' South.

June 15

23° 20' North.

„ 16

1° 40' „

„ 16

23° 22' „

, 17

1°16' „

„ 17

23° 24'

J

, 18

0° 53' „

„ 18

23° 25'

, 19
0° 29' „
„ 19
23° 26'
t
, 20
0° 5' „
„ 20
23° 27'
s
, 21
0° 19' North.
„ 21
23° 27'
, 22
0° 42' „
„ 22
23° 27'
f
, 23
1° 26' „
„ 23
23° 27'
i
, 24
1° 29' „
„ 24
23° 26'
, 25
1° 53' „
„ 25
23° 24'
,
, 26
2° 17' „
„ 26
23° 22'
J
, 27
2° 40' „
„ 27
23° 20'
)
40 Prom this table we may see that in March the Sun moves northward
at the rate of about 24' per day, or 2° in five days ; whereas, in June hia whole
northerly motion from the 15th day of the month to the 20th is only 7' ; and
from the 20th to the 23rd his motion is not perceptible.
The position of the Sun, when at his greatest distance from the equator
was hence caUed Solis Statio, or the Solstice, because he became stationary for
a short time at that point. In June, it was caUed the Summer Solstice, and
in December the Winter Solstice. The times in March and September, when
the Sun crosses the equator, were caUed the equinoxes, because then aU over
the world the length of the night is the same, which is not the case except at
those particiUar periods of the year.
41 But the Sun has another proper motion besides that we have just
explained, which may be made apparent by means of the instrument above
described, and a watch.
The axis A P minat be pointed towards the pole as before, and the tube B C
must be fixed, so that the telescope or rod with sights, may be capable of
moving only in one plane — ^i. e., about the axis C. If we make the axia C
horizontal, the telescope wUl move in a vertical plane ; in fact, in what is
called the Plane of the Meridian, of which we shaU speak more presently-
We shaU suppose the mstrument to be thus disposed, the axis A P pointing to
the pole, the tube fi C fixed so as not to be capable df turning round, and fixed
in such a position that the telescope may move in a vertical plane, or nearly
so. Another plane would answer as well, but it wUl save circumlocution to
suppoae it to be a vertical plane — ^i. e., the plane ofthe meridian.
* 42 Now at night let the teleacope, thus moving in the plane of the
meridian, be placed so aa to point to any particular atar that happens to be at
that time in the plane of the meridian. Let the hour and minute shown by
the watch be immediately noted. Let a sinular observation be made on the
same atar the next night, and of course aboutthe same hour, and let the hour
and minute shown by the watch be again noted. In this way the time, as
shown by the watch, in which the star completes its reTolution wiU be
detennined : for instance, suppose that at the first obserTation the watch
shows twenty minutes past nine, and at the second seTenteen minutes past
nine ; then it foUows that the star completes its rcTolution in twenty-three
14 MATHEMATICAL GEOGRAPHY.
hours and fifty-scTen mmutes, as shown by the watch. We do not suppose
the rate of the watch to be perfectly accurate ; it should be ot course a
tolerably good watch, but it ia no consequence if it gain or lose a few mmutes
in the day, „
43 Again, let precisely the same observation be made upon tUe bun on
two successiTe days, and ui this way let the time, as shown by the watch, m
which the Sun completes his reTolution be determmed. In the example aboTe
supposed, it wUl be found that the Sun's tune of completing his rcTolution
will be Tery nearly twenty-four hours and one minute, as shown by the watch.
And in aU cases, whateTer star we make our obserTations upon, it wUl be
found that the Sun takes Tery nearly four minutes longer to complete his
revolution than the stars do, for aU the stars, as we have already stated, will
complete their revolutions in exactly the same length of time. The Sun,
therefore, is about four minutes later than the stars every day.
44 Now what is the cauae of this ? It is not the motion of the Sun
towards or from the pole, because such a motion would not in any way affect
the time of the Sun's coming into the plane of the meridian, it wotud only
make him cross that plane nearer to or further from the pole, as the case
might be. The cause must be, therefore, a backward transverse motion
— 1. e., a motion perpendicular to the motion towards or from the pole,
which makes the Sun arrive at the plane of the meridian four minutea late
every day — i. e., four minutea later than if the Sun were, like the atars, fixed
in the heavens, and only subject to an apparent motion caused by the rotation
of the Earth about its axis. If we suppose the watch to be regulated by the
stars — ^i, e., if it shows twenty-four hours as the time of each star's completing
its revolution, then, if the Sun crosses the meridian plane at twelve o'clock
to-day, he wiU not cross it to-morrow tUl about four minutes past twelve. At
twelve o'clock to-morrow, therefore, the Sim wUl be one degree behind the
meridian; for in four minutes of time each heavenly body describes one degree
of its apparent circular motion, and therefore as the Sun wiU arrive at the
plane of the meridian at four minutes past twelve o'clock, he must be one
degree behind that place at twelve o'clock.
45 We have now made out in a rough way the proper motions of the
Sun ; he has two proper motions, one towards or from the pole, as the case
maybe, the other a backward motion perpendicular to the former, at the rate
of about one degree daUy.
By the combination of these motions the Sun appears to describe an
obUque circle in the heavens, moving backwards, (that is, from west to
east.) Moving in thia circle, he creases the equator, at the time of the
equinoxes, at an incUnation to the equator of about 234°. This circle is
called the ecliptic, because ecUpses of the Sun and Moon occur only when the
Moon crosses or comes near this circle.
46 The proper motion of the Sun ia only apparent, being caused by the
Earth's real motion about the Sun, The Earth is one of the planets, being
the third in order from the Sun ; the planets aU revolve round the Sun in
planes, but little incUned to each other, and in nearly circular orbits, Thia is
the Copernican theory, and it is the only rational way of accounting for the
Sun's apparent proper motion, and the apparent proper motions of the planets —
of which we shall speak unmediately , Newton's theory of universal gravitation
appUed to determine the motions of the solar system, confirmed as it is in
the most astonialiing manner, by predictions of eclipses and occultations, and
by solar, lunar, and planetary tables calculated from it, and verified with the
greatest exactness by repeated obsei-vations, proves beyond doubt the truth
of the Copernican theory, as alao dooa the phenomenon of aberration, to which
we have already alluded.
47 The apparent motion of the Sun towards and from the pole is caused
by the inclination of the Earth's axis to the plane of the ecUptic— i. e., the
plane in which the Earth moTea round the Sun, If the Earth's axis were
perpendicular to this piano, thc Sun would always appear to be 90° from the

THE CELESTIAL MOTIONS. 15
pole, as is maiufest. But this not being the case, the Sun sometimes appears
to be nearer to, and sometimes further from, the pole, as the Earth moTes
round. 48 To show this, we must obserre that the Earth's axia remains paraUel
to itself, or Tery nearly so, during the year — i. e., it always points in the
same direction ; also its inclination to the plane of the ecliptic is 66|° in
round numbers.
Now, this being the case, suppose E, fig. a, to be the Earth's centre, E P

its axis, and S the Sim, the angle PES being 66 J°; then, in this position of
the Earth with reference to the Sun — the polar (Ustance of the Sun — i. e.,
the angle P E S, is 66i°.
But in six months the Earth wUl describe half ita orbit round the Stm, and
therefore come into the position E', just opposite E on the other aide of S, aa
ia represented in fig. 0 ; also the axia E' P wiU be paraUel to its former
direction E P, as is shown in the figure. Therefore the angle P E' S, which
is the Sun's polar distance, wUl be CTidently greater than 90° — in fact, aa
much greater than 90° as P E S is less than 90° ; in other words, the Sun
wfll be 113i° from the pole.
49 It appears, therefore, that in one position of the Earth, the Sun wUl
be 66|° from the pole, and in six months after 113|° from the pole. During
the six months, the polar distance wiU graduaUy increase from 66|° to 113^°
being 90° at the end of three months. In the remaining six months of the
year, the polar diatance vriU dimimsh tUl it becomea 66^^° again — namely,
when the Earth comes back to the position E.
The Earth in the aboTe figures is supposed to moTe about S in a plane
perpendicular to the plane of the paper. Hence it appears that the supposi
tion of the paraUeUsm of the Earth's axis, as it moTcs round the Sim, accounts
for the changes in the Sun's polar distance.

16

MATHEMATICAL GEOGRAPHY.

VII, Proper Motion of the Moon amd Planets.
go The proper motion of the Moon is similar to that of the Sun, only
about 13 times quicker, and rather irregular, at least, apparently irregular,
but reaUy obeying a regular, though compUcated law. The Moon s proper
motion may be obaerred by the instrument we haTo described, and exactly m
the same way aa the Sun'a, It takes place in a circle indined about 5° to the
ecUptic, in which she moves from west to east in less than a calendar i?o?^th-
The foUowing table wUl beat explam the nature of her motion, which, hke
that ofthe Sun, ia twofold— one motion towards or from the pole, the other a
backward motion: —

Day of

Moon'9 distance

Hour that the Moon comes

Month, 1849.

from equator.

to the meridian plane.

July 1

14° 10' South.

9" 15°" aftemoon.

„ 2

16° 28' „

10" 1"

„ 3

18° 4' „

10" 48°"

,. 4

18° 53' „

11" 36""

„ 5

18° V „

12" 0"

„ 6

16° 20" „

0" 24'" moming.

„ 12

1° 8' North.

5" 7-" „

„ 13

5° 27' „

5" 56"°

The proper motion ofthe Moon is not apparent, but real ; the Earth being
the body about which the Moon actuaUy revolTes.
51 The proper motions of the planets may be observed in the same
manner as those of the Sun and Moon ; they are much more comphcated, as
the foUowing table for Mercury wiU show : —

Number of minutes by which

Corresponding motion
backward or forward.

Day of 1849.

Mercury is too late or too
soon in crossmg the meridian
plane each day.

January 1

7 minutes late.

1*° backward.

., 15

7 „

1|°

February 1

H ;

ir

5

^ „

1^°

„ 10

2

0-°

„ 11

H ..

or

„ 12

1

Oi°

., 13

0

0°

.. 14

0

0°

.. 15

1 „ too soon.

Oi° forward.

„ 20

n „

0*°

„ 25

4

1°

March 1

2

Oi°

5

1

Oi°

6

i „

Oi°

7

0

0°

8

0

0°

9

h „ late.

0i° backward.

10

1

0i°

15

3

0|°

20

4

1°

From this table it is CTident that m the first half of January, Mercury was

THE CELESTIAL MOTIONS.

17

continuaUy moTing backward among the stars, (i. e., from west to east,) at tho
rate of about 1|° per day. Up to the 13th of February, this daUy backward
motion became continually smaUer, being 1|° on the 1st of February, 1|° on
the 5th, only |° on the 10th. Between tiie 13th and 14th, Mercm-y had no
proper motion backwards or forwards, and ao far became stationary. On the
15th, Mercury began to moTe forward (i. e., from east to west) at the rate of
i° per day ; on the 20th, this forward motion had increased to -1° daUy ; on
the 25th to 1° ; on the 1st of March it had diminished again to ^° ; on the
5th to ^° ; and between the 8th and 9th, Mercury became stationary again ;
after tms the motion became again retrograde.
§2 From this description of the apparent proper motion of Mercury
among the stars, which apphes to Venus likewise, it is easy to understand
the words of Cicero aboTC quoted, ' quorum motus tum incitantur, tum
retardantur, asepe etiam insistunt.'
We haTC considered Mercury in the aboTe description on account of his
rapid motion, but it is difBcult to see him on account of his proximity to the
Sun. Venus would be the proper planet to make obserTations upon with the
instrument aboTe described, by the assistance of whioh, aa in the case of the
Sun, the proper motions of the planet may be made out.
VIII. Tlie Complicated Motions of the Planets are explained by supposing
that they and the Earth move about the Sun as centre.
53 The explanation which Copernicus gaTe of the apparently complex and
irregular motion ofthe planets was, that they all, along with the Earth, moTe
round the Sun as centre. This motion takes place nearly in one plane, (at
least as regards the principal planets,) namely, the plane of the ecUptic. Au
the planets moTe the same way, which is from west to east — i. e., contrary to
the apparent diurnal motion of the heaTens, but in the same direction as the
Earth's rotation about its axis, which causes that apparent motion.
g4 It is the combination of the motion of the planet and that of the
Earth, that makea the former appear sometimes to moTC forward, sometimes
backwards, and sometimes to be stationary. To a spectator in the Sun, the
motions of the planets would appear aimple enough, the Sun being the centre
about which they aU move. But to a spectator on the Earth, which is not
the centre of motion, and whioh moreover is itself moving round the Sun,
the planetary motions must necessarily appear very complicated. To explain
the fact that the planet's apparent motion ia sometimes from east to west,
sometimes from west to eaat, and
sometimes ceases altogether, we
haTC only to consider the dif
ferent relative positions of the
Sun, the Earth, and the planet.
55 Let ua suppose the planet
to be what is called inferior —
i. e., nearer to the Sun than the
Earth is, ofwhich kind there are
two. Mercury and Venus. In
this caae the motion ofthe planet
abont the Sun wiU be quicker
than that of the Earth, for the
nearer a planet ia to the Sun,
the faster it moves. In the first
place, suppose the three bodies
to be in the positions represented
in fig.^', E denoting the Earth,
S the Sun, and P the planet —
say Venus, for example. The
arrows show the directions in C

18

MATHEMATICAL GEOGRAPHY.

which E and P are moving in the circular orbits about S. WhUe ^ '^ movin|
OTer a space of 10 mUes along_its orbit, E wUl describe a space ot aliout Og
mUea, for the Telocity of the Earth ia, in round numbers, to that oi venus,
as 84 is to 10. , . J „ „„
Now the effect of the Earth's motion of 8^ mUes, wUl be to produce an
apparent motion in Venus of 8J mUes, but in the opposite du-ection to tnat
of the Earth*— i. e., in the direction of the arrow B. This apparent motion
must therefore be added to the real motion of Venus—namely, 10 nuiea—
which gives altoffcther a motion, in the direction B, of I85 mUes.
" 56 Secondly, suppose the
three bodies to be in the posi
tions represented in fig. h, then
the motion of the Earth wUl, as
before, communicate an apparent
motion of 8^ mUes to P, but
now in the contrary direction to
the arrow B, which shows the
direction in which Venus de
scribes her real motion of 10
mUes. The apparent motion
must therefore now be sub
tracted from the real motion,
and this wUl leave altogether a
motion of IJ mUes in the direc
tion B.
57 Hence, to a spectator on
theEarth, Venus, when sitnated
as in fig. _;¦ with respect to the
Earth and Sun, wUl appear to
move with almost double her
real velocity, from west to east, for that is evidentiy the direction in
which B pomts in fig. j, being the dfrection in which the Sun wUl appear to
move, in consequence of the Earth's motion about him. But when situated
as in fig. Ic, Venus wUl appear to move, with not one-fifth of her real velocity,
in the opposite to the former direction, that is, she wUl appear to move from
east to west.
58 Thirdly, when the three
bodiea are situated as in fig. I,
the real motion of Venus wUl
be oblique to the hne E P, and
so wiU the apparent motion
which arises from the Earth's
real motion, and is equal and
opposite to it. But the former
motion wUl be more obhque
than the latter, and therefore
the former motion, which is the
greater of the two, wUl appear
more diminished in conse
quence of the obhquity of the
line E P, than the latter, so
much so, that supposing E and
P to be in the proper relative
positions in thefr orbits, the
s^mTo^iTstS^^!" *° ''°'"*"-'"^* ^'^'^ °*^^'' '^^ ^' Pl-«twm tiien
moving backwards at the same rato that ho is re'al?y m™,^g forwtds. ' ^^^^' ^- "^ ""

THE CELESTIAL SPHERE AND ITS CIRCLES, 19
59 Thua it is evident that the Copernican hypothesis (that the planets,
with the Earth, move round the Sun as centre) clearly explains tho otherwise
unaccountable fact of the planets sometimes appearing to move from west to
cast, sometimes from east to west, and sometimes to be stationary.
60 The same reasoning as the above would apply to the superior planets,
or those farther than the Earth from the Sun, of which the principal are
Mars, Jupiter, Saturn, Uranus, and the lately diacovered Neptune. Only
a shght difference must be made because of thefr real motions being
always greater than the apparent motion produced in them by the real motion
of the Earth.
61 We have now given a suflScient general statement of the principal
celestial motions, to serve as an introduction to the subject of astronomy.
In the foUowing chapters we shaU confine our attention to the practical part
of astronomy, as far as it is important to our present purpose, and space wUl
permit.

CHAPTER II.
THE CELESTIAL SPHERE AND ITS CIRCLES.
THE CONSTELLATIONS.
I. Importance ofa hnowledge ofthe ConsteUations.
A KNOWLEDGE of the manner in which the stars are grouped together
and distributed over the heavens, and some degree of familiarity ^vith
the names and positiona of the different conatellations, and of the prmcipal
stars composing them, are highly desirable, not only as matters of deep
interest, but also of practical importance. It is true, indeed, that an astro
nomer in his observatory may make his observations without CTer having
looked upon the heaTens with the naked eye, he may, by means of his
catalogues, his tables, and his clock, point his telescope to any particular
heavenly body without looking out for it beforehand ; and so far the know
ledge we speak of is of no importance to him. But, if he vrishes to compare
his observations with those of others in past times, and to study the records
of astronomers, both ancient and modern, he must be perfectly famihar with
the classification of the stars into constellations which has prevaUed over
the whole civUized world for centuries, and which has the sanction of every
great astronomer since the earhest times.
63 But there are very few who haTe an obserTatory to make uae of; the
great majority of peraons who study astronomy practically must make their
observations with portable instruments, in unknown latitudes ; indeed, the
object such persons have in view is to determine where they are on the
Earth's surface, and it is chiefly for this purpose that they study astronomy.
Now to such persons, catalogues and tables can be of no use, as far as finding
any particular star is concerned ; for an aatronomer cannot point his telescope
by such means except he knows his exact position on the Earth's surface. A
saUor who wishes to dfrect hia course over the ocean by astronomical observa
tions, must know where to look for each heavenly body he makes uae of for
that purpose ; and the aame is true of every obserTer in an unknown locahty;
he must be perfectly famihar with the different groups of stars, the nanies
they are called by, and thefr relative positiona in the heavens ; otherwise,
however weU versed he may be in the theory of astronomy, he wiU not be
able to make any use of it practicaUy.
64 But it may be said that the classification of the stars which has been
so long in use, is perfectly arbitrary, having no absolute relation to their actual
distribution and arrangement ; that a much better, and less absurd system of
c 2

20 MATHEMATICAL GEOGRAPHY.
frouping might be adopteJ than the monsters and figures of the celestial globe.
his may be true, to a certain extent, but exactly the same thmg might be
said of the division of England into counties. If any one proposed to make a
new and more convenient division of England, by formmg it mto squares, or
rectangles, or any other regular figures, it would be easy to show the useless
ness and inconvenience of such a proposition, by saying that the present
division into counties has been in existence for a long period of time, that it is
recogniaed in our lawa, our hiatorical records, and our Uterature, and that it is
in many cases weU suited to the natural divisions of the country. We may
make a simUar answer to any one objecting to the present division of the
heavens into consteUations. It has been in existence for centuries. Astro
nomers have always made use of it in describing celeatial phenomena, and in
recording thefr obaervations ; and ancient writers are full of aUusions to it,
not only astronomical and geographical writers, but poets, historians, chro
nologers, and even the writers of the inspfred volume. Besides, the division
is by no means unsuitable to the actual grouping of the stars, and makes a
much more lasting impression on the memory than a more regular division,
as, for example, into zones and segments of zones, would do.
65 To the geographical student, a perfect acquaintance with the constel
lations is absolutely necessary, if he wishes to make any practical progress in
the scientific part of the subject. We ahaU therefore devote the present
chapter to this part of astronomy, and endeavour to give a fafr general idea of
the manner in whioh different consteUations are distributed over the heavens,
and the positions of the principal stars composing them.
II. Prelimina/ry Observations respecting the Celestial Sphere
and its Circles.
66 Before we proceed to the description ofthe consteUations, we must first
say a few words respecting the celestial sphere and its cfrcles, as we shaU have
to refer to these points constantly in all that we say respecting the constel
lations. 67 Celestial Sphere. — A sphere is the surface in soUd geometry, whieh
correaponda to the cfrcle in plane geometry. Every point of a spherical
surface is equaUy distant from the centre, and every part of the surfece has
the same degree of curvature. The diatance of any point on the surface of a
sphere from the centre is caUed the radius of the sphere, in the same inanner
as in the cfrcle.
The Celestial Sphere is a sphere described about the eye of the observer
as centre, with a radius of very great length. On the surface of this sphere
aU the heavenly bodies are projected, by lines drawn from the eye — that is to
say, if P Q E be supposed to represent
a portion of the spherical surface, E, the
eye of the observer — i. e., the centre,
and A B C any heavenly bodies at
different distances from E ; then, if Unes
be drawn from E through A B and C,
to meet the spherical 'surface at the
points A' B' C, these pomts are said to
be the projections ofthe heavenly bodies
ABC upon the spherical surface, and the
heavenly bodies are said to be pryected
by these lines upon the spherical surface,
68 In point of fact, the heavenly
„„„„•, 4.1 ¦ j.jv. , ,. hodies are ao far off that the eye cannot
appreciate their different distances, and they appear as if tiiey were aU at tiie
same distance from it-i. e., we view them as k they were ai projected on a
sphere of immenae extent, deacribed round the eye as centre
69 It IS very convenient to make use of an imaginary sphere as a means

THE CELESTIAL SPHERE AND ITS CIRCLES.

21

of representing the apparent positions of the heavenly bodies. The common
celestial globe is intended to exhibit this sphere in miniature, with the various
stars and constellations placed upon it, as they actuaUy appear to the eye to
be placed in the heavens.
70 It is important to explain for what reason we suppose the radius of
the celestial sphere to be of immense length. It is not merely because it
appears to be so, but because, by such a supposition, we avoid the necessity
of defining very exactly the position of its centre. It would be very incon
venient if we considered this sphere to be described with a radius equal to the
Moon's distance from us, great as that distance is ; for then a change of the
observer's position would sensibly alter the position of the celestial sphere.
Eyen the Sun's distance, and we may, in the present perfection of astronomical
science, say, even the distance of the nearest fixed star, would be too short a
radius for our purpose. As this is a point of considerable importance, espe
ciaUy as it relates to what ia caUed Parallax, we must endeavour to make
our meaning clear by means of a figure.
71 Let A and B, (figs. 2 and 3,) be two centi-es, about ^"S'
which two cfrcles of equal radius are described. The distance
between A and B, in fig. 3, is the same as in fig. 2, but the
radius of the cfrclea in fig. 3 is much longer than iu fig. 2. It is
eaay to see, by a simple mspection of the two figures, that the
two cfrcles in fig. 3 are much more nearly coincidentwith each
other than the two circles in fig. 2. This is made more mani
fest by fig. 4, which representa the two circlea in fig. 2 magnified so much as
to become the same size as the circles in fig. 3.

Fig. 3

Fig. 4

72 Now, we may suppose A and B to be the positions of two observers
on the Earth's surface, and the two cfrcles to represent celestial spheres de
scribed about A and B as centres. If the radius with which the spheres are
described he so smaU (compared with the distance of A from B) as is repre
sented in fig. 2, it ia clear that the observer at B wUl employ a celestial
sphere sensibly different in position from that employed by the observer at A.
But if the radius of the spheres be as large (compared with the distance of A
from B) as is represented in fig. 3, then the two spheres wUl not differ, as
regards thefr position, in anything like the same degree as in the former case.
If we had space on this paper to represent two spheres described with a
radius immensely exceeding the distance between the centres A and B, it ia
easy to conceive, by comparing figs. 3 and 4, how little the two spheres would
differ from each other in position.

22 MATHEMATICAL GEOGRAPHY.
73 Hence the importance of auppoaing the radius of the celestial sphere
to be Tery great, compared with the greatest distance at which two places of
observation on the Earth's surface may be from each other; for then we
may auppose that the celestial sphere at both places is the aame both m
magnitude and position, at least, we may consider the change of position of
the celestial sphere, in consequence of the observer's change of place, to be
practicaUy insensible, compared with the magnitude of the sphere. We may,
m fact, assume, without any error worth taking into account, that observers
at different places on the ifiarth's surface, however distant from each other,
project the heavenly bodies on the same celestial sphere.
We must remember that, in consequence ofthe Earth's motion round
the Sun, an observer changes his place in every half year, by a distance of
190 miUions of mUes, in round numbers. Therefore, we must consider the
radius of the celestial sphere to be immensely greater than 190 miUions of
miles. The simplest thmg to say on the subject is this — that the imaginary
celeatial aphere la of auch enormous dimensions, that the whole space occu
pied by the solar system is a mere point compared with it, just as the hole
made by the point of a compass in describing a large cfrcle on paper is con-
aidered as a mere point, though in reality it is of sensible magnitude, and
might be made to appear large enough if magnified.
74 Circles of the Celestial Sphere. — Cfrcles described on the celestial
sphere, with the observer's eye as centre, are employed very conveniently to
measure the angles, made by lines drawn from the observer's eye, in the
foUowing manner : —
Let E, fig. 5, be the observer's eye, P Q E a portion of the celestial
sphere, A and B two heavenly hodies,
which are projected upon the celestial
sphere by the Unes E A and E B, which
meet the sphere at A' and B". With E as
centre, describe onthe sphere a cfrcle. A'
B' C, passing through the points A' and
B', and divide the whole cfrcumference of
this cfrcle into 360 equal parts or degrees.
Then, if the portion A' If of ita cfr
cumference contains 10 of these equal
pai-ts, it is clear that the angle A' E B'
is an angle of 10 degrees ; if it contains
20 of the equal parts. A' E B' wiU be an
angle of 20 degrees, and so on If, there
fore, we conceive every cfrcle described
,,..,, on the spherical surface about the eye
as centre, to be divided mto 360 equal parts, each of these parts into 60
equal subdivisions, or minutes, and each subdivision into 60 equal subdivi
sions, or seconds, again; these divisions and subdivisions wiU show how
many degrees, mmutes, and seconds there are in the angle contained by any
two Imes drawn from the eye. By producmg the two hnes to meet the
sphere and then connectmg the points of meetmg by a cfrculararc, described
about the eye as centre, the divisions and subdivisions ofthis arc wiU show
Iww many degrees, mmutes, and seconds there are m the angle made by tiie
^.,Ji<,^^\^^^^^^ f exhibitmg the angles, which hnes drawn from tiie
eye make with each other, by means of cfrculai- arcs described on tiie surface
oi the celestial sphere, is Tery couTement, as it greatiy helps tiie mind to
understimd and make out how such angles are related to each other ^s is
sSaSotrretftS^* '^ ^^^^ ^''^'-^'^"^ ^^^o'^ometry, of which .Til
76 Small and Great Circles of the Sphere— T:\ie cfrcles we haTe iust
spoken of are called Great Circles ofthe ^here, the distSgu sW pTopertv
of which is-that they arc described about the centre of the^spS^T the

THE CELESTIAL SPHERE AND ITS CIRCLES.

23

eye) as centre. A circle described on tho
aphere, about any other point as centre, is
called a Small Circle.
It is easy to see that a great cfrcle
divides the spherical surface into two
equal parts (which are therefore called
Hemispheres) ; but a smaU cfrcle divides
it into two unequal parts.
In fig. 6, A B C D shows a great
circle, and A' B' C D' a smaU circle of
the sphere, the centre of the former
circle being O, which is supposed to be the
centre of the sphere, and the centre of
the latter being O', which does not coin
cide with the centre of the aphere,
77 If we make a section of a sphere
by a plane, the section wUl be circular. If the centre of the aphere be in the
cutting plane, the section wiU be a great circle, as is shown in fig. 7; if not.

it wiU be a smaU cfrcle, as is shown in fig. 8; A B C D ahowing the cutting
plane, and O the centre, in both figures.
78 We may therefore define a great cfrcle to be the section resulting from
cutting the sphere into two equal parts by a plane, and a smaU cfrcle to be
the result of cutting it into two unequal parts. 70 Pole of a Circle of the Sphere.—
Let O, fig. 9, be the centre of the sphere ;
draw any line P Q through O to meet
the surface of the sphere at the points
P and Q ; and let O B be a Une drawn
from the centre O, perpendicular to the
line P Q, to meet the spherical surface
at the point B,.
Now suppose P and Q to be two
points, or pivots, about wMch the line
P Q may turn, carrying the line O B
with it ; in fact; let P Q be an axis, and
O B a perpendicular rod firmly attached
to it. Then, if thia axis be tumed round,
it is clear that the extremity B of the
rod O B wiU trace a circle C B A on
the spherical surface, which cfrcle, since
its centre ia evidently at O, is a great cfrcle.
80 IfO'B' be another line, or rod, perpendicular to the axis P Q and
firmly fixed to it, and if B' be the point where it meets the spherical surface,
then the pomt B' wUl trace out another circle, C B' A', when the axis is

24

MATHEMATICAL GEOGRAPHY.

turned round about ita pivots P and Q; and this circle wUl be a smaU cfrcle,
because its centre, O', does not coincide with the centre of the sphere.
8 1 P and Q are caUed the Poles of these circlea ; the word Pole being
derived from the Greek, whioh signifiea a hinge, pivot, or bearing, about which
a body may smoothly tum.
82 All circles deacribed about the same poles are caUed Parallel Circles,
or Parallels, because they are at aU points equidistant from each other.
Thus the two circles, C B A and C B' A', being desciibed about the same
Eolea, P and Q, in the manner above described, are paraUel circles. An in-
nite number of circles paraUel to C B A, may be described by assuming the
point O' in different positions along the axia P Q.
Every point of a great circle is 90 degrees from its pole ; for if B (fig.
10) be any point of the great circle
C B A, and if we draw another great
cfrcle P B Q, connecting the points P B
and Q, it is clear that P B Q is a semi
circle, and therefore measures 180°,
and, since B ia half way between P and
Q, P B and Q B must each measure 90°.
Every point of a smaU cfrcle is less
than 90° from one pole, and more than
90° from another pole.
83 Comparative Magnitudes of
Small and Great Circles. — Let PBQ
(fig. 11) be a semicfrcle, P Q its dia
meter, O its centre, O B and O' B' lines
perpendicular to P Q. Then if we con
ceive this semicfrcle to be tumed about
P Q as an axis, P and Q being the
pivots or poles, the semi-cfrcumference P B Q wUl evidently describe, or, as
it IS said, sioeep out a spherical surface, the pohit B wUl describe a great
cfrcle, and the point B' a smaU cfrcle, O and O'
being the respective centres of the two cfrcles.
Our object is to compare the magnitudes of these
two cfrcles.
Now it is weU known, that the greater the
radius of a cfrcle is, the greater is tiie circum
ference in proportion ; if ttie radius of one cfrcle
be twice that of another, the cfrcumference of
the former wUl be twice as long as that of the
latter; if three times, three times ; if four times,
four times, and so on. Hence, whatever be the
proportion of O' B' to O B, the same wUl be the
proportion of the smaU cfrcle (which is described
with O B' as radius) to the great circle (which is
described with O B as radius.)
„„„„ - ^ ^ ..X. \. - -, V^^ cfrcular arc P B' shows the distance of
™ qJo^+i, tlie small circle from its pole P; if PB' contain 10°, or 20°,
ole 'p B'^™"— -•-^1--'^--'^°"°''-^^- ^^^^° ^® ^^'-°^ ^°' °^ ^°° fr°™ *^^

Kg 11

of the circular arc P B' ; thus, U" O' B' be i of O B the <;;
be I; tf 0' B' be i of O B, th^ sine of P B'^s said to be I

trigonometry the sine
sine of P B' is said to

Q m? P "O^J^oJ^ly f ^'ri^'ie -P"^"'- I>>^ta,ice of tiie smaU cfrcle
84 The fraction which O' B' is of O B, is caUed in trisonometrv tii
of OB, thei
are-calculated,>/which7he7inel~ora;cs"of™m4'nl'uTe'^f^^^^^^
m|5^S^^S-^^--K^fi;S^^n^Si»I^ cir^dSeltS^-r^-/^^S-'--rdS^°S^^S

THE CONSTELLATIONS.

25

centre. Hence we have the foUowing rule for finding what fraction the former
cfrcle is of the latter.
To find what fraction the circumference of a smaU cfrcle of the sphere is
of a great circle, look in a table of sines foivthe sine of the polar distance of
the smaU cfrcle, and that wUl be the fraction requfred.
If the length of the great circle be given, that of the smaU cfrcle is found
by multiplying the length of the great cfrcle by the proper fraction — i. e. by
the sine of the polar distance of the smaU cfrcle.
86 The foUowing short table shows the sines of cfrciUar arcs for every
five degrees, from 0° to 90° : —

Circular Arc

0 5°
10°
15°
20°

Sine.

Circular Arc.

25° 30°35°40°45°

Sine

Circular Arc.

50°55° 60°65°70°

Sine

Circular Arc.

75° 80°85°90°

Sine.

87 If we suppose the smaU circle, like the large cfrcle, to be divided into
360°, a degree of the smaU circle wUl be the same fraction of a degree of the
large cfrcle that the whole cfrcumference ot the small cfrcle is of the whole
cfrcumference of the great cfrcle. Hence the length of a degree of a small
cfrcle is to be fovmd by multiplying the length of a degree of a great cfrcle hy
the sine of the polar distance of the smaU circle.
Thus, if we suppose a smaU cfrcle described on the Earth's surface at 40°
from the north pole (which is the polar distance of the southern extremity of
England), the circumference of that cfrcle vriU be (the sine of 40° being feoq)
¦f^ of the whole length of the equator ; and the length of a degree of this
small cfrcle wUl be got by multiplying 69^ nUles (the length of a degree of
the equator in round numbers) by ^'oljo-
Having dwelt sufficiently on these points, we shaU now go on to describe
the appearance and arrangement of the stars on the celestial sphere.
III. Classification ofthe Sta/rs with re-'vect to Brightness.
88 The apparent brightness of the stars is very different ; some shine
with consideraole brilUancy, some are leaa bright, others almost invisible to
the naked eye, and multitudes to be seen only by the aid of the telescope.
As the apparent brightnesa of a star is, to a certain extent, a distinguiahmg
mark of it, it is important to have some classification of the stars with respect
tothe quantity oflight they emit to the eye. .
89 Stars visible to the naked eye are divided into six classes ; those of
the m-at class are the brightest, and are about twenty in number : they are
caUed stars of the^ra* magmtude. The second class includes about seventy
stars which, though clear and bright, are not so remarkable as those m the
first olasa ; they are called stars of the second magnitude. The third class
consists of about 220 stars, fainter, ot course, than the former, but stUl very
obvious to the eye ; these are said to be ofthe third magnitude. There are
ahout 500 atars of the fourth magnitude, 690 of th.e fifth, and 1500 of the sixth.
The stars of the fifth and sixth magnitude are not visible on a clear moon-
hght night to the naked eye, and therefore on auch a night thoae of the fourth
magnitude wUl be the faintest visible without telescopic aid. Altogether, there
are, in round numbers, about three thousand stars that are visible to the
naked eye.

26 MATHEMATICAL GEOGRAPHY.
90 Stars which can be aeen only through a telescope are caUed telescopic
stars. They are spread over the whole expanse of heaven, in some places
close together, as in the MUky Way, in other places far apart. Where they
are close together, they are seen by the naked eye like cloudy spots or
streaks in the heavens, which, when examined by a powerful teleacope,
completely change thefr appearance, and become assemblages of innumer able
bright points oflight sprinkled, as it were, over a dark ground. The MUky
Way, which appears Uke a famt, narrow cloud of irregular shape encirchng the
whole celestial sphere, is weU known. Besides this, there are a number of
small cloudy spots of various shapes caUed Nebulae seen by means of a tele
scope of moderate power, many of which, on nsing a h^her power, are
resolved, aa it is said, into aaaemblages of atars. Some of them have never
been resolved even by the magnificent instrument of Lord Eosse, seen through
which they stUl present the same indistinct and hazy appearance as in a less
powerful teleacope.
91 The classification of the stars visible to the naked eye into six classes
or magnitudes is very convenient in a general way ; but for accurate pur
poses it is too rough, and subject to great uncertainty; so much so that many
stars, whioh are considered in some maps as of one magnitude, are in other
maps put dovm aa of a different magnitude. Thus, for instance, in littrow's
maps (Atlas des geatimter Himmels) the seven stars in the Great Bear are
represented to be aU of the second magnitude, except the star marked S,
which is put down aa of the thfrd. But in the maps published by the Society
for the Difiusion of Useful Knowledge, the star a is considered to be of the
first magnitude, /3, y, and yj of the second, and 8, e, f of the thfrd.
92 There is, however, a good reason for uncertainty with respect to the
magnitudes of several stars, in the fact that they appear to change thefr mag
nitude from time to time, being subject, from some cause or other, to a
periodical variation of brightness. Thus, for example, the remarkable star
Algol (|3 Persei) suffers a considerable change of brightness in a period of not
quite three days, being at one time during tiiat period of the second magni
tude, and at another tune only of the fourth.
93 The most probable way of accounting for this change of brightness is
by the supposition that it is caused by the revolution of spots on the star's
disk, as in the case of the. Sun, or by large planetary bodies moving round
the star as their Sun. The manner in wluch the brightnesa of Algol varies
makes this Tery likely, for it changes rapidly from the second to the fourth
magnitude, and then as rapidly back again to the second, after which it
remains imchanged for the remainder of the period. The change from the
second magnitude to the fourth and back again occupies only seven hours ;
whUe the time during which the star retains its brightness unchanged is about
sixty -two hours. This is accounted for easUy, if we suppose a spot or opaque
body to revolve round thf star in ahout sixty -nine hours, during seven hours
of which time it is between the eye and the .-star.
For full information respecting this interesting point, we may refer the
reader to Captafri Smyth's Celestial Cycle, in the second volume ofwhich com
plete .and accurate information is given respecting almost every star and ob
ject of interest in the heavens. This is a most valuable, and we may say
amusing book, and ought to be in the hands of every one who takes an
interest in astronomy.
94 A good method of gettfrig an idea of the magnitudes of the different
stars is to watch them as they become visible iu succession after sunset. As
the dayUght fades away, those of the first magnitude are seen flrst ; soon after,
those of the second come out, then those of Uie thfrd, and so ou. The light
of the Moon may also be used as a test of the comparative brightness of the
stars. For more accurate mctiiods, see Smyth's Celestial Cycle, toI. i. p. 272.
It IS scarcely necessary to observe that the word magnitude, as applied to
the stars, is not used m its proper signification; it has, of course, no reference

THE CONSTELLATIONS.

27

to the real magnitudes or dimensions of the atars, but only to thefr apparent
brightness. 95 We ahaU now proceed to deacribe the principal conateUations, and show
how and where they are to be found in the heavens. As we go on, we shall
explain the meaning of various astronomical terms which have relation to the
celestial sphere, and to the apparent motion of the Sun.
In describing the consteUations, we shaU endeavour to do so in such order,
and to classify them in such a manner, that any one may, in a short time,
make himself quite famiUar with thefr appearance and relative positions in
the heavens. rv. Ofthe North Circumpolar Begion ofthe Heavens.
96 Method of finding the Pole Star by means of the Great Bear. — If we
observe the motion of the stars for four or five hours, we ahaU perceive, as
haa been already stated, that they aU revolTe about a particular point of the
heaTens, wliich is caUed (in these latitudes) the North Pole, Near this point
is a tolerably bright atar, which is known by the name of the Pole Star.
There is no other star of equal brightness in the immediate vicinity of the
North Pole, and therefore the Pole Star, once pointed out, is easUy recogniaed
again, especiaUy aa it is always to be seen in the same direction on account of
its nearneaa to the Pole ; for the cfrcle it describes ahout the Pole is so small,
that its motion is not sensible to the eye without the assistance of some
inatrument, 07 To find the Pole Star, we muat haTe recourse to the remarkable
and weU-known group of stars commonly knovro by the name of the Great
Bear, of which imaginary animal they form the taU and hind quarter. They
are often caUed Charles' Wain, and sometimes the Plough, and this latter
name giTes the best idea ofthe form ofthis group of stars.
Thefr Latin name was Sep
tem Triones, or the SeTen Oxen ;
Trio signifying an Ox, The
Greek name, apia-os, {arctos,) sig
nifies a bear, and hence the
northem region of the heaTens
is caUed the Arctic region. The
Latin name of the whole con
stellation of the Great Bear is
Ursa Major,
The group consists of scTcn
rather bright stars, which are
usuaUy denoted by the Greek
letters, a ^y 8 e f ij, as is shown
in fig. 12. The tla:ee atars, e f >),
form the taU of the Great Bear,
a ^ y and 8 the hind quarter.
The whole consteUation, with the
imaginary figure of the Bear, is
shown in fig. 13, (on next page,)
which includes all the stars as
far as the fourth magnitude.
98 The star a is caUed
Buhhe, (an Arabic name, signify
ing the Bear ;) it is the brightest
star of the seven, and may be
considered as of the first mag
nitude. The star 8 is the faintest of

28

MATHEMATICAL GEOGRAPHY.

the group, and is of the thfrd magnitude ; the other stars may be considered
as of the second magnitude.
This consteUation is constantly aUuded to by ancient writers. In Homer
(Od. V. 272) we find the foUowing Unea: —
ovie o't vnvoi ^«-i BXe^apoiTt ?wtitT€v
nXtjidias t' iiropSiVTt Ka'i o^i ivovra SowTrli.
"ApKTOv 0' riv Kai "A/iafav eTTiKXneriv KaXeotxriv
^t* avTov arp^^erat Kai t' *Qpitava doKEuei
otn 6' Sfifiopot i-crTi XocTpSif *tlKeavoto.
' Nor did sleep faU upon his eyeUds as he watched the Pleiades, and tiie late-
setting Bootes, and the Bear, which also is commonly caUed the Wain, which
revolTes in that part of the heavens, and watches Orion, and alone is never
bathed in the ocean.'
99 The atars a and ^ are commonly caUed the Pointers, because they
Eoint nearly towards the Pole Star. If an imaginary line be drawn in ths
eaTens through the Pointers, it wiU pass near the Pole Star, as is repre*'
sented in fig. 12, where a' denotes the Pole Star. ' '
In findmg the Pole Star by means ofthe Pointers, it is important to re
member that this line is to be drawn in the dfrection represented by the arrow,
i, e., from 0 to a, not from a to^. From a' to a is about five times the distance
between a and /3, a' is on the offside ofthe Une of dfrection of the Pomters,
with reference to tho seven stars, i. e., not on the same side as the taU We
may therefore give the following rule for finding the Pole Star 
100 Draw an imaginary line in the heavens from |3 to a, and produce it
on tUl the produced part IS about five times the length of the distlmce from
/3 to a ; then near the extremity ofthis hne, onthe contrarv side to tiie Bear's
the Pok star'^'' '^ '*''''' ''° °*^" ^''"^^^^ ^'''^'^^ ^ its vicinity, which is
loi Of the Little Bear, or Ur.^,i Minor.— The Pole Sfnr r,r. t>„j,^;, oa
it is often caUed, forma the extremity of the taU of wLt Is' rnown by tie

THE CONSTELLATIONS.

29

name ofthe Little Bear. This con
stellation is by no means so obvious
to the eye as the seven stars of the
Great Bear, the atara composing it
being fainter, with the exception of
Polaris. The Little Bear is repre
sented in fig. 14, with the form of
the animal toaced out. The relative
positions of the Great Bear and
Littie Bear are shown in fig. 15.
The stars ofthe Little Bear form
a figure not unlike that of the seven
stars of the Great Bear. It may
be weU to observe, that the tails of
the two Bears are on contrary aides.
The atars of the Little Bear are de
noted by Greek letters, aa is repre
sented in fig. 15, and the same plan
is adopted m aU the other constel
lations. The Pole Star is a ot the
Little Bear, and in most caaea a de
notes the brightest star of a con
stellation. It is usual to specify any particular star by prefixing the Greek
letter by whioh it is denoted to the Latin name of the constellation to which

Fig. 15 ^
0

• S
? \ \ 1

« •
•

p\ a
•

it belongs in the genitive case. Thus, Polaris is spoken of as a Ursse Minoris,
(3 of the Great Bear as 3 Ursse Majoris, and so on. Sometimes stars are
marked by Eoman lettera and by numbers ; for instance, we have 61 Cygni,
m Uraae Majoris.
102 The use which was made of Polaris in navigation is weU known, and
is very ancient. Polaris is often called the Lode Star — ^i. e., the leading or
guiding star. It waa formerly called Cynosura, or the Dog's Tail, Ursa Minor
having been figured as a dog in those times.
The word cynosure has passed into our language, denoting whatever ia
a centre of attraction to the eye : thus, in MUton's L' Allegro we have —
Where perhaps some beauty lies,
The Cynosure of neighbouring eyes.

30

MATHEMATICAL GEOGRAPHY.

In the Latin translation of the poem of Aratus we have-
Ex his altera apud Graioa Cynosura vocatur
llac fidunt duce noctuma Phoenices in alto.
Probably this hue explains why Polaris was often caUed Phoenice,
103 The two atars /3 and 7 of the Little Bear were caUed the Guards,
from a Spanish word signifying ' to watch,' because they were used by aaUors
to mark the hour of the night before watches and chronometers were in
vented. The star /3 was nearer to the pole than Polaris two thousand years
ago, and it was the North Star of the Arabian astronomers, whence it was
caUed Kocah.
104 The position of the pole may be nearly found by means of the Pole
Star and the Guards, in the foUowing manner: —
In fig. 15, draw a Une through Polaris (a) perpendicular to the line joining
the two Guards 0 and y, and m that line, about 1^^° from Polaris, is the
North Pole, represented by P in the figure.
105 To get an idea of the distance of the Pole from Polaris, we may
observe that the Pole is about twice as far from the star 3 as it is from 0,
and that the line drawn from 8 to P is inclined, as is represented in the figure,
to the Une drawn from a perpendicular to that passing through /3 and y.
At present the Pole is getting nearer to the Pole Star ; in about 140 years
the Pole wUl be about \° from Polaris, afterwards it wUl recede from it.
106 Method of Setting the Instrument described in the former Cliapter. —
We shaU here explain the manner in which the instrument, described in the
former chapter, may be placed with the axis A P (fig. e) pointing towards
_,- _ the Pole nearly.
,.•' "* _ First, the telescope (or the rod wiUi
sights) must be tumed round its pivot
^ p C, until it points in the same direc-
.'•' tion as the Une A P, as is represented
in fig. 16. This may be easUy done
by pointing the telescope, placed as
in fig. 16, towards any distant object,
S, and then turning the tube B C
round. If, on doing this, the ohject
S does not appear to change its posi
tion in the telescope, then it is easy
to see that the line D S must be pa
raUel to the axis A P, about which
the tube has tumed. If, however, the
object S appears to change, the tele
scope must be shghtiy tumed ahout
its pivot C, until the apparent position
of the object S, in the telescope, is
not affected by the motion of the tube
about its axis.
107 When the telescope is thns
, , _, , adjusted, the graduated cfrcle. which
IS attached to C, to measure tho angle made by the Imes A P and D S, ought
to show zero, since tho two hnes are then parallel. This gives us a method
of finding whether the graduated cfrcle is properly placed or not, and tf not,
of making the necessary adjustment.
io8 l!^ow, supposing the teleacope to be nlaced with its hne of collima
tion, D S, parallel to the axis A P let the whole upper portion of the insfru-
ment be turned about the joint A and the vertical stem^A G also if necessary,
untu the telescope points to the Pole, the position ofwhich must be gues^d
by the eye, by drawmg from Polaris an imaginai-y line, pernenScite a.i
neary as can bejudgea, to tho hne joining le t/o Gu^rd^S^^Jiw a
pomt on that line twice as for from tiib Star 8 as from PoWis TlUs may

TIIE CON.STELLATIONS.

be easUy done without losing more than a half of a degree from the true
place of the Pole, and tins wiU be sufficiently accurate, considering the rude
ness of the instrument. The axis A P, having been once directed to the
Pole, should be fixed in that position, which may be done by tightening the
joint A, and by putting three marks on the cfrcumference of the base of the
mstrument G, and three corresponding marks on the pedestal out of doors
upon whioh the instrument is placed , so that the instrument may be put
back in its proper place, should it have been removed.*
109 With the instrument thus placed, the general facts stated in the
former chapter, respecting the cfrcumpolar motion, and the proper motions of
the Sun, Moon, and Planets, may be easUy observed according to the method
described in the case of the Sun.
no Cassiopea's Chair.— -H an
imaginary line be drawn from any
one of the three stars forming the
tail of the Great Bear (f, f, or 17,
TJrasB Majoris) through Polaris, it
wUl lead to the consteUation Cas-
siopea, the five principal stars of
which form Cassiopea's Chair, which
is something like a distorted M or
W Tlie Pole is about half-way
between the taU of the Great Bear
and Cassiopea's Chair. Fig. 17
shows the five principal atara of
this consteUation.
Ill It is worth remembering, that the Utc stars of the Chair form two
triangles, one nearly a right angled triangle, consisting of a, /3, and y, and
the other a Tery obtuse angled triangle, consisting of y, 8, and e. We make
this observation, because, without it, it is not easy to distinguish /3 from e, and
it is of some importance to remember which of the five stars is (3.
112 /3 CassiopesB ia a atar of the aecond magnitude, and is the extreme, on
tie side ofthe right angled triangle, of the five atara. If a great cfrcle be drawn
through Polaria and /3 Cassiopeae, it coincides very nearly with the great
cfrcle caUed the Equinoctial Colure — ^i. e., the great cfrcle passing through the
poles and the two equinoctial points of the Equator. AU great circlea passing
through the Poles were formerly called Colures, (Kokovpoi,) because, as the
word signifies, they were partly cut off, or, as it were, maimed, by the horizon.
The name is now restricted to two great cfrcles passing through the Poles, one
cutting the Equator at the equinoctial points, the other at points 90° from
the equinoctial points. The former was
caUed the Equinoctial Colure, the latter
the Solstitial, because, as we haTe al
ready explained, the points where the
Sun becomes stationary for a short
time (as far as his motion towards or
from the Pole is concerned) are in the
latter great cfrcle.
113 In fig. 18, which ia supposed
to represent a sphere, these cfrclea are
shown. A B C D represents the Equa
tor, P the North Pole, Q the South
Pole, A the Vernal Equinoctial point,
C the Autumnal, B and D the points
of the Equator which are 90° from A
and C : then the great circle P A Q C
is the Equinoctial Colure, and the great

Fig. 18 ^
A r — -^

I

^_Z^I^^^

\ ^

\

jJ

* A projecting piece at A, with a clamp and screw, would malie it easy to point A P to the
Pole, and keep it flxed at the proper inclination.

32

MATHEMATICAL GEOGRAPHY.

circle P B Q D the Solstitial Colure. The Equmootial Colure is marked by
the Stars 8 Ursse Majoris, Polaris, and 0 Cassiopese ; the position of 6 Ursse
Majoris is about at E, and that of /3 Caasiopeae at S.
The star a of this consteUation is one of those remarkable stars, the
brightness of which is continuaUy changing, a generaUy appears fainter
than 0, but sometimes it becomes brighter. What the cause of this change
of splendour may be we can only guess. It is likely, as we haTe afready
stated, that there are apots on the star's disc, and that they sometimes appear
and sometimes disappear, m consequence of the star's rotation about its axis,
so causing a Tariation in the quantity of light emitted from the star ; or the
change of bnghtneas may be caused by large planetary bodies revolving about
the star as thefr aim, and: sometimes interceptmg the light of the star.
114 Ofhe Dragon. — The oonateUation Draco, the Dragon, commences
between the Great Bear and the Little Bear, runa almost halfway round the
latter, and then tums off m the opposite dfrection. It is represented in fig.
19, with the form usuaUy given to the Dragon traced out, Ursa Minor on one

side of the taU, and the Septemtriones on the other. It is worth observing,
that this consteUation, commencing not far from a Ursse Majoris. (the first of
the Pointers,) lies on the tail side of the Septemtriones, and on the same side
as the body, not the taU, ofthe Littie Beai-. In the Isi Georgic of VirgU,' the
position 01 Draco between the two Bears is described —
Maximus hic flexu sinuoso elabitur Anguis
Circum perque duas in morem fluminis Arctos,
Arctos Oceani metuentes tequore tingi.
' Here the enormous Dragon gUdea round with winding flexure, like a river,
between the two Beara, the Bears that fear to dip in the ocean.'
115 The star a Draconis, which is not far from half way between the two

THE CONSTELLATIONS.

33

Guards in the Little Bear and the tail of the Great Bear, was formerly the
Pole Star, the Pole having been very near it (not a quarter of a degree from
it) in the times ofthe Chaldean observers.
ii6 The two principal stars of this consteUation are those marked
^ and y in the head of the Dragon, and their position should be weU remem
bered ; they are of the aecond magnitude. To find them, we have only to
draw an imaginary line through a and 8 Ursse Minoris, near which they wUl
be foimd, or, what is the aame thing nearly, a line from Polaria, perpendicular
to the Une from Polaris to y Ursse Majoris, wUl find them. They are about
at the same distance from the Pole as the second of the Pointers (/3 Ursse
Majoris). A line through the Guards O and y Ursse Minoris), goes nearly
through the head of Draco.
y Draconis is a most remarkable star in the history of astronomy ; it
passes nearly verticaUy over Greenwich, and was on that account chosen by
the great astronomer, Bradley, as the moat auitable for his observations, which
led him to the twofold discovery of the Aberration of Light and the Nutation
of the Earth's axis.
117 Cepheus. — Between the Dragon and Cassiopea wUl be found the atars
ofthis consteUation ; they are not easUy distinguished from the stars of Draco,
but, by remembering, that an imaginary line through y Urase Majoria and ^
Ursse Minoria, (the inner Guard,) aeparates Draco from Cepheus, there will
never be any difficulty in making out the limita of Cepheus. Fig. 20 shows
Cepheus.

118 Camelopa/rdus. — This consteUation is by no means remarkable; 1,.
occupies the space on the opposite side of the Dragon beyond Polaris, and
between the head of the Great Bear and Cassiopea,
119 Position of the Colures with reference to the Circumpola/r Stars. —
We haTe described the constellations in the immediate vicinity of the Pole at
D

34 MATHEMATICAL GEOGRAPHY.
some length, because, when thefr poaitionswithreferencetothePde^toe^^^
other are weU understood and remembered, they {"^ ^° ^^y^fo^d
pomts of departure, whereby the other consteUations "^flf^l^^^^i^^^v
^ We have afready stated that the Equinoctial Colure 'leariy coin^des^t^
the great cfrcle passing through /3 Cassiopea, a Pola™, and betw^^^
UrsS Majoris, nearer to 8 than to y.TheSohtitial CoUre rm^ It hflwaTS
Pole at rieht ansles to the Equinoctial, close by y Draconis. Xt is always
worth remfmlei^g that the C^otoes are marked by PoUr^, »-r^^ch t^iey
intersect, bv /3 Cassiopese and 8 Ursse Majons, which show the direction ot
the Equinortial Cdm-e, and by y Draconis, (in the Dragon s Head,) which shows
the diSon of the Solstitial 6olure. In fig. 21 the colures and the circum-
polar constellations are represented.

Fig. 21

Andromeda 1
Srring Colnre •

•

Cygnus
a • Ceph
eus 1 "•f'^
•
• Eer«'*
Lyra
Capella
•
tVega
E
t. Polaris
C--V-*-'
.^
Wilier Cohire
• Dragon's
^ , Head
dummer Colure
Dragon's Tail
IlerculC!)
P
; Ursa MfMor
Bootes
Autumn Colure
120 Pole of the Ecliptic and the Sun's Motion. — The position of the Pola
of the Ecliptic is shown at E, fig. 21. It is nearly in the imaginary hne
joining Polaris and y Draconis, half way between the Pole and the Dragoii's
Head, which is worth remembering. The EcUptic is, as has been stated, th*,
great cfrcle along which the Sun appears to move from west to east at tie
rate of nearly one degree daily, so completing the entfre cfrcle in 365 days in
round numbers. The sun is therefore always 90° from a point of the heaveM
about half way between Polaris and the Dragon's Head,
121 About the thfrd week in March and September the Sun crosses the
great cfrcle, passing through Polaris andjS Cassiopese, and at the corresponding
period in June and December he crosses the great circle, passing througn
Polaris and y Draconis. We shaU find it convenient to divide each of the
two Colures into semicfrcles, and consider that there are four Colures, whieh
we shaU call Vernal, Summer, Autumnal, and in»fer Colures. The half great
circle drawn from pole to pole through 0 Cassiopese nearly is the Vernal
Colure, because the Sun crosses it in spring. The other half of the Equinoctial
THE CONSTELLATIONS. 35
Colure is the Autumnal Colure, because the Sun crosses it in autumn. Tho
half great cfrcle drawn from pole to pole through y Draconis nearly is the
Winter Colure, because the Sun crosses it in winter ; and the other half ofthe
Solstitial Colure is the Summer Colure, because the Sun crosses it in summer.
The four Colures, therefore, are marked as foUows :—
The Vernal Colure— by Cassiopea.
The Summer Colure— by Camelopardus.
The Autumnal Colure— by the Septemtriones.
The Winter Colure— by the Dragon's Head.
The Sun's distance from the Pole is, when he crosses
The Vernal Colure, 90°.
The Summer Colure, about 665°.
The Autumnal Colure, 90°.
The Winter Colure, about 113^-
Having dwelt at some length on the cfrcumpolar constellations for the
reason above mentioned, we must now aUude only briefiy to the other con
steUations, at least the principal of them.
V. Segion of the Heavens along the Vernal Colure.
122 In fig. 23 (see next page) this region is shown extending from Casaiopea
to the Equator, and some way south of it. The first group of atara that catches
the eye in this region is the square formed by the four stars, Alpherat, Algenib,
Markab, and Scheat, shown in the figure. The Vernal Colure, which, it will
be remembered, is drawn from the Pole through /3 Cassiopese nearly, passes
through Alpherat and near Algenib, the two eastem stars of this square.
123 Andromeda. — The consteUation Andromeda comes next after Cas
siopea, as we go from the Pole to the Equator along the Vernal Colure, lying
on the east side of the Colure : Alpherat is a Andromedse.
124 Pegasus. — This consteUation is on the western side of the Colure,
Markab, Sheat, and Algenib, are a, /3, and y Pegasi,
125 Pisces, the Fishes. — This consteUation is figured as two fishes tied
together by a long string. One fish is marked by three small stars a Uttle
west of the Colure, just below Algenib and Markab. The other fish is higher
up, near Andromeda, on the east of the Colure. This is one of the twelve
consteUations, caUed the Signs ofthe Zodiac.
126 Aries, the Bam. — ^The head of Aries is marked by two stars of the
thfrd magnitude, easUy recogniaed, situated aome way east of the Colure.
Aries is one of the signs of the Zodiac.
127 Vernal Equinoctial Point. — The figure shows the equator and ecliptic
meeting the Colure at the vernal equinoctiafpoint, which is about as far below
Algenib, as Algenib is below Alpherat. The Sun's proper motion takes place
along the echptic in the direction represented by the arrow, contrary to the
diurnal rotation of the heavens, the dfrection of which is represented by the
arrow pointing along the equator.
128 The equinoctial point is continuaUy but very slowly moving along
the ecliptic, in a dfrection contrary to that of the Sun's proper motion. This
point was formerly in Aries, and was caUed the Ffrst Point of Aries, It is
now in Pisces, and is moTing towards Aquarius. It stUl, notwithstanding,
retaina the name of the First Toint of Aries.
129 Aquarius, the Waterman. — This ia another of the signs of the Zodiac,
next to Pisces, but lower down, on the western side of the Colure.
130 Cetus, the Whale. — Opposite Aquarius, on the other side of the
Colure, is a large constellation, caUed Cetus, the stars ofwhich, near the tail,
are shown in the figure.
131 Piscis Australis, the Southern Fish. — A bright star ofthe first mag-
d3

36

MATHEMATICAL GEOGRAPHY.

Fig. aa

Eastern Side

CoHiopea

.P ^

l^

Alpherat
o ?

Algenib

^'i.

""I-,

*-c

°f.

¦°fl

Fqiiator_

Equinox

Diurnal Rotation

Cetus

Western Side

gclieat

Aquarius^

Fomalhaut • P'so>».
Auslralis

THE CONSTELLATIONS.

37

nitude, called Fomalhaut, which
means the Fish's Mouth, being a
corruption of an Arabic word,
marks the mouth of the Southern
Fish, which lies immediately be
low Aquarius. This star being so
much to the south of the equator,
is ncTer seen much above the ho-
lizon in these latitudes, and is
therefore seldom visible, the stars
near the horizon being generaUy
obscured by mists and clouds;
besides, the more to the south a
star is, the shorter time is it above
the horizon each day,
VI. Begion ofthe Heavens along
the Summer Colure.
132 Auriga, the Charioteer. —
The first remarkable group that
catches the eye as we go from the
Pole along the Summer Colure,
is the beautiful consteUation of
Auriga, shown in fig. 23, which
Ues close to the Colure, on the
westem side. The brilUant star,
Capella, or the Goat, is the Lu-
<ada of this consteUation, near
which Ue three Uttie atara, caUed
Hiedi, or the kida. The two stars
below Auriga, in the figure, are
the tips of the homs of Taurus,
the BuU, one of the signs of the
Zodiac, The upper of these two
stars, together with a and |3 of Auriga, form an iaoaceles triangle, or with
two other smaUer stars, shown in the figure, make an irregular pentagon.
Thia pentagon is a remarkable object in the heavens, on account of CapeUa
and the Hsedi, which, once pointed out, are always recognised again imme
diately. 133 Taurus, the Bull. The Hyades and Pleiades. — The horns of Taurus,
aa we have atated, Ue below Auriga, a Uttle west of the Colure. Taurus con
tains the two groups, the Pleiadea and Hyadea, so often aUuded to in the
ancient poets (see fig. 24, on next page) ; the Hyades form the face of Taurus,
and the Pleiades the shoulder. The star, Aldebaran, is one of the Hyades ; it
ia of the first magnitude, but not brUUant. The Pleiadea are Tery smaU and
close together, hut they glisten with a remarkable degree of brightness ; only
six of them can be seen by most persons, but a good eye detects a seventh,
and Bometimea one or two more, and hence the story of the loat Pleiad. The
Pleiadea derive their name from irk^iv, to saU, because they were supposed to
indicate the season favourable to navigation ; they were called Vergilise by the
Latins. In Cicero's translation of Aratus we find : —
Farvas Vergilias tenui cum luce videbis
Hsec septem vulgo perhibentur more vetusto
Stellie cemuntur vero sex undique parvse.
' You will behold the little VergUise faintly shining. These are commonly
said to be seven in number, after the ancient tradition, but only six small
stars can be seen.'

Fig. 23

1

Western Side

•

Capella

•
a •
i
0 uii
II
Auriga
• •
e
Horns of TauniB
Gemini i
•
Orion
38

MATHEMATICAL GEOGRAPHY.

ft
Capellu

Fig. 21

Auriga

Fig. 25 shows a telescopic view of the Pleiades.

Fig. 25

^ The Hyades wcre aupposod to indicate rain, and hence thefr name, from
vciv, torain; they were, by a mistaken translation, caUed Suciila, or httle
pigs, by (he Latins, {Cicero dc Kaf. Deorum, Ub. ii. cap. 43 )
134 Orion.— Ths splendid consteUation Ues below the horns of Taurus,

THE CONSTELLATIONS.

39

close on the western aide of the Co
lure ; it is represented in fig, 26 ;
like the Hyades and Pleiades, it is
continuaUy aUuded to by the Greek
and Koman writers. The stars a
and j3, Betelgeux and Bigel, are of
the first magnitude ; y, or Bellatrix,
and the three stars which form
Orion's Belt, are of the second mag
nitude. The stars rj, «, and k form
the sword; close to t are a great
number of smaU stars, and a most
remarkable nebula, which had never
been resolved into stars untU Lord
Eosse's telescope was brought to
bear upon it.
135 Gemini, the Twins. — We
shall now briefly mention the con
steUations on the eastem side of the
Summer Colure. The consteUation
Gemini, shown in fig. 27, is opposite
the homs of Taurus, close to the
Colure on the eastern side. The
bright stars, a and j3, Castor and
Pollux, were anciently much noticed,
especiaUy by mariners. Gemini is
one of the signs of the Zodiac.
136 Canis Minor, the lAttle Dog.
—Under Gemini, but more to the
east, is Canis Minor, which contains
only two stars that are readUy no
ticed by the eye. One of these, a,
or Procyon, is a brUUant star of the
first magnitude. See fig. 27.
137 Canis Major, the Great Dog.
— Some way farther downwards,
close to the Colure, and on the
eastem side, is the celebrated con
steUation, Canis Major, containing
the brightest star in the heavens

FiR. 26

Horns of Tavirus

Solstice Ecliptic

Sun's Motion

Betelgeux

• Bellatrix

Orion

t £quator

aigel

Fig. 27

FoUux •
•

Caator • u
•
s

•

0

1 \
• 1

1 0
0

•
V
Sol3tice_|_
•
9
• \
?
/*
n \
•
•
e
I'rocyon
•
•
Canis Minor
40

MATHEMATICAL GEOGRAPHY.

Fig. 28

Sirius
•

•

•^

Canis Major

•
•
s

•3o

o
•

•
•
•
TJ
*
Sirius, or the Dog Star. See fig. 28.
The star Aldebaran of the Hyades,
the Belt of Orion, and Sirius, are
nearly in the same straight line.
There is no possibUity of missing
Canis Major, if we look a httle below
Orion, and somewhat to the east
of it. 138 In ancient times, the dog
days, which commenced when Sfrius
rose at the dawn of day, were con
sidered to be most fatal in producing
fevers and madness ; but these days
are chiefly to be noticed on account
of thefr chronological importance
with reference to the Annus Magnus,
or Great Year, of the Egyptians.
We have the following passage from
Censorinus, (Cory's Ancient Frag
ments) -. —
' Ad .^Igyptiormn vero magnum
annum luna non pertinet, quem
Grseci Kvvikov, Latine Canicularia vocamus. Propterea quod initium UUus
Bummitur, cum primo die ejus mensis, quem vocant .Sgyptii Bad, Caniculae
sidus exoritur,' &c. &c.
The substance of what he says is this: — That the Great Year of the
Egyptians was not determined by the Moon, but by the fact of thefr civil
year containing always 365 days, without any leap year, which caused a slow
change of the seaaona, in consequence of the year being nearly six hours
shorter than it ought to have been. This change was completed in 1461
years, at the end of which period the seasons aU came back to thefr proper
places in the year. This period of 1461 years was called the Great Tear;
also, by the Greeks, the Cynic, or Dog Tear ; and by the Latins, the Cani
cular Year, because it began when the Dog Star rose at dawn, on the first
day of the Egyptian month Thoth. But the year which Aristotie calls the
Greatest, rather than tlie Great, ia that in which the Sun, Moon, and planets
aU return and come together in the same sign of the Zodiac from which
they originaUy started. The winter of this year is the Cataclysm, or Deluge,
the summer is the Ecpi/rosis, or Conflagration of the World.
Tlieon of Alexandria gives an example of a formula for finding the nsing
of the Dog Star, entitled, IIEPI -njs roi kwos e7r«ToX^s v7rdS«y/«i.
The connexion between astronomy and chronology that is thus established
by the numerous references of ancient writers to astronomical phenomena,
is most interesting and important, inasmuch as astronomy can as accu
rately teU the past, as predict the future motions of the heavenly bodies,
and therefore it oecomes an instrument for penetrating tiirough the dimness
of antiquity. 139 Summer Solstice — Ecliptic — Equator. — The echptic 11ms midway
between the Hyades and Pleiades, also between the horns of Taurus. The
solstitial point is close to the stars r/ aud /u Geminorum. Tho equator runs
through the top star of Orion's belt very nearly, a Uttie beyond which, towards
Procyon, is the point of the equator wliich is 90° from each equinox.
VII. Begion ofthe Heavens along the Autumnal Colure.
140 Canes Venatici, the Hounds. — The Autumnal Colure is drawn from
the Pole towards the taU of Ursa Major ; it runs between y and S Ursse Ma
joris, close by S, On the eastern side of tiiis Colure, nnd immediately below
the taU, are the two Hoimda of Bootes, fig. 29, in the neck of one of which is
the star often caUed Cor Caroli, the Heai-t of Charles (II). These hounds do
not belong to the ancient constellations.
THE CONSTELLATIONS. 41

Fig.

;u

•
. s
. /3
• •
•
•
•
^ Cor Caroli
i
•
.
•
•
•
Arcturus
•
a
•
."
141 Bootes, the Herdsman, is made up of the bright stars to the east and
south east of Cor Caroli, among which Arcturus ahines conspicuously. (See
fig. 29.) Arcturus is found by drawing an imaginary line through ^
Ursse Majoris, which runs a little above Cor CaroU, and, farther on, a Uttle
below Arcturus.
142 Coma Berenices, the Hair of Berenice. — A group of small, bright stars
•lose on the eastern side of the Colure, and due west of Arcturus, See fig. 31.
42

MATHEMATICAL GEOGRAPHY.

143 Leo, the Lion. — One of
the signs of the Zodiac on the
west of the Colure, and opposite
ArctuTOS. (See fig. 30.) aLeonis,
(which is also called Cor Leonis,
the Lion's Heart, and Eegulus,)
is a star of the first magnitude.
^ Leonis is caUed Deneb, or the
TaU ; it is within 5° of the Colure,
144 Virgo, the Virgin. — An
other of the signs of the Zodiac,
immediately under Coma Bere
nices, and aU, except a few stars,
lying on the east of the Colure —
see fig. 31. The star a of this con
steUation is caUed Spiea, or the
ear of com, and is of the first
magnitude. Arcturus, Eegulus, and Spica
being joined by imaginary hnes,
form a right-angled triangle, hav
ing the right angle at Spica : which
fact being remembered, wiU pre
vent any mistake about the posi
tion of these stars.
145 Autumnal Equinox — Ecliptic — Equator. — The autumnal equinoctial
point is close to i; Vfrginis, fig. 31. The echptic runs through Eegnlus, and
nearly through, but a little above, Spica. The equator is shown in the figure,
passing through r) Virginis nearly.

Fig. 31 .' I I
Coma 1^
Berenices • [^ , •
* . ' . I 'rail
I of Leo
1 *^
£ • I I •
I •
s. I
Virgo ] • ^,-'
Equator  _  •  ^J-llI 
• y ^^^^ \ Autuinnai
^,-'' 1 Equino.^
• -^' '
^'^^
..--^ I
-' Splca ]
• a

VIII. Begion ofthe Heavens along ilie IVintei- Colure.
146 Lyra, the Lyre ; and Cygnus, the Swan. — The winter Colure is drawn
from the Pole nearly through y in the Dragon's Head ; farther on, we come
upon Lyra, in which is the bright star Vega, of the first magmtude. Lyra
is near the Colure on the eastern side ; Cygnus is east and somewhat north-
cast of Lyra, not far from Cepheus. ITie five brightest stars of Cygnus
form a croaa, of which a, or Deneb, thc taU, is of the first magnitude. Lyra
and Cygnus are ahown in fig. 33.
147 Hercules, and Corona Borealis, the Northern Crovm. — Hercules
includes the stars opposite and a Uttle south of Lyra on the other — i, e,, the
western side — of the Colure. West of these is Corona BoreaUs, which is
nearly a cfrclel of stars, one, a, being of the aecond magnitude, (see fig. 33,)
a Herculis is a variable star.
- 148 Aqnila. the Eagle; and Delpldnus, the Dolphin.— Some'viha.i south
of Cygnus and Lyra, on Ihc eastern side of the Colm-e, we find Aquila and

THE CONSTELLATIONS.

4.3

•

Fig. 38
•
• »
•
•
•
Drauo •
•
7
m
s
•
Cygnufc
Vega
•
a •
•
•
•
(3
'• 5
Lyra
fe
Fig, 33
1 •
«
m •
Bootes
Lyra
o
• 1
Corona
Borealia
• a
• -V
•
1 c
•
•
s
a
1 •
• j .
11 - s
^.^^^
•
•
T
1 ¦
• j
ma
•
Serpens
1 • «
1 Ophiuchua
44

MATHEMATICAL GEOGRAPHY.

Delphinus, fig. 34. The stars of
Delphinus are very bright, though
small, and form a diamond-ahaped
figure, a AquUse, is a star of the
first magnitude ; it is caUed Altair.
The three stars, 0 a and y AquUae,
(which are in a line,) with the dia
mond-shaped and glistening Del
phinus, are remarkable objects in
the heavens, and not likely to be
forgotten when once seen.
140 Ophiuchus, the Snake Holder; and Serpens, the Snake.— These two
constellati^s Ue on the east of the Colure below Hercules, and mclude a
number of bright stars. See fig. 35.

*.*. ^eW-^"'

Fig. 34 Aquila

•

• Altair

•

I Fig. 30 'a Hercules
j •
I a •
\ •
£1 • .iS
t Equator *
I .;
[ Opbiuchu9 «
I part of Serpens
I •
j •
I Sagittarius.
I Winter Solstic
I EoUpUc • *^''

150 Libra, the Balance; Scorpio, Sagittarius, and Capricomus. — These
are four of the signs of the Zodiac. Scorpio and Sagittarius are shown m
fig. 36. a Scorpionis is a star of the first magnitude, called Ant ares.
Sagittarius la cloae on the east of the Colure, and Scorpio somewhat
farther oflT on the west, Scorpio is a remarkable consteUation, and easUy
recognised, 151 Winter Solstice — Ecliptic — Equator. — The ecUptic rims between
^ and S Scorpionis, and a few degrees below (i SagittarU, immediately under
which star is the winter solstitial pomt. The equator Ues about 8* below
Altair. ^ ^
152 We havo now sufficiently pointed out the position and appearances
of a sufficient number of the principal consteUations, in such an order that it
will be easy to find tiiem out and remember them. Wc have dwelt at some
length on this part of thc subject, because mere maps or figm-cs of the con-

THE CONSTELLATIONS. 45

/ Fig. 30

-•-. f- /

0
• '^ >^„,^
\
/ ° ""^^^
/ ¦»¦
/ ?
/ •
• /
f /
'^'-.^
/ •
/
• /
/ • \
^^
,p
"V •
steUations, without any remarks respecting them, do not produce much efi'eet
on the memory. Por complete and accurate information, we may refer the
reader to the six maps of the stars published by the Society for the Difliision
of UsefiU Knowledge, and to Smyth's Celestial Cycle, vol. u. We shaU
conclude this chapter with a few words on the stars and consteUations which
come on the meridian at certain hours at diff'erent times of the year.
IX. Constellations visible on the Meridian at different Hows ofthe Night,
and at different Seasons ofthe Year.
153 It is easy to make out what stars are on the meridian at midnight at
any particular time of the year, by considering the position of the Sun m the
heavens : thus, at the Vernal Equinox, the sun is on the Vernal Colure, and
tiierefore at midnight, when the Stm is on the meridian below the horizon,
the Vernal Colure must be so also, and therefore the Aulumnal Colure must be
on the meridian above the horizon. Hence aU the stars lying along the
Autuinnai Colure wiU be on the meridian at midnight at the v emal Equinox.
It is also easy to make out what stars are on the meridian at any other
hour, by making the proper aUowance for the diurnal rotation ofthe heavens,
154 The foUowing table exhibits the conateUations visible on or near
the meridian at nine o'clock, (three hours before midnight,) at different times
ofthe year.
46

MATHEMATICAL GEOGRAPHY.

Third week in March.

Head of Ursa Major. Cancer. Head of Leo. Eegnlus.
C!or Hydrae.

A

April.

The Pointers. Deneb. Tail of Leo. Coma Berenices.
Head of Virgo.

B

May.

Tail of Ursa Major. Cor Caroli. Bootes. Arcturus.
Coma Berenices. Virgo. Spica.

C

„ June.

Body of Ursa Minor. Bootes. Corona Borealis. Head
of Serpens. Libra.

D

July.

Tail of Ursa Minor. Head of Draco. Hercules. Ophiocbns
and Serpens. Scorpio.

£

August.

3 Draconis. Cygnus. Lyra. Vega. Aquila. Altair.
Sagittarius.

P

„ September,

Cepheus. Tail of Cygnus. Delphinus. Head of Fegasns.
Aquarius. Capricomos.

G

October.

/3 Cassiopese and Head of Cepheus. Scheat. Markab.
Pegasus. Pisces, (westem fish.) Tail of Cetns.
Aquarius. Fomalhaut.

H

„ November.

S and y Cassiopeae. Andromeda. Aries. Pisces, (eastem
flsh.) Alpherat. Algenib. TaU of Cetus.

I

„ December.

Perseus. Algol. Pleiades. Aries. Head of Cetns.
Eridanus.

J

„ January.

Capella, Auriga, Hyades. Gemini. Canis Minor.
Orion. Canis M^or.

K

„ February.

Gemini. Castor and Pollux. Canis Minor. Procyon.
Canis M^jor. Sirius.

L

155 We have chosen nine o'clock in the above table as a convenient hour,
for observing the stars, instead of midnight, which would be rather late foi?;
most pecmle. Tbe table may, howcTer, be easUy adapted to any hour by
means of the foUowing, in which ABC &c, denote the constellations in
the above table.
Table showing the Constellations on or near the Meridian at different J
Hours in different Months. ; ..ja

EVENING.

1  '  ~^^
MORNING.

''

e
o'clock.

7
o'clock.

9
o'clock.

11
o'clock.

I
o'clock.

s
o'clock.

s
o'clock.

o'ao(k

March . .

K

L

A

B

C

D

e:

P

April . .

L

A

B

C

D

E

F

G'

fill

May. . ,

A

B

C

D

E

F

G

H*^

i

June . .

B

C

D

E

F

G

H

I

July. . .
c
D
E
P
G
H
I
J
August . ,
D
E
F
G
H
I 1 J
K
THE CONSTELLATIONS.
Table — continued.

47

EVENING.

MORNING.

6
o'clock.

7
o'clock.

9
o'clock.

11
o'clock.

1
o'clock.

3
O'clock.

6
o'clock.

7
O'clock.

September.

E

F

G

H

I

J

K

L

October

F

G

H

I

J

K

L

A

November .

G

H

I

J

K

L

A

B

December . H

I

J

K

L

A

B

C

January .

I

J

K

L

A

B

C

D

February . j J

K

L

A

B

C

D

E

For example: What conateUations wUl be on or near the meridian at
seven o'clock in February ? Looking in the column under seven o'clock, we
find K opposite February; and therefore jTeferring to the former table, to see
what consteUations are represented by K, we find that CapeUa, Auriga, the
Hyades, Gemini, Canis Minor, Orion, Canis Major, wUl be on or near the
meridian at the time specified. X. ^gns of tlie 2^diae.
156 As the motions of the Sun, Moon, and Planets take place among
these consteUations, it is necessary to say something respecting them. The
Zodiac is the celestial region lying along the EoUptic;it8 name is derived
from £tiSiov, zodion, a little animal, because its different parts are marked by
figures' of animals. Fig. 37 shows the animals as represented on the ceiling of

48

MATHEMATICAL GEOGRAPHY.

an apartment in the Temple of Denderah in Egypt, which we may conclude,
from inspecting the ceihng, was adomed witii these curious figures about
700 B.C. See Penmy Cyclopcedia, Art. Zodiac, where an account of the ceU
ing is given, together with information respecting the ancient consteUations.
157 The order of the Zodiacal
signs, and the symbols by which
they are represented, are as fol
lows : —
Aries, the Ham . . . . (yi
Taurus, the Bull . . . \i
Gemini, the Twins . . . n
Cancer, the Crab ... 93
Leo, the Lion • • • . SI
Virgo, the Virgin . . . rqj
Libra, the Balance . . . &
Scorpio, the Scorpion . . m
Sagittarius, the Archer . f
Capricomus, the Goat . vjp
Aquarius, the Waterman . ^
Pisces, the Fishes ... X

Fig. 38 -/3

•

• •

Libra

•

a •

. ../ .

• •

We have already spoken of the
stars composing all these constel
lations, except Cancer, Libra, and
Capricomus, which are shown in
figs. 38, 39, and 40.
Fig. 39
Aquarius
a ,
•
• •
•
•
•
•
*
*
«
•
c*^'^^'*
, •
•
•
•
•
Sagittarius
158 In all the above figures of the constellations we have represented
the principal stars only, generaUy aU as far as the fourth magnitude, but
sometimes as far as the fifth, where such stars were necessaiy to be put down,
in order to make it easy to find out the consteUation in the heavens.*
• The different magnitudes of the stars are not represented as aoonrately as in the drawings
sent to the engraver, but there are uo errors of any consequence. In a few ofthe figures the
constellations are a little distorted in shape.
ASTRONOMICAL TERMS EXPLAINED. 49

CHAPTER III
ASTEONOMICAL TEEMS EXPLAINED. — MEASUREMENT
OE TIME.
BEFOEE we proceed to the practical appUcation of Astronomy, it wUl be
necessary to explain the meaning of certain terms constantly made uae
of in the science, whereby the positions and the motions of heavenly bodies
are defined, and to describe the different measures and periods of time, which
is so important an element in astronomical observations and calculations.
I. Terms relating to Veridical and Horizon
1 60 Vertical. — When a body is aUowed to fall towards the Earth's
surface, it describes a straight Une tending towards the c^tre of the Earth
nearly. We say nearly, because, on account of the Earth not being exactly
spherical, bodies do not fall exactly towards the centre. The motion of
falling bodies is produced by the attraction of the Earth, or the attraction of
Gravi^, as it ia caUed. If the body, instead of being aUowed to faU, is sus
pended by a string ,the string shows the direction in which the body would
laU, if aUowed to do ao, because it shows the direction in which the force of
gravity puUa the body.
The straight line which a falling body describes is caUed the Vertical or
Vertical Direction, This direction is determined by auapending a heavy
body, such as a piece of lead, by a string, and then the string wUl show the
vertical. A string thus used is called a plumb line (trom pl-umbum, lead).
161 The vertical ia, then, the direction in which the force of gravity
acts, and therefore Astronomers always determine or observe the Tertioai

50 MATHEMATICAL GEOGRAPHY,
du-ection by meana of the force of graTity. We must remark, howerer, fchat
in the neighbourhood of large mountain masses, especiaUy where there is a
flat country on one side, ancl moimtains on the other, the direction of the
force of gravity ia sensibly, though very sUghtly, affected by the attraction of
the mountains. In this case the plumb Une is aaid to be drawn out of the
proper Tertical, which is considered to be the direction in which the force of
gravity would act, if the ground were on aU sides perfectly level. We must,
therefore, in defining the vertical to be the direction in which a plumb line
hangs, add, that the Earth'a surface is supposed to be perfectly level, or, in
other words, to be the same as the surmce of the ocean would be if it
covered the whole Earth.
162 We must also observe, that when a body is aUowed to faU from a
very considerable height, it falls a Uttle eastward of the tme vertical (as
shown by a plumb Une), in consequence of the Earth's rotation about its
axis. The deviation from the vertical is, however, extremely smaU.
163 Horizontal. The plane to which the vertical Une is perpendicular
is caUed the Horizontal Plane. The surface of stUl water, or any other fluid,
such as mercury, shows the horizontal plane, provided it be of Umited
extent : for fluitt surfaces of considerable extent are sensibly curved, aa we
see in the case of the ocean. Astronomers employ thia property of fluids to
determine the horizontal plane, as we shall presently explam when we come
to speak of the Spirit Level, and the method of obserring heaTenly bodies
reflected in a trough of mercury.
164 ETery plane containing the vertical Une, or, what is the same thing,
every plane perpendicular to the horizontal plane, is caUed a Vertical Plane.
The intersection of two vertical planes is therefore a vertical line.
16s Zenith and Horizon. — We have, in the previous chapter, explained
what the celestial sphere is, and what great circles and smaU ciroles are. The ;
points of the celestial sphere, where the vertical line produced meets it, are
caUed the Zenith and Nadir (terms of Arabic origin), the zenith being the
point of the celeatial aphere exactly over the obaerver's head, and nadir the
opposite point beneath his feet.
166 The horizontal plane cuts the celestial sphere in a great circle,
which is caUed the Horizon. The word was originaUy apphed to the circle
whioh sensibly boimds the view of a spectator at sea, or on a height, and
hence the word is derived from the Greek opi^a, to bound or hmit.
The Horizon ia therefore a great circle of the celestial aphere, the poles
of which are the zenith and nafir. Every point of the Horizon is 90° from
the zenith.
167 Meridia/n. — That vertical plane in which the Earth's ayis of rotationhes
is caUed the Meridian Plane, or Plane ofthe Meridian : and the great cirde'
in which this plane cuts the celeatial sphere is caUed the Meridian. The
Meridian is therefore the great circle which passes through the North and
South Poles and the Zenith. The name
is derived from the Latin word si^ufying
half-day, or mid-day, because it is mid
day when the Sun crosses the Meridian,
168 Altitude and Azimuth. — Let
ABC, fig, 41, represent half the Hori
zon, P and Q Qie North and Soutii
Poles, Z and N the Zenith and Nadir,
and A P Z C Q N the Meridian: let S
denote the position of any star on the
celestial sphere, and let a great circle be
drawn throng Z and S meeting the ho
rizon at S', Then the circular arc S S'
expressed in degrees, minutes, and se
conds, is oaUed the Altitude of the star S,
and the circular arc A S', expressed si
mUarly, is caUed the Azimuth of ihe star.

ASTEONOMICAL TERMS EXPLAINED.

51

The arc Z S, in degrees, minutes, and seconds, is caUed the Zenith Distance
of the star ; Z S is the complement of S S' — i. e., Z S added to S S' completes
or makes up 90°.
Since the circular ai'c S S' shows how high the star is on the celestial
sphere above the horizon, it is properly caUed the Altitude of the Star. Tho
word Azimuth is a corruption of an Arabic word signifying ' the way' or ' dis
tance,' meaning thereby the number of degrees, minutes, and seconds we
must go along the horizon ABC, from the point A, in order to get to S',
which point marks the vertical plane in which the star is.
169 The position of a star on the celestial sphere is completely defined
by stating its altitude and azimuth ; for example, if the altitude of the atar
be 30° and its azimuth 50°, we find the place of the star by measuring along
the horizon from A, a circular arc A S' equal to 50°, then from S' drawing a
great circle to Z, and measuring S' S equ^to 30°, which wUl give the place of
tiie star S.
170 It is important to remember that the great circle Z S S' N shows on
the celeatial sphere the vertical plane in which the star is ; for this ch'cle, since
it passes through the zenith and nadir, Z and N, Ues in a vertical plane, and
therefore shows on the celestial sphere the vertical plane in which the star is.
We shaU apeak of this plane as the plane Z S S' N.
171 The arc A S' mows the angle which thia vertical plane makes with
the meridian plane ZAN; for, if we conceive the semicircle Z S' S N to turn
about the points Z and N, the point S' starting from A and moving towards
B, itis clear that the number of degrees, minutes, and seconds through which
the point S' moves along the horizon, show the number of degrees, minutes,
and seconds through which the vertical circle or plane Z S S' N turns about
the points Z and N, or, what ia the same thing, the angle of inclination of the
plane Z S S' N to the plane of the meridian.
The angle at Z, which the two circles Z P A and Z S S' make with
each other, also shows the incUnation of the plane Z S S' N to the plane of
the meridian ; for, conceiving the plane Z S S N to turn as before, it is clear
that the number of degrees, minutes, and seconds, in the angle at Z, which
the arc Z S S' makes with Z P A, shows the number of degrees, minutes, and
seconda through the plane Z S S' N turns about Z — i. e., ita inclination to the
plane of the meridian.
Hence the azimuth of a star shows the inclination of the vertical plane
in which the star ia to the meridian plane, or, what is the same thing, the
angle which the zenith circle of the star makes with the meridian.
Bythe zenith circle of a star, we mean the great circle passing through the
zenith and the star.
172 Prime Vertical. — The vertical plane, which is perpendicular to the
plane of the meridian, is called the
Prime Vertical Plane, smA-the gcea.t Fig. 42 ^ ^
circle in which thia plane cuta the
celestial sphere is called the Prime
Vertical ; in other words, the Prime
Vertical is the zenith circle, Z B N,
which cuts the horizon half way be
tween A and C, B being supposed to
be 90° from A.
173 Points of the Compass. —
A, fig. 41, is caUed the North Point
of the horizon, C the South Point,
B the East Pomt, and the point op
posite B (on the other half of the
horizon) the West Point. These are
generaUy known as the Points ofthe
Compass, which are represented in
fig, 42, the circle being the horizon,
and N E S and W bemg the north.

52

MATHEMATICAL GEOGRAPHY.

east, south, and west pomts respectively. There are altogether tiiirfry-two
pomts of the compass, at equal distances from each other, dividing each qua
drant of the horizon mto eight equal parta, each part being therefore one-eightli
of 90°— i. e., 11° 15'. Each of these diviaiona ia suppoaed to be further sub
divided into what are caUed Quarter Points, each containing 2° 48' 45", which
make the fourth part of 11° 15'. It may be weU to remember the foUowmg
table for one quadrant, whieh wUl apply to the other quadranta hy a simple
change of points and corresponding letters . —

Azimuth.

Corresponding Point of Compass.

0°
23° 30'
45° 67° 30'
90°

N. North Point.
N. by E. North by East.
N.N.E. North North East.
N.E. by N. North Bast by North.
N.E. North East.
N.E. by E. North East by East.
E.N.E. East North East.
E. by N. East by North.
E. East Point.

One point (i. e., 11° 15') East of North,
Half way between North and North East.
One pomt North of North East.
Half way between North and East.
One point East of North Eiet.
Half way between East and North East.
One point North of East.
90° from North.

174 It should be home in mind, that when a star is rising or setting, it
is 90 from the zenith ; and that the circumpolar motion of the heavens causes
aU the heavenly bodiea which are at a sufficient distance from the Pole to
cross the horizon twice in twenty-four hours, ascending or rising on the
eastern side, and descending or setting on the weatem side.
II. Terms relating to Pole and Equator.
175 In the same manner that we define the place of a star with reference "
to the zenith and horizon, we may do also with reference to the Pole and
Equator, by means of what are caUed Bight Ascension and Declination, as we
shaU now explain.
176 Let P and Q (fig. 43) repreaent the north and south Poles, E A S' G
half the Equator, PE Q G the meridian, S
any star, A the Vernal Equinoctial point of
the Equator, P A Q a great circle paaaing
through P A and Q, P S S' Q a great cirde
passing through PS and Q, and cutting
the Equator at S'. Every point of the
Equator is 90° from each Pole. A is the
pomt where the Sun crosses the Equator
m spring, at which time he is moving north
ward. A is usuaUy caUed the first point
of Aries, because m former times, when
these names were brought mto use, the
Vernal Equinoctial point was at the begin
ning of the consteUation Aries, the Ram.
At present the Vernal Equinoctial point,
in consequence of its slow motion, called the
, Tl, 1 Precession ofthe Equinoxes, is in the con
steUation Pisces, the Fishes. The name—' First point of Aries'— is, however,
atUl used to denote the Vernal Equinoctial point.
177 It is from this point that aU distances along the Equator are measured,
just as we haTe meaam-ed diatancea along the horizon from the nortii pomt.
It should be remembered that this point moTes round the Pole in twenty-foui
hours with the reat of the heavens, crossmg tiie meridian when it comes to E,
and again when it comes round on the other side to G, the motion being
in the direction represented by tiie arrow in the figure. The imagmaiy

ASTRONOMICAL TERMS EXPLAINED. 53
circles P A Q and P S S' Q are of course supposed to be carried roimd by the
circumpolar motion, always keeping at the aame diatance from each other.
178 The great circlea P A Q and P S S' Q, may be caUed Polar Circles,
aince they paas through the Poles ; and the planes in which these circles Ue
may be called Polar Planea. The polar circle P A Q is the Vernal Colure,
which, as we have already stated, is the great circle passing through the Poles
and the Vernal Equinoctial point, or First Point of Arica, as it is caUed.
1 79 Bight Ascension and Declination. — The circxUar arc A S' is called the
Bight Ascension oi ihe star S, andthe circular arc S' S ia caUed its Declination.
The arc P S is the complement of the declination, and is caUed sometimes the
co-declination, but more frequently the Norih Polar Distance of the star.
Eight Ascension and DecUnation completely determuie the positions of
heavenly bodies on the celestial sphere ; thus, for example, if the right
ascension of a star be 20° and the declination 40°, we find its position by
measuring from A an arc A S' of 20° along the Equator, then dravring a great
circle from S' to P and measuring upon it an arc S' S of 40°, whioh wiU give
S, the place of the star.
180 It is important to remark that right ascension is always measured
from A, not in the direction of the arrow (fig. 43), but in the contrary direc
tion. The reason of this is, that the Earth and planets move round the Sun
and round their axes in the same way that we measure right ascension — i. e.,
contrary to the way in which the arrow points, which, as we have stated,
indicatea the direction of the apparent motion of the heavens caused by the
real motion of the Earth round its axis in the opposite direction.
181 Declination is always expressed in degrees, minutes, and seconds ;
it is, so to speak, the altitude of the star above the Equator, or, we may say,
the number of degrees, minutes, and aeconda by which the star declines from
the Equator, using the word ' dechne' in its original signification of ' turning
aside.' 182 If the atar is below the Equator, as at T (fig. 43), S T ia the dech
nation of the star, and it is caUed south declination, because measured towards
the South Pole, the declination of S being caUed north dechnation, because it
is measured towards the North Pole.
183 The right ascension of a star is the distance, from the first point
of Aries, of the point where the polar circle, in whioh the star is, cuta the
Equator. The right ascension of a star shows alao the angle which the polar
plane, in which the star is, makes with the plane ofthe ^rnal Colure. The
angle at P, which the two circular arcs A P and S P make with each other,
contains the same number of degrees, minutes, and seconds that the arc A S'
does (which may be easUy seen as in the caae Azimuth, previously explained) :
hence the angle, which the polar circle passing through the star makes, at
the pole, with the Vernal Colure, shows the right ascension of the atar. The
polar circle paaaing through a atar ia often oaUed ita dechnation circle.
184 The right ascension of a heavenly body is often, or rather, generaUy,
expressed in time, at the rate of one hour for 15° — (i. e., twenty-four hours
for 360°), since the heavens turn roimd the Pole at this rate, every star
describing 15° of ita circular course in an hour. The feason of expressing
right ascension in time wUl appear aa we go on, eapeciaUy when we come to
speak ofthe transit instrument.
Thus, if we say that the right ascension of S is four hours, we mean that
AS' corresponds to four hours — i. e., that A S' contains four times 15°, or 60°.
A right ascension of six hours ia 90°, of twelve houra 180°, of eighteen hours
270°, and of twenty-four hours 360°, which brings us round the whole equator.
185 If the right ascension of S be four hours, A wUl evidently come on
the meridian at E four hours before S', for the space A S' wiU be described in
four hours, in consequence of the circumpolar rotation. Hence, obaerving
that S and S' come on the meridian at the aame inatant, we may define right
ascension as foUows : —
The right ascension of a star (expressed in hours, minutes, and seconds,) is

54

MATHEMATICAL GEOGRAPHY.

the time that elapses between the transits acroaa the meridian of the flrst
point of Aries and the star. If the star crosses the meridian two hours, ten
minutes, and eight seconds after the first point of Aries, its right ascension
ia two houra, ten minutes, and eight seconds, or briefly, 2" 10"" 8'.
The Transit Inatrument, of which we shaU speak fuUy in a fature chapter,
is nothing more than an instrument for observing the times at which heavenly
bodies cross the meridian, or, aa it is aaid, the transits of heavenly bodies. It
is perhaps the most accurate and important instrument used by astronomers. •
i86 Origin of the terms Bight and Oblique Ascension. — These terms
often occur in astronomical books, but
the latter haa now fallen into disuse.
They have reference to the times of rising
of heavenly bodies, as shown by the ce
lestial sphere in what are called its right
audits oblique positiona. When the poles
are in the horizon, aa is the case when
the observer ia on the Earth's equator,
the sphere is said to be a right sphere,
for then aU the heavenly bodies rise at
right angles to the horizon. Fig. 44
representa a right aphere, P and Q being
the poles, PBQ the horizon, S' S the
circular course of any atar, which is evi
dently at right angles to the horizon at
the point S', where the atar rises. In
. . this caae, the time elapsing between the
rising of the first point of Aries and that of the star, was caUed the right
ascension, — i. c, the time of the ascension of the star above the horizon in
the right position of the sphere.
When the poles, P and Q, are not in
the horizon, ABC, fig. 45, the stars
cross the horizon obUquely when they
rise. In such a case the sphere is said
to be oblique, and the time of ascension
was caUed obUque ascension.
187 Hour Angle. — The angle which
the polar circle, P S S', fig. 43, makes at
the pole, with the meridian, PE, is caUed
the hour angle of the star S', because, if
reduced to time, at the rate of 1 hour
for 15°, it shows what time must elapse
before the atar crosses the meridian. The
number of degrees, minutea, and seconds,
in this angle, ia evidently the aame as in
the arc S' B.
188 Latitude and Longitude ofa Place. — The temis latitude and longi
tude, with reference to a place on the Earth's surface, correspond to dechna
tion and right ascension, with reference to the celestial sphere. The Earth's
surface, supposed to be spherical, is caUed the terresti-ial sphere ; the terrestrial
equator is the great circle of the terrestrial sphere, every point of which is 90°
from each ofthe terrestrial polea. The latitude of a pomt on the terrestrial
sphere is the same thmg as its dechnation ; the longitude the same thing as its
right ascension, with this difference, that the longitude is not measured from
the first point of Ariea, but from some fixed pomt of the terrestrial equator.
189 But this way of defining latitude and longitude is not sufficiently
exact, taking mto account the fact that the Earth's surface is not spherical.
Wo must define these terms with reference to the celestial sphere m the fol
lowing manner : — ^
Every pliuo on Iho Earth'a surface may bc considered as marked uponthe

ASTRONOMICAL TERMS EXPLAINED.

55

celestial sphere, by that point of the celestial aphere which is verticaUy over
the place, — i. e., by the zenith of the place. The zenith of London marks the
position of London, that of Paris the position of Paris, and so on ; in fact, a
correct map of the Earth's surface would be formed on the celestial aphere by
marking the zenith of every place, and so tracing out on the celestial sphere
the Tanous coasts and boundaries of countries, the Tarious towns, &c. &c., by
their zeniths.
igo Taking, then, the zenith of a place as the point representing that
place on the celestial sphere, we define latitude and longitude aa foUowa : —
The latitude of a place is the declination of its zenith ; the longitudo of a
glace ia the right ascenaion of its zenith, measured, howcTcr, not from thc
rst point of Aries, but from aome particular meridian, such as the meridian
of Greenwich. Longitude is not measured from the first point of Aries,
because that point is always moving over the Earth'a aurface, and longitude
meaaured from it would be an ever varying quantity.
191 In 6e. 46, P and Q represent the
polea ; E Z' F, the equator ; G, the zenith
of Greenwich ; P G E F, the meridian of
Greenwich; Z, the zenith of any other
place ; P Z Z' Q, the meridian of the place ;
then the arc Z Z' is the latitude of that
place, and E Z' is its longitude.
192 The apparent motion ofthe heavens
takes place in the direction ofthe arrow,
and it must be remembered that the meri
diana P Z Q, and P E Q F, must be aup-
Eosed to be fixed, whUe aU the heavenly
odies appear to be carried round by the
circumpolar motion. Since this motion takes
place at the rate of 15° per hour, it is evi
dent that, if the longitude of the place be
15°,— i. e., if E Z' be 15°, every star wiU
cross the meridian of the place, E Z Z' Q, one hour before it croaaes the meri
dian of Greenwich, P G E Q ; if the longitude be 30°, every star wUl cross
the former meridian two hours before the latter ; if 45°, three hours, and so on,
193 Longitude, thua considered, is
measured towards the east, and is caUed
east longitude , K measured towards the
west, it is caUed west longitude.
194 The Altitude of the Pole at any
place shows the Latitude of that place. —
For let P, fig. 47, be the pole ; Z, the
zenith ; A B C, the horizon ; E B F, the
equator -. then E Z is the latitude of the
place; E P is 90°, also Z A is 90°;
therefore E Z=90°— Z P, and P A^gO"
— Z P ; therefore P A=E Z.
Now, P A is the altitude of P above
the horizon ABC; hence the altitude of
the pole is equal to the latitude of the
place. 195 The circular arc Z P is caUed
the co-latitude, or the complement of the latitude, because with the latitude
it makes up or completes 90°.

56 MATHEMATICAL GEOGRAPHY.

III. Of Time, Sidereal and Solar.
196 Sidereal Time. — The most accurate obserTations show that the ap
parent circumpolar motion of the heaTens is perfectly uniform, always taking
place at the rate of 15° m an hour, 15' in a mmute, 15" in a second. ^ Indeed,
we may conclude from mechanical considerationa, that the Earth's niotion
about its axis, and therefore the circumpolar motion ofthe heavens, is uniform.
From thia uniformity of motion, CTery star may be used as a clock to indicate
and measure time, proTided we haTe proper instruments for observing the
motion of the star.
197 Time, measured by the motion of the stars, is caUed sidereal time;
the interval of time in which, a star completes its revolution is caUed a sidereal
day; the twenty-fourth part of that interval, a sidereal hour. We muat, of
course, choose some particular star or point of the heaTens to mark the
sidereal hours by its motion ; the first point of Aries is that fixed upon for
this purpose. When the first point of Aries is on the meridian, it is 0 o'clock,
sidereal time ; when the first point of Ariea has moved 15° west of the meri
dian, it is 1 o'clock, sidereal tune ; when it has gone 30° west, it is 2 o'clock;
90°, 6 o'clock ; 180°, 12 o'clock : 270°, 18 o'clock. Astronomers generally go
on from 12 o'clock to 13 o'clock, 14 o'clock, &o., up to 24 o'clock, when a new
day commences.
198 Hence the sidereal time at which a star crosses the meridian is evi
dently the right ascension of the star expressed in time ; for, as we have
shown above, the right ascension of a star, expressed in time, is the number
of hours, minutes, and seconda that elapae between the transit of the first
point of Aries and the transit of the atar ; therefore, when the star is crossing
tbe meridian, the first point of Ariea is that number of houra, minutes, and
seconds past the meridian, — ^i. e., the sidereal time is that number of hours,
minutes, and seconds past 0 o'clock.
199 Solar Time. — Solar time is time meaaured by the Sun's motion, in
the same manner as sidereal time by the motion of the first point of Aries.
The interval of time in which the Sun completes his revolution is called a
solar day, the twenty-fourth part of it a solar hour. Alao the solar day
commences when the Sun comes on the meridian.
200 Hence sidereal and solar time differ in two respects : First. The
sidereal and solar days commence at different inatants of time, for the Sun
and the firat point of Aries never cross the meridian together, except at the
vernal equinox, when the Sun coincides with the first point of Aries. We
have already explained the nature of the
Sun's proper motion, which carries him
backwards among the stars (i. e., contrary
to the apparent motion of the heavens)
about 1° each day, which corresponds to 4'
of time. Let P and Q, fig. 48, represent
the poles ; P E Q G, the meridian ; E A G,
the equator ; A, the first point of Aries ;
S, the Sun ; P S S' Q, the polar circle in
which the Sun is, intersecting the equator
at S'. Then S and S' wUl croaa the meri
dian at the same inatant, and therefore, with
respect to solar time, we may consider the
Sun to be at S' ; in fact, it will be 0 o'clock,
solar time, when S' comes on the meridian,
and the solar day wUl be the interval of
time in which S' completes ita revolution.
201 The arrow in the figure ahows the direction ofthe apparent diurnal
rotation of the heavens, which carries A and S' round and through 15° every
hour. But we must remember that, as the year goes on, the point S' is con-

MEASUREMENT OP TIME. 57
tinuaUy moving backwards, (i. e., contrary to the arrow,) in consequence of
the Sun's proper motion, completing the whole 360° in a year. The distance
of S' from A is therefore continuaUy increasing at the rate of about 1°
daUy ; for 1° is very Uttle greater than the 365th part of 360°, and therefore
the daily increase of the distance, A S', is about P daUy.
202 About the third week in March, S' wUl coincide with A, and there
fore, since both points cross the meridian together, it wiU be 0 o'clock, side
real time, at the same instant that it is 0 o'clock solar time.
In a quarter of a year afterwards, — i. e., in June, A 8' wUl be 90°, or 6", in
time ; therefore A' wUl cross the meridian 6 hours before S' ; in other words,
it wUl be 6 o'clock, sidereal time, when it is 0 o'clock, solar time.
In September A S' wiU be 180°, or 12" in time ; therefore it wUl be 12
o'clock sidereal time, when it is 0 o'clock solar time.
In December A S' wiU be 270°, or 18" in time ; therefore it vriU be 18
o'clock sidereal time, when it is 0 o'clock solar time.
203 Secondly. Solar time is longer than sidereal. For since S' moves
back about 1° eveiy day, it wiU cross the meridian about 4"" late every
day — ^i. e., 4°" later than it would do if it remained stationary in the heavens.
It is clear, therefore, that the solar day wUl be about 4" longer than the
sidereal day. This may also be ahown by considering what has just been
stated — namely, that in a quarter of a year (i. e., 90 days in round numbers)
after the equinox, it wiU be 6 o'clock, sidereal time, when it is 0 o'clock, solar
time. Hence 90 days, solar time, are equivalent to 90 days and 6 hours,
sidereal time ; and therefore, taking the 90th part of 90 days and 6 hours,
which is 1 day and 4 minutes, it appears that 1 day solar time is equivalent
to 1 day and 4 minutes sidereal time — i. e., the solar day is about 4"" longer
than the sidereal day.
204 Apparent and Mean Solar Time. — Solar time, defined as above by
the Sun's motion, is not regular and uniform as sidereal time ia. This arises
from two causes — first, the oval form of the orbit in which the Earth moTes
round the Sun, which makes the Earth moTe sometimes quicker and some
times slower, and therefore renders the apparent annual motion of the Sun
irregular ; and, secondly, the obhquity of the ecliptic to the equator makes
the interval between two aucceaaive tranaits of the Sun acroaa the meridian
longer at the aolstices and shorter at the equinoxes.
Trom both causea, the day shown by the Sun's motion is sometimes longer
and sometimes shorter. It would, of course, be very inconvenient to employ
the Sun's motion, suWeot to such irregularities, to mark time ; and yet, for
civil purpoaes, it would be quite as inconvenient to use sidereal time — e. g., in
March it is two hours past mid-day at two o'clock, sider aal time ; in July, it
is two hours before midnight at two o'clock, aidereal time.
205 To obviate these inconveniences, we use for civU purposes, a,nd in
astronomical observations also, what ia caUed mean solar time, which is no
thing but regulated solar time, the irregularities of the Sun's motion being
aUowed for and corrected. The word ' mean' signifies ' average ;' the length
of the mean solar day is the average length of the solar day : which is deter
mined aa follows : —
It is found by observation that the backward motion of the Sun, or rather
ofthe point 8', fig. 31, in the interval between two successive transits of the
Sun across the meridian, is, taking its average or mean length, not quite 1°,
but 59' 8", (we omit fractions of 1" ;) on some days it is greater than this, and
on aome daya leaa ; but ita average length in a great number of daya is 59' 8".
Therefore, considering the average niotion of the Sun only, and supposing the
Sun to be on the meridian now, it is clear that the heavens must turn round
59' 8" more than a complete revolution— i. e., 360° 59' 8", before the Sun
comes on the meridian again ; in other words, the average or mean length of
the solar day corresponds to a revolution of the heavens through 360° 59' 8",
which, expressed in sidereal time, at 15° per hour, 15' per mmute, 15" per
second, amounts to 25" 3'" 56i'. Hence it appears that the mean or average

58

MATHEMATICAL GEOGRAPHY.

solar day consists of 24" 3'" 56^' sidereal time, and is therefore longer than
the aidereal day by 3 minutes 56^ seconds. j- i i. ,,
2o6 A well-regulated clock shows mean solar time ; a sun-dial shows the
actual irregular solar time, or, as it is caUed, apparent solar time.
207 Equation of Time.— The equation of time is the number of minutes
and aeconda that muat be added to or subtracted from the apparent solar
time, or the time shown by a sun-dial, in order to make it equal to, or, as it is
said, to equate it to the mean solar time, or the time shown by a clock. The
equation of time is sometimes greater and sometimes smaUer ; sometimes it is
additive — i. e., to be added to the apparent time — and sometimes it is stib-
tractvoe. It is given in the almanac, often in columns headed 'Sun -too
slow,' ' Sun too fast,' or ' Clock after Sun,' ' Clock before Sun.' Thus, in
White'a Ephemeris for 1849, on March 30, in the column headed ' Clock
before 0,' we find 4" 33' ; which meana, that 4"" 33* must be subtracted
from the apparent time to get the mean time. Again, on November 4, in the
column headed ' Clock after ©,' we find 16"" 16', which means that 16"° 16'
muat be added to the apparent time to get the mean time.

CHAPTER IV.

METHOD OF SOLVING ASTEONOMICAL PEOBLEMS
BY CONSTEUCTION ON PAPER,
I. Instruments necessary.
WE have now sufficiently explained the meaning of astronomical terms
to enable us to proceed to the solution of a Tariety of interesting and
useftd problems. These problems may be solved in a rough way by means of
a pair of globes, and they are the principal problems usuaUy treated of in
what is called the ' Use of the Globes.' "rhey may be solved accurately by
mathematical calculation, deduced from the formulse and rules of that branch
of mathematics caUed ' Spherical Trigonometry.' We shaU now explain
a method of solving astronomical problema, which is at the same time
simple and exact, and requires no acquaintance with the technicahties of
abstract science. AU that is necesaary for the immediate appUcation of this
method ia a drawing-board, rule, compaaa, and graduated circle, or protractor,
for laying down and measuring angles on paper.
209 If a rough aolution of astronomical problems, such as that attainable
by the use of the globes, is aU that is required, these instruments may be of
a Tery ordinary description;
Fiff 49 a table wUl serve in place
of a drawing-board, and a
common graduated ruler or
brass semicircle wUl answer
perfectly weU for laying
down and measuring angles.
See fig. 49.
If, howeTcr, accuracy
is required, a good flat
drawing-board must be pro
cured, and the paper must
be atrained upon it, having
been previously damped ;
the ruler must be perfectly
straight, and should be
mado of hard metal; the

ASTRONOMICAL PROBLEMS.

59

points of the compass must be fine, and one leg ought to have an adjusting-
screw, for the purpose of opening the compass with great exactness to any
required distance ; and, lastly, the circle or protractor, which is ahown in
fig. 49, ought to be capable of measuring j,, ^ p
an angle accurately to a minute by meana °
of a Vernier, (which we shaU presently speak
about.) Eespecting the protractor, we may
observe here that it consists of a ^aduated
cttcle, E F G, fig. 50, and an arm P H I Q.
which tums round about the centre of the
graduated circle, carrying Verniers at G andF;
the centre is marked by the intersection of two
fine lines, A C and B D, generally drawn on
a smaU piece of plate-glass, A B C D, fixed in
the middle of the arm ; at P and Q are two
fine points, which may be pressed down on the
paper so as to mark it aUghtiy ; the line join-
mg these points pasaea through the centre of
the circle. **
2IO The use of this instrument ia as foUows : — Suppose it ia required
to draw a line through the point C, making an angle of 30° with the hne
A B. Place the protractor on the paper with the centre (i. e., the inter
section of the two lines dravra on the piece of
glaaa) exactly on the point C ; bring the points
(i. e., P and Q, fig. 50) exactly over the Une
A B ; then, by looking at the graduations on
the circle, turn the arm through 30° ; this being
done, mark the paper by pressing down the
points, and suppose E and D to be the two
marks ; then join E and D, and E D wUl be the
required line, making an angle of 30° with A B.
In Uke manner we might apply the instrument to meaaure the number of
degreea and minutea contained m any angle drawn upon the paper.
211 Thia inatrument, if weU made, is capable of great accuracy. We
may observe that, by always using the two points and reading off at the two
Verniers, we may entirely get rid of any error there may be, either in the
position of the centre, or in placing the centre on the point C, fig. 51 ; but we
have not space to say anythmg on this head.
212 In using the simple instruments ahown in fig. 49, we have only to
place the point M, which la the centre of the graduationa, upon C, fig. 51,
and the Une L N on A B ; then by looking at the graduationa we ahau see
what angle C D makes with C B.
The rnethod we are abont to explain haa the advantage of giving, with
great facUity, and without supposing any knowledge of fiigonometry, the
means of solving astronomical problems much more accurately than could be
done by means of globes. It also gives very aimply the various mathematical
formulse employed in aatronomy.

60

MATHEMATICAL GEOGRAPHY.

II. Qf Spherical Triangles.
213 We must say a few words, before we proceed, m order to explain what
a spherical triangle is, and what its several parts represent. In the same way
that an ordinary or plane triangle is formed
"^ by three straight Imea drawn on a plane
surface, and meeting at three angular points,
so a spherical triangle ia formed by three
area of great circlea drawn on a spherical
aurface, and meeting in three angular points.
214 Fig. 52 represents a s^erical sur
face, vrith a spherical triangle, ABC, drawn
on it ; A B, B C, and C A represent arcs of
great circles ; they are caUed the sides of
the spherical triangle. The angles of this
triangle showthe indinations of the three sides
to each other at their respective points of in
tersection ; but we must explain more folly
what the a^les of a spherical triangle are.
215 Angles ofa Spherical Triangle. — LetAB „. jj
and A C, fig. 53, be any two circular arcs, or other '^
curved Unes meeting at a point. A; then we cannot
speak generally of the incUnation of the arc A B to
the arc A C, as we could do if they were straight lines,
because, being curves, they are differently inclined to
each other at different parts. But we may speak ofthe
incUnation of these two curves to each other at the
point A ; for take two points, D and E, on A B and
A C respectively, very near A, so near that the por
tions A D and A E may be too smaU for their curvature to be sensible, and we
may regard them aa two very smaU straight lines. These two lines make a
certain angle with each other, whatever it may be, and that anrfe ia the
angle at which the two curves meet each other at the point A. This suffi- ';
ciently explains what we mean by the angles of a spherical triangle.
2 1 6 If we produce the two smaU lines A D and A E to any points, F and
G, the straight linea A F and A G are reapectively coincident with the two
curvea A D B and A E C, in the immediate vicinity of the point A ; these
linea are therefore said to touch the curves at A ; A F ia said to be the tangent
to the curve A D B at the point A, and A G is said to be the tangent to the
curve A E C at the point A.
217 Hence, the angle which the two tangents make vrith each other is the
aame thing as the angle which the two curves make with each other at the
point A. 218 If A F, fig. 54, be the tangent at any
point, A, of a circle, whose centre ia O, it is easy
to aee that A F ia perpendicular to the radius A 0 ;
for if A D be an extremely smaU portion of the
circumference, so smaU that we may consider it a
straight line, the tangent A F is simply A D, pro
duced to any point F; now aince, in dfeacribing a
circle, the point of the compasa alwaya moves per
pendicularly to the radius, A D must be perpen
dicular to A O, and therefore A F is so also.
219 It is important to remember, that the
tangent at any point of a circle is perpendicular to
the radius or line di-awn from that point to the
centre. We may also observe, that tho tangent always lies in the same plane
as the circle.

ASTRONOMICAL PROBLEMS.

61

220 A Spherical Triangle com
pletely represents a Solid Angle. —
Let ABC, fig. 55, be a spherical
triangle, O the centre of the sphe
rical surface, on which the triangle
is drawn, O A, O B, O C, the radii
drawn to the angular points ABC.
Then AB is a circular arc described
with O as centre ; therefore A B
reOTesenta or measures the angle
A O B, which the two radU A O
andBOmake with each other — i. e.,
the number of degreea, minutea,
and seconds in A B, and in the angle A O B are the same, as has been faUy
explained in Chapter II. In like manner the circular arc BC shows the
angle B O C, which the two radU drawn from B and C make with each other,
and the circiUar arc C A, the angle COA, which the two radu drawn from
C and A make with each other.
221 Again, if we draw from A the two linea A F and A G, touching the
circular area A B and AC at A, the angle PAG which theae two tangents
make with each other, is the aame thing aa the angle A of the apherical
triangle. But the angle FAG also ahows the inclination of the two planes
A O B and A O C to each other, as we may prove in the foUowing manner.
222 By the plane A O B, we mean the plane in which the two radii, A O,
B O, the circular arc A B, and of course the tangent A F, aU Ue ; by the plane
A O C, we mean the plane iu which AO, CO, the circular arc A 0, and the
tangent A G, aU lie. A O is the line of intersection of these two planes, and
the tangents A G, A F, are perpendicular to the radius A O. Now the angle
at which two planes are inclined to each other ia ahown by drawing from a
point in their line of intersection, a line in each plane perpendicular to the
Ene of intersection. That this is the case is easilV seen, by marking with a
knife a line E F, fig. 56, on a piece of card A B CD, and drawing a perpen
dicular Une E P Q in pencU : then turn the two parta A E F D and B E F D
about the cut line E P, so as to make them make an angle vrith each other, as
in fig. 57 ; and it wUl be immediately seen, that, at whatever angle we incUne

Fig.S?

Fig. 58

\

A

R

p a

the two planes A E P D and B E F C to each other, the two Unes E P and
P Q wUl always make the aame angle vrith each other. But if we draw two
lines, P S and P T, not perpendicular to E F, the angle these two Unes make
with each other wUl alwaya be leas than the angle at which the two planea
are incUned,
223 Hence, retuming to fig. 55, it is manifest, that the angle FAG, or,
what IS the same thing, the angle A of the spherical triangle, shows the angle
at which the two planes A O B and A O C are incUned to each other. In hke
manner we may show that the angle B shows the angle at which the two

62 MATHEMATICAL GEOGRAPHY.
planes BOA and B O C are incUned to each other, and the angle C shows the
angle at which the two planes COA and 0 O B are incUned to each other,
224 The triangular point O, which ia formed by the meeting of the three
planes A O B, B O C, C 0 A, ia caUed a solid amgle, the three planes are called
the pla/nes, or faces, ofthe solid angle, and the three Unes O A, O B, O C, are
caUed its edges.
225 Hence, it appears, that the spherical triangle ABC representa, m
aU its parts, the soUdT angle O, which is formed by drawing radii from the
angles ABC to the centre O — namely, the three sides of the spherical
triangle, AB, B C, C A, repreaent reapectively the three anglea, AO B, BO C,
COA, which the edges, O A, O B, O C, of the sohd an^e make with each
other ; and the three angles. A, B, C, represent the angles at which the planea
A O B, B O C, C O A, of the aoUd angle are inclined to each other,
1 1 1, Method of representing the different parts ofa Spherical
Triangle on Flat Paper.
226 First Construction. — Let ABC, fig, 58, be the apherical triangle,
O the centre of the sphere ; draw B F, a tangent to the circular arc B A, at B,

and B G a tangent to the circular arc B C at B ; let these tmgents meet O A
and O C produced at P and G respectively, and join F G. Then, as we have
explained, the angles B O F, BOG, and F O G, are shown by the sides of the
spherical triangle — namely, B A, B C, and A C respectively ; also the angle B
of the spherical triangle is the aame thing as the angle E B G.
Now let us conceive the solid figure O B G F to be formed of four
triangular planes of thin board or card— namely, B O F, BOG, B C F, and
FOG, fastened together by hinges along the edges OF, O G, and i G, and
by a clasp of aome kind at B, so that, if the clasp at B be unfastened, the plane
O B F may be turned about the edge O F, the plane O B G about the edge
O G, and the plane B G F about the edge F G. Thia being supposed, let the
clasp at B be unfastened, and let the planes OBF, OBG, and BFG, be
turned about the hinged edges, untU they aU form one plane with O G F, so
that the four planes may be laid flat upon the table, as is represented ui fig,
59, where O F G, G B F, and O B' F, and O B" G, represent respectively the
planes O F G, G B F, O B F, and O B G, in fig. 58.
227 Hence, fig. 69 represents on fiat paper the three sides and one angle
of the spherical triangle — namely, the angles F O B', F O G, and G O B", show
the sides A B, AC, and C B respectively, and the angle G B F shows the
angle B. It is important to obserTc that the angles O B' F, and O B" G, fig.
69, being respectiTcly equal to O B F and O B G, fig. 58, are right angles,
that thelines O B' and O B", fig. 69, being each equal to O B, fig. 58, are of
equal length, that G B" and G B, fig. 59, being each equal to G B, fig. 58, are

ASTRONOMICAL PROBLEMS,

63

of equal length, and that the aame is true of F B' and F B, fig, 59, which are
each equal to F B, fig, 58,

Fig.dg

228 We have, therefore, the foUowing construction on flat paper for
representing the three sides and one angfo of a spherical triangle, whose
angles we shaU denote by A B and C, and the sides respectively opposite
those angles by the smaU letters a be.
Choosing a point O on the paper, draw the Unes O B', OF, O G, and
O B", fig. 60, making angles with each other equal to the three sides a b and c

ofthe spherical triangle — i. e., the angles a b and c at O, contain respectively
the same number of degrees, minutea, and aeconds, as the sides a b and c of

64

MATHEMATICAL GEOGRAPHY.

the spherical triangle. Puttmg one point of the compass at O, strike off
O B' and O B" equal to each other ; draw B" G perpendicular to O B , and
B' F perpendicular to O B', to meet the Unes O G and O F, at G and F ; with
G as centre and GB" aa radiua, and vrith F as centre and FB as radius,
deacribe two cu'cular arcs B" D B and B' E B, intersecting each other at the
point B, and join B G and B F : then the angle G B F so formed, is equal to
the angle B of the spherical triangle.
229 This construction wiU enable us to solve any astronomical problem
in which we are concemed, with the three sides and one angle of a spherical
triangle. We shaU now give another construction for representing the two
other angles of the spherical triangle, A and C,
230 Second Construction. — As before, let A B C be the spherical triangle,
and O the centre of the sphere ; draw the lines B E perpendicular to O A, and

B F perpendicular to O C ; in the plane O A C, draw E D perpendicular to
O A, and F D perpendicular to O C, to meet in D, and join B D. The two
planes BED and BED, being thus made perpendicular to the plane O A C,
their line of intersection B D wUl also be perpendicular to tiie plane O A C,
and therefore to the two lines E D and F D, which Ue in that plane : the two
angles B D E and B D F, are therefore each right angles.
In this construction E B and E D are perpendicular to O A, the line of
intersection of the two planes O A B and O A C, and therefore, as we have
previously explained, the angle BED shows the inclination of these two
planes to each other, or, what is the same thing, the angle A of the spherical
triangle ; the angle B E D is therefore equal to the angle A ; and in like
manner, we may show that the angle B F D is equal to the angle C, of the
spherical triangle.
231 Now, just as in the former construction, let us suppose the sohd
figure OBEDF to be formed by four triangular planes, OBE, OBF,
BED, BFD, hinged at their lower edges to the quadrangular plane
O FD E, and fastened at B by a clasp. Let tlie clasp be unfastened, and the
four triangular planes turned about their hinged edges, until they form one
plane with the quadrangular plane O F D E, so that five planes may be laid flat
on the table, as is represented in fig. 62, where O F D E is the quadrangular
plane, and OFB", OEB', DEB'", DEB, the four triangiUar planes—
namely, OFB,OEB, DFB, DEB, m fig. 6L
232 Hence, fig. 62 represents on flat paper the thi-ee sides and the other
two angles ofthe spherical triangle — namely, the angles at O show the sides of
the spherical triangle, just as m the former construction, and the angles
D E B, D F B'", show the two angles A and C.

ASTRONOMICAL PROBLEMS,

65

233 It is important to
observe, as before, that
angles marked thus L>
in figure 62, are right
angles, because they are
respectiTely equal to
angles in fig. 61, which
we know to be right
angles. Also, as before,
OB' and OB" are equal,
FB" and FB'" are equal,
D B'" and D Bare equal,
and E B and E B*^ are
equal, each pair of lines
being equal to O B, F B,
D B, and E B, respec
tiTely, in fig. 61.
234 We haTC, there
fore, the foUowing con
struction on flat paper
for representing the
three sides a b and c,
and the other two angles
A and C of the spherical
triangle.
Draw OB', OE, OF,
and O B", fig. 63, making, as before, angles, ab c, with each other ; make
O B" equal to O B' ; draw B" F perpendicular to O F, and B' E perpendicular
to O E, and produce thoae perpendiculars to meet in D ; draw D B'" per
pendicular to F D, and D B perpendicular to B D ; with centre F and
radiua F B", and vrith centre E and radiua E B' describe two circular arcs,
cutting the perpendiculars last drawn in B'" and B, and join B'" F and
B E ; then the angle BED wUl be equal to the angle A of the spherical
triangle, and the angle B'" F D wUl be equal to the angle C.

/

Fig. 63

235 This construction ia of considerable importance, and solves a great
number of astronomical problema, only in practice it ia much simpler than it
appears to be here, stated as it is in all its generaUty.
This construction is also of importance, because it gives immediately all
tiie mathematical formulse of spherical trigonometry used in the most exact
astronomical calculations,
236 Application of the Second Construction to Bight Angled Spherical
F

66

MATHEMATICAL GEOGRAPHY.

Triangles. — When one of the angles of a spherical triangle is a right angle or
90°, it is caUed a right angled spherical triangle. Suppose C to be a right
angle m the second constmction ; then B'" F, fig. 62, is_perpendicular to FD,
and therefore, since B'" D is also perpendicular to F D, the two lines B'" F
and B'" D coincide ; in other words, the points F and D coincide. Hence the
construction becomes what is represented in fig. 64, in which O B' and 0 B"
are equal, D B" and D B are equal, E B' and E B are equal, and the angles
thus marked, L . are right angles.

/

/ N

237 Hence we have the foUowmg simple constmction for a spherical
triangle, one of whose angles, C, is 90°.
Draw from O Unes, aa before, fig. 64, making the angles ab c with each
other ; make O B" equal to O B', ifraw B" D perpendicular to O D, and B'E
perpendicular to O E^ which two perpendiculars produced wiU always meet
at a point D of the line O D, when the an^ C is 90° ; with radius D B" and
centre D, and with radius E B' and centre E, describe two circular arcs inter
secting at B, and join B D and B E ; then the angle B D E wiU be 90°, and
the angle BED wiU be equal to the angle A of the spherical triangle.
238 This constmction solves
rig.es bh  every case of right angled spherical
triangles, and merefore, aa wUl ap
pear, a great number of practi
caUy uaeftU aatronomical problems.
We might eaaUy show that this
conatmction gives immediatelywhat
are known as Napier's Eulea, and
obviates the necessity of the use
of these rules, which is often very
troublesome. 239 Observations respecting the
Second Construction. — It sometimes
happens, in making the second con
struction, that one of the two per
pendiculars, B" F and B' E, wnen
produced, meets the other in the
manner shown in fig, 65, in which
case the point D Uea between E
and B', or, it may be, even beyond
B' in E B' produced. In this case,
the construction is precisely the

ASTRONOMICAL PROBLEMS.

G7

same as before ; we must draw D B'" perpendicular to F D, F B'" equal to
F B", and D B perpendicular to E D, making E B equal to E B', There
is, however, a caution necesaary respecting the angle A — namely, the angle
B E D is not A, but BED' is, where E D^ is D E produced. It is therefore
necessary to make the following statement respecting the angles A and B.
240 In aU cases, wherever the
point D may faU, the angle A is
the angle which the line E B
makes with the perpendicular B' E,
produced beyond E — ^i. e,, the angle
contained between E B and the
produced part of the perpendicu
lar ; and, in Uke manner, the angle
C is the angle which the Une F B'"
makes with the perpendicular B" F
produced beyond F — i, e., the angle
contained between F B'" and the
produced part of the perpendicular.
No mistake can be committed if it
be remembered that the angles A
and C are thoae made, not by the
perpendiculars, but by the perpendi
culars produced.
241 When any of the angles
a J c, as for instance a, happens to
be greater than 90°, the point E
vriU faU on the other side of the
point O, as ia shown in fig. 66. In
this case, the construction is the
same as before, without the least
alteration, and the aame rule holda
with reference to A and C. A is
the angle BED which is contained
between E B and the produced part
E D of the perpendicular B' E, and
C ia the angle B'" F D', which ia
contained between F B'" and the produced part F D' of the perpendi
cular B" F.
242 We have been particular in diacussing the aecond construction on
account of ita importance, but no mistake can be made iftbe following points,
which apply to all cases, be remembered.
O B' = 0 B", FB" = FB"', D B'" = D B, E B = E B' ;
O F B", O F D, O E B', O E D, F D B'", and E D B, are right angles ;
The three angles at_0 are the aides of the spherical triangle ;
The angle of the spherical triangle wMch is opposite the side B' O E
is the angle contained between F B'" and B" F prdduced ;
The angle opposite the side B'' O F is the angle con-
*- tained between E B and B' E produced.
243 Observations respecting a spherical triangle, two
of whose sides are each 90°. — When this is the caae, aa in
fig. 67, where b and c are each 90°, it ia important to re
member, 1st. that a and A are equal (i. e., they contain
the aame number of degreea, minutes, and seconds,) and
2ndly, that B and C are each right anglea. To prove
) c this, let O be the centre of the sphere, and join O A, OB,
and O C ; then, aince c is 90°, A O B is a right angle,
and aince b ia 90°, A O C is a right angle ; therefore A O,
being perpendicular to O C and O B, it is manifest that
F 2

Fig. 67

68

MATHEMATICAL GEOGRAPHY.

rig. 68

the planes A O B and B O C are at right angles to each other, and that the
same is trae of the planes A O C and BOC; wherefore the angles B and C,
which show the incUnations of these planes to each other, are right angles;
also O C and O B being at right anglea to the intersection O A of the two
planes O A B and O A C, the angle COB (which equals a) shows the inclina
tion of these two planes — i. e., tiie angle A ; therefore a and A are equal.
244 It ia alao important to remember that, if from
any point P of O A we draw P E and P D perpendicular
to O A, as is shown in fig. 68, and describe the circular
arc D E, (which is a portion of a smaU circle described
about the pole A,) then the proportion of the arc D E
to the arc B C ia the aame thine aa the proportion of
the Une P D to the Une O B. Thia wUl become evident
if we consider the arcs C B and E D, to be described hy
the points B and D, when we tum the plane O A D B
abont the axis O A ; for then if P D is half O B, the
point D wUl only move half as fast as the point B, and
therefore the arc E D wUl be always half of the arc
B C ; in the same manner, if P D be one-third of 0 B,
B wUl move three times faster than D, and therefore C B wiU be three times
E D, and so on. In whatever proportion, therefore, P D is less than 0 B,
the arc E D wiU be less than the arc C B in the aame proportion. See
Chapter II.
Having now said enough of apherical triangles, we shaU proceed to the
solution of aatronomical problema.
IV. Solution qf various Astronomical Problems.
245 In the aolution of the foUowing problem, it wiU be necessary to have
an Ephemeris, or almanack, with astronomical tables. White's Celestial
Atlas, which only costs a shilling, and is published regularly every year, wiU
answer every purpose..
Pkoblem I.
To find the Time of Sunrise on any given day of the Year.
246 Solution. — Draw a line O B',
of any convenient length, fig. 69, and
another O E, making the angle EOB'
equal to the Sun's north polar dis
tance, which is given in the Ephe
meris ; and draw B' E perpendicular
to O E. Draw O D, making the angle
DOE equal to the latitude of tiie
place, (which is of course known,) and
meeting B' E produced at D. Draw
D B perpendicular to E D, to meet a
circular arc B' H B, described with E
as centre. Measure the angle DEB,
and convert it into time, aUowing one
hour for every 15° ; then that time
is the hour of sunrise, aa ahown by
the sun-dial.
'''^ .v^^^f"!"^^ \^^\^l^^ '^^' '^^ t^e meridian, A S' C tiie hori
zon, P the Pole, 8 the Sun and H S S' K the circle which the Sun describes,
(in consequence of the rotation of the heaveua about P,) crossmg the horizon
at S'. When the Sun is at K, it ia midday; when at H, nndnight; and
when he cornea to 8' he rises ; therefore the angle A P S', being described
about P by the polar circle P S m the mterval between midnight lnd sunrise,
is, when expressed m time at 15° per hour, the number of hours, minutes, and

ASTRONOMICAL PROBLEMS.

69

Fig. 70

seconds between midnight and sun
rise, or, what is the aame thing, the
hour of sunrise.
Now thia angle is the angle at P
in the spherical triangle A S' P, in
whioh triangle the angle at A ia
90°, the side P S' is the Sun's polar
distance, and the side P A ia the
latitude of the place (see art. 194.)
Hence, employing the second con
struction, (as it appUes to a right-
angled triangle, art. 236,) supposing
A §', AP, and P S' to be a, b, and c,
respectively, and therefore the angle
at ]? to be A, we obtain immediately
the above solution.
248 Example. — On the 2nd of
May, 1849, at what hour wUl the
Sun riae in London ?
Looking in White's Celestial Atlas for 1849, we find —
Page 47. Latitude of London, 51° 31'.
Page 10. Sun's declination 15° 26' north, and therefore polar distance 74° 34'.
, Therefore in fig. 69 we must make BOB' 74° 34', E O D 51° 31', which
if we do, we ahaU find the hour of aunrise to be twenty-nine minutes past four,
as ahown by the sun-dial.
249 It appears by the Ephemeris, that the Sun is about three minutes
after the clock on the 2nd of May, therefore the time of aunrise by the clock
wfll be thirty -two minutes past four.
250 If we examine the tables of the hours of sunrise and sunset in the
Ephemeris, we shaU flnd that twelve o'clock ia not half way between aunrise
and sunset ; the reason of thia ia, that twelve ahown by the clock, is not the
same as twelve shown by the dial. Twelve, as shown by the dial, would be
exactly half-way between sunrise and sunset, only for the motion of the Sun.
In fact, in working out the above problem, we have for simpUcity supposed
the Sun to remain fixed in the heavens during
FiCT 71 the day. This is not true, and therefore our
result ia sUghtly erroneoua.
251 We ahall preaently show that, in con
sequence ofthe refraction of Ught bythe atmo
sphere, heavenly bodies appear to rise a Uttle
before, and to set a Uttle after, they actually
come on the horizon.
Pkoblem II.
To find at what Point^fthe Compass the
Sun rises.
252 Solution. — Draw the Unes O B', O E,
and O D, (fig. 71,) exactiy as in Problem I.,
making BOB' equal to the Sun's polar dis
tance, EOD equal to the latitude of the
place, and B' D perpendicular to O D. Draw
D B" perpendicular to O D, to meet a circu
lar arc, B'^H B", described about O as centre,
at B" Measure the angle D O B", and the
result will be the Sun's azimuth at rising,
whioh, as we have explained in the previous
chapter, shows the point of the compass
at which he rises ; for example, if D O B"

70

MATHEMATICAL GEOGRAPHY.

be 0, the Sun riaes in the north ; if 45°, in the north east ; if 90°, m the east,
and so on. • • j »
253 Proof— In fig. 70, A S' ia the Sun's azimuth at nsmg, and A S' is
the tMrd side of the right angled spherical triangle, A P 8', considered in
Problem I. ; therefore, employmg the second construction as appUed to a right
angled triangle, we find the azimuth in the manner just stated.
254 By means of this problem, or rather, by a mathematical calculation
equivalent thereto, the variation of the compass is often found at sea. The
magnetic needle does not point truly to the north ; the error is caUed the
variation of the compass ; and it is chfferent at different points of the Earth's
surface. It is, of course, necessary for the navigator to determine this error,
and how it changes as he saUs over the ocean ; thia he doea by observing
with the compass at what point the Sun rises, — ^i. e,, the Sun's azimuth at
rising ; he then, by means of a mathematical calculation equivalent fo
Problem IL, finds what the Sun'a azimuth ought to be, and takes the dif
ference between the result and the azimuth obserTcd by the compass ; which
difference is manifestly the error or variation of the compass.
Problem LU,
On a given Day of tlie Year, to find at what Hour any given Star
crosses the Meridian.
25,5 Solution. — Look in the Ephemeris for the Sun's right ascension and
that of the star; subtract the former from the latter, and the result wiU be
the hour (i. e., the number of aidereal hours, minutes, and seconds, after
mid-day by the dial) at which the star crosses the meridian.
If the Sun's right ascension should happen to be greater than that of the
atar, add 24" to the latter before subtractmg.
256 Proof— Let 8, fig. 72, be the Snn; T,
the star ; E S' T' F, the equator; P S S' Q and
P T T' Q being respectively the declination or
polar circles ofthe Sunandafau-. Then S' T', reduced
to time, is evidentiy the number of hours, minutes,
and seconds between the transits of S and T; but
if A be the first point of Aries, A S' and A T*
are the right ascensions of 8 and T, and there
fore S' T' is the difference between the ri^t as
cension of the star and that of the Sun. Hence
the truth of the solution is manifest.
257 By adding 24" to the right ascension of
a heavenly body, we do not alter its position on
the celestial sphere, aince 24" corresponds to
360°, — i. e., a complete revolution. We may therefore, if we please, add 241^
to the star's right ascension, should it happen to be leaa than that of the Sun,
in order to make the subtraction of the former from the latter possible.
258 Examples. — At what hour does Arcturus cross the meridian on the
25th of September, 1849 ?
Looking in the Ephemeris we find, omitting aeconds : —

Eight Aacenaion of Arcturus (a Bootes) , . .
Ditto of Sun, (September 25tii, 1849) ,

14" 9"
12" 8""
2" 1""

Difference,
Therefore Arcturus crosses the meridian 2" 1"" after apparent noon.
259 We have taken here the Sun's right ascension at mean noon, on the
25th of September, which is given in tho Ephemeris. A smaU correction is
necessary in this, to aUow for backward motion of the Sun in the interval
between noon and the transit of thc star.

ASTRONOMICAL PROBLEMS. 71
260 To determine tho same for the 25th of December, we haTc : —
Eight Ascension of Arcturus + 24"  38" 9"'
Ditto of Sun (December 25th) . . . 18" 16'"

Difference, 19" 53""
Therefore Arctimis crosses the merichan 19" 53"" after apparent noon.
Pboblbm rv.
To find at what Homr any given Star rises or sets on any specified
Day ofthe Year.
261 Solution. — Precisely as in the case of the Sun, Problem I., find what
time elapses between the rising of the star and its transit OTer the meridian ;
subtract this from the hour of the star's transit found by Problem IIL, adding
24^ to the latter if necesaary ; then the reault is the hour of rising of the star.
To find the hour of setting, add inatead of subtracting.
Example. — Supposing that we flind by Problem I. that the star's
tranait takes place eight hours after its rising, and, by Problem IIL, that on
the 1st of August the star crosses the meridian at 4 o'clock ; at what hours
does it rise and set ? — 4 -f 24 = 28 4
Subtract 8 Add 8
20 12
Therefore the star rises at 20 o'clock, (four hours before noon,) and sets
at 12 o'clock.
262 The hours in these and the preTious examples are sidereal hours,
which are a Uttle shorter than mean solar, or the ordinary ciril hours. In
round numbers, we may consider that a mean solar hour is ten seconds
longer than a sidereal hour.
Peoblem V,
Ha-aing given the Bight Ascensions and Declinations of two heavenly bodies, to
find the Distance of one from the other, in degrees, minutes, and seconds.
263 Solution. — ^Find the polar diatance of each body, (by aubtracting ita
declination from 90°, or adding, if the body be south of the equator,) andthe
difference of the right ascensions in degrees, minutes, and aeconda ; and then
make the foUowing conatmction, fig, 73 : —
Draw O B" (of any
length) and O F, mak- j-j^ 73 JC
mg the angle B" O F ^'
equal to the polar dia- b"
tance of one body ; and
draw B" F at right
angles to O B" ; draw
alao L M equal to O B",
M N perpendicular to
L M and L N, making
the angle N L M equal
to the polar distance of
the other body; draw
N K equal to B" P,
making the angle M
N K equal to the dif
ference of the right
ascensions of the two bodies ; and with centre F, and radiua M K, and with
centre O, and radius L N, describe two circular area intersecting at E ; then

72 MATHEMATICAL GEOGRAPHY.
the angle EOF being meaaured, gives the required distance between the two
bodies, in degreea, minutes, and seconds.
264 Proof. — Let 8 and T, fig. 72, be the two bodies, and join 8 T by an
arc of a great circle, which arc is the required distance between S and T;
then, in the spherical triangle S P T, (P being the pole,) we have given the
two sides P 8 and P T, which are the polar distances of 8 and T, and the
angle S P T, which, as we have explained in the previous chapter, is the same
thing aa the arc 8' T' (the difference of the right aacensions) on the equator,
in degreea, minutes, and seconds. Hence we have given two sides and the
included angle of a spherical triangle, and it is required to find the third side,
S T. Thia can be done by meana of the first construction ; for, referring to
it, suppose a c and B to be given : then, fixing upon any length we please
for O B", and therefore O B , we may construct the two trianglea, O B" G
and O B' F, and so find the sides B" G and B' F, which are respectively equal
to G B and F B ; but B is known, and therefore, having found G B and P B,
we can construct the triangle G B F, and so find G F : then, since we have
thus determined O G, O F, and F G, we can construct the triangle 0 F G,
and BO find the angle b, which ia the third aide of the apherical triangle.
This ia exactly what we have done in fig. 73, where the triangles L M N
and K M N are the same as the triangles OFB' and F B G in the first
construction. 265 We might also solve this problem by the second constmction, by
supposing a b and C to be the given quantities, as foUows : —
Draw O B", O F, and O E, making a and b equal to the given polar dis
tances, and B" F at right angles to O B", making O B" of any lengtii we
please : draw F B'", making C equal to the given difference of right ascen
sions : measure F B'" equd to F B", and draw B'" D at right angles to
B" D : draw D E at right angles to O E, and produce it to meet a circular
arc, described vrith O as centre and O B" as radius, at the point B' : then
E O B', or c, the required third side of the spherical triangle, is found.
Problem VI.
Having given the Latitudes and Longitudes of tmo places on the Earth's
surface, to find the distance between them in miles.
266 Solution. — Proceed exactly as in Problem V., putting latitude for
declination, and longitude for right ascension, and then convert the result into
miles, by allovring 69^ mUes for every degree, which wiU give the required
answer. 267 It is not necesaary to say anything to prove this, beyond observing
that it is found by actual measurement, that a degree of a great circle on the
Earth's surface ia about 69^ mUea long.
268 To solve thia problem accurately, we ought to take into account the
fact that the Earth's surface ia not an exact sphere ; without, however, going
to such a degree of accuracy, thia problem is very useful geographicaUy.
269 We might insert here a great number of useful and important
problema, but, as our space is limited, we shall not dweU longer on this sub
ject now.
The problema given here are chiefly with a view of showing generaUy how
the two constructions may be appUed in astronomy.

73

CHAPTER V.
OPTICAL PEINCIPLES EEQUISITE IN ASTEONOMY.
ALL astronomical obaervations are made through the medium of Ught,
and by means of instruments whose construction mainly depends upon
optical principles; it is therefore highly important for an astronomer to
understand something of the science of optica, in order that he may be able
to make the beat use of his instruments, and avoid many errors into which he
ia likely to faU from ignorance of the lawa which regulate the tranamission of
Ught. It vriU not be possible to dcTote sufficient space here to the fuU
dcTelopment ofthe principles of optics ; aU that we can do ia, to explain those
phenomena of hght which haTe immediate reference to astronomy, and the
laws upon which the construction and use of astronomical instruments
depend. We shaU, in the first instance, state eTerything of practical importance
relating to the tranamission of Ught from luminous bodies : we shaU then
explain briefly the laws of reflection and refraction, the diapersion of Ught into
different colours by refraction, and certain other points of practical import
ance ; and lastly, we shaU show how these laws enable us to construct instru
ments for ascertaining direction, and subdividing space with the greatest
possible accuracy. I. Ofthe Transmission of Light from luminous bodies.
271 The transmission of light is not instantaneous. The common and
natural notion reapecting the transmission of light is, that it comes from
luminous bodies to the eye instantaneously ; but this ia not the case, though
the almost inconceiTable speed vrith which light travela is auch, that it might
be considered instantaneous, only for the extreme accuracy of astronomical
observations, which require us to take account of the velocity of light.
272 The fact that light travela with a certain velocity was ascertained by
the Danish astronomer, Eomer (to whom we owe the invention of thc transit
instrument) in the foUowing manner.
The planet Jupiter ia accompanied by four sateUites, which move round
him in the same manner that the Moon does round our Earth, but in shorter
periods. As theae bodies revolve round their central planet, they appear to
us to move backwards and forwarda on each side of Jupiter, never receding
far from him. Sometimes they manifestly pass in fronj; of him, which is
Eerceived by their casting ahadows on hia disk ; and at other timea they pasa
ehind him, which ia perceiTcd by their sudden disappearance after they have
come close to hia disk. Sometimes also they are ecUpsed by their entering
the shadow which .Jupiter oasts. AU this may be aeen by means of an
ordinary telescope.
By watching these ecUpaea, occultationa, and immeraiona, aa they are
caUed, of Jupiter's sateUites, we may determine the rate at which they move
round him. It is thus found that the foUowing are their respectiTC periods of
rcTolution: —
The first sateUite completes its rcTolution in about If days.
The second  SJ „
The third  7 „
The fourth  16f „

74

MATHEMATICAL GEOGRAPHY.

It is important to uotice the shortness of these periods, for upon that fact
the discovery of the velocity of Ught in a great measure depended. In little
more than a fortnight, it would be possible to ascertain these periods by
watching the eclipses and occultations of the sateUites ; in fact, in tiiat length
of time the motion of the first sateUite might be completely determined.
Having once made out these periods of revolution, we can of course always
predict when the eclipses and occultations wiU occur during the lapse of a year
or several years ; and this Eomer did. But he found that there was apparently
a manifest error in his predictions ; he observed that there was some unaccount
able irregularity in the eclipses and occultations ; at one period of the year
they appeared always to take place too late, and at another period too soon.
AU this seeming irregnlarity was, how
ever, explained in the most satisfactory man
ner by Eomer, by the supposition that light is
transmitted, not instantaneously, but with a
certain finite, though very great velocity. The
foUowing was his explanation: —
1 Let B and J, fig, 74, represent the Earth
and Jupiter revolring in their orbits about the
I Sun, S ; and suppose it to be that period ofthe
' year when the Earth is between the Sun and
Jupiter, as is shown in the figure. Now, in
somewhat more than six months, the Earth
and Jupiter wiU have come into the positions
shown in fig. 75, the Sun being between
Jupiter and the Earth; for the motion of
Jupiter being much slower than that of the Earth, the former describes but
a smaU portion of his orbit whUe the latter performs half the whole circuit,
so that in a Uttle more than half a year the two
bodies wiU have come into the position repre
sented by fig. 75.
Now, Eomer found that, in the position re
presented by fig. 74, the eoUpses and occultations
of the sateUites appeared to take place eight
minutes and thirteen seconds too soon, and in
the position represented in fig. 75, they appeared
to take place eight minutes and thirteen seconds
too late. In fact, auppoaing the motions of the
sateUites to have been determined by observa
tions made when Jupiter and the Earth were on
the same side of the Sun, as in fig. 74, and the
eclipses and occultationa to have been predicted
from the motiona so determined, it waa found,
that in aix months— i. e., when the Earth and Jupiter were on opposite sides
of the Sun, as in fig. 75, the ecUpses and occultations took place nearly six
teen minutes and a half later than the times predicted.
This was immediately explained, by supposing that the light, which
couTcyed to the eye, as it were, the intelligence of the ecUpse or occultation
haTuig taken place at Jupiter, did not arriTe mstantaneously, but traveUed
with a certain Telocity— namely, a Telocity just sufficient to transmit it across
the Earth's orbit in sixteen minutes and twenty-six seconds, or in round
numbers, a Telocity of twelTe mUlions of miles per minute, the diameter of
the Earth's orbit being about 190 miUions of mUes. For on this supposition
it is clear, that since the Earth ia fai-ther from Jupiter in the position repre
sented m fig. 75 than m fig. 74, by a diatance equal to the ^ameter of the
Earth a orbit, tlio eclipse or occultation would be seen sixteen minutes and
twenty-six seconds later in tho former position than in the latter, amce the
light would take that additional time to travel .across the Earth's orbit when
Jupiter nnd the Earth were on opposite sides of the Sun,

OPTICAL PRINCIPLES. 75
273 That this is the real cause of the dif
ference between the obserTed and predicted ^'g-l^
times of the echpses and occultations, is in a
great measure proTcd by making observations
on the satelUtes during the whole year. It wiU
be found that when the bodies are situated as in
fig. 76, where 8 and E are at equal distances
from J, the ecUpses and occultations wiU occur
eight minutes and thirteen seconds later than
in the position fig. 74, the Ught then having
to travel an additional distance equal to half
the diameter of the Earth'a orbit. And in
the intermediate positions which the bodies
occupy at different times of the year, it wUl
be found that the number of minutes and
seconds, which the ecUpse or occultation appears to be later than in the
position fig. 74, is always proportional to the additional distance the Ught
has to traTel OTcr, in consequence of the Earth being farther from Jupiter
than he is in the position fig. 74.
274 Stellar Aberration. — But the Telocity of Ught ahowa itaelf in
another curious phenomenon, caUed stellar aberration, which was dis
covered by the astronomer, Bradley. Eespecting this subject we have
only time to remark, that Bradley found out that the stars are observed
to describe every year Uttle orbits in the heavens ; in fact, they always appear
to be displaced from their true positions in the direction in which the Earth
is moving. For instance, in sprmg the star y Draconis when seen near the
zenith, as it vriU be in the south of England, wUl appear to be nearly 20"
south of its real position, in summer nearly 20" east, in aut'omn about the
same distance north, and in winter about the same distance west of its true
place ; at wliich times the Earth is moving southward, eastward, northward,
and westward, respectively. Stars 90° distant from the pole of the ocUptic,
which it vriU be remembered is about half-way between Polaris and y Dra
conis, appear to suffer no displacement when the Earth is moving either
directly towards them or from them. In fact, this apparent displacement is
foimd to diminish as the distance of the star from the point of the heavens
towards which the Earth ia moving diminishea.
27^ Bradley showed that this phenomenon ia completely and aatia-
factorUy explained, by auppoaing it to ariae from a combination of the Earth'a
motion and the motion of Ught. He waa able to calculate what ought to be
the velocity of Ught to give rise to this apparent displacement of the stars,
and he found it to be the same as that determined by Eomer from the eclipses
and occultationa of Jupiter's sateUites. That the velocity determined by
Bradley should agree vrith that given by Eomer from such totaUy different
observations and reasonings, is of course a most satisfactory proof of the truth
of the hypothesis, that light moves with a velocity of about twelve millions of
miles per minute.
We have dwelt longer on thia optical fact than we shall do on others, on
account of its great importance in aatronomy.
276 The Bectilineal Transmission of Light. — That light ia transmitted
from luminous bodiea in atraight Unes or rays, ia ao obrioualy true, that we
need not aay much on the aubject. If we make a smaU hole in the shutter
of a darkened room, so aa to aUow the sunUght to enter through it, the
rectilineal course of the light wUl be made very evident by shaking out some
dust from a puff-bag, which wUl be iUuminated by the light. The fact that
we cannot see roimd a corner, or through a bent tube, is a famihar proof that
light travels in straight lines, and so dso is the shadow cast by any opaque
object, which is always exactly the shape traced out by straight lines drawn
from the luminous point from which the light comes, through the different
extreme points of the object.

76 MATHEMATICAL GEOGRAPHY.
277 Upon this property of Ught depends entirely its use as a means of
aacertaming direction. We can teU in what direction an object ia by looking
towards it, but we cannot judge, by Ustening to sound, the direction of a
sounding body, because sound does not proceed in straight lines or rays. We
shaU presently explain fuUy the means by which astronomers ascertain dkee-
tion, by means of Ught. II. Inflection amd Diffraction qf Light.
278 But though it be a fact, that in ordinary cases Ught proceeds in rays
from luminous bodies, there are cases, often of practical importance, in which
light spreads Uke sound. If the sunUght be aUowed to enter a darkened room
tm'ough a very smaU hole, (or, what is better, through a lens of short focus
placed in front of a hole not quite so smaU,) the shadows cast by it wfll exhibit
very curious appearances. 'They vriU be amaUer than they would be if the
light entered the room through a hole of moderate size, and of a totaUy
different shape if the body casting the shadow be small ; and their edges will
be aurrounded by coloured banda and bara, and, wherever there are aharp
comers, by beautiful curved fringes.
279 To see these in great perfection, aU that is necessary is a common
spy-glass or telescope. Get .a round piece of card the size of the object glass,
and cut a hole in the middle, say the size of a shilling, over which gum a
Eieoe of sound tinfoU. Then, with a aharp pointed knife, cut carefnUy a small
ole in the middle of the tinfoU of any shape, such as a triangle, a square, a
cross, a star ; or, with a needle, prick one, or two, or three, or a great number
of holea in the tinfoU. Cover the object glass wdth this card, fastening it on
vrith a httle bee's wax, or otherwise. Then drop a Uttle globule of mercuiy
on a piece of black velvet, and lay it on a table or on the ground in the Sun's
rays : in this manner a bright point of Ught wiU be produced. AU that is to
be done now is to look at this point of Ught through the telescope, holding it
very steadUy, or, what is better, fixing it on some stand, or supporting it on
some books. When this is done, the most beautiful optical phenomena wUl
be seen, which may be varied by drawing in or out the tube ofthe telescope,
or by viewing the globule of mercury at a greater or less distance.
280 We have space here only barely to notice these phenomena, and to
state that they arise from the fact that light spreads Uke sound when it enters a
darkened room through a very smaU hole. The curious figures and colours
are produced by what ia called the interference of Ught, respecting which we
caimot say anything here. These phenomena constitute what are caUed the
inflection and diffraction of Ught.
281 We have thought it necessary to aUude to these optical facts here,
because they often prove a source of aerioua imperfection in astronomical
and surveying inatruments, and they often greatly add to the difficnlfy
of making certain aatronomical observations. We have seen leveUing tele
scopes wnich could scarcely be used, on account of the wires in the focus
being so affected by diffraction, as to appear like a number of indistinct bars ;
and we are convinced that opticians ought to be more famiUar with this
subject than they are. In microscopes of high power, vrith very smaU ohject
glasses, the diSraetion completely spoUs the unage formed by the instrument,
especiaUy when the object ia Ulummated by a smaU, weU defined luminouB
surface, III, Beflection and Befraciion of Light.
282 We have atated that Ught is transmitted from luminous bodies in
straight Unes or rays, but this is true only when the Ught passes through
vacuum, or through a perfectly uniform transparent medium, — \. e,, either
empty space, or apace filled with aome gaaeous, liquid, or sohd matter, which
is alf through of the aame conaistenoe and density. The air immediately
surrounding the Eai'th's surface may be regni'dcd as a imiform medium, but

OPTICAL PRINCIPLES.

77

at some distance upwards from the surface, the density of the air diminishes
rapidly as we ascend. Near the Barth's surface, therefore, light pasaes
through the air in straight lines, but this is not true except cloae to the
surface. 283 Befraciion. — Whenever the density or conaiatence of the medium
through which light ia passing changes, the direction in which the Ught moves
is altered. In the case of Ught coming from a heavenly body to the eye, the
path which the light pursues is continuaUy bending aa the Ught movea on, in
conaequence of the continual change of denaity of the atmosphere. When a
ray of light enters a piece of glaaa, ita direction ia immediately changed, in
consequence of the consistence of the glass being different from that of the
air, out of which we auppose the Ught to paas into the glass. The same is
true of water, oU, spirit, and of every transparent substance, in a greater or
lesa degree.
284 The change of direction whioh a ray of light experiences in paaaing
from one medium into another, as, for instance, from air mto glaaa, ia caUed
refi-oKtion, or the breaking or bending of the ray, as the word signifies. Ee-
fraotion takea place generaUy whenever there is any change in the denaity,
conaiatence, or natm-e of the transparent medium through which the Ught
is passing. 285 The continual bending which a ray of.Ught from a heavenly body
experiences as it is passing through the atmosphere, is oaUed astronomical
refraction. This error, as it is called, affects a large and important class of
astronomical observations, and it is therefore necessary to understand it, ao as
to be able to aUow for it, and ascertain the true direction of the heavenly
body from which the ray comes.
286 Beflection. — The refraction of Ught is always accompanied by what is
caUed reflection, or a casting back of the light. When Ught is passing from
one medium into another, a certain portion of it is always thrown back, or
reflected, so that only part of the Ught enters the second medium. In the
case of glass, when light enters it from the air, the portion of Ught which
Buffers reflection ia smaU compared with that which enters the glass. In the
caae of a metaUio medium, such as mercury- or sUver, a considerable portion
of the Ught is reflected, and only a very amaU part enters the metal. Glass
is therefore said to have a weak reflective power, but mercury or sUver are
said to be highly reflective.
287 Lcms of Beflection and Be
fraciion. — Let A E P, fig. 77, be any
medium, a piece of glaaa for inatance,
and let P A be a ray of Ught which,
passing out of air, or any other medium,
enters the glass at A. Draw B A B' at
right angles to the surface of the glass
at the point A. The ray P A is said
to be incident, — i. e., to faU upon the

glass at A, and therefore this ray is
caUed the incident ray. The plane in
which the ray P A and the perpendi-
cnlai BAB' Ue, ia caUed the plane of
incidence. When the ray entera the glaaa, it
is refracted, and proceeds in a different
direction to that in which it was going
before ; let that direction be A E,
A E' being the former direction P A
produced. The broken Une P A E shows the whole course of the Ught,
which proceeds in a straight Une from P to A, is broken or refracted at A,
and then goes on in a straight line to E.

78

MATHEMATICAL GEOGRAPHY.

Fig.'TB

Fig. 78 shows a case of reflection. The
incident ray PA, instead of going on in the
straight dn:ection A E', is thrown back or
refiected at A, and proceeds through the
air in the direction A Q.
A E, fig. 77, is caUed the refracted ray,
and A Q, fig. 78, the reflected ray.
288 The first law of reflection and re
fraction is this: — The reflected and re
fracted rays always Ue in the plane of inci
dence ; in other words, the three lines,
_ P A, B A B', and A E, fig. 77, and the three
i' Unes, P A, B A B', and AQ, fig. 78, always
Ue in the same plane, — ^i. e., the incident
ray, the perpendicular to the surface, tiie
reflected ray, and the refracted ray, aU he
in the aame plane.
289 The second law maybe atated in the foUowing manner : — Let PA,
A E, and A Q, fig. 79, be the three rays as before ; A B, the surface of the
medium, which we shaU sup-
Eose to be a plate of glass ; draw
'om any point B ofthe surface
of the glass, a perpendicular,
C P B D, meeting the incident
ray at P, and the reflected and
refracted rays produced back
wards at D and C respectiTely ;
then the second law is, that A D
is always equal to A P, and A C
ia alwaya about one-half greater
than A P, — i. e., three h3.Te8 of
A P.
290 Whatever the medium
may be, whether glass, or water,
or oU, or any other substance,
A D ia always exactly equal to
A P, and A C always exceeds
(or faUa short of) A P by a cer
tain fraction of A P.
291 Befr active Index. — The
proportion of A C to A P varies
with the nature of the substance
of which the medium A B E F
is composed, and that of the
medium out of which the Ught passes into A B E F. This proportion
is caUed the refractive index; thus, if A C is always four-thir£ of AP,
which is very nearly the case when the medium A B E F is water, and
the upper medium air, the refractive index is said to be f . AC may be
always found by multiplying A P by a certain number or decimal, de
pending on the nature of the two media, and that number is caUed the
refractive index.
292 The foUowing table gives the refractive indices of different sub
stances, supposing thelight to enter each substance out of vacuum :—

OPTICAL PRINCIPLES.

79

Substance.

Refractive Index.

about ^g»^

Atmospheric air ... .

1-000-294

Water . . .

1'336
about f
Alcohol . .
1-372
OU of oUves
1-470
Plate glass .
from 1-500 to 1-550
about j
Flint glass .
from 1-576 to 1-642
Oil of cassia
1-641
Sapphire . .
from 1'768 to 1-794
Diamond
from 2-439 to 2-755
about f
In this table it wiU seem that the refractive index is not always exactiy
the same for the same substance ; as, for instance, in the ease of sapphire, in
some specimens it is aa high aa 1-794, and in others as low as 1-768. In the
case ofglass there is a considerable diversity of refractive index, on account
of the Afferent ingredients of which glass is made, and the different propor
tions in which they are mixed together.
293 The angle P A B which the incident ray P A makes with the
perpendicular B A B', figs. 77 and 78, is caUed the angle of incidence. Tho
angle Q A B is, in Uke manner, caUed the angle of reflection, and E A B', the
angle of refraction.
Since A D is always equal to A P, it foUows that both these Unes
are incUned at the same angle to the perpendicular C D ; in other words, the
reflected ray makes the same angle with the pei^endicular to the surface that
the incident ray does, — i. e., the angle of reflection is always equal to the angle
of incidence. 294 Fig. 79 enables us to determine the course of the refracted ray by
construction on paper, as foUows :—
Having drawn a line A G, to represent the surface, and a perpendicular,
B C, from any point of it ; draw P A at the proper inclination to represent
the incident ray. Measure A P, and open the compass to once ana a half
that distance, supposing the medium to be glass of the lowest refractive
power ; then, puttmg one point of the compass at A, describe a circular arc
with the other, meeting B C at C, from which point draw the Une CAE
through A. This will give A E, the refracted ray.
295 The refractive index, when the Ught passes out of glass into air, is
the reeiprocal of that out of air into glass ; that is, if the former be f , the
latter is |. This is trae of aU subatancea ; the refractive index, when hght
pasaea out of one medium (A) into another (B), is the reciprocal of that ont
of B into A.
296 The refractive index is always
less than unity, that is, A C is always
less than A P, when the light passes out
of a denser into a rarer medium. Fig. 80
shows the course of the refracted ray in
snch a case. We may aee, by comparing
figs. 79 and 80, that when the light paaaes
out of a rarer into a denser medium, the
refraction, or bending of the ray, is to
wards the perpendicular, but out of a
denser into a rarer it is away from the
perpendicular. 297 If the refractive index, when
light passes out of a medium A into a
medium B, be multipUed by that out of
B into another medium C, the result is
the refractive index out of A into C. It
80

MATHEMATICAL GEOGRAPHY.

follows from this, that the refractive mdex out of A into C, diTided by that
out of A mto B, giTes the refractiTe index out of B into C. Thus, if the
refractiTC index out of vacuum into glass be f , and that out of vacuum into
water be |, that out of water into glass vriU be | divided by f, that is, f .
IV. Dispersion qf light.
298 Index ofBefraetion depends upon Colour. — ^It is found by experiment
that the refractive index depends, not only on the media out of and into
which the Ught passes, but also on the colour of the light. The refractive
index is greater when the colour is orange that when it is red ; it is stiU
freater when the light is yeUow, stUl greater when green, greater again when
lue, and greatest of aU when violet,
299 White Light Compound. — It is also found that white light, such as
the hght of the Sun, or of a candle or lamp, is not simple but compound; each
ray of white Ught being a union of aeveral coloured rays, which are usually
classed into seTen kinds — namely, red, orange, yeUow, green, blue, indigo,'
and Tiolet. Each of these classes includes a Tariety of mfferent shades ; in
fact, we may say that in reaUty a white ray of light is compounded of an
infinite number of rays of different colour and shades of colour.
As we have stated, all these colours have different refractive indices. The
foUowing table for different substances wiU show the nature and amount of
this diversity of refractive index,
Eefeactive Index poe

Colour

FUnt Glass,

Crown Glass.

Water.

Eed 

1-628

1-526

1-331

Orange

1-630

1-527

1-332

YeUow

1-635
1-530
1-334
Green,
1-642
1-533
1-336
Blue .
1-648
1-536
1-338
Indigo
1-660
1-542
1-341
Violet
1-671
1-547
1-344
300 Dispersion of White Light by Befraciion. — Let P A be a ray of
white Ught incident at A, on the surface of any medium, say crown glass ; then,
in order to find the course of the Ught
after it has entered the glass, we
must proceed to make the constmc
tion already explained, remembering
that the different colours which com
pose P A have aU different refi:active
mdices, as shown in the table we
have just given. Thus for red the
index is 1-526; therefore if we suppose
A P to be 1, and make A C equal to
1-526, AE, which is AC produced, will
show the course of the red ray after
refraction. In Uke manner, aince 1'647
is the index for violet, if we make AD
equal to 1-547, A V, which is AD pro
duced, vrill show the course of the
violet ray after refraction. In the
same way we may find the inter
mediate refracted rays, the orange,
yeUow, green, &c.
Hence it is manifest that the va-
OPTICAL PRINCIPLES.

81

rious coloured rays which were united in the white ray P A, wUl, after refrac
tion at A, be separated, and pass through the piece of glass in different direc
tions ; the red ray A E being least bent out of its original direction P A Q,
the violet most, and the intermediate colours in order in an intermediate
degree. The white ray P A is therefore, as it were, dispersed as soon as it
enters the glass into a set of coloured rays diverging from the point A. In
this maimer the dispersion of white Ught is produced by refraction.

V, Passage oflight through Plates, Prisms, and Lenses.
301 Passage qf Light through a Plate of Glass or other transparent Sub-
stance. — ^By a plate ofglass we mean a piece bounded by plane surfaces which are
£araUeI to each other.
,et E F G H, fig. 82, »/
represent a section of
snch a piece ofglass at
right anglea to the pa
rcel pmie aurfaces re
presented by E F and
GH. Suppose that a
ray of Ught P A faUs
upon the surface E F
at the point A; then
the course of this ray
in passing through the
glass vriU oe as foUows :
The ray vriU of
course be refracted at
A, and inatead of going
on in the direction A Q,
which ia P A produced,
it wiU paaa tMough the
flaas m the direction
L B, which, as we have
stated, is less inclined
to the perpendicular to
the refracting surface than A Q is. At B the ray wUl pass out of the
glass into the air, and therefore again suffer refraction ; but since it passes
from a denser into a rarer medium, it vriU be bent away from, not towards,
the perpendicular. In fact, the refraction or degree of bending at B, wUl be
precisely of the same amount as at A, only it will take place in the opposite
direction ; this may be easUy proved by making the proper construction for
the refraction at A and B, according to the method we have explained above,
remembering that the index of refraction at B is the rcTcrse or reciprocal of
that at A.
The consequence ofthis wiUbe,that the ray wUl emerge from the glass at
B in a direction B E, paraUel to the original direction P A Q ; for whatcTer
be the angle through which the ray is bent at A, it vriU be bent through the
same angle in the opposite direction at B, and therefore be restored to its
original direction.
302 Hence, when a ray of Ught passes through a plate of glass, it vriU
emerge paraUel to its original direction, but it wUl suffer a certain degree of
lateral displacement — ^i,e„ BE wiU be paraUel to, but not coincident vrith, PAQ,
303 Passage of Light through a Prism. — By a prism we mean a piece
of glass or other transparent substance, bounded by plane surfaces which are
not paraUel, but inclined to each other at a certain angle. Let BFG, fig.
83, represent a section of such a piece, at right angles to the two plane sur
faces which are shown by the lines E F and E G. Suppose that a ray of
G

82

MATHEMATICAL GEOGRAPHY.

Fig. 83

light P A faUs upon
the surface E F ; then
the course of this ray
in passing through the
glass -(viU be as fdlows :
The ray, being re
fracted at A, WM be
tumed towards the per
pendicular to the sur
face E F, and pass
through the glass in
the direction A B. At
B it wiU suffer a second
refraction, and wfll be
tumed away from the
perpendicular to the sur
face E G. The effect of
the second refraction wUl be, not to tum the ray back to ita original direc
tion, but to make it deviate atiU farther away from it, as is evident from
the figure. Thus the ray, instead of going on in the direction A Q, which
is P A produced, wUl emerge out of the glass in the direction B E.
The effect of the prism here is to tum the ray, not towards the angle
E, but towards the thicker part of the prism F G ; and thia ia always the
case, supposing the prism to be made of glaaa, or any transparent substance
denaer than the air ; the ray wUl always be bent away from the angle ofthe
prism towards the thicker part.
304 Dispersion produced by a P-rism. — The two refractions which take
place when a ray of hght passes through a prism have the effect of producing
a considerable degree of dispersion, and showing the composition of white
Ught, and the different refrangibUity of the coloured rays composing it, in a
very striking manner. All that is necessary to exhibit the dispersion of Ught
in great perfection by a prism is, to aUow a ray from the sun to enter a dark
room through a hole or alit in a abutter, and then to intercept it by a prism, and
receive the transmitted Ught on a screen, or on the waU or ceiling. Let E F G,
fig. 86, represent the prism, P A, the ray from the Sun falling on the surface

at A. Suppose the red ray to pass through the prism in the direction A B,
and to emerge into the air again in the direction B E j then the violet ray
will be more refracted at A than the red, and therefore pass tiirough the
prism in a direction A C, more inclined to A Q (A Q being P A produced)
than A B is. Again, the violet ray wiU be more refracted at C than the red

OPTICAL PRINCIPLES.

83

is at B, and therefore it wiU emerge in a direction C V, more incUned to
A Ij tnan ij xt is.
Hence, if the emergent Ught be received on a screen Q E V, at some littie
distance from the prism, a red spot wUl be seen at E, and a violet spot at V
Inthe space mtermediate between E and V wUl be seen the intermediate
colours. The order of the colours wUl be as foUows :—
Eed at E,
Orange,
YeUow, Green,Blue.
Indigo. Violet at V.
The coloured space between E and V is commonly caUed the Prismatic

305 K the sides E F E G of the prism be curved instead of plane, the
effect it produces on Ught passing through it wUl be the same— see figs. 84

and 85, which represent prisms with curved sides, and where the course of
the light is represented by the same letters as in fig. 86,
It ia important to obaerve v
the double difference of the
effect produced by the two
prisma repreaented in figs, 84 sig.sa
and 85.
lat. The emergent rays
B E C V are below A Q (the
original direction of the Ught)
in fig. 84, and above A Q in .?.  - 
flg. 85. In other words, the
light in both cases is bent to
wards the thicker aide of the
prism. 2ndly. The violet is below the red in fig  ,  „ 
other words, the yiolet is in both cases on the thicker side of the prism, and
the red on the thinner side.
306 The Compound Achromatic Prism. — ^A prism which produces refrac
tion vrithout dispersion — ^i. e., one which bends aU the coloured rays equally,
IS said to be achromatic — i. e., without colour. A single prism, such as one of
those we have just spoken of, cannot be achromatic, as is evident from what
we have explained. But by putting two prisms together, as in fig. 87, it is
possible to make a compound prism which shaU be achromatic or nearly so.
We shaU briefly explain how this is done. The two prisms, E F G and
E' F' G', are placed in opposite positions, and therefore produce opposite
g2

84, and above it in fig. 85-

84

MATHEMATICAL GEOGRAPHY.

Fig.ST

R *"-- a
F' G'
refractions and diaperaiona ; the prism E P G will bend the rays upwards,
and throw the violet above the red ; whUe the other prism E' F' G will
have the reverse effect. P A B A' B' E representa the course of the red ray
through the two priama, the dotted Une A C C V, the course of the riolet,
and A Q is P A produced.
Now, suppose that the refraction produced by the first pnsm amounts to
10°, and the dispersion to 1°. By saying that the refraction is 10°, we mean
that the prism tums the red ray 10° out of its original direction A Q, and by
saying that the dispersion is 1°, we mean that the violet ray ia turned 1° more
than the red out of its original direction — i. e., that the violet ray ia tumed
11° out of ita original direction. Secondly, suppose that the refraction pro
duced by the second prism is 8°, and the dispersion 1°. The effect of the two
prisms may be calculated aa foUows : —
Eefraction produced by first prism  10° upwards.
„ „ by second  8° downwards.
Total refraction produced by both priama . . 2° upwards.
Dispersion produced by first prism  1° upwards.
,, „ by second  1° downwards.
Total dispersion produced by both prisms. . 0°
Hence these two prisms wiU produce a total refraction of 2° without
dispersion, and so form a compound achromatic prism.
307 Whether it is possible to make prisms which wiU produce such
effects as we have here supposed, is a point to be decided by experiment,
Newton concluded from some imperfect experiments that it was not possible
to do so ; that if the dispersions produced oy the two prisms were equal and
opposite, as we have supposed, the refractions would ato be equal and oppo
site — that is, that if the total dispersion were nothing, so also would the total
refraction ; in other words, he concluded that it was a physical impoaeibihty
to obtain refraction without diapersion. From this erroneous conclusion, he
gave up all hope of making achromatic telescopes, and turned his attention
to reflecting telescopes.
308 ]\&. HaU, a Worcestershire gentleman, and after him the celebrated
optician DoUond, found that Newton's experiments were inaccurate, and
proved that, by making one of the prisms of ffint glass, and the other of crown
glass, a compound achromatic prism might be formed, which would produce
a certain amount of refraction without dispersion.
309 Secondary Spectrum. — It is possible in this way to destroy the disper
sion, as far as the red and violet rays are concerned ; but this will not, at the
same time, answer for the other colours, as, for instance, the red and green.
If, on the other hand, the dispersion is deatroyed as far aa regards red and
green, it wUl not be quite deatroyed as far as regards red and blue. A com-

OPTICAL PRINCIPLES.

85

pound prism, such as the above, cannot be made perfectly achromatic for all
the colours ; but by putting three or more prisms together this may be done,
at least to a sufficient degree of accuracy. The Ught which pasaea through
the compound priam, Ss. 87, wUl therefore exhibit some traces of colour if
received on a screen. The slightly coloured spot it makea on the screen is
caUed the Secondary Spectrum.
310 Passage of Light through Lenses. — A lens (from lens, a bean) is a
circular piece of glass, bounded by two curved surfaces. GeneraUy these
surfaces are spherical, and not very much curved, except in a lens of very high
power. When the surfaces are convex or curved outwards, the lens is said
to be convex ; when inwards, concave. The best way to distinguish between
the two kinds of lenses is to say that a convex lens is thicker in the middle
than at the extreme parts, and a concaTe thinner.

311 Convex Lens. — ^Fig. 88 represents the passage of rays through a
conTex lens, G H K L represents a section of the lens by a perpendicular
flane through the middle, G A H showing one of the boimQing surfaces, and
i B K the other. A number of rays P G, P E, PA, P F, P H, are sup
posed to diverge from a point P, and faU on the surface G A H of the lens.
The ray P A, which is supposed to pass through the central part of the lens,
wUl not suffer any deviation, but pass straight through the lens in the
direction A B Q, which is P A produced. 'Sie reason of this is, that the
surfaces of the lens at A and B are paraUel to each other, and therefore the
ray passing through the lens in the direction A B, wUl be transmitted in the
same manner as if the lens were a plate of glaas vrith paraUel planea. Now,
we have ahown in such a case, that the Ught on coming out of the glass vriU
resume ita origin 1 direction, and auffer only a shght degree of lateral displace
ment (see fig, 82;, The lens is generaUy so thin, that we may neglect taking
any account of this lateral displacement, and therefore we have drawn the
ray P A B Q atraight through the lens in one unbroken Kne,
As we have explained in the case of the prism, the other rays, P G, P E,
P F, P H, wUl be bent towards the thicker part of the lens, and tiierefore
they wiU emerge from the lens as shown in fig, 88, or aa in fig, 89.

86

MATHEMATICAL GEOGRAPHY.

312 In one case, fig. 88, the lens is supposed to be sufficiently powerful
to bend the rays ao as to make them converge towards, or nearly towards,
some point Q, on the Une P A produced. In the other case, the lens not
being so powerful, the rays are not bent sufficiently to converge to a point
in front of the lens, they are only made less divergent than they were
before passing through the lens. In fact, if we produce them backwards
they wfll meet, or nearly meet, in a point Q, behind P on the hne P A
produced backwards.

313 Concave Lens. — Fig. 90 represents a concave lens and the passage of
the light through it, the lettera denoting the same things as before. The ray
P A which passes through the central part of the lens wUl go on straight
without deviation ; the other rays, P E, P F, P G, P H, wUl be bent towards
the extreme parts K and L of the lens, which are now thicker than the
central part A B. The effect of thia wiU be to increaae the divergence ofthe
raya, so that, on producing them backwards, they wiU meet, or nearly meet, at
a point Q, in front of P on the hne P A.
314 We have in aU theae cases represented the ray PA as passing
somewhat obUquely through the lens ; of course aU that has been said will
apply equaUy when P A paaaes perpendicularly instead of obUquely.
315 Focus. — A point in whioh rays of Ught meet is caUed a focus, a name
derived from the Latin word signifying ' fire-place,' because objects placed in
the focus of a burning lens were set fire to. The point P is caUed the/ociw
of incident rays, and the point Q ^e focus of emergent rays.
In fig. 88, the emergent rays actuaUy cross at Q ; but in figs. 89 and 90,
thia is not the case, the emergent raya proceed, however, just as if they
diverged from the point Q, and we may regard Q as an imaginary focus. Q,
in fig. 88, is caUed a real focus, and in figs, 89 and 90, a virtual or imaginary
focus. 316 Prindpal Focus. Focal Length. — When the incident rays come
from the Sun, or any other very distant body, the focus of emergent rays is
caUed the principal focus of the lens, and the distance of this focus fixim the
lens is caUed the focal length ofthe lens. When the point P is very distant,
the raya P G, P E, P A, P F, P H, wUl be incUned to each other at extremely
smaU angles, so smaU, that we may consider the rays to be paraUel to each
other. We may therefore define the principal focus to be the focus of
emergent rays when the incident rays ai'e pai'allel.
317 If paraUel rays faU on a convex lens, as in fig. 91, where the focus P

Fig. 91

OPTICAL PRINCIPLES.

87

of incident raya la supposed to be at a great distance from the lens, it is
erident, from what has been said, that the emergent rays wiU converge
towards a point Q in front of the lens. Hence the principal focus of a
convex lens is in front of it, and is a real focus.

318 If paraUel rays faU on a concave lens, aa in fig. 92, the emergent
rays vriU diverge, and therefore the principal focus is virtual, and behindthe
lens, 319 If the diatance P A be equal to the focal length of the convex Iena,
the raya wUl emerge paraUel to each other, as is ahown in fig, 93, where Q is
supposed to be at an infinite distance from the lens. That thia wfll be the
caae is erident, by supposing the course ofthe Ught in fig. 91 to be reversed
— i. e., to come from Q instead of P.

320 If P A be less than the focal length, the rays wiU emerge diverging,
and if P A be greater than the focal length, the rays wUl emerge convergmg.
321 Hence we may make the foUovring comparative statement reapecting
convex and concave lenses,
A convex lens either diminishes the divergence of rays or makes them
convergent. We may say that the effect of a convex lens is always to
produce a certain degree of convergence, for we may consider that diminishing
the divergence ofthe raya is nothing more than producing a certain amount of
convergence, which partly deatroya the divergence of the rays, and therefore
has the effect of making them less divergent than before.
A concave lens always increases the divergence of rays.
A convex lens sometimes brings the emergent rays tt) a focus in front of
the lens, but a concaTe lens neTcr doea so.
A oouTex lens may be used to make diTerging rays paraUel ; a concaTe to
make conTcrging rays paraUel. In both cases, the distance from the lens of
the point from which the rays diverge, or to which' they converge, must be
equal to the focal length of the lens.
322 Achromatic Lens. — A single lens, such as one of those we have
just described, produces its effect by refracting the rays just Uke a prism, and ao
bending them towards or from the central ray, according as the lens is convex
or concave ; but this refraction vriU be accompanied by diaperaion ; the riolet
rays wiU always be more refracted than the red rays, and therefore, in the
case ofa conTex lens, the Tiolet raya wUl emerge more inwarda — i. e., more
towards the central ray, than the red rays do ; but in the case of a concave
lens, the violet ray will emerge more outwards than the red.

88

MATHEMATICAL GEOGRAPHY.

If, however, we put two lenaea together^ one convex and the other concave",
such that the outward diaperaion produced by one may be just equal to the
inward dispersion produced by the other, the total amount of dispersion
produced by the two lenses in combination wiU be nothing; as in the case of
the two prisms above explained. At the same time, by making one lens of
crown glass, and the other of fiint glass, there wUl be a certain amount of
refraction stUl produced. In this manner the lenses wUl bend the rays
sufficiently for practical purpoaea without dispersing them, at least, vrithout
any serious amount of dispersion, for there wUI always be some arising from
the secondary spectrum. 323 It is usual to put
the lenses together as in
fig. 94, G H bemg the
convex, and K L the con
cave lens, the former
being made of crown
glass, and the latter of
flint glass. In the tele
scope, the convex lens is
always that on which the
light first falls, and in the
microscope the reverse is the case. The manufacture of achromatic lenses is
now brought to great perfection. The difficulties of grinding, polishing, and
fitting them properly together are considerable, especiaUy when the combina
tion is required to be powerftJ — ^i. e., of short focal length.
324 Spherical Aberration of Lenses. — We have hitherto, in the figures we
have given, represented the emergent rays as meeting in one point Q; bnt this
is only true approximately ; the extreme rays P G and P H, after paaaing
through the Iena, wUl meet the central ray P A B at a point Q', (see fig. 95,)

p
=» — >-

at aome little distance from the point Q, where the intermediate rays P E
P F, after emerging from the lens, meet the central ray P A B. In other
words, the focus of the extreme emergent raya wUl be a different point from
the focus of the intermediate emergent raya. If we suppoae the raysPE
and P F to be near the central ray, Q is considered to be the true focus, and
Q' is regarded as an erroneous focus. The error in the position of the focus
Q', which ought to coincide with Q, is caUed spherical aberration, because it
arises from the spherical form ofthe two surfaces of the lens. It is impossible
mechanicaUy to grind the surfaces of lenses in any but spherical forms ; but
such forma are not thoae which cause the extreme and intermediate rays to be
refracted to the same point ; this error or aberration is therefore caused by
the spherical forma of the lenaea.
325 In moat casea a convex lens produces a backward aberration of the
focus, that is, the point Q' is behind the point Q,, as in fig. 95 ; but a concave
lens generally produces a forwai-d aberration, that is, Q' is in front of Q. In
other words, ono lens refracts the extreme rays too much, the other too Uttle.

FORMATION OF IMAGES.

89

Now, by putting the two lenses together, as in fig. 94, one convex, the other
concave, and by giving a proper spherical shape to their surfaces, we make
the two opposite aberrations produced by the lenses almost entirely neutralise
each other, and so cause all the emergent rays to converge very nearly to the
same point. When the two lenses are properly made, the over refraction of
the extreme rays by the first lens vriU be counterbalanced by their under
refraction by the second lens. In this manner a compound lens may be
constructed free from any serious amount of spherical aberration. Such a
lens is said to be aplanatic, from the Greek, signifying ' free from error.'
Lenses which form the object glass of good telescopes and microscopes,
are always made both achromatic and aplanatic.
Having now explained briefiy those optical principles which are absolutely
necessary to be known by peraons who vrish to understand astronomy prac
ticaUy, and to use astronomical instruments, we shaU go on in the next chapter
to consider the formation of optical images, by rays passing through a hole or
a lens falling on a screen; from which simple, though reaUy instructive
caae, we shafl derive the construction of the telescope and microscope, and
explain their uses.

CHAPTER VI.
FOEMATION OF IMAGES— VISION— THE TELESCOPE, MICEO-
SCOPE, AND MICEOMETEE-THE VEENIEE.
I. Formation of Images by a Hole or a Lens.
"rilOBMATION of Images on a Screen by means of a Hole. — Let A B C D,
J? fig. 96, represent a box or tube, in one end of which A B is a very small
hole H, and at fhe other end a semi-transparent screen C D, made of ground
glass, or thin silver paper, or a piece of smooth glass vrith a film of mUk dried

upon it. The eye is supposed to look at this screen, and an object G Y is
placed before the hole H : then the foUowing effect wiU be produced :— •
Supposing for an instant that the object G Y consista aimply of three
luminous points, one green, another red, and the third yeUow, which are re
presented by G E and Y, reapectively. Then green rays wUl issue in aU
directions from G, some of which, proceeding in the direction G H, wUl pass
through the hole H, and, going straight on, wUl faU on the screen C D at G',
the points G H and & being in the same straight Une. The eye wUl
therefore see a smaU green spot on the screen at Gr'. In Uke maimer some
of the red rays from E, passing through the hole and going straight on to E',
the points E H and E' being in the same straight line, wUl form a smaU
red spot at E', which the eye wiU see. In like manner, also, a small yeUow
spot wUl be seen at Y', the points Y H and Y' being in the same straight
line. Hence the eye wUl see three smaU spots on the screen, exactly sinular to,
and at the same relative distances from each other as the points G E and Y
of the object, only inverted in position ; in fact, an inverted image or Ukeness
ofthe object wUl thus be cast on the screen C D.

90

MATHEMATICAL GEOGRAPHY.

Precisely the same reasoning would apply to an object consisting of any
number of luminous points, and therefore it foUows, that whatever object i!
placed in front of the hole H, a perfectly accurate inverted image of it will
be formed on the screen C D.
327 Defect qf the Image thus formed. — The hole H must necessarily be
a very small hole, otherwise a distinct image wiU not be formed onthe acreen.
This wUl be evident immediately, from fig. 97, in which H is supposed to be
large. It vriU be seen in this figure that the red and yeUow raya, after passing

Fig. 97

through the hole, get mixed together, and faU nearly on the same part ofthe
screen. The consequence of this vriU be, that inatead of two diatinct small
apota, one red and the other yeUow, being seen on the screen, as in fig. 96,
there vriU be but one large spot seen, consisting of a confusion of red and
yeUow. Hence it is manifest that, \)y enlarging the hole H, we make the
image on the screen indistinct and confused. Indeed, however smaU the hole
may be, there wUl always be a certain degree of indistinctness, arising fi^im
the mixture and confusion of rays coming from points of the object very near
each other. In fact, a Uttle consideration wiU show that the rays from two
points of the object, not farther from each other than a distance equal to the
diameter of the "hole, wiU always be mixed together before they reach the
screen. Now, this is a serious defect ; for, when the hole is extremely smaU, the
Ught that faUs on the acreen becomes too faint, and can scarcely be seen.
Hence there is an inevitable fault in this instrument ; the image on the screen
is either too faint or too indistinct, and we cannot diminish one imperfection
vrithout increasing the other.
328 Use ofa Lens placed in the Hole. — Let us now suppose that we en
large the hole, and put a lens in it, as is represented in fig. 98, of sufficient

explained, — - ,t . x
the lens from Y, to meet the acreen in Y', In Uke manner, if we draw a hne
from any other point E ofthe object, through the centre of the Iena, to meet
the acreen in E', the rays diverging from E wiU be brought to a focus at E' ;
and the same may be said of G, and of every other point of the object.
Hence it is evident that an image wfll be formed on the screen of exactly
the same size and shape, and as distinct and free from confusion as the image
in fig. 96, supposing the hole in that figure to be extremely small. But there
wUl be this important difference between the two images: the quantity of
light admitted through the lens wiU be very much greater than that admitted
through the hole in fig. 96, and therefore, wliUe the image in fig. 98 is per
fectly distinct, it will at tho same time bo bright and clear.

VISION. 91
The use of a lens is, therefore, moat important ; vrith a good aplanatic and
achromatic lens, avery perfect image may be formed on the screen, aa we know
by the beautiful photographic pictures which are produced by an instrument
of the kind represented in fig. 98.
329 This mstrument ia caUed a camera obscura, or " dark chamber ;" we
introduce it here vrith a view to the better explanation of the telescope, and
its various uses in astronomy.
330 It is important to observe that the different points of the image are
found by drawing straight Unes from the corresponding points of the object,
through the cenlre of me lens, to meet the screen ; and from this it foUowa
that the image, though inverted, must be accurately simUar to the object.
II. Of Vision.
331 The Eye is a sort of Camera Obscura. — A section of the eye is re
presented in fig. 99. It is a roimd baU consisting of certain transparent fluids
enclosed in an opaque mem
brane. In front tnere is a Fig. 9 9
hole H, caUed the pupil, be
fore which is a transparent
fluid, caUed the aqueous hu
mour, enclosed in a ^eUcate
membrane, the whole being
kept in and protected by a
strong homy andtransparent
substance, E F, caUed the
cornea. Behind the hole H is a very clear lens A B, caUed the crystalline lens,
between which and the back of the eye ia another humour, oaUed the vitreous
humour. Lastly, C D ia a nervoua membrane, caUed the retina, spread out to
form a acreen at the back of the eye : it conaists of a network of fine nerves,
which, uniting at a point called the puncium ccecum, form the optic nerve O, by
which luminous impressions made on the retina are conTeyed to the brain.
The interior surface of the eye is darkened, probably to prcTent stray Ught,
by a black substance, caUed the pigmentum nignrni.
332 It vriU be eaaUy seen from this description that the eye is a sort of
camera obacura. The pupU H correaponds to the hole in front of the tube
in figs. 96, 97, 98 ; the retina corresponds to the acreen C D; and the cryatal-
line Iena, assisted by the cornea, which is a sort of lens, aervea, like the lens
in fig. 98, to bring the rays to a focus on the retina or screen. The humours
in the interior of the eye serve to keep it xn its proper globular shape, though
they are also intended to assist in the optical performance of the eye to a
certain extent.
In fig. 99 the course of rays falUng on the eye from a luminous point E
is shown ; a certain portion of these rays are admitted through the pupU or
hole H, and, are then caused to conTcrge to a point E' of the retina or
screen. In this way cTcry point of an object placed before the eye has a
corresponding image on the retina, and therefore an image ofthe whole object
wfll be formed on the retina, clearly iuTcrted, as in the case of the camera
obscura. The optic neiwe couTcys this image to the brain in some mysterious
way, and an idea ofthe external object is thus produced in the mind.
333 It is, of course, necessary that the image* formed on the retina should
be perfectly distinct and free from confusion, otherwise no clear idea of the
external object could be conveyed to the mind. The lenses in front of the
eye— namely, the cornea and crystalline lens, must therefore be just of suffi-

* It is enough that a very small portion of the image should be distinct, (namely, that por
tion formed at the point of the retina called the foramen centrale.) This appears from the
fact that we can see only one point of an object distinctly at a time.

92

MATHEMATICAL GEOGRAPHY.

This is represented in

cient power to bring the rays to a focus on the retina.
fiff. 99
\-^i In fig. 100 is represented the case when the lenses of the eye are too
„,..«« ^— -^^^-^ strong, so that they cause
the rays to converge too
rapidly, and so bring them to
a point E', in front of the
retma- The consequence of
this wriU be, that instead of a
point on the retina, we shall
have a spot of light of some
size, and this vriU destroy the
distinctness of the image ; for the different spots which correspond to neigh
bouring points of the object, wfll overlap each other, and so be inixed and
confusedSrith each other, exactly in the manner we have already explained in
speaking of the effect of enlarging the hole in the camera obscura. Art. 327.
335 When, however, the point E ia much nearer to the eye than is re
presented in the figure, the rays which faU on the eye from it wUl be very
divergent, and it vml require more powerftd lenses to make them converge;
therefore, though the lenses were too powerful before, they may not be so
now ; in fact, they may be only just sufficientiy strong to overcome the
increased divergency of the rays, and make them conv^ge to a point on the
retina exactly. Hence it appears that, when the lenses of the eye are too
powerful, an object which cannot be seen distinctly at some distance, will
become distinctly visible when it is brought sufficiently near the eye.
This is the case with short-sighted persons, and therefore such persons
have too powerful eyes, which is generally evident by the more than usual
roundness of the cornea.

336 In fig. 101 is represented the caae where the lenaea of the eye are
too weak, ao that they do not cause the rays to converge vrith sufficient
rapidity, the consequence of which ia, that the rays are intercepted by the
retina before they come to a focus. This wiU of course produce indistinctness
of vision, just as in the former case.
When the lenaea are too weak, the object may be made more diatinctly
visible by removing it to a greater diatance fi-om the eye, and so diminishing
the divergence of the rays, which wUl aUow the weak lenses to produce a
greater degree of convergence, and so bring the point E', towards which the
rays converge, nearer to the retina. Persons vrith weak lenses are therefore
long-sighted, 337 Most eyes are adapted for vision of distant objects, the lenses being
only just powerftd enough to bring rays from a distant point to a focus on the
retma. But the lenses may be made more powerful by the action of certain
muscles, which, by compressing the baU of the eye, and so making the cornea
rounder, increaae the power of the cornea, and poasibly that of the crystalline
lens also. By the almost involuntary action of these muscles, the eye has a
power of adapting itself to near objects ; but generaUy this power of adapta
tion ia hmited to objecta not nearer to the eye than six inches, or thereabouts.
The eye is perfectly incapable of seeing nearer objects without the assistance
of a microscope.

THE TELESCOPE. 93
338 It is easy to understand, from what has been stated, how the vision
of short-sighted persons is assiated by their looking through a concave lens,
for that Iena increasea the divergence of the rays, and has the same effect as
if the object were brought nearer to the eye.
339 In Uke manner, it is evident how long-sighted persons are benefited
by convex lenses, which diminish the divergence of the rays, and therefore
have the same effect as removing the object to a greater distance from the
eye- . .
340 It is important to observe here, that it foUows from what we have
explained respecting the eye, that a near object and a distant object can never
be seen distinctly at the same time ; for it is plain that if the lenses are of
the proper power to bring the more diverging rays, which come from a nearer
object, to a focus on the retina, they wUl not be of the proper power to pro
duce the same effect on the less diverging rays which come from more distant
objects. This is a point of some importance in practice.
We have now said enough respecting light generaUy, and the formation
of images, to enable us to proceed to the two special subjecta we have to con-
eider in the present chapter — namely, the telescope as a means of ascertaining
direction, and the microscope as a means of measuring minute distances.
1 1 .1 . Qf ihe Telescope as a means of ascertaining Direction.
341 Direction how determined by Sights. — Simple as it may seem at first
eight, it is no easy matter to determine and define the direction in which any
distant object appeara to be. In a rough way, we might point a atraight rod
at the object, and say that that rod showed the direction of the object ; but
it is not possible to point a rod in this way with any degree of accuracy.
By putting a pair of sights on the rod, the direction of the object may bo
much more accurately ascertained. Fig. 102 represents a rod C D, with two
%^°^ C\v.  ¦*«

sights A and B fixed upon it, A being a small hole, and B a larger hole, vrith
two cross wires. By looking in such a manner through the hole A, and
putting the rod in such a position that the point of intersection of the wires
appears to coincide vrith a distant object 8, and at the same time with the
centre of the hole, it is evident that we ascertain the direction in which S is
seen, for the line joining the centre of the hole and the poifit of intersection
ofthe cross wires ahowa that direction.
342 Thia method of ascertaining direction is, however, by no means suffi
ciently accurate, for several reasons, and among the reat for thia — that the eye
caimot possibly see the hole at A, the cross wires at B, and the object S, aU
distinctly at the same time. If the attention be fixed on S, it will be seen
^tinctly, but the cross wires vriU not, and the hole wUl appear quite indis-
tmet. Ll practice, the hole at A is often very amaU, and the eye is put quite
close to it, in which case the hole is scarcely seen, and only serves to snow
the place where the eye should be put.
We shaU now show that the camera obscura, above described, affords a
most simple and accurate method of determining direction, especiaUy with
certain additions, which convert it into a telescope.
343 Direction how determined by a Camera Obscura. — ^We shaU suppose

94 MATHEMATICAL GEOGRAPHY.
the camera obscura to consiat of a tube, A BCD, fig. 103, C D being the
semi-transparent screen on which the image is formed. At the other end
A B, is the lens, which is of the proper power to make the rays which come
from a distant luminous point 8, converge to a focus on the screen C D ;
but, as we have shown sibove, this lens produces precisely the same effect
on the screen as an extremely smaU hole H, only the image formed by the
lens is not extremely faint, like that formed by the hole.

As we are only concemed vrith the size and shape of the image, and not
with its brightness, we shaU for simplicity suppose that there is a hole H,
instead of a lens, at A B, the hole representing, in fact, the centre of the lens.
On the screen C D there are two fine wires or linea, interaecting each other
at right angles ; the use of these Unes is to make, by their intersection, a
fixed mark at a particular point of the screen.
344 The imaginary hne drawn from the point of intersection of the two
cross wires through the point H, is caUed the line of collimation of the in
strument, that is, as we have explained before, the Ime which is pointed or
aimed at any distant object, and which is the direction in which that object
is seen. 345 Now, we can evidently ascertain, vrith the greatest precision, whe
ther the line of coUimation points to any distant point 8, or not ; for we
have only to look at the image 8' of the point S, found on the semi-trans
parent screen, and see whether it coincides with the intersection of the cross
wires or not. If it does, then the line of coUimation must point exactiy to
the point S, for, as we have explained above, 8' H and 8 are always in the
same straight line, and therefore, if S' is seen at the point of intersection of
the cross vrires, it foUows that the point of intersection of the cross wires, the
point H, and the point S, are in the aame right line ; or, in other words, the
line of coUimation points to 8.
346 K S' were a material point, instead of being a mere optical image,
as it is, it would not be possible to see whether S' comcided exactiy with the
intersection of the cross wires or not ; for, in point of fact, it is impossible to
see with accuracy whether two material points coincide or not ; indeed, two
material points cannot coincide with each other. It is altogether different
when one point is material and the other only an optical image ; in auch a
caae actual coincidence ia possible, and it is easy to see whether mere is actual
coincidence or not, especiaUy if we use a microscope to magnify the cross
wires, in which case the coincidence of the image S'^of tiie diatant point S,
vrith the intersection of the cross wires, may be seen with wonderfiil dis
tinctness. 347 The great advantage of the camera obscura, fig. 103, over the two
sights, fig. 102, for the purpose of ascertaining the direction of the distant
point S, IS now manifest. In ono case the eye nas to look whether two points,

THE MICROSCOPE.

95

that are reaUy at some distance fi-om each other, appear to coincide or not,
which it is impossible accurately to determine, because the eye cannot see dis-
tinotiy two objects at different distances from it at the aame time. In the
other case the eye has only to see whether an optical image formed on a
screen actuaUy coincides with a mark on that screen or not, which may be
done with the greatest exactness.
In order, then, to determine accurately the direction in which any distant
luminous point 8 is seen, we have only to point the instrument represented
in fig. 103 towards S, and move it carefuUy untU the image of S, which vriU
be seen on the semi-transparent screen C D, coincides exactly with the point
of intersection of the cross wires. Then the line drawn from that point
through the point H — i. e., the line of coUimation, must point directly to S.
In this manner the direction in which 8 is seen is ascertained,
348 By using a microscope to magnify the cross vrires, this may be done,
as we have stated, with extraordinary accuracy. When a microscope is attached
to the instrument for this purpose, the whole compound instrument so formed
becomes the regular astronomical telescope. We shaU now say a few words
respecting the proper kind of microscope, or eye piece, as it is generaUy caUed,
which is thus employed. IV. Of the Eye Piece, or Microscope.
349 Simple Microscope. — By looking through a convex lens, placed close
to the eye, we may see objects distinctly much nearer to the eye than we
could do without such assistance. Now, the nearer an object ia, the larger it
appears, and therefore a convex lens thua uaed wiU enable ua to aee an object
larger than it can poaaibly appear to the naked eye.
To explain this point the better, let us suppoae that the naked eye cannot
aee an object diatinctly nearer than aix inches, and that the focal length of the
convex lens ia one inen; then, if we place the object at an inch from the eye,
andlookthroughthe Iena at it, we shaUsee it diatinctly; for,aswehave explained
above, rays diverging from a point whose distance from a lens is equal to the
focal length, emerge from the lens paraUel to each other, and therefore are
brought to a focua on the retina by the action of the lenses of the eye, as has
been stated above. Hence, the effect of the convex lens is simply to enable
us to aee an object placed at a diatance of
one inch from the eye, which could not be
aeen vrithout the Iena nearer than six
inches. The result of thia wUl be, that
the object wiU appear, when aeen through
the Iena, six times larger than when seen
by the naked eye.
350 This wiU be seen by comparing
figs. 104 and 105 ; in the former, E S, the
object, is supposed to be one inch from
the eye ; in the latter, E 8 is supposed to
be six inches from the eye. The image of
E 8 on the retina is found by considering that it is produced by the lenses
of the eye, in the same manner aa the image on the aoreen in the camera
obacura by the lens in the hole ; and therefore if we suppose H to be the centre

96

MATHEMATICAL GEOGRAPHY.

of the lenses of the eye, we have only to draw straight lines from S and B
through H, to meet the retina at S' and E', and then S' and E' wiU be the
points where the rays from S and E respectively are brought to a point on
the retina. This being the case, it immediately foUows, that if E S be six
times farther from H m fig. 105 than it is in fig. 104, the size of the image,
E' S', wUl be six times greater in fig. 104 than it is in fig. 105.
Now, in fig. 104, the eye, imassisted, cannot see E 8 distinctly, because
the rays diverge too much, and the lenses of the eye vriU not be poweriW
enough to make them converge to the points E' and S' onthe retina. There
fore tiie convex lens above spoken of vriU be necessary to make the vision
distinct, by helping the lenses of the eye to overcome the great divergency of
the rays, and make them converge with sufficient rapidity to form an uncon-
fiised image on the retina.
351 A very simple way of showing the truth ofthis account of the manner
in which a lens placed close to the eye magnifies, is to look at the object E S,
fig, 104, through a pin hole in a card, instead of through a convex lens. The
hole, like the lens, wiU evidently diminish the divergence of the rays, and
therefore assist the lenses of the eye. Of course the hole greatly weakens
the brightness of the image, because it cuts off a great portion of the rays,
or rather, aUows only a smaU portion of them to enter the eye ; but still
it makes the object distinctly visible, and, as we have explained, magnifies it
by enabling the eye to see it so much nearer than it could do without the
hole. 352 To try this experiment, it is only necessary to look at smaU print
through the hole in the card, placed very close to the eye ; it wUl be found
that we may, by so doing, bring the print within a few inches of the eye, and
stiU see it distinctly, though it vriU not appear strongly marked, on account
of the smaU quanttty of light aUowed to pass by the hole. The card should
then be removed, keeping the eye stiU at the same distance from the print,
and it wUl be perceived immediately how much the hole assisted in making
the vision distinct ; for the moment the card is removed, the print wUl be
come utterly confused and indistinct, so that one letter cannot be distinguished
from another,
353 A convex lens used in this manner, that is, put close to the eye, is
called a simple microscope. It is important to remember that a lens thus used

magnifies simply by enabling the eye to get nearer to the object than it could
do naturaUy, and this it does by helping the lenses of the eye to overcome the
increased divergence ofthe rays.
354 Vision through a Lens not placed close to tlie Eye.—Th&ts is a very
important difference in the action of a lens not placed close to the eye, from that
we have just explained, as we shaU now show.

R,-.

Fig.lOe

Fig, 106 represents a short tube A B C D, at one end of which is a lenS
A B, and at the other a hole H K, not much lai-ger than the pupUof theeye:

THE MICROSCOPE. 97
it is caUed the eye hole, the eye being always placed close behind it, as is re
presented in the figure. E S is any object placed before the lens at a distance
equal to the focal length. The use of the tube A B C D, and the hole H K,
ia to keep the eye always at a certain distance from the lens.
The course of the rays which enter the eye from the two points E and S is
shown in the figure. The rays from E falling on the lens wUl emerge paraUel
to each other, or nearly so, because the distance of the object from the lens is
equal to the focal length ; but the ray E T, through the centre of the lens,
vriU suffer no deviation ; therefore the other rays, after emerging from the
lens, wUl be paraUel to E T, and those which are aUowed to pass through
the hole wiU enter the eye. To find the rays which pass through the hole,
we have only to draw hnes towards the lens from H and K parallel to T E,
and all the rays between theae two hnes wUl get through the hole. Hence the
rays drawn in the flgure, and those only, wUl get through the hole to the
eye ; all the rest wUl be stopped by the tube. The course of the rays from 8
is exactly simUar to that of the rays from E.
355 Now thia being the caae, it is evident that the lens A B discharges
a two-fold office.
lat. It diminishes the divergence ofthe rays, and so assists the lenaea ofthe
eye to make them converge to pointa on the retina. It therefore so far acts in
the same manner as the simple microscope.
2ndly. It magnifies the object, not merely by enabUng the eye to get
closer to it, but also by bending aU the rays in the manner ahown in the
figure. This is a point of considerable importance, as wiU appear more
clearly when we come to speak of the teleacope ; for in the telescope the rays,
without the action of a Iena thua disposed, would enter the eye almost perpen
dicularly, and the image would appear very smaU, or rather, very httle of it
would be seen.

356 The degree in which this instrument magnifies the object E S wiU
ojipear better by comparing the vision tlirough it vrith vision by the naked
eye. In fig. 107, E 8 is supposed to be viewed by the naked eye ; the point

O in thia figure, and in fig. 106, representing the centre of the lenses of the
eye ; the dotted Unea E' O and S' O are the central rays which enter the eye
from E and S produced backwards ; the distance of E' S' from the eye in
fig. 106, is supposed to be about one foot, and E S, in fig. 107, is also sup
posed to be about one foot from the eye. We aay a foot, becauae at that
distance the eye may aee an object distinctly without any axertion ; in fact,
in readir^ smaU print, a person vrith good eyes would naturally hold hia book
at that diatance, or thereabouta, from the eye. The eye could see an object
at aix inches, but not vrithout fatigue.
Now, in flg. 106, if we supposed the instrument removed, the points E' and
S' would eridently be seen by the eye in the same directions as the points E and
S appear to be when seen through the instrument ; in other words, the object
E S appears, when aeen through the inatrument, to be of the same size as
the object E' 8' seen by the naked eye. As far, then, as apparent size ia con
cerned, we may aubatitute the object E' 8' aeen by the naked eye, in place
of the object E S seen through the inatrument.
Then, since E' S', fig. 106, and E 8, fig. 107, are at the same diatance
from O, and aince the images of these two objects on the retina are found by
drawing straight Unes from them through O to meet the retina, it is manifest
H

98

MATHEMATICAL GEOGRAPHY.

that those images wiU be exactly proportional in size to the objects respec-
tively. If, for i latance, E' 8' be ten timea E S, the image on the retina in
fig. 106 will be ten timea larger than that in fig. 107 ; if E 8' be twenty times
E S, the former image vriU be twenty timea the latter, and ao on.
357 Hence the degree in which this inatrument magnifies is obrious ; at
the same time we must observe, that the above explanation is to be received
merely as a general account of the nature of the magnifying power of the mstm.
ment ; for the eye in judging of magnitude is greatfy influenced by a variety
of circumstances which we have not time to speak of here. Thia instrument
ia the astronomical eye-piece in its simplest form.
R' --..

358 Tlie Compound Eye-Piece. — This is shown in fig. 108. It consists of
two lenses instead of one, but in other respects it is exactiy the same as the
simple eye-pie(te just explained. It is, however, a much more perfect instru
ment, and its optical effect, when weU made, is almost fanltieas. The front lens
A B is caUed the field-glass, becauae it enables us to aee a greater extent of
the object E 8 distinctly, than we could possibly do vrith the single lens,
fig. 106. The extent of the object visible through the instrument is com
monly caUed the field of view, and hence the name _/JeW-glass. The lens C D
being next the eye, is caUed the eye-glass. The light coming from the object
E S is bent by each of the lenses, aa ahown in the figure, and enters the eye
as if it came from a larger object E' 8', All that we nave just said respecting
fig, 106 applies, therefore, equaUy weU in thia case.
359 How the Compound Eye-Piece is made Achromatic. — One great
defect of the single lens, fig. 106, is, that it is not achromatic ; in consequence
ofthe different refrangibUity of the different colours, the image seen by the
eye is imperfect and confiised, the violet being more magnified than the red,
and tiie intermediate colours in an intermediate degree. In the compound
eye-piece thia defect ia remedied in the foUowing manner :—
il fig. 109, A B and C G are the two lenses, and E D is any ray from the
object incident on the field-glaaa at D. This ray is of course separated into
its component colours by the dispersion which inevitably accompanies refrac
tion (except the lens be compound). The violet ray wul be more bent than
the red, so that the former wUl fall below the latter, as is shown in the figure,
where D B represents the red ray and D E' the violet.
But the consequence of this wUl be, that the violet ray vriU fall on the
second lens nearer the central part than the red ray, and therefore so far
the second lens wUl produce a less effect on the violet than on the red ray;
for the nearer to the central part a ray is incident on a lens, the leas is it
bent by the lens. Hence, if the two lenses be at a sufficient distance from

THE ASTRONOMICAL TELESCOPE. 99
each other, the fact that the violet is more refracted than the red by the first
lens, and less by the second, may lead to a mutual correction between the two
lenses— i. e., the under refraction of the second may just correct the over
refraction ofthe first. This, it may be shown, wiU take place when the dis
tance between the two lenses is half the sum of their focal lengths. When
the lenses are so placed, it is found that the red and violet, and the other
colours, emerge from the second lens paraUel to each other, and are aU caused
to converge to the same point of the retina by the action of the lenses of the
eye ; for the lenses of the eye are so far achromatic that they always cause
parallel raya, whether of difierent coloura or not, to converge to the same
point on the retina.

R 

360 This eye-piece was the invention of Huygens, but the principle
upon which it acts was pointed out by Boscovich. Tn astronomical instru
ments this eye-piece cannot be uaed in ita perfection on account of ita being
neceaaary to nave the object E S too close to the field-glass, whereby every
spot and flaw in that glass is made visible, and spoils the clearness ofthe field
of view. To remedy this defect, Eamsden placed the lenses a Uttle closer to
each other, and so was enabled to keep the object E 8 at a greater distance
from the field-glass. The lenses are each of the aame focal length in Eams-
den's eye-piece ; they are also plano-convex — i. e., convex with one side plane,
the convex surfaces being tumed towards each other, as is shown in the
figure. 361 The compound eye-piece has many other advantages over the simple
one represented in fig. 106, chiefly arising from the refraction in the former
being divided, aa it were, between two lenses, instead of being entirely
effected by one ; but we have not space to say more on the subject,
V Ofthe Astronomical Telescope.
362 It wUl now require but a few words to explain the construction of
the astronomical telescope ; it is, in fact, nothing more than the camera
obacura repreaented in fig. 103, vrith the addition of Eamsden's eye-piece, to
enable the eye to see more accurately whether the image of a diatant lumi-
noua point, formed on the semi-transparent screen, coincides with the centre
of the cross vrires or not. Furthermore, the screen is either removed or made
transparent, as its semi-transparency is of no use where an eye-piece is used to
view the image and the cross wires, and only has the effect of diminiahing the
brightneaa of the image. It would be abaolutely necessary to retain the
semi-transparent acreen, if a aimple microscope were used inatead of an eye
piece, for without the aemi-transparent acreen the raya that would get into
the eye through a lens placed close to it would be only those whioh come from
the central part of a distant object, ao that the fleld of view would be ex
tremely Umited. But vrith an eye-piece, if the eye-hole is placed in the
proper position, the raya from a comparatively great extent of a distant object
are Drought to the eye. H a

100 MATHEMATICAL GEOGRAPHY.
363 Fig. 110 represents the astronomical telescope. AEFB is thetube,
and C D is me screen, which in the camera obscura above described was semi-
transparent, but is now supposed to be perfectly transparent; it maybe a
piece of plate glass with two flne cross hnes drawn upon it, or it may be
simply a round hole in a piece of brass fixed inside the tube, with two ex
tremely thin wires drawn tight across it. At A B is the lens which produces
the image ofany diatant object at which the telescope is pointed, which image
muat be formed exactly at the transparent screen or hole C D, where the
cross lines or vrires are placed. This lens is caUed the Object Glass, and is, of
course, achromatic and aplanatic, ao aa to form a perfectly diatinct and well-
defined image ofthe object.

X ia the point of intersection of the cross lines or .toss wires, which are
supposed to be so flme and deUcate that the point X ia defined by them in
the most perfect manner poaaible.
Two interaecting lines are found to form the beat kind of mark for defining
a particular point in the interior of an instrument ¦ these linea are generally
at right angles to each other but they are sometimes made to intersect
obUquely. Y is the centre ofthe object glass correaponding to the hole H infig. 103,
and the imaginary straight hne X Y Z, drawn from X through Y, is the line
of collimation, which we have spoken of before. This line is the great and
principal thing to be attended to in the instrument. The instrument itaelf is
nothing but a contrivance for pointing this Une very accurately towards any
particular atar or diatant luminous point. When the line of coUimation
points towards any star, an image of tnat atar ia aeen to coincide exactly with
X, the centre, or point of mtersection, of the cross wires, and this ia the
teat whereby we know whether the line of collimation points in the proper
direction or not.
G M K L is the eye-piece (Eamsden's) already described, the nae of
which is simply to magnify the image of the atar and the croaa wirea, and so
enable the eye to judge the better whether that image ia exactly at the point
X or not. Thia eye-piece is capable of shding in a tube attached to the large
tube, aa shovm in the figure, for the purpose of accurate adjustment, and for
adapting the rision to eyes of different powers,
364 It is impOHant to observe that there is no connexion whatever
between the line of collimation and the eye-piece ; the eye-piece may not be
placed quite straight, or it may distort the image and the wires, which it
always does to a certain extent ; but if it shows the image of the star distinctly
coincident with the centre of the cross wires, we may be sure that the line of
coUimation points exactly to the star,
365 It is also necessary to remark that the cross wirea need not he
placed exactly in the middle of the tube, they may be moved a Uttle to one
side or the other if necesaary ; though it is better that their intersection X
should be as nearly as possible opposite to the centre of the object glass Y,
in order that the hne of collimation may be perpendicular to the object-glass,
or very nearly so,
366 Adj-usiment and Movement ofthe Cross Wires.~The piece of plate
glass on which the cross lines are drawn (or, what is the same thing, the
piece of brass with a circular hole, across which the cross wires are fixed) is
generally made capable of movement backwards and forwards across the
instrument, in the foUowing manner :—

THE MICROMETER.

101

C Q D P, fig. 111, represents the piece of plate glass, having the cross
linea C D P Q traced upon it.
It ia fixed in a flat piece of  6'^^  .p
brass N O, vrith a circular hole
C Q D P, If there is no piece
of glass, the lines C D and P Q
are simply wires fixed tightly
across this hole. The piece
N 0 shdes in a frame of brass
ST, A screw U, and a spring ^
W, act upon the piece NO,''
in the manner shown in the figure, so that by turning the head of the screw
U, the piece N O is caused to sUde in the frame S T towards S, and by the
opposite motion of the screw the spring W acts upon N O, and makes it sUde
the opposite way. Sometimes, however, instead of the spring W there is
another screw, the counterpart of U, and by means of the two acrewa the
piece N 0 ia moved at pleasure, and kept fixed if necessary. The two screws
are used instead of the screw and spring, where it is not necessary to move the
piece N 0, except occasionaUy by way of adjustment.
The frame 8 T pierces the tube of the telescope, and is fixed across it
near the eye end, m the
manner shown in fig. 112, Fir iia
where A B K L is the tele- A ^  Ti
scope, A B the object glass,
K L the eye-piece, S T the
frame ahown in fig. Ill, and
U the screw, by whicli the
piece N O (fig. Ill) ia moved.
In tiiis manner we may, by turning the acrew U one way or the other,
move the croas vrires backwards or forwards across the tube ofthe telescope,
and so adjust the point of intersection of the wires in its proper position, as
wm be explained preaently. VI. The Micrometer.
367 Where it is required to measure the image formed by the object
glass, the thread of the screw D is formed
with great accuracy, and the motion of N O
is made as steady and even as possible.
The head of the screw is also graduated,
as shown in ^. 113, where T Q E S is a
portion of the frame, HE the screw, work-
S5g^oi^gli the end T Q of the frame;
U A U C IS the head of the acrew, consisting
of twoparts— namely, a mUled or grooved
cu-cle Ll, which the fingers lay hold of in
order to tum the screw, and a graduated
P"^ 1 \^^' ^^ graduations bemg shown
m the figure on the rim of this cfrcle. D ia
the mdex, which ia fixed to the end ofthe
frame T Q, and which juat touches the
graduated cfrcle, without, however, imped-
mg its motion. The acrew in this case does
not work exactly in the same manner as that ahown in fig. Ill ; for it is
necessary, evidently, that it ahould move the piece N O after the manner of
an endless screw— tiiat is, the female acrew ia not in the frame as in flff. Ill,
but m the piece N O. In this way the acrew itself does not move in and out
wnen it is tumed round.

102

MATHEMATICAL GEOGRAPHY.

This is shown in fig. 114, which represents a section of the micrometer;*'
where A B C U is the head of the screw, E 8 Q T the frame in wMch the piece
N O moves ; the end of the screw pierciiig the piece NO. D is the index,
which is attached to the end of the frame T Q.

Fig.US

368 a, a, a, a, &c. represent a set of brass points equidistant from each
other, proj lc Ling from the upper side E T of the frame. Iliese pointa are seen
in the field of view, along with the cross-wires : the use of them is to help in
counting the number of tums we give to the screw in any case. When the
screw is tumed round, the vertical croaa-wire passes each of theae pointa in suc-
cession, and they are placed at such distances, that one tum of the screw makes
the vertical croaa-wire move from one point to the next. It is not necessaiy
that these points should be placed with great exactness, as they only serve to
count the number of turns given to the screw.
369 An example wUl best show the use of this micrometer. We shall
suppose that A B and C (fig. 115) are three stars, or
rather, images of stars, seen on the horizontal cross-
wire, and that we wish to measure thefr relative dis
tances from each other. We shaU also suppose that
there are 100 graduationa on the head of the acrew,
which are numbered 0, 1, 2, 3, 4, &c. in order. Bv
means of these graduations, we can teU how mucn
we tum the head of the screw ; for every graduittiBn|5
that passes the index D, as we tum the screw, cor
responds to the hundredth part of a complete revolution.
Suppose now, that we turn the screw until the vertical wire is brought to
meet the star A, and that the graduation seen at the index D is ten. Let ns
then turn the screw untU the vertical wfre comes to the star B, and suppose
that as we do this, the vortical wire passes across four of the points a, a, a, a,
and that the graduation seen at D, when the wfre comes to B, is thirty-
five. Then it follows, the motion of the wfre from A to B corresponds to four
complete tums of the screw, and twenty-five graduations, or twenfy-five
hundredth parta of a complete tm-n.
In Uke manner, let ua move the wfre from B to C, watehing the points and
looking at the graduationa at D, when the wfre comes to C ; and auppose that
the number of points the wfre passes across is two, and the graduationa forty.
Then the motion of the wfre from B to C corresponds to two complete turns
of the screw, and five graduations.
Hence it foUows, that the distance AB is to the distance BC as four
units and twenty-five hundredth parts of unity to two units and five hundredth
parta — that ia, A B is to B C as 4'25 to 205.
370 From this example the use of the micrometer ia manifest. The above
is but a rude representation of the simplest kind of micrometer ; there are
many details and niceties in the construction, which we could not give
without entering into the subject more at length. There ai-e several other
kinds of micrometers, nearly aU, however, depending on the principles above
explained, and consiating of various contrivancea for meaauring the image
seen in the focus of a tclosoope, by meana of tho motion of a graduated screw.

THE DIAGONAL EYE-PIECE.

103

Fiff.iie

VII. The Diagonal Eye-piece.
371 Before we leave the teleacope, we must mention the diagonal eye-
ffljece, which is indispensable in smaU instruments. It is often necessary to
look through a telescope at stars near the zenith, and this requirea the head
ofthe observer to be placed in a very inconvenient position,
except the instrument be so large that a reclining chair
may be placed under it, upon the back of which the ob
server may lay his head, and look dfrectly upwards with
out fatigue. In a smaU instrument it is impossible to do
this, and therefore the foUowing kind of eye-piece, oaUed
diagonal from its shape, is used.
AB C D, fig. 116, represents the tube of the telescope
pointed upwards, and F the field-glass ; between the field-
glass and eye-glass is placed a plane mirror H E, diago-
naUy, so as to reflect the Ught which comes down the tube
in a horizontal dfrection towards the eye; then the eye
glass E receives thia Ught, and transmits it through the
eye-hole to the eye. The only difference between this
and the common eye-piece is, that the mirror is inter
posed between the field-glass and eye-glass, so as to make
the light emerge at right angles to the tube, which arrange
ment requires the eye-glass to be placed, not at the end,
but at the aide of the tube, as is shown in the flgure. The
ray of Ught P F whioh comes down the centre of the tube,
is reflected by the mirror in a horizontal dfrection, and
enters the eye as if it came from the point Q. It ia evi
dent that, aince the eye-piece is only a contrivance for
better ascertaining whether the image of a atar coincides
with the centre of the croas-wfrea or not, this change in
the form of the eye-piece doea not, in
any way, alter the nature of the in- a
strument, but aimply enables the eye "" *^ *
to look at the wfres and image hori
zontaUy intead of verticaUy.
372 The diagonal eye-piece is made capable of sUding on or off the instru
ment at pleasure, so that it may be used whenever occasion requires it.
Good telescopes have generaUy several eye-pieces, or powers, as they are
caUed by opticians, of different magnifying power, which may be employed
according to the nature of the observations, and the state of the atmosphere.
VUI. Of the Astronomical or Beading Microscope.
373 We need say. but little here respecting the misoroscope, as we haTC
already stated what the simple microscope is, and the compound miscroscope
is precisely the same instrument aa the telescope ; being, in fact, a tele
scope, if we may ao use the word, employed to Tiew near instead of diatant
objects. Dr. Goring has proposed to call the compound microscope by the

name engiscope, which weU expresses its nature, as compared with the
telescope ; the former word signifying that which views near, and the latter
distant, objects.
374 Tne compound microscope is shown in fig. 117, with the course of the

104

MATHEMATICAL GEOGRAPHY.

rays, which come from a near luminous point P, through the instrument.
The tube A B C D, tapers towards the object end A B, because the object
glass, being of high power, is necessarily smaU. The object glass is of high
power, in order that it may be able to OTcrcome the great diTcrgency of the
rays coming from an object so near as P, and make them couTerge to a focus
at C D, which, as in the case of the telescope, is supposed to be a piece of
plate glass with cross lines drawn upon it, or simply a hole in a brass plate
vrith cross wires stretched across it. The eye-piece consista of a field-^ass,
eye-glasa, and eye-hole, and ia, in fact, preciaely the same that has been
described in the case ofthe telescope. In microacopes which are used simply
for magnifying, but not measuring, a different eye-piece ia uaed — ^namdy,
Huygen's eyo-piece, aboTe aUuded to.
375 This instrument, though precisely the same in principle aa the tele
acope, differs from it in one important particular — ^namely, that in the miscro
scope, the image formed at CD ia always much larger than the object,
whereas, in the telescope, it ia much smaUer. We may ahow this Tery easily
as foUowa : —
Let A B C D, fig. 118, repreaent the telescope, at least the telescope without

the eye-piece, which we do not now requfre to consider ; C D the screen, T
the centre of the object glass, and E S a distant object, but which, for want of
room on the paper, must necessarUy be drawn near. Then E' 8', the image
of E S, formed at C D, is found by drawing straight lines from E and S
throilgh Y, to meet C D at the points E' and S' ; from which it ia erident
that E' 8' beara the same ratio to E 8 that the length of the tube doea to the
distance of E S from Y ; for inatance, if the length of the tube be three feet,
and E S be 3000 feet from Y, it is evident that E'^S' vriU be 1000 times smaller
than E S.
Now, in the telescope E 8 is always a distant object, and therefore the
image E' 8' formed by the object glass is always considerably amaUer than
the object E 8.
In the microscope this ia reversed, aa is evident immediately from fig. 119 ;

where the image E' S' is found as before, by di-awing straight Unes from E
and S through Y, the centre of the object glass A B, to meet C D at E' and
S'. Now, here E S is very close to Y — in some of the good instruments lately
made, the distance may not be more that jSjth of an inch* — but suppose we
call it an inch, and assume the length of the" ttibe to be aix inches ; tiien it is
clear that E' 8' wUl be six times greater than E S.
376 In both the telescope and microscope, the eye-piece magnifies in the
manner we have explained; hence, in the telescope, the eye-piece alone

' In tills ciitic the object glass is a triple achromatic, consisting
in pairs.

of si:

: lens altogctlicr, united

THE ASTRONOMICAL MICROSCOPE. 105
magnifies, but in the microscope both the object glaas and the eye-piece
magnify. 377 From what has been juat explained, it is clear that, cceteris paribus,
the magnitude of the image E' 8' in hoth inatrumenta is proportional to the
length ofthe tube; the longer the tube, therefore, the greater the magnifying
power of the instrument.
378 In the microscope, the size of the image ia evidently increased by
bringing the object E 8 nearer to the object glaaa : to do thia, the power of
the object glass must be increased, for it must be sufficient to overcome the
divergence of the rays, and make them converge to a focus at C D. Now,
when the object is placed at a distance from the object glass equal to its focal
length, the power ofthe glass is then just sufficient to overcome the divergence
of the rays, and cause them to emerge from the lens paraUel to each other :
hence, to make the rays converge to a focus at C D, either the object glass
must he made a little more powerful, or the object must be moved a Uttle
farther from the lens, in order to diminish the divergence of the rays a little.
It appears, then, that the distance at which the object must be placed from
the object glass of a microscope is a Uttle greater than the focal length of
that glass.
379 Great improvements have of late been made in the manufacture of
object glasses for microscopes, which are now ground, poUshed, and centred
in thefr proper positiona, with perfectly wonderful accuracy. Object glaases
are now made of a focal length of x^th of an inch, which are capable of over
coming a divergence of 120° in the incident rays, and bringing them to an
accurate focus at C D.
380 Till' Beading Microscope. — The astronomical or rearfi»y_ microscope,
which is used for readmg and subdividing the graduations in large instruments,
is a compound microscope, vrith a micrometer such aa that we have above
described. Each graduation of the instrument is generaUy about 5' ; five
complete turns of the screw move the wire of the micrometer from one
graduation to the next, and the graduated head of the screw ia divided into
— suppoae sixty graduations. In this manner each graduation of the screw
corresponds to 1 -
381 As the reading microscope ia a Tcry important part of seTeral useful
inatruments, we must explain the manner in whioh it ia used. In fig. 120,

Kp.120

P Q E 8 T represents a graduated cfrcle capable of moving about its centre O.
The graduations are supposed to be cngraTcn on the rim of this circle, as
ahown in thc flgure, and they are viewed by a fixed microacope A C. i'he
wholo rim P Q E S T is divided into 360 equal parts, and each part sub-

106

MATHEMATICAL GEOGRAPHY.

divided into twelve equal parts, so that each of these subdivisions ia the
twelfth part of a degree, or 5'. The microscope is furnished with a micrometer
and graduated acrew, as above described, the graduated head of the screw
being divided into 60, or 120, or 240, or 300 equal parts — say 60, for simphcity.
Fig. 121 shows the field of riew
of the microscope — ^i. e., what the
eye sees on lookmg throiM;hit. mn
is a portion of the rim P Q EST
of the inatrument seen in the mi
croscope, and, of course, greatly
magnified; a and b are two con
secutive graduations ofthe rim, so
that the space a 6 ia the image of
5' of the rim formed in the focus
of the microscope , C D is a fixed
wfre, paraUel to the graduations a
and b, and firmly fixed in the focus ;
efiB another paraUel wfre — ^viz.,
that which is moved by turning
the acrew of the micrometer, as
above explained. Pointa are seen
on the field of view, to help in counting the number of complete tums of the
screw, as we have described before.
The fltxed wfre c d serves as a mark, and the moveable wfre ef serves to
measure the space between this mark and the next graduation a or b. Five
complete turns of the screw move e/" from ato b, that is, over a apace of 5';
therefore, one tum movea e foyer a space of 1', and the sixtieth part of a turn
movea it over a apace of 1"
Suppoae now that the cfrcle P Q E S T is tumed round, and we wish to
find out through how many degrees, minutes, and seconds we have tumed it.
Let the hinder graduation a, seen in the microscope before moving the rim, he
20° 10', and therefore the graduation b, 20° 15', and suppose that it requfres two
turns and four sixtieth parts of a tum of the micrometer screw to make the
wire e/move from ato c d; then it is erident that iftbe rim were dirided so
minutely aa to show seconds, the graduation opposite the mark c d would be
20° 12' 4"; for a is 20° 10' and it is 2' 4" farther to c d, as shown by the
micrometer screw. After the rim has been moved, suppose that the hinder
graduation a seen in the microscope is 43° 35', and that it takes three tums
and twenty-four sixtieth parts of a turn of the screw to move e firom a to
c d; then the graduation of the rim opposite the mark c rf is 43° 38' 24", a
bemg 43° 35', and c d beuig 3' 24" farther on.
Since, then, the graduation opposite the mark is 20° 12' 4" before, and
43° 38' 24" after turning the rim, it foUows that the difference — namely,
23° 26' 20" — is the nuniber of degrees, minutes, and seconds through which
we have tumed the rim.
382 Thus the use of the reading microscope is obvious ; for though the
rim is only dirided to 5', we can read off and observe as accurately as if it
were dirided to seconds. Now, to diride the rim of a large inatrument accu
rately to 5' — that ia, into twelve times 360 exactly equal parts — is no easy
matter, and costs a large simi of money ; it is eaay, then, to conceive what it
would be to divide it to aeconda — that is, into 60 X 60 X 360 equal parts—
if the engraving of such a, number of Unes so close together were possible.
Hence the importance of the reading microscope is obrious.

THE VERNIER.

107

IX. Ofthe Vernier.
383 We must here briefly describe a very useful contrivance caUed the
Vernier, from the name of the inventor, which takes the place of the reading
microscope in smaUer instruments, being much leaa expensive.
Let P Q, fig. 122, be a portion of the rim of a graduated cfrcle, similar to

that we have just described, which we shaU suppose to be divided into 360
equal parts, each part being therefore 1°. In the figure these graduations
are ahown from 20 to 27°. C D represents the Vernier, which, m this caae,
is supposed to be fixed : it consista of a short graduated piece of brass or
other substanee, the graduation extending from f tog, and in the present in
atance we ahaU suppose them to be six in number ; the graduated edge of the
Vernier Ues as close aa poaaible to that of the rim, without preventing the
motion of the rim round ita centre.
a' is the mark corresponding to the fixed wfre c rf in the reading micro
scope, (fig. 121.) Our object is to fimd what graduation of the rim is exactly
opposite this mark.
Now, if the graduation a of the rim were exactly opposite a', we should
have no difficulty in doing this, for it is manifest that the arrow would then
point at 23°; but this is not the case ; a is a Uttle behind a', and before we
cau teU at what graduation a' points, we must find what fraction of a degree
it is from a to a'.
To do this, suppose that the six graduations of the Vernier, from/to g,
are exactly equal to five graduations ofthe rim, so that, if/ were opposite 20°,
g would be opposite 25°. Furthermore, suppose that the graduation b of the
V emier is just opposite 25, then six graduations of the Vernier are equal to
5°, and therefore one graduation is the sixth part of 5° — i. e., 50' — conse
quently from a' to b is twice 50' or 100' ; but from a to J is tvrice 60' or 120' ;
therefore, from a to a' ia the difference between 120' and 100' — ^that ia, 20'.
It appeara, therefore, that the mark a' points to 23° 20'.
Hence the principle of the Vernier ia obvious ; it enables us to find at
what graduation of the rim the mark a' points, though none of those engraven
on the rim may be exactly opposite a'.
384 GeneraUy, to find how far it is from a to a' we have the foUowing
rule : — Look for that graduation of the Vernier which is exactly opposite a
graduation of the rim ; count on the Vernier what number of graduations it
IS from that graduation to a'; multiply 10' by that number, and then the
result is the number of minutes from a to a'. 10' in this case is the difference
between a graduation of the Vernier and a graduation of the rim, one being
50', the other 60'. In every case the distance from a to a' is found by multt-
plying this difference, whatever it may be, by the number of graduations
from a' to b.
385 If the Vernier consist of thfrty graduations, and these thirty gradu
ations are equal to twenty -nine graduations of the rim ; and further, if the
whole rim be divided into twice 360 equal parts, so that each division is half

108

MATHEMATICAL GEOGRAPHY.

a degree or 30', then each division of the Vernier wiU be the thirtieth part of
twenty-nine half degrees, or, what is the same thing, each dirision of the
Vernier wiU be 29'. In this case, suppose that the graduation b of the Ver
nier, which is exactly opposite a graduation of the rim, is ten graduations from
the mark a'-, then from ato b will be 10 times 30', or 300', and from a' to b
vriU be 10 times 29', or 290'; and therefore froma to a' vriU be the difference-
that is, 10', In Uke manner, if the graduation b oi the Vernier be tweniy
graduations from a', the distances from a to b and from a' to b wUl be
respectively 20 times 30', and 20 times 29'; and therefore the distance from a
to a' wUl be clearly 20', And, in general, the distance from ato a' wfll always
be as many minutes as there are graduations from a' to that graduation ofthe
Vernier which is opposite one of the rim.
386 If there be no graduation of the Vemier exactly opposite one of the
rim, we must m place of it look for that graduation which is most nearly
opposite one ofthe rim. In this case we shall be subject to a small error,
not, however, exceeding 30" in the case just deacribed.
387 The graduations of the Vemier are always numbered, beginning
from a', as js shown in fig. 123. There should always be a lens or simple
Fid 123

microscope attached in some convenient way to the Vemier, in order to mag
nify the graduations, and make it more easy to see what graduation of the
Vernier is exactly opposite one of the rim, or moat nearly so.
388 The Vernier ahown in fig. 123 is one very frequently uaed ; the rim
being dirided into half degreea, and the Vernier into thirty equal parts, which
are together equal to twenty-nine half degreea ; and the graduations of the
Vernier are numbered, beginning from a'. In thia caae we nave the foUowing
simple rule for reading off: —
Look for the graduation of the rim (a) which is just behind the mark a' of
the Vernier ; look alao for the graduation (b) of the Vemier which is exactiy,
or most nearly, opposite one of the rim ; then the number of minutes from a
to a' is the number on the Vernier opposite b, and the mark a' therefore
points to that graduation of the rim which is the number of degrees, or
degrees and a half, shown on the rim at a, together with the nmnber of
minutes ahown on the Vernier at b. In this manner, therefore, we read off
very quickly the graduation the mark a' points at.
In fig. 123, a is supposed to be at 21° on the rim, and J is at 12 on the
Vernier ; therefore a' points at 21° 12'. If a were at 26|° on the run, and
b at 16 on the Vernier, the reading would be 26|° -f 16', or 26° 46'.*
389 We have now sufficiently explained, for our present pm-poae, those
optical principles whioh are most essential to be knoflu in astronomy ; we
have also described the two groat instruments, the telescope and microscope,
by whioh the eyo ia enabled to judge ao accurately of direction, and measure
auch amaU aubdivisions of space. Wc ahaU now proceed to the Transit Tele
scope or Instrument.
* Tlio graduations in ligs. ]'J2 imd 123 have not been made exactly equal to each other by
tlic engraver, but tlie error docs not aflcct the exi'Iauation.

109

CHAPTEE VII.
THE TEANSIT INSTEFMENT.
I. Description ofthe Transit Instrument.
THE Transit Inatrument conaists of a telescope auch aa we have just de
scribed, mounted in such a way that the Une of collimation may move
freely in a vertical plane, which plane ia generally the plane of the meridian,
but sometimes the prime vertical plane, or some other vertical plane suitable
to the observer's purpose.
The transit instrument may be said to be the most perfect, simple, and
useful of aU astronomical instruments : it is capable of the following important
apphcations : —
1st. To determine the position of the meridian plane, and therefore the
true points of the compaaa, at any place.
Znd, To determine the correct time at any place, and so to serve as a
regulator of clocks and chronometers,
3rd. To determine the right aacenaion of any heavenly body.
4th. To determiue the longitude of any place.
5th. To determine the latitude of any place.
When appUed to any of the four former uses, the instrument ia set in the
meridian plane ; but for the latter use it is aet in the prime vertical generally.
H

Fig. 124

E[

^D

K;

391 The Pivots. — The transit instrument consists of a telescope ABC,
fig. 124, attached firmly to a perpendicular axis P Q, which is made of a
conical shape on each side, in order to combine strength and lightness. The
extremities P and Q of thia axia are cyUndncal, of the aame size, and having

no

MATHEMATICAL GEOGRAPHY.

Fig. 125

the same imaginary axis F G— that is, the imagmary line F G runs exactly
through the middle of each (wlinder P and Q, and the cyUndrical surface of
each runs exactly paraUel to F G.
P and Q are caUed the Pivots oi ihe tranait instrument, and the imaginary
line F G is caUed the Axis ofthe Pivots, or, what is the same thing, the Axis
ofthe Transit. It is of the utmost importance that these pivots should be
correctly made, as the goodness of the instrument depends mainly upon them.
Three things are necessary to the perfection of the pivots — ^riz.,
1. They must be truly cylindrical.
2, They must have the same imaginary axis.
3. They must be equal in diameter.
Hence it is obvious, that not only must great paina be taken by the
workmen in turning theae pivots so as to secure the above requisites, but the
observer must take care when he uses the instrument to keep the pivots clean,
and to preserve them from being indented in the least degree by any blow or
rough handling. This caution is given, because it is necessary frequentiy to
Uft the pivots off thefr bearings, and put them down again.
392 Bearings ofthe Pivots. — The pivots do not turn in cfrcular holes, as
might at first be supposed, because cfrcular bearings are not
sufficiently steady, inasmuch aa the cfrcular hole inwMchapivot
tuma must always be a Uttle larger than the pivot, to aUow of
free motion. Instead, therefore, of cfrcular bearings, the pivots
are supported on forks, or Y's, as they are caUed, being of the
shape of the letter Y, (see fig. 125,)
or something approaching thereto.
In fig. 126 is shown the manner
in which the pivot P rests on ita forked bearing
yy, LMN being the pillar or stand to which
the y or bearing is attached. 8 is a fine acrew,
which, being turned, givea a horizontal motion
to the Y, for the purpose we shaU explain pre
sently.* The other pivot Q is supported on a
simUar Y and pUlar, only instead of having a fine
screw such as 8 to move it horizontaUy, it has
one to move it verticaUy up or down. P is
caUed the horizontal Y, and Q the vertical Y.
393 The Telescope. — The telescope has cross
wfres in the focus such as we have described in
the former chapter, which are moved horizontaUy
ly a screw D, in the manner we have explained.
GeneraUy, in smaU instruments, there are one
horizontal wfre and three vertical wfres equi
distant from each other, as is represented in
fig. 127, but in large instruments there are five,
and often seven, vertical vrires.
There are three or four eye-pieces of different
powers which slide in at C, one of which is

* We have represented S aa an ordinary screw with a milled head ; generally, instead ot
BUCh a screw, there are two opposing screws, for the sake of greater steadiness, which are
worked by a lever.

THE TRANSIT INSTRUMENT.

Ul

always a diagonal eye-piece — see former chapter. When we wish to use the
telescope, we must slide in a suitable eye-piece, and move it in or out until
the wfres are seen distinctly, and sharply defined. We must then dfrect the
teleacope to a atar. and if the star is also seen distinctly and weU defined, the
telescope is properly adjusted as far as the focus is concerned ; if not, the
wirea in the locus must be moTed in or out tiU the image of the star becomes
weU defined. If, on moring the eye a little to one side or the other of the
eye-hole, the star appears to keep steadUy on one of the wfres, this shows
that the focus is correctiy adjusted.
394 The Stomd and Pillars. —
Theae are shown in fig. 130, where P N
and QM are the two piUars which
support the Y'a and piTots P and Q.
A C is the telescope, N M is the base
of the atand, which ia generaUy cfrcu
lar, and, for greater steadineaa, sup
ported on three short legs 8 U and T,
which haTC screws for shortening or
lengthening them, in order to make
the stand as nearly as possible hori
zontal, and therefore the piUars Ter
tical. The piUars in large fixed in-
sfrumenta are made of stone, firmly
imbedded in a hard foundation, but in
smaU portable instruments they are of
metal, finnly braced to the stand N M,
so that they may not be capable of
shaking or trembUng.
395 Illumination ofthe Wires in the Focus. — At night it is necessary to
flluminate the wfres, in order to make them visible. This ia done by means
of a lamp L, placed on a atand close to one of the pivots. The pivot ia
pierced, and the conical axis is hoUow, so that the Ught from the lamp, pass
mg throi^h the hole in the pivot, enters the middle of the tube of the tele
scope at E. There is a plane reflector placed diagonaUy acroaa the teleacope
tube at E, by which the hght from the lamp ia reflected down the tube to the
focus, and in this manner the vrires are iUuminated. The reflector haa a
good-sized hole cut in the middle of it, so that it may not intercept any of
the Ught which comes through the object-glasa down the tube to the eye.
The lamp has a moveable shade, by which the degree of illumination may be
diminiahed, which is necesaary when observing faint stars.
396 Object of Mounting the Telescope in this manner. — The object ia, in
the firat place, to make the telescope move with great steadiness in a plane ;
this is effected by the long axia P Q ; for it is evident that the longer the
axia is, the leas effect vriU imperfections in the pivots have in making the
teleacope move unevenly. In the second place, the bearings of the pivots are
made moveable horizontaUy and verticaUy, by means of fine acrewa, aa above
deacribed, in order to place the axia more accurately in any requfred poaition
—as, for inatance, in or perpendicular to the plane of the meridian ; the stand
is placed in the proper position at first, as nearly as can be judged, and then
the further and complete adjustment of the axis is effected by the deUcate
motion ofthe screws.
397 The Level. — The tranait instrument ia always accompanied by a

Fig. 129

spfrit level, for the pur
pose of making the axis
perfectly horizontal. The
construction and use of
the level is as follows : —
A B, fig. 129, is a glass
tube, sUghtly curved, and

112

MATHEMATICAL GEOGRAPHY.

almost, but not quite, fiUed with alcohol, ao that a bubble C D is left in the
tube. Thia bubble wUl, of course, always ascend to the highest part of the
tube, in whatever poaition it may be held, and so vriU serve as a mark of the
inclination of the tube ; for if the inclination be altered, the highest part is.
not where it waa before, and therefore the bubble wiU change ita positidft, ;
since it must alwaya ascend to the highest part of the tube.
The curvature of the tube, as shown in the figure, is considerably ex
aggerated, for the purpose of showing the nature of the level ; in practice,
the curvature is so smaU that the tube appears quite straight to the eye.
The amallneaa of the curvature makea the leaat change of inclination of the
tube evident ; for the more nearly atraight the tube ia, the more does the
bubble move when the incUnation of the tube is altered. The tube is not
made quite straight, because, if it were so, the moment one extremify was
elevated in the least degree aboTC the other, the bubble would immediately ;
move to the former extremity — in fact, the inatrument would then be too
sensitive, and would requfre the tube to be placed always in a horizontal .
poaition vrith a degree of exactneas not attamable in practice. This is the
reason why a sUght curvature is given to the tube.
398 The line C D joining the extremities of the bubble wUl be always
horizontal if the tube be of uniform bore and curvature, otherwise, in conse
quence of capUlary attraction, thia wUl not be the case. However, the hori-
zontaUty of this line is not by any meana essential, for the principle of the
instrument consista in this, that any change in the inclination of the tube to
the horizon wiU be immediately shown by the motion of the bubble.
399 Hence we have the foUovring conclusion upon which it wiU be seen
the use of the level depends — ^riz., that if the bubble does not move when
we change the poaition ofthe tube, it foUowa that the incUnation of the tube
to the horizon has not been altered by the change of poaition.
400 The tube is fixed in a
S frame of brass A B, shown in
r.  .^ fig. 128 ; the upper part ofthe
c >_<¦ J \\\B frame is open so as to snow
the upper surface of the tube; ,
on the top is a straight scale
F G, marked with a number of
equidistant vertical Unes, the
use of which is to enable the
observer to note the position of the bubble vrith accuracy. The frame A B
has two legs A C and B D of equal length, and cut at the bottom in the shape
of invertedTY's, for the purpose of being placed upon the pivots ofthe fransit
instrument, the distance from C to D being the same as the distance between
the two pivots, ao that C may reat on one pivot, and D on the other.
401 From what has been above stated, it foUows, that if we place the
level vrith the legs C and D upon a rod or axis P Q, in the manner ahown in
fig. 133, and note the place ofthe bubble by looking at the scale FG; and
Fig.ia.-i

F

a

 i
J^
^
¦J ^
.-.  r
c
D
tiiis being done, if wo change the position ofthe level by placing the leg C at
tho end Q, and D at P, and again note the place of the bubble; then, if the
bubble is not in the same place as before, one of the extremities of the
THE TRANSIT INSTRUMENT. 113
rod P Q must be higher than the other ; but, if the place of the bubble is un
changed, the extremities must be exactly on the same level, and therefore the
rod ia horizontal. Thia ia manifeat : for, if one of the extremitiea, P or Q, be
higher than the other, the above change in the position of the level evidently
changes ita inclination to the horizon, and therefore the bubble must move ;
but if one extremity of the rod is not higher than the other, then the change
of position does not alter the incUnation of the tube to the horizon, and there
fore the bubble does not move.
n. Examination and Adjustment ofthe Transit Instrument.
402 Examination ofthe Transit. — It is very important that an observer
should be able to examine anew instrument he is about to purchase, to deter
mine whether it is accurately constructed or not, and an inatrument which has
been for aome time in use, to discover whether it has suffered any injury.
The first thing to be looked to is the steadiness of the stand and piUars on
which the instrument rests : they should be weU braced together, and the
three screws, or short legs on which the whole stands, should turn tightly,
and be perfectly free from any tendency to shake. The Y's should be made
with great care, and of hard material, and thefr motion should be smooth and
steady. The telescope shouldT^e strongly supported and well balanced, so as to rest
at any inclination, and to be eaaUy turned about the pivots. The wfres in the
focua ahould be seen aharply and diatinctly defined when the telescope is pointed
towards the edge of a tolerably bright distant object by dayUght, Sometimes,
owing to bad workmanship in the object-glass or eye-piece, and to the eye
hole being too large and too near the eye-glass, the vrires appear to be doubled
or frebled, and very indistinct, and uo adjustment of the focua wiU make
them appear sharp and single. This defect arises from Interference or Dif
fraction, and may sometimes be remedied by diminishing the eye-hole, which
need not be larger than the pupU of the eye, and ought to be exactly in its
proper place.
The vrires should move perpendicularly across the tube of the telescope
when the screw which moves them is turned. If they continue to appear
weU defined when the screw ia turned, thefr motion is correct.
403 Examination ofthe Pivots. — Iftbe pivots are imperfect in any way,
the instrument ia good for very Uttle. To test the pivots, place the level on
them in the manner represented in fig. 127 (bis), and turn the telescope

slowly and careftdly round, watching the bubble aU the time ; then, if the
bubble keeps steadUy in the same position, we may be sure that the pivots
are truly cyUndrical, and have the same imaginary axis ; at least, if there bo
any inequaUty in the shape of one pivot, there must be precisely the same in
the other, and the two errors destroy each other. Of course the pivots ought
to be cyUndrical, and they may always be so made ; but corresponding and
exactly equal deviations from the cyUndrical form in each pivot would not

114 MATHEMATICAL GEOGRAPHY.
affect the performance of the transit inatrument. That auch equal imperfec
tions should exist is, of course, a scarcely possible accident, and therefore we
may conclude that, if the bubble does not move as the telescope is turned
slowly round, the pivots must be cylindrical and conaxial, if we may use the
word in imitation of ' concentric'
404 But it is necessary also that the pivots should be of exactly the same
size ; the reason why wiU appear when we come to apeak of the adjustments
of the instrument. To examine this point, place the level as before, the leg
C on the pivot P, and D upon Q, (see fig. 127, bis,) and note the position of
the bubble ; then raise the level off the pivots, and, taking up the telescope,
carefuUy reverse the pivots, that is, place the pivot P on the Y upon which
the pivot Q rested before, and Q on the Y upon which P rested before ; P
wUl then be on the side M, and Q on the side N. Haring done this, put the
level again on the pivots in the same poaition as before ; that is, the leg C on
the aide N, and D on the aide M, so that now the leg C wUl reat on the pivot
Q, and D on P. Then note the position of the bubble, and if it remains
exactly where it was before, and continues in that position when the telescope
is turned slowly round, we may be sure that the pivots are of exactly equal
size. 405 It might be easier to test the equality of the pivota otherwise, hut
the method just described ia that most suitable with reference to the use of
the equaUty of the pivots. In fact, it is necessary often to reverse the pivots,
and it is on thia account that their equaUty ia a matter of importance ; other-
wiae they might differ in aize without cauaing any error in the performance of
the instrument.
406 Hence the goodness of the pivota is completely tested by the fol
lowing methods of examination, viz. : —
1. Place the level on the pivots, turnthe teleacope slowly round, and wateh
the bubble.
2. Eeverse the pivots (but not the level) and note the bubble again as the
telescope is turned slowly round.
If in both cases the bubble remains unmoved, and in exactly the same
place after the reveraion of the pivota as before, then we may place perfect
reUance on the accuracy and equaUty of the pivots.
III. Adjustments ofthe Transit Instrument.
407 We have not space to say more respecting the examination of the
transit instrument than what haa been juat stated. It ia highly important
for an observer to be able to examine an instrument, and determine whether
it has any imperfections or errors which ought not to exist, and which he
has neither the skiU nor the means to correct. Such errors are those just
alluded to, which it is the part of opticips
. K and not the observer to correct, and which
completely spoU the performance of the instru
ment. But there are other errors, which the
observer and not the optician must get rid of,
and which requfre repeated correction. These
are usuaUy called the Adjustments of the tran-
Q sit inatrument.
J^^^^  ¦'- 408 Adjusimentof the Line of Collimation.
O —In fig. 130 (bis), A B is the telescope, P and
Q the piTots, and F G the imaginary axis of
the pivots; then, the pivots being supposed
to be perfectly cyUndrical and conaxial, it w
manifeat that the Une F G remains unmoved
when the telescope is turned about "the pivota.
Now H K, the line of coUimation, ought to be

THE TRANSIT INSTRUMENT.

115

perpendicular to this line, in order that it may move accurately in the same
plane ; for, if it be not at right angles to H K, it wUl describe a conical and
not a plane surface. It is neceaaary, therefore, to adjuat the Une of coUima
tion 80 that it may be perpendicular to the imaginary axis F G about which
it turns. To do this we must remember that by turning the screw D, we move one
extremity of the line of coUimation ; for the Une of collimation is that line
which ia drawn from the point of interaection of the cross wirea through the
centre of the object-glass, and by turning the screw D we may moTe the
cross wfres either to the right or to the left at pleasure, and ao place them in any
requfred position. Hence we only requfre a method or test for determining
whether H K is perpendicular to F G or not. The following simple method
ia the moat accurate that oan be employed :—
409 Beversion a test of Per -
pendicula-rity. — Suppoae P Q
and A C, fig. 131, to be two
rods fixed together, not quite
at right angles to each other,
the extremity A of the rod
A C being a Uttle on the right
ofthe true perpendicular E S.
Let us now reverse the extre
mitiea P and Q — that ia, let us
take up the rods and tum them
over, ao as to place P where Q
was before, and Q where P was
before ; which, being done, it
ia clear that the rod A C wUl
now he in the position A' C,
the extremity A' being as much
to the left ofthe tme perpendi
cular E S as A was to the right
of it. ThuaPQACrepresentthe
rods in one position, and P' Q'
A' C in the reversed position,
the line E S, which is perpendicular to P Q, being exactly half- way between
AC and A' C'.
Hence this reveraion ia a test by whioh we can determine practically whether
A C is perpendicular to P Q or not. If A C is not perpendicular to P Q, as
above supposed, the reversion of P and Q wUl cause the rod A C to Ue in a
different position to that in which it lay before ; that is, after the reversion
the extremity A of A C wfll fall as much to the left of the true perpendicular
aa it was to the right before, or vice versa. But if A C ia perpendicular to
P Q, then the reveraion vrill produce no change in the poaition of A C.
410 To apply thia to the tranait instrument, we have only to auppose
P Q to be the imaginary axis of the pivots, and A C the lime of collimation ;
then, if we take up the telescope and put it down again, reversing the pivots,
we ahaU not alter the position of the Une P Q, becauae the pivota are of
exactly equal size, (and here the importance of the equality of the pivots is
manifest ;) in other words, after the reversion the imaginary axis of the pivota
will lie exactly in the same Une as before. Hence, if the Une of coUimation
points in exactly the same dfrection after the reversion as before, it must be
at right angles to the imaginary axis ; but if this is not the case, the two Unes
are not perpendicular to each other.
411 Hence we derive the foUowing method of adjuating the line of collima
tion so aa to make it perpendicular to the imaginary axis about which it turns.
Point the telescope to some distant object, say a star, and suppose that the
star ia seen at the centre of the croaa wires : take up the instrument off tha
i2

116 MATHEMATICAL GEOGRAPHY.
Y's, and put it down again carefully, with the pivots reversed, and point it at
the atar again ; then, if the atar appeara again at the centre of the cross wfres,
the Une of collimation is perpendicular to the axis; but if the star is aeen
either on the right or left of the centre of the wfres, the Une of coUimation is
not perpendicular to the axis.
To adjust the line of coUimation, let C, fig. 132, be
the centre of the wfres, and 8 the star, seen, after the
reveraion, to the right of C ; then, by turning the screw
D, (fig. 130, bis,) move the centre of the cross wfres to
the nght until it comes to the point C, which is half
way between C and S. This being done, the line of coUi
mation becomes perpendicular to the axis. The reason
why we moTC the centre of the cross wfres half-way
towards the star, is because the point 8, which marks
where C waa before the reversion, falla aa much to the
right of the true perpendicular as C, after the reveraion, doea to the left.
412 Iftbe acrew D has a graduated head, we may move C half-way
towards S with accuracy ; but if not, the eye must judge as weU as it can the
half-way point C. To test whether the centre of the cross vrires has been
moved into the proper poaition exactly, reverse the pivots again, and if no
change takes place m the position of the star, the position of the vrires is
correct. Otherwise the adjustment must be made again. A few trials will
answer to make the adjustment of the Une of coUimation complete.
In each case, before the reversion, the star should be brought to the cenfre
of the wfres ; this is easUy done by turning the telescope tUl the star comes
on the horizontal wire, and then turning the acrew of the horizontal Y, until
the star (which vrill appear to move along the horizontal wfre as the screw of
the Y is turned) comes to the centre of the wfres.
The atar made use of for thia adjuatment ahould be the pole star ; the
apparent diurnal motion of any other star, whUe the pivots are being re
versed, would give rise to some error, but the motion of the pole star is too
slow to be perceptible in so short a time. A distant mark on some building
ia what is generally employed for thia adjustment in large fixed instruments;
but it may not be easy for a traveUer to find auch a mark when required, in
asmuch as it must be a well-defined point at a considerable distance from the
observer. 413 Adjustment of the Aris of ihe Transit Instrument by the Level. —
The next thing to be done is to make the imaginary axis of the pivots
oerfectly horizontal by means of the level, so that the plane in which the
line of collimation moves may be a vertical plane.
Before making this adjustment, the instrument should be placed, as nearly
as itis possible to judge, mits proper position, either inthe meridian or in the
prime vertical, aa the occasion may requfre. To place the instrument nearly
in the meridian, point the telescope towards the Pole star, or rather about a
degree and a half on one side of the Pole star, towards the middle of the
Septemtriones, at the same time keeping the bubble as near the middle ofthe
level as possible. If this be done, the instrument wiU not be much out ofthe
meridian ; at least it wiU be sufficiently near the meridian plane to enable the
observer to place it accurately in that plane by a further adjustment, which we
ahall soon explain.
414 Another point to be attended to before making the adjustment of
the axis with the level, is to examine the motion of the horizontal Y when its
screw is turned, in order to secure the perfect horizontaUty of that motion.
If this be not done before adjusting the axis, then any motion of the horizontal
Y which may be afterwards neceaaary, wiU derange the adjustment of the
axis. To make the motion of the horizontal Y perfectly horizontal, we must
give its screw a few turns, and note the effect produced on the bubble of the
level. If tho bubble remains stationary, we may be sure the horizontal Y

THE TRANSIT INSTRUMENT.

117

moves truly horizontaUy ; but if the bubble moves, this is not the case. If the
motion of the Y is not found correct in this way, we have only to turn one of
the foot screws or short legs on which the stand is supported, untU the bubble
ceases to move, when the screw of the horizontal Y is turned.
415 These points being attended to, we may proceed to adjust the axis
by die level as foUows : —
Place the level with its legs C and D resting uponthe pivota P and Q, and
note the place of the bubble ; afterwards take up the level, reverse it, and put
it down again, ao that C may rest on Q, and r on D, and note the place of
the bubble again. Then, if the bubble haa not altered ita position, we may
be sure that the imaginary axis of the pivots ia perfectly horizontal ; but if the
bubble haa moved, tum the acrew of the vertical Y tUl the bubble moves half
way towards its original poaition. It wUl then be found, on reversing the level
again, that the bubble does not move, and therefore that the axis is horizontal.
If, however, the bubble should move a Uttle after the second reversion,
(which may happen if the adjustment is not carefaUy made,) it vriU be neces
sary to move the bubble, by turning the screw of the vertical Y half way
towards its position after the ffrst reversion. A few trials will soon make the
?xis qmte horizontal, which wiU be made manifest by the position of the
hubble not being affected by the reversion of the level.
416 We have here described the adjustment of level, as being made by
moving the vertical Y. In most portable instruments, however, the vertical
Y is immovable, and the adjustment of the axis is made by turning the foot
screw or short leg which is

Fig .13 7

under the horizontal Y. The
stand on which the two pUlara
are aupported is often cfrcular,
as is ahown in fig. 137, where
N P M Q are the two pUlars ;
P Q the axis of the pivots, the
horizontal Y being at Q ; H, K,
L the three foot screws, one of
which, L, is immediatehr under
Q, and the other two, !^and H,
equidistant from L. By turn
ing L, it is evident we raise or
depress Q, and so we may make
the line P Q horizontal. The
previous adjuatment, above de
scribed, by which the motion of
the horizontal Y is made truly
horizontal, ia effected by turn
ing either of the screws H or E. The subsequent turning of L wUl not
derange this adjustment, if H and K be equidistant from L, and N exactly
oppoaite M.
417 Adjustment of the Vertical Wire. — It is important that the vertical
wfre in the focus of the teleacope ahould be truly vertical, for then it wUl
ahow, through its whole length, the vertical plane in which the centre of the
wfres movea when the telescope is turned about its pivots, or rather, the
vertical plane described by the line of coUimation : so that, if a star be seen
on any part of the vertical wfre, we may be aure that it ia in the plane
deacribed by the line of colUmation, without having to turn the teleacope, ao
aa to bring the atar exactly to the centre of the croas wfres. Thia wUl often
aave trouble ; and indeed it ia essential in nice observations not to be obliged
always to bring the centre of the cross wfres to bear upon any star we may be
obserring, but simply to aUow the star to move acroaa the field of view, and
meet the vertical vrire wherever it may happen to do ao, whether at the centre,
or above it, or below it. It is, lowjver, better to point tho teleacope ao that

118

MATHEMATICAL GEOGRAPHY.

the star may move across the central part of the field of view; for the vision is
not alwaya distinct near the extreme parts of the field of view.
To determine whether the vertical wfre is truly vertical or not, we have
only to bring a star upon it, and gently turn the telescope, the axis having
been made truly horizontal by the previous adjustment; then if the star
appears to run along the wfre, the wfre is truly vertical ; but if the turning of
the telescope makes the star appear to move off the wfre, then the wfre is not
truly vertical.
If the wfre be found, on examination after this manner, to be out of the
vertical, the wfres must be tumed round a Uttle by means of a screw, which
is generally accessible to the observer ; but sometimes it is not, or there is no
screw, and then this adjustment must be left to the instrument maker.
418 Meridian Adjustment of the Transit Instrument. — Having placed the
inatrument vrith its axis perfectly horizontal, and the telescope moving nearly in
the plane of the meridian, and having made the motion ofthe horizontal Y truly
horizontal, one more adjustment is requfred, in order to place the instrument
exactly in the meridian — ^that ia, so toplace it, that the line of coUimation may
move truly in the meridian plane. Tnis may be effected, vrithout deranging
the previous adjustment of the axis, by simply turning the acrew of the
horizontal Y. It remains, therefore, to explain the test by which it may be
known whether the Une of coUimation movea in the vertical plane or not.
419 Superior and Inferior Transits of a Circumpolar Star test the
Meridian Adjustment. — Let ua conaider the cfrcumpolar motion of any par
ticular star not far from the pole, as, for instance, a tTrsae Majoris. This star
describes a cfrcle about the pole in twenty-four hours, and never sets ; it wiU
therefore cross the meridian twice every twenty-four hours, once below the
pole, and once above the pole. The star's tranait across the meridian below
the pole is caUed ita inferior transit, and that above the pole ita superior
tranait. The interval of time between the auperior and inferior fransite of
every atar is exactly twelve hours, sidereal time.
Hence we have an accurate test by which to determine whether the line
of colUmation moves in the meridian plane or not ; for if it does, the interval
between the two appearances of the star on the vertical wfre wiU be exactly
twelve hours aidereal time ; but if it does not, the interval wUl be either
greater or less than twelve hours. All that we have to do, therefore, is to
watch a Ursa; Majoris, or any other
cfrcumpolar star, when it is below
the pole, and note the exact time
when it crosses the vertical wire ;
and in about twelve hours, when it
wiU be above the pole, watoh it
again, and note the exact time of
its coming on the vertical wire:
then if the interval between the
two times is exactiy twelve side
real hours, the Une of collimation
moves in the meridian plane;
otherwise it does not.
420 To explain thia important
point more completely, let P (fig-
134) be the pole, Z the zenith,
Q 8 8' E T' T the cfrcle which the
atar deacribes about the pole, S
being the place of the superior
tranait, and T that of the inferior.
Also suppose that the line of colli
mation does not move exactiy m
the meridian plane, and that Z S x
is the portion of the great circle

THE TRANSIT INSTRUMENT. 119
it describes on the celeatial sphere, whioh circle of course passes through the
zenith Z, aince the plane in which the line of colUmation movea ia made
fruly vertical by the adjustment of the axis of the tranait inatrument.
Now, when the atar is at 8' it wiU bc seen on the vertical wfre, if the
telescope be pointed towards it ; and again, when it comes to T', it wUl also
appear on the vertical wfre, the telescope, of course, being sufficiently lowered,
that the atar may be seen again in the fleld of view. The interval of time
between these two appearances on the wfre wiU be the time the star takes to
move over the space 8' 8 Q T T'. Now the time the star takes to describe
the space S Q T is twelve hours exactly ; therefore the interval between the
two appearances of the star on the vertical wfre wUl be a Uttle greater than
twelve hours, the excess being the time the atar takes to move from 8' to S,
together with that from T to T'.
Hence it is manifest that if the line of colUmation move eastward of the
pole, aa ia represented in the figure, the time reckoned from the superior
to the inferior tranait across the vertical wfre vrill exceed twelve hours ; and
vice versa, if the line of colUmation move westward of the meridian, the same
interval of time wiU faU short of twelve hours.
421 To find out the angle of deviation 8 Z 8' of the plane in which the
line of coUimation moves, mathematicians give a formula by whioh it can bo
computed from the observed interval between the two transits across the
vertical wfre ; but thia formula requfres both the latitude of the place and
the dechnation of the star to be known. We shaU give here a different
method, which has the advantage of being easUy underatood, and requfres
neither the latitude nor the declination of the star to be known.
To apply this method it ia necessary that the screw of the horizontal Y
should be very accurately made, in fact, that it ahould be a fine micrometer
screw, and have a graduated head, auch aa we have afready described. There
would be practical difficulties in making a screw of this kind work correctly ;
but a micrometer acrew, to move the wfres of the focus, which is often added
to transit instruments, would answer the same purpose. It is easier, in
explanation, to consider that the Y is moved.
IV. Method of finding the True Time of Transit ofa Star across the Meridian
with a Transit Instrument not exactly in the Meridian Plane.
422 Ofthe Clock, or Chronometer. — We must say a word respecting the
instrument for measuring time, which must alwaya accompany the tranait
instrument. When the observer never has to move from place to place, the
clock wUl be the proper instrument to use for measuring time; otherwise, as a
clock ia not portable, he must employ a chronometer, which is a large watch of
peculiar and very accurate constmction. The chief thing to be noticed
respecting the chronometer is, that it has a peculiar scapement, which gives
a distinctly audible and sharp tick. It is by Ustening to thia tick that the
observer counts time ; for he cannot look at the hand of the chronometer at
the same time tbat he is looking through the telescope, and therefore he
must use his ear for observing time. The seconds hand of the chronometer
is the large hand, and not the minute hand, as in a common watch. Ihe
seconds hand doea not move Uke that of a watch, but'dropa from one aecond
mark to another on the dial plate in a remarkably ateady and regular manner,
making a aharp tick each time. The chronometer, we shaU auppose, is regu
lated exactly to sidereal time.
423 To determine the effect of turning ihe Screw -of the Horizontal Y. 
Suppose the telescope to be pointed at any particular star, S, fig.134 (bis), and
that by turning the screw of the horizontal Y the vertical vrire A B ia made
to Used the star, that ia, to paas exactly through the centre of the image of
the star, so that half that image may appear on one side of the wire, and

120

MATHEMATICAL GEOGRAPHY.

Kg.l3 4

half on the other. Then, in consequence of the
diurnal motion of the heavens, the star wiU move,
but by turning the screw of the horizontal Y, we
may make tbe vertical wire always to foUow the
star, so that, when the star has moved to S', the
vertical wfre shaU move to the position A' B', and
still bisect the star. It wUl requfre some practice
to be able to tum the screws so as to keep the
wfre always bisecting the star; also the screw
must be accurately made, and the motion easy and
smooth: but very soon an observer wfll acquire
the power of doing this with the greatest ease,
in fact quite mechanicaUy and habituaUy.
Now this being the case, listen attentively to the ticking ofthe chronometer,
keeping the vertical wire upon the star by turning the screw of the Y, and
just at a tick cease turning the screw and let the star move off the wfre ;
then look at the graduated head of the screw, and note the graduation shown
by its index. Having done thia, look again at the star, which of course wfll
now have moved some way from the wfre, and tum the screw tiU the wire
comes up to the star ; then, just at a tick, cease turning the screw, look at
the graduated head, and note the graduation shown by the index.
During these operations the ticks of the chronometer must be carefiilly
counted, so as to observe by the ear the number of seconda that elapse
between the two ticks at which the motion of the screw was stopped.
424 Now suppose that A B, fig. 134 (bis), ia the place of the vertical wire
at the inatant (or tick) when the motion of the acrew ceaaea the firat time,
and A' B' its place the second time ; and suppose also that the number of
seconds counted whUe the star was moving from 8 to 8' is ten, and that the
number of tums of the screw of the Y which produced that motion is two,
then it is evident that since two tuma of the screw correspond to ten aeconds
of time, one turn corresponds to five seconds ; that is, one tum of the screw
moves the wfre over a space which the atar takes five seconds to describe,
so that if the star be on the wfre at any instant, and one forward tum be
given to the acrew of the Y, it wUl be five aeconds before the star comes on
the wire again.
In general, divide the number of seconds counted by the corresponding
number of tums of the screw, and that wiU give the number of seconds
corresponding to one tum of the screw, and so determine the effect of
turning the screw.
425 It wUl be found that the number of seconds corresponding to one
turn of the screw of the Y wiU be greater at the infe
rior than at the superior transit. The reason of this is
manifest from fig. 136 ; for, supposing that one tum
of the screw moves the cfrcle of coUimation* from Z T
to Z T', T T' is greater than 8 8', and therefore it wUl
take a longer time for the star to perform the former
distance. 426 To find ihe exact Time of Transit across the
Vertical Wire in any position. — Let Z 8 P T, fig. 136,
be the meridian, Z the%enith, P the pole, S' S Q T T' E
the circumpolar course of the stai-, Z S' T' the vertical
cfrcle deacribed by the line of collimation, which is not
supposed to move exactly in the meridian,
A Uttle before the atar comea to 8', that is, a httie

FdgJ.35

» That i.s the circle which the line of collimation describes on the celestial sphere as the
telescope is turned about its axis.

.THE TRANSIT INSTRUMENT. 121
before it comes on the vertical wire at its superior transit, look at the chrono
meter, and note the hour, minute, and second ; note alao the graduation of
the screw of the Y, shewn by its index. Then, counting the aeconda or
ticka carefuUy, watch the star, and by turning the screw, bring the wire upon
the star just at a tick ofthe chronometer; note the graduation of the screw,
(as descnbed in Art. 424,) bring the wire again on the atar, and again note the
graduation of the acrew, counting the ticka all the time. Suppose the results
of theae observations to be as follows : —
(1) Graduation of screw before it ia moved  0
(2) When the wfre ia brought upon f Time noted  l" 2"" 3»
the star the first time , , ,lGraduation of screw shows IJ turns,
(3) Ditto, ditto, the second time ,{ J™J ^2*^* i. " ' i " oi l" ^'
^ ' ' ' (-Graduation of screw shows 3^ turns.
Then from (2) and (3) it foUows, as we have explained in Article 424, that
one tum of the screw corresponds to 2' : therefore, if we auppose 3^ tums to
be given to the screw backwards, whioh wUl put the line of coUimation
where it was orignaUy (that is, at 8'), this wUl correspond to 6J' ; in other
words, the star was at 8' 6^' before the time (3), and therefore the exact
time of the star's crossing the vertical wire in its original position was 1" 2'° J".
In this maimer the exact time of a star's crossing the vertical wfre, in
whatever position it is placed, may be easUy found. The rule in general is
as foUows : —
Supposing the graduation of the screw originally to be 0 (any other number
wfll do aa well), subtract the time (3) from the time (2), and the number of
tuma (3) from the number of tums (2), divide the former difference by the latter,
multiply the quotient by the number of turns (3), and subtract the result
from the time (3) : then the time so obtained wUl be the exact time when the
star crossed the vertical -wfre in its original position (1).
427 The above method, or something equivalent, is absolutely necessary
for accuracy, because it may happen, and generaUy happens, that the star
crosses the wfre between two ticks. Astronomers always guess the instant,
or fraction of a second, between the two ticks, when the star ia ou the wire,
and to attain greater accuracy they have three, five, or seven wires in the
focua, equidistant from each other (see fig. 127). They judge, as weU as they
can, how far the star is from each wfre at the tick just before it crosses it, so
determine the time of transit across each wfre, and, by taking an average,
the time of tranait across the middle wfre.
428 To find the exact Time of a Star's TraTisii across the Meridian.—-
Eeferring to the aame figure and letters as in Art. 426, and supposing everj-
tbing the same as in that article, find the exact time of the star's being at S',
by the method just explained : find also, in the same way, the exact time of
the star's being at T', by making the observations at the inferior transit, and
suppoae that one turn of the acrew corresponds to 2' at S', and to 3^ at T'.
Furthermore, let the time of the star being at S' be P 2'" I", and the time of
its being at T', 13" 2" 10|'. Then it foUows, that the time the star takes to
move from S' to T' is 12" 0°" 10', and therefore, since the time from 8 to T
is 12'" exactly, the two times, from 8' to S and from T to T', must together be
10'. But since one turn of the acrew of the horizontal Y at 8' correaponds
to 2', and at T' to 3', the apaces S S' and T T' must be in the proportion of
two to three, and therefore the whole time of describing these spaces being
10", it foUows, that 8 S' ia described in 4', and T T' ia 6'. Now the time of
the atar'a being at 8' is 1" 2"" |' ; therefore the star wUl be at 8 in 6' more,
that is, at the tune 1" 2"" 65'. It appeara therefore that the exact time ofthe
atar'a creasing the meridian at S ia 1" 2™ 6|'.
429 In general, to find the time of the star's being at S, we must find the
timea of its being at 8' and T', by the method above explained, and thence
the time it takes to move from S' to T', The excess of thia time over 12"

122

MATHEMATICAL GEOGRAPHY.

is the time the star takes to describe the two spaces S' 8 and T T', and these
two apaces are deacribed in times proportional respectively to the times cor
responding to one tum of the acrew at 8' and T'. Hence, if we assume t
to represent the excess over 12" of the time of moving from S' to T', and a
nnd b to represent respectively the times correspondmg to one turn of the
screw at 8' and T", we have the foUowing proportion —
a-\-b : t :: a : the time of moving from 8' to S.
From thia proportion the time of moving from S' to 8 being found, and being
added to the time of the star's being at 8', the reault wUl give the exact time
of the atar'a crossing the meridian at S.
V. Method of obser-ving Transits across the Prime Vertical.
430 One ofthe beat methoda of finding the latitude of aplace consists m
observing the transit of a known star across the Prime Vertical ; we shall
therefore explain how such a transit may be observed.
431 Method of placing the Transit Instrument nearly in the Prime
Vertical Plane. — First place the instrument as nearly as can be judged in the
meridian plane, in the manner afready explained, and fix a common magnetic
needle or mariner's compass on some convenient part of the stand, so that the
needle may move freely in a horizontal plane.* Furthermore suppose, for
the sake of simpler explanation, that the needle is made to point to the North
point of the compass. Having done this, Uft up the whole instrument and
turn it round tUl the needle points to the East or West point ofthe compass,
and put it down again caremUy, so that the needle may continue to point in
either of theae directiona. The instrument wUl then be placed nearly in the
prime vertical plane.
For it is obvious that the plane of colUmation is now at right angles to
ita original position, in which it was nearly coincident with the meridian
plane, and therefore, since the prime vertical is perpendicular to the
meridian, the plane of coUima-
riQ-.l38 tion is now nearly coincident
with the prime vertical plane.
432 When the instrument
has been thus placed, the level
should be appUed, in the man
ner afready explained, in order
to make the axis perfectly hori
zontal. When this is done, the
line of coUimation wiU describe
a vertical plane nearly coincident
with the prime vertical.
433 To determine, by means
of the instrument thus placed,
the exact time of Transit ofa
Star across ihe PriineVei-tical. —
Let P, fig. 138, be the Pole, Z
the Zenith, 8 Z P T the Meri
dian, Q Z E the Prime Vertical,
which is at right anglea to the
Meridian, and Q' Z E' the circle
of coUimation— that ia, the circle
which the line of coUimation
describes on the celeatial sphere. Observe the Unes S T Q E and Q' E
represent circles of the sphere which appear to be projected as sfraight lines
on a horizontal plane to an oye looking verticaUy upwards on the sphere.

• U will be artvifable, in pui-oliasing a transit instrinnent, to order a magnetic compass to
be fitted to it on Pomc convenient part ofthe stand,

THE TRANSIT INSTRUMENT. 123
The cfrcle of coUimation Q' Z E' is auppoaed to deriate a Uttle from the
prime vertical QZE, but the amount of deviation is unknown. We can
observe, in the manner already explained, the exact time when the star crosses
the cfrcle of coUimation, that is, supposing S Q T E to represent the cfrcular
course of the star round the Pole, we can observe the exact times of the star's
being at E' and Q', We suppose the star to croaa the prime vertical twice,
(whioh it wUl do, if it crosses the meridian beyond the zenith at its superior
fransit S,) once on the east of the meridian, and once on the west,
434 We must observe, before proceeding, that the time of the star's
fransit across the meridian at Q', is supposed to be known, either by actual
observation (as above explained), or from the star's known right ascension.
If it be the same star as that by which we have detei-mined the meridian (as
above explained), of course its time of transit at 8 is known by observation ;
if not, the right ascensions of both stars must be found from the Ephemeris,
or Nautical Almanack, and the difference taken, and this vriU determine the
time that elapses between the transits of the two stars, and therefore the
time of fransit now requfred.
For example, auppose that the auperior tranait of the atar (caU it a) by
which the meridian waa determined was observed to take place at 1" 4"* 10',
and that the right ascension of another star (call it ;3) exceeds that of a by
4" "Z"" 3' ; then |8 vriU cross the meridian 4" 2™ 3' after a, and therefore the
time of transit of j8 wUl be the aum of —
1" 4"" 10'
and 4" 2"" 3'

that is, 5" 6" 13"

124

CHAPTER VIII.
THE GEOGEAPHICAL USES OF THE TEANSIT INSTEUMENT.
HAVING explained foUy the constmction of, and method of observing
vrith the Transit Instrument, it will not requfre many pages to show
how it may be used for geographical purposes.
The chief things wmch a traveUer nas to determine at any place, hy
means of astronomical observations, are aa foUows : —
The Position of the Meridian.
The Latitude.
The Longitude.
We shaU now explain, in order, how theae three things are to be deter
mined. I. Determination of the Position cf the Meridian,
438 To determine the meridian, we have only to determine, by the
method explained in the preceding chapter, the exact time when any par
ticular star crosses the meridian ; and, knowing this, we may, by turning the
screw of the horizontal Y, bring the line of collimation into the meridian
plane, with great accuracy, as an example vrill best show : —
Suppose that any particular star is observed to croas the wfre at the time
6" 12"" 17', and that it ia calculated, by the method explained in the prerious
chapter, that the atar croaaea the meridian exactiy at the time 6" 12'° 23';
also, auppose that one tum of the acrew correaponds to 3'. Then it follows,
that the atar takes 6' to move from the vrire to the meridian, and, conse
quently, that two tuma of the acrew wiU bring the wfre up to the meridkn.
We have only, therefore, to give the screw two turns, and we shafl so bring
the Une of coUimation exactly into the meridian plane. Since the star crosses
the meridian after the wfre, the screw must be tumed so as to make the wire
move the same way that the star does — ^that is, westward at a superior
transit, and eastward at an inferior,
Tti general, to bring the line of coUimation exactiy into the meridian
plane, we must divide the time the star takes to move from the wfre to the
meridian, by the time corresponding to one turn of the screw, and the result
wiU show how much we must tum the screw in order to bring the wfre into
the meridian,
439 Having thus ascertained the precise position of the meridian, some
mark, as distant as possible, is generaUy chosen to indicate either the north
or the south point of the horizon. This mark is called the Meridian Mark.
Its use is — to enable the observer to place his transit instrument in the
meridian plane on any future occasion, without having to make fresh astro
nomical observations ; it also serves to determine wheSier the insteument has
been in any way displaced or disturbed, by accident or otherwise.
Thia mark should be, if possible, aome small, weU-defined object, auch,
for instance, aa the point of a church apire, or the top of a pole fixed in the
ground ; or it may be tbe vertical edge or extremity of some object, such aa
a chimney or house. It is not possible, of course, to get a mark of this kind
exactly in the meridian, nor is it necessary to do ao ; it wUl be sufficient 11
the mark is near the meridian, — that ia, within a few tiirna of the screw, or,
to speak more definitely, so near, that a few tiu-ns of the horizontal scrJW

GEOGRAPHICAL USES OP THE TRANSIT INSTRUMENT. 125
may be sufficient to make the vertical wfre move from the mark to the
meridian. Of course the exact number of tums of the acrew, by which the
wfre ia moved from the mark to the meridian, must be noted, in order that
we may be able to place the instrument in the meridian, which is done by
first making the wire coincide with the mark, and then giving the screw the
proper number of turns to bring the wfre into the meridian. If the mark be
a smaU round or narrow vertical object, the wfre may be considered to coin
cide with it when it appears to be bisected by the wfre.
440 It is important for several reasons not to trust entfrely to a meridian
mark, and therefore obaervations should always be made to determine whether
the inafrument ia exactly in the plane of the meridian or not. The uae of a
meridian mark, geographicaUy, ia to define the north or south points of the
compass in any particular locality.
H. Determination ofthe Latitude.
441 A very exact and simple method of finding the latitude of any
place by observation is by means of transits across the prime vertical, as
proposed by Beaael, and adopted vrith great succeas in the Euaaian surveys.
We have afready ahown how the tranait instrument is to be placed in the
Erime vertical, and it is only necessary to explain the method of finding the
ititude bythe use of the transit inatrument thua placed. The great advantage
ofthis method is, that it requfres no corrections for refraction and paraUax,
which are sources of error in other methods of finding the latitude.
442 Method of finding the Latitude of a place by observing Transits
across the Prime Vertical. — Let P, fig. 138, represent the Pole ; S Q' Q T E' E
the cfrcumpolar cfrcle, which any star describes in twenty-four hours ; Z the
zenith ; S Z P T a portion of the meridian ; Q Z E a portion of the prime
vertical, whieh is, it wiU be remembered, at right angles to the meridian.
Let the transit instrument be placed as nearly as possible in the prime
vertical, that is, let it be placed in such a manner that the line of coUimation
of the telescope may describe a plane very nearly coincident with the prime
vertical plane. This may be done by means of a magnetic compass fixed on
the stand of the instrument. The instrument is firat to be placed as nearly
as possible in the meridian, as above explained, and then the whole ia to be
hfted up, tumed round tiU the magnetic needle moves through 90°, and then
set down again.
443 Sometimes the instrument has an azimuthal motion, that is, it is
capable of being tumed round a vertical pUlar or axis; and it has a graduated
horizontal cfrcle. In this case, after having placed the instrument as nearly
as possible in the meridian, we have only to tum it round the vertical axis
through 90°, by means of the graduated horizontal cfrcle ; and, this being
done, the instrument is placed nearly in the prime vertical.
444 When the instmment is thus placed, the axis of the telescope must
be carefuUy leveUed, as above explained, otherwise the observations made
wUl be erroneous. It is very important, in aU observations vrith the transit
insteument, to attend particularly to the horizontal afljustment of the
axis of the teleacope.
445 Supposing, then, that the instrument ia placed aa nearly as possible
in the prime vertical, let E' Z Q' repreaent a portion of the vertical cfrcle,
whioh the line of coUimation deacribes on the celeatial aphere when the
telescope is tumed round its axis. Thia circle passes through the zenith Z,
becauae, the axis being properly leveUed, the line of collimation deacribea a
vertical plane ; alao, thia cfrcle, aa we have auppoaed, ia nearly coincident
with the prime vertical QZE.
Now, the atar whioh ia auppoaed to describe the circle S Q T E will be
seen crossing the vertical wn-e when it arrives at E', and afterwards at Q'.
In the former case the teleacope ia pointing eastward, in the latter westward.
Let the exact time of the star's being at E' be observed, according to the
method afready explained with reference to transits across the meridian;

126

MATHEMATICAL GEOGRAPHY.

alao, let the exact time of the star's arriving at Q' be observed in the same
manner. Furthermore, thc exact times %vhen the star crosses the meridian,
at its superior and inferior transits at 8 and T, muat be determined by
observation, or by calculation, aa we have explained. Then the exact time of
the atar'a crossing the prime vertical at E or Q may be immediately deter
mined, as an example wiU best show.
446 Example. — Let the observed times when the star arrives at T E'
S and Q' be as foUows : —

At T
At E'
At 8
AtQ'

1"

10""

3'

10"

gm

2'

13"

IO-"

3'

16"

17"

0'

Then the interval of time from the star's being at E' to ita being at S is —
3" 7'" 1"
and the interval from S to Q', is —
3" 6'" 57"
Now, the time the star takes to move from E' to E may be considered as equal
to that from Q' to Q ; for, inasmuch as the ciroles E Q and E' Q' are very
nearly coincident, the spaces R' E and Q' Q differ only insensibly from each
other. Therefore, aince the interval from E to S ia the same as the interval
from 8 to Q, S being eridently mid-way between E and Q, it foUows that
the interval from E' to E, and that from Q' to Q, must be each 2", and the .
interval from E to S, and that from S to Q, muat be each —
3" 6"" 59'
for then the intervals from E' to S and from S to Q' wUl be respectively—

3"

1' and 3" 6'"

Tig. 139

as they ought to be.
447 In general, the interval of time the star occupies in moving from
E to S wiU be half the sum of the two intervals from E' to S and from
S to Q' ; for it is manifest that the interval from E' to 8 exceeds, and that
from S to Q' falls short of, the interval from E to S, by the same quantity,
so that twice the latter interval wiU be equal to the sum of the two former
intervals. 448 Thus the time the star takes to move from E to S may be easily
determined by observation ; and this also determines the angle Z P E (P fi
representing a portion of the polar circle, or cfrcle of de3ination, drawn
from the pole to the ster), for, as
z the time of the star's moving from
E to 8 is to 24", so is the angle
Z P E to 360°.
Thus, in the case of the example
just given —
24" : 3" 6"' 59' : : 360° : angle ZPE,
when the .ingle ZPE may be de
termined by "the Eule of Three.
449 W e are now prepared to
show how the latitude may be
found. Let A P Z C (fig. 139) re
present the meridian ; Z E B a por
tion of the prime vertical ; Z the
zenith ; E the star crossing the
prime vertical in the triangle ZPE
111 the present figure, the same as
the triangle Z P It in fig. 138, only

GEOGRAPHICAL USES OF THE TRANSIT INSTRUMENT. 127
represented in a different projection or view. Then Z P E ia a spherical
triangle in whioh we know three things ; namely, the side P E, the angle
ZPE, and the angle P Z E. The side P E is known, because the star R is
supposed some known star, whose distance from the pole P is given in the
Ephemeris, or Nautical Almanack. The angle Z P E la determined, as above
explained, and the angle P Z E ia a right angle, because the prime vertical
Z E is perpendicular to the meridian Z P.
Hence, three things being known in the apherical triangle Z P E, we may
find the remaining parts of the triangle ; namely, the angle Z E P, the aide
Z E, and the side Z P, either by mathematical calculation, or by the method of
construction we have given in a former chapter. Now Z P is the complement
of the latitude, being the distance of the zenith from the pole ; for the
latitude is the distance of the place of observation — in degrees, minutes, and
seconds — from the terrestrial equator, or, what is the same thing, the distance
of the zenith from the celestial equator.
It appears, therefore, that the latitude may be found from the spherical
triangle Z P E, by determining by observation the angle ZPE, as above ex
plained. 450 The foUowing is the construction for finding Z P. Let us take the
letters I, c. A, h, to represent respectively the latitude, the colatitude Z P,
the polar distance P E of the star,
and the hom- angle ZPE. Then O T' un
the relation between these quanti- A^~-~~^ '^
ties is represented by construction
in fig. 140, where the Une O M is
perpendicular to the Une N L ; N K
also perpendicular to N L ; and
M K equal to M L. The angle
NMEis/t; NOM, c- LOM, A;
and O N M, being the complement w ,
of N O M, is I. That this is the
proper construction for represent
ing the relation between c. A, and
h, wUl be aeen immediately by re
ferring to the article where the
construction for exhibiting the parta
of a right angled spherical triangle
is given. Hence, to find the latitude I, A,
and h, the polar diatance and hour
angle being known, as we have stated, we proceed as follows : —
Draw two lines, O L, O M, fig. 140, making the angle MOL equal to the
knovm polar distance A of the atar ; and, taking O L of any convenient
length, draw L M perpendicular to O M ; draw M K equal to M L, making
the angle N M K (MN being the production of the line ML) equal to the
hour angle h, which has been detennined from observation ; then draw E N
perpendicular to M N, and join N O, and measure the angle O N M, and the
angle thus measured wUl be the latitude requfred.
451 We may here observe that the time of the star's transit across the
meridian need not be observed, prorided we know the time of transit of any
other star, (as, for example, the star made use of in determining the poaition
of the meridian,) and the right ascensions of both stars. For the difference
between the two right ascensions vriU be the interval between the transits
of the two stars across the meridian ; and therefore, if the time of transit of
one star ia known, that of the other may be immediately determined.

128 MATHEMATICAL GEOGRAPHY.

TTI, Determination ofthe Longitude.
452 Cotmexion between the Longitude of a Place and the Time. — ^When it is
12 o'clock at London, itia 1 at a place 15° of longitude eaat of London;
for, aince the Sun deacribes the whole 360° of longitude in 24 hours, that ia, at
the rate of 15° per hour, he comea on the meridian of London an hour later than
on the meridian of a place 15° east of London, and therefore the time at that
place wUl be an hour in advance of that at London. In Uke manner, the time
at a place whose longitude is 15° west of London, ia one hour behind the time
in London. And in general, if we conaider the meridian of London to be the
Ffrst Meridian, reckoning longitudes from it, the difference between the
time at any place and that at London wiU be found by converting the longi
tude of the place into time at the rate of 15° per hour, the time at the place
being in advance or beMnd that at London, according as the longitude is east
or west, 453 Method of fi/nding the Longitude of ariy Place. — ^Hence, in order
to find the longitude of any place, we have only to determine how much the
time at that place is in advance or behind the time at London, and convert
the difference into degrees at the rate of 15° per hour. For example, if the
time at a place be 3" 6"" behind London time, what is the longitade of the
place P To determine this, we have the proportion :
1" : 3" 6"" : : 15° : longitude requfred,
which, by the Eule of Three, gives for the requfred longitude,
46° 30' west.
Now, in order to determine how much the time at a place is in advance
or behind the London time, we must determine two things — namely, the
London time and the time at the place. How this is to be done we shall now
briefly explain.
454 Method of dMerminirig the Time at any Place. — We have explained
how time is measured by the Sun's apparent diurnal motion, corrected by the
equation of time, in order to make the proper aUowance for the inequalities
in the Sun's motion. To determine the time at any place, that is, the mean
solar time, we must determine the exact instant vvhen the Sun crosses the
meridian of that place, and make the proper correction for the equation of
time, and then the time at the place vpUI be determined.
For example, suppose that the observer has a chronometer and transit
instrument, and that he obtains the foUovring result by observation with
them, and the equation of time from the Ephemeris : —
Time of the Sun's transit as shovm by chronometer , 2" 4"" 18'
Equation of time, (Sun too slow)  0" 7"" 42'
Sum ... 2" 12°' 0'
Hence the chronometer is 2" 4°" 18' faster than the time actuaUy ahown
by the Sun; for it is 0 o'clock by the Sun when he is on the meridian ; and the
equation of time ahows that the Sun is 7™ 42' slow; therefore tiie chro
nometer is 2 hours and 12 minutes faster than the mean solar time at the
place of observation, and thus that time is determined,
455 But putting back the hand of the chronometer 2 hours and 12
minutes, we may make it show the exact time of the place of observation ;
but this is never done, becauae it woiUd spoU the chronometer to move the
hand backwards or forwards as in a common watch. The error of the chro
nometer is noted, and this is quite sufficient ; for instance, in the example
juat given it wUl be aufficient, instead of putting back tbe hand, to make a
note that the chronometer ia 2 hours 12 minutes fast at the place of obser
vation. 456 Thus the time at any place may be determined by observing, with a

GEOGRAPHICAL USES OF THE TRANSIT INSTRUMENT. 129
transit instrument and chronometer, the instant at which the Sun crosses the
meridian. The aame may be done by observing the inatant when any known
star crosses the meridian, and making the proper aUowance for the difference
of the Sun's right ascenaion and that of the star.
For example, suppoae the star's transit to be observed, and the right
ascensions of the Sun and star taken from the Ephemeris, or Nautical Al
manack, aa foUows —
Sun'a right ascension ... 4" 12"" > , .
Star's right ascension , , . e" 16" ^ °^^^'^ *™®-
Difference , ... 2" 4""
Therefore, when the star is on the meridian, the Sun is 2" 4"" past the
meridian ; or, in other words, it is 4 minutes past 2 by the Sun.
Time of star's transit by chronometer . 10" 13""
Ditto by Sun , , . . 2" 4"
Difference  8" 11"
Equation of time (Sun too fast) 0" 10""

Sum ... 8" 21""
The chronometer is 8" 11"" faster than the time actuaUy shown by the
Sun ; but the Sun is 10"" too fast ; therefore the chronometer is in advance
of the mean time at the place of observation by the quantity —
8" 21""
which, being noted, determines the mean time at the place of observation.
457 Determination of the London Time. — The simplest method of doing
this is by means of good chronometers, set to London time, and transported vrith
great care to the place of observation. Now, chronometers, however good,
are always subject to aome error in thefr rate of going ; thia error ia deter
mined aa weU as it can be, and is noted, Alao, aa we have already stated,
the chronometer is not actuaUy aet to London time by moving the hand, but
the error ia simply noted. Thus, two kinds of error are noted, the error in
London on a certain day and hour, and the gaining or losing rate of the
chronometer ; and, by making the proper aUowance for these errors, the
London time may be found from the chronometer at any place to which it
has been transported.
For example, auppoae the foUowing caae —
Error of chronometer in London at 12 o'clock, June 1.0" 2*" 3' faat.
Gaining rate 1' per day.
Error from gaining rate at 12 o'clock, June 23 . , , 0" 0"" 23» „
Whole error at 12 o'clock, June 23  0" 2"" 26' fast.
So that, according to London time, the chronometer ia 2"" 26' too fast on
the 23rd of June.
458 Thia presumes of course on the invariabUity of the gaining rate ofthe
chronometer, for thia calculation auppoaea that the chronometer gaina regu
larly one second per day. When chronometers of first-rate construction are
transported by sea, vrith proper precautions against the motion of the ship, it
is vvonderfid how Uttle the gaining or losing rate changes. Good chronometers
are therefore invaluable in navigation, for they give the London time with
great facility, and therefore, aa we have explained, serve to determine the lon
gitude. The means of transport by land are by no meana so favourable to the
correct going of the chronometer.
459 Method of determining London Time, by observing the Moon's motion
among the fixed stars. — The apparent diurnal motion of the heavenly bodies
serves to determine the time at any particular place where the observer

130 MATHEMATICAL GEOGRAPHY.
actually is, but not the time at a different place, except the difference of the
longitudes of the two places be known. An observer at New York may
determine the time at New York by observing the daUy motion ofthe Sun or
other heavenly body ; but there is nothing in the diurnal motion of the
heavenly bodies which wUl enable him to find the time at London, except he
knows how many degrees New York is west of London, It is different,
however, with regard to the proper motiona of the heavenly bodies among the
fixed stars, for these motions are capable of showing the time at a place
different from that in whioh the observer is stationed, vrithout his knowing
anything about difference of longitude of the two places. With the excep
tion of the Moon, however, the proper motions of the heavenly bodiea are too
slow to be made use of for the purpose of determining time vrith any degree
of accuracy : the Moon alone movea with aufficient quickness among the stars
to enable us to make use of her motion with this view ; and even in the case
of the Moon, it requfres considerable nicety on the part of the observer to
attain sufficient accuracy in the results of his observattons.
460 The Moon performs the cfrcuit of the heavens among the fixed stars
in less than a calendar month, and therefore describes more than 12° per day,
or 30' per hour. Suppose for a moment that she moves over 30' per hour,
and therefore 30" per minute. Suppose also that the Moon ia seen to coincide
vrith a certain star at 0 o'clock in London, and that an observer in some other
place ia aware of this, but is ignorant of his longitude. Suppose that he
determines the time at the place he is in, according to the method above
explained, and that at 2 o'clock he observes that the Moon is 6° 10' from
the star. Now at 0 o'clock, London time, the Moon coincided with the star,
but now she ia 6° 10' from the atar ; therefore, since she deacribea 12° per
day, or 30' per hour, it foUows that at the time of observation it is 13" 20"
London time — ^for
6° correaponds to  12" 0" 0"
10' „  0" 20"° 0'
Total  12" 20" 0"
Hence the London time is determined.
We have then the foUowing calculation for finding the longitude of the
place of observation : —
Time at place of observation  2" 0° 0'
Correaponding London time  12" 20" 0'
Difference  10" 20" 0'
Hence the time at the place of obaervation is 10" 20" behind the London
time, and therefore 1" : 10" 20"" : : 15° : longitiide of place.
Whence the longitude of the place is
155° west.
461 In the foregoing example we have assumed that the motion of the
Moon is perfectly imiform, in order to explain more simply the principle upon
which the method of finding the London time, and thence the longitude of
any place, by means of the Moon's proper motion, depends. The Moon's
motion is, however, very variable, but astronomers have determined thenatare
and law of that variation with great exactness. They can therefore make due
aUowance for every inequaUty m the Moon'a motion, and employ it to deter
mine the longitude with the same exactness aa if it was perfectly invariable.
462 Method of finding the Longitude by Transits of the Moon. — This
method is founded upon the principle juat explained, and is in fact the simplest
way of applying it in practice. It consiats in observing with a fransit instru
ment and chronometer the times at which the Moon and a fixed star cross the

THE ALTITUDE AND AZIMUTH INSTRUMENT. 131
meridian at the place of observation, and so determining the interval of tune
between the two transits. The interval thus found is compared with the
interval between the two transits as seen at London, which can be easily
calculated from tables given in the Nautical Almanack ; and the comparison
immediately shows the London time at which the two transits took place
when seen by the observer. The London time being thus found, of courae
the longitude foUows, as we have explained.
For example, suppose the foUowmg case : —
Observed interval between the two transits , , . 12" 6'
Interval at 0 o'clock, London time, given by the
Nautical Almanack  18" 6'

Difference  6" 0'
Now, suppoae that we find from the Nautical Almanack that a change in
the Moon's right ascension, amounting to 6" in time, takes place in 3" 4" 2' ;
then it foUows, that when the observer sees the Moon's transit, the London
time is 3" 4" 2'
Whence the longitude may be found.
463 Lunar Method. — The method of finding the longitude which we haTe
just explained, is caUed the method of Moon Culminating Stars, because it
consists in observing when the Moon and certain convenient stars come on
the meridian, or culminate. There is another method of finding the longitude,
whioh is nsuaUy caUed the Lwnar Method. It consists in observing the
distance of the Moon from some convenient fixed star, and it depends upon
the principle just explained. The instrument employed in this method is one
speciaUy adapted for observing on board ship, called Hadley's sextant. A
mathematical calculation is requfred to obtain the longitude, and the observa
tions must be corrected for refraction and paraUax. On the whole, it is much
more compUcated than the method of Moon culminating stars : but, since a
transit instrument could not be employed on board ship, the latter method
cannot be employed at sea.

CHAPTER IX.

THE ALTITUDE AND AZIMUTH INSTEUMENT— HADLEY'S
SEXTANT— EEFEACTION AND PAHALLAX,
TTTE have dwelt at some length on the transit instrument, because of its
VV great practical utiUty, and the simplicity of its details and adjustmente;
besides, a knowledge of the method of using it is valuable, because other
instruments are adjusted on exactly the same principles, and by simUar
contrivances ; so that one who imderstands the transit instrument weU, may
be aaid to underatand a good deal about astronomical instruments in general.
We have now only space to say a very few words respecting two other very
important astronomical inatruments — namely, the Altitude and Azimuth
Instrimient and Hadley's Sextant.
I. The Altitude and Azimuth Instrument.
465 This inatrument conaists of a telescope C A, fig. 140, of exactly the
same description as that in the transit instrument, capable of turning round
a horizontal axis, the pivots of which reat on two Y's, which are fixed on two
vertical pUlara, one 01 which, PE, ia represented in the figure. In fact, the
e2

132 MATHEMATICAL GEOGRAPHY.
Siouo A telescope, axis, pivots, and pUlars, are preciaely
° '"~~- the same as in the transit instrument, only the
axis is generaUy shorter, and the pUlara are
cloaer together.
D,^_t_^ The atand to which the two piUars are fixed
is a cfrcular horizontal piece of metal, capable of
moving round ita centre about a vertical axia.
_ >- w \ This vertical axis is supported by another cir-
p ^f \)A ciilar piece of metal, which reste on three foot
m(®_'j^ ! . I i-~n£-/^ screws, Uke the base of the transit, as we have
above described it.
So far, then, the altitude and azimuth instru-
fN^JjC I \^^y<!^y ment is nothing more than a tranait instrument,
E whose piUars, instead of being immoveable, are
capable of moving round a vertical axis; thus
the teleacope haa a motion about a horizontal
^ «0l \ axis, and that axia has another motion about a
1 vertical axis. The telescope, or rather the line
.  .  !  . of colUmation, moves in a vertical plane, and the
f \. axis of the telescope moves in a horizontal plane.
^-f-j-  TJ-  II The former is caUed a motion in altitude, because
'-rj-' '-ffi 'tt' it measures the altitudes of heavenly bodies;
the latter is caUed a motion in azimuth, because
it measures thefr azimuths; and hence the name Altitude and Azimuth
Instrument. The telescope has a graduated vertical circle, DEF, fig. 140, attached fo
it, which is caUed the altitude circle; and the vertical axis, about which the
piUars tum, has a graduated horizontal cfrcle attached to it, which is caUed
the azimuth circle. Both these cfrcles are correctly centred, at least aa
correctly as possible, that is, the centre of the graduated cfrcle is also the
centre of motion about which the cfrcle turns. W^e shaU not have time to
say anything here reapecting the azimuth cfrcle, but we shaU confine our
attention altogether to the altitude cfrcle ; in fact, we shaU consider the
instrument merely vrith reference to its use in measuring the altitudes of
heavenly bodiea.
466 The graduations are read off by means of two readingmieroscopes,
M and N, fixed at opposite extremities of a piece of metal, MP N, which is
attached to one of the piUars at P. We need not aay much respecting
microscopes, as we have afready ftdly explained the nature and use of the
microscope employed to read off the graduations of a cfrcle. (See Articles
373—382, &c.)
In smaU instruments these microscopes are simply employed to magnify
the graduations, which are read off by verniers, (see Articles 383, &c.,) at
M and N. They are always placed exactiy opposite each other ; in other
words, the line joining the zero point or index point of each vernier or
microscope passes through the centre of the graduated cfrcle. The object of
this is to correct any error of centering that may exist in the cfrcle ; for it is
easy to see that, if the centre of the graduated cfrcle does not exactiy coincide
with the cenfre of motion, the graduations wUl not correctiy indicate the
motion of the telescope in altitude. But whatever error maybe made on one
side, at M, for instance, it is clear that exactly the opposite error wfll be
made at the opposite point N: so that, if the reading at M giTcs the altitade,
say 10" too great, the reading at N wiU give the altitude 10" too — "
Suppose, then, the foUovring case : —
True altitude  350 20' 17"
Altitude by reading at M  35° 20' 7"
Ditto „ N  35° 20' 27'
Half sum of two readings  35° 20' 17"

THE ALTITUDE AND AZIMUTH INSTRUMENT. 133
Whence it appears that half the sum ofthe two erroneous readings at M and N
ia the trae altitude ; and this, it is easy to see, wUl always be the case. The
use of a pair of microscopes to read off at opposite points of the graduated
cfrcle is therefore obvious, inasmuch as it is extremely difficult, in making an
instrument, to avoid aU error of centering.
467 In larger instruments there are often aa many as three pafrs of
reading microscopes, in order to attain greater accuracy, AU these micro
scopes are read off at each observation, and the mean, or average, of the whole
set of readings ia taken : in this way considerable accuracy is secured, for
not only are the consequences of erroneous centering thua obviated, but also
errors of graduation, tliat is, errors committed by the instrument-maker in
engraving the graduations are made in a great measure to balance and destroy
each other.
468 The graduations of the azimuth cfrcle are read off in a simUar
manner, either by verniers or reading microscopes. Both circles may be
either tumed by the hand or by meana of certain fine screws caUed tangent
screws. A tangent screw is a screw which gives to a graduated cfrcle a very
deUcate motion, and so enables the observer to make hia observationa vrith
greater eaae and certainty than he could otherwise do. The tangent screw
may be made to act upon the graduated cfrcle at pleasure, by means of what
is caUed a clamping screw. When the clamping screw ia tightened, the
tangent screw acte upon the cfrcle; but when the clampmg screw ia
relaxed, the tangent screw produces no effect, and the cfrcle may be tumed
round freely by the hand.
469 There are horizontal and vertical wfres in the focus of the telescope,
which, as in the transit instrument, determine the line of coUimation by
thefr interaection. These wfres are moveable by means of screws, and are
adjusted in thefr proper positions in a similar manner to that described in
Chapter VIL
n. Adjustments, and Method of Observing with tlie Altitude and
Azimuth Instrument.
470 Adjustments. — Having ao fuUy described the adjustments of the
transit instrument, which are the same in kind and principle aa those of the
instrument we are at present considering, we muat not dwell upon this
subject here. The axis of the telescope must be leveUed, by means of a
level and the principle of inversion, as in the transit ; the vertical axis about
whioh the azimuth circle turns must be truly vertical, and both axes must be
at right angles to each other. AU these conditions of good adjuatment are
satisfied if, when a level is placed upon the pivots, and the instrument turned
about its vertical axis, the bubble keeps ateadUy in the aame position, even
when the level is reversed. If no alteration is made in the position of the
bubble, either by reversing the level, or turning the instrument round its
vertical axis, we may be sure that the vertical axis is truly vertical, and the
axis of the teleacope truly horizontal.
471 Index Error. — This is an error affecting the verniers or reading
microscopes, or the poaition of the telescope with reference to the graduated
cfrcle, but aa it ia entfrely destroyed by a method of obserring which we shaU
now explain, it vrill not be necessary to say anything about it.
472 Method of observing Altitudes by Beflection. — This method consista
in olaaerring the altitude of a atar or heavenly body directly and by reflection
in a trough of mercury, in the foUowing manner : —
Let ACB, fig. 142, repreaent the telescope of the altitude and azimuth
instmment pointmg towards a atar in the dfrection C S ; let P Q be the
stUl aurface of some mercury in a trough, placed somewhat below, and in
front of, the instrument ; let A' C B' represent the poaition of the telescope
when it is made to point towards the reflection of the star seen in the
mercury, in the direction C S' ; and let C D be a horizontal line.

134

MATHEMATICAL GEOGRAPHY.

c Then, by the laws of re-
Egi43 y* flection, the line C S' wiU
be as much incUned below
the line C D (which ia pa
raUel to P Q, both being
horizontal) as C S is in-
a: / ^y\y^ cUned above C D ; and
Y \ yjK> therefore the angle SC8'
y^yy^  T^ wiU be double the angle
^ <^S^:"  " S C D, Now the angle
' • V '%> 8 C D is the angle of alti-
!b/ ¦ ¦ ... tude of the star above the
p ' ¦ a horizon, since C D is a ho-
I f-^ rizontal line. Hence, the
\ correct altitude of the star
\. is half the angle made by
\ ^ the Unes C 8 and C S', which
''-19 s' are drawn respectively to
the star, and to its image
or reflection in the mercury.
Let us now suppose the foUovring case, with reference to the two positions,
A C B and A' C B^ of the telescope.
Eeading given by vemier in first position .... 29°
Ditto „ „ second ditto .... 99
Difference  70
This difference ia evidently the angle S C 8', and therefore half thia difference,
35°, ia the altitude of the atar.
But suppose there is some error in the position of the venuer or telescope,
which makes the first reading 33° instead of 29°, and of course equaUy affecte
the second reading, making it 103° instead of 99°; then the case vriU stand
as foUows : —
Eeading in first position  33^
Ditto second ditto  103
Difference  70
And therefore altitude — 35°
Hence it appears that an index error, that is, an error in the position of *i^
vernier, or m that of the telescope on the graduated cfrcle, doea not affect
the result of an observation according to this method. It is generaUy in this
manner that altitudes are taken by means of the altitude and azunuth
instrument. KpllS
473 Artificial Horizon. — The artificial horizon .,s==_B
is a small veaael or trough of wood, roofed in, as
it were, with glaaa, iu order to prevent the wind .,#^S^^===i^Ss.p
from diaturbing the surface of the mercury, a i^k^^^^^^^^^^"
A D E C, fig. 143, is the trough for containing the
mercury. A B C is the roof; F, and the oppoaite
slanting side, which does not appear in the flgure, °
being glaas. This is a necessary instrument, when either an altitude and
azimuth instrument, or a Hadley's sextant, which we shaU soon describe, is
used. It is made to be portable, and is rather more expensive than a pur
chaser generaUy expects, on account of the importance of haring the glass
roof made of accurately polished plates of glass. The mercury ought to be
allowed to run into the trough through a very sniaU hole, in order to clear
the surface of the scum which will otherwise obscure it.

THE ALTITUDE AND AZIMUTH INSTRUMENT.

135

Kg.l44

HI. Uses of the Altitude and Azimuth Instrument.
474 We can only very briefiy touch upon this part of the subject. We
shaU auppoae the instrument to be placed in the plane ofthe meridian, that is, so
that the line of coUimation of the telescope may move in that plane ; and this
may be done exactly in the aame manner aa in the case of the tranait
instrument, aa above explained; only the axia of the teleacope ia moved
horizontaUy by means of the tangent screw of the azimuth cfrcle inatead of
by moving the horizontal Y by a screw, as in the transit instrument. The
inatrument thus placed is equivalent to what ia caUed the Mural or Meridian
Circle in large observatories.
Altitudes of heavenly bodies observed by means of the instrument thus
placed are caUed Meridian Altitudes.
475 To determine the Latitude by
observing the Meridian Altitude of a
heavenly body whose declination is known.
—Let A Z E B F (flg. 144) be the Meri
dian, A B the Horizon, E F the Equator,
S the heavenly body on the Meridian,
and Z the Zenith. Then B 8 is the
meridian altitude of the heavenly body,
and this is supposed to be observed by
means of the altitude and azimuth inatru
ment. Therefore Z 8, which is the com
plement of B 8, ia known. But E 8 is
the declination of 8, which ia also known,
and E Z ia the latitude of the place.
Hence, by adding Z S and E S, both of
which are known, we find the latitude.
Thua, if the observed altitude be 60° 10', and the known dechnation
20° 15', we have— BZ ... 90°

Subta:act B 8

Add ES.

0'
60° 10'
29° 50' which gives Z 8.
20° 15'

50° 5'
which gives E Z, or the latitude requfred.
476 To determine the Latitude by ob-
serving an unknown circumpolar Star. — ^'
Let APB (fig. 145) be the Meridian, P
the Pole, 8' T S the cfrcumpolar cfrcle
described by the unknown star crossing
the Meridian at 8 and S', and A B the
Horizon. Then let the meridian altitudes
S A and S' A be observed, and added to- b
gether, and the sum found wiU giv( PA,
the altitude of the Pole ; whence the
latitude, which is equal to the altitude
of the Pole, is known.
For example, let the observed meri
dian altitudes be 79° 14' and 49° 30' ;
then we have — S A  79° 14'
S'A  49° 30'
Adding  128° 44'
Half of which is 64° 22', which is the required latitudo.

136 MATHEMATICAL GEOGRAPHY.
The reason why P A is half the sum of 8 A and S' A is, because P is half
way between 8 and S', therefore 8 A exceeds P A by the same quantity that
8' A faUs short of P A, and therefore S A and S' A added together muat just
make double of P A.
477 Theae results must be corrected for refraction, and sometimes for
other errors, as we shall briefly explain, and hence it is that these methods of
finding the latitude are not by any means so simple as they appear to be.
rv, Hadley's Sextant.
478 This instrument is invaluable where the observer is not able to use
fixed instruments, as, for instance, at sea. It consists of a stout frame DAC,
flig. 146, of a triangular (or rather, secto
rial) shape, of which A B C is a flat gra
duated circular arc, generaUy a sixth part
of the whole cfrcumference, (whence the
name sextant,) but oflen it is a fourth
part or quadrant. D B is an arm which
movea about a centre — ^namely, the centre
of the graduated arc ABC. The end B
of thia arc movea in close contact with
the graduated arc, and carries an index
and Vemier by which the graduations
are read off. (See Article 383, &c.) S is a
tangent acrew, which, being tumei causes
the arm D B to move very slowly ; and
T ia a clamping acrew, which, being tight
ened, causea the acrew S to act on the
arm, but, when relaxed, the arm may be
moved freely by the hand.
Perpendicular to the plane ofthe graduated arc AB C, in which plane the
arm D B movea, are two mirrors E and D, one fixed at E on the side D C of
the frame, and the other attached to the arm at D, immediately over the
centre roimd which the arm turns. The mirror E is immovable, but the
mfrror D moves vrith the arm D B. Both are plane mirrors of sUvered glass,
but E has this pecuharity, that the upper half of the sUvering is rubbed off,
so that E is partly a refiector and partly transparent.
F is a telescope fixed on the side D A of the frame, and pointing dfrectiy
towards the half-sUvered mirror E. Behind the instrument is a handle (not
shown in the figure). By this handle the instrument is held in the right
hand, the left being used to move the index arm D B, or turn the screws
S or T.
479 When the instrument is in proper adjustment, and the arm D B is
moved, tUl its index B is at the zero of the graduated arc ABC, which zero
is near the point A, then the two mfrrors D and E are so placed as to be
exactly paraUel to each other.
480 Principle of Hadley's Sextant. — Let ADC, fig. 147, represent the
principal lines in fig. 146 ; A B C being the graduated arc, E the half-sflvered
mirror, D tho moveable mfrror on the index arm, B the index, A the zero
point of the graduated arc, F tho place of the telescope. Suppose S D E F
to be the course of a ray of light, whioh, falUng on the mfrror D, is reflected
to E, and thence again reflected towards the tdescope at F, through which it
passes to the eye. We may obaerve here, that the telescope is always ao
placed that the lines F E and D E make equal angles vrith the mirror E ;
and then, by the law of reflection, a ray falUng on the mirror E, m the
dfrection D E, is always reflected in the dfrection E F.
Furthermore, let ll E be another ray of light, which, falling on the un-
silvorcd part of tho muTor E, pasaea straight through thc telescope at F to
the eyo.

hadley's sextant.

137

Then it may be proved
geometricaUy, from the
law of refiection, that the
angle A D B is always
half of the angle at which
the two rays S D and H E
are incUned to each other;
so that double the number
of degrees in the graduated
arc A B is the angle which
the ray 8 D msies vrith
the ray H E. Now, the
arc AB C is not graduated
in the usual way, but every
half degree of it is repre
aented as a whole degree,
ao that there would be
twice 360 degrees in the
whole cfrcumference if
completed. This being the
caae, it is evident from
what has been stated, that the number of degrees from A to B shows the
angle at which 8 D and H E are incUned to each other. For example, if
the index B points to 20°, the rays S D and H E make angles of 20° with
each other.
Now, if S and H be two distant objecta, two atars for instance, from which
theae rays come, it is clear that to the eye 8 wUl appear to be in the same
place as H, for the rays of Ught which come from S will, by the two refleotions
at D and B, enter the telescope in the dfrection E F, in which dfrection the
rays from H also enter the teleacope. Whence it ia evident, from the expla
nation we have given of the nature and action of the telescope, that both sets
of rays wiU be mixed by the telescope, and enter the eye just as if they came
from one object. To the eye, therefore, looking through the telescope, 8 wUl
appear to coincide vrith H.
Hence we may state the principle of Hadley's sextant as foUows : — When
the telescope is dfrected towards a star H, and the index arm is moved tiU
another star 8 is seen to coincide apparently vrith H ; then, the number of
degreea, minutes, and seconds shown by the index B on the graduated arc
A C, gives the angular distance of the star S from the star H, that is, the
number of degrees, minutes, and aeconds between 8 and H on the celestial
sphere. 481 Method of observing with Hadley's Sextant. — Suppose we wish to
obaerve the angular diatance between two stars 8 and H. Holding the in
strument by the handle in the right hand, and the plane of the instmment
(that is, the plane DAC, fig. 147,) as nearly as possible in the plane in which
the two stars are situated, direct the telescope towards tbe lower starH, and,
holding the instrument as steadUy as possible, move the index arm back
wards and forwards with the left hand tUl the other star S appears in the
field of view. The moment the two stars are, as it were, thus caught in the
field of view, tighten the clamping screw T, and then turn the tangent screw
untu the star S appears to come exactly unto the same place aa H, so that
both seem to be coincident vrith each other. When this is done, the observa
tion is made, and the observer has only to look at the index B, which, with
the help of the vemier, wiU ahow in degrees, minutes, and seconds, the an
gular distance between the two atara.
482 Adjustments of Hadley's Sextant. — We shaU only mention here the
adjustments which it is always neceaaary for the observer to attend to, which
are effected by meana of two screws at the back ofthe instrument, close under
the half-silvered mirror E, and by a screw at the back of the index mirror D,

138 MATHEMATICAL GEOGRAPHY.
Ofthe two former screws, one alters the inclination of the half-sUvered mirror
to the plane of the instrument, that is, the plane A B C D, fig. 147 ; and the
other alters the incUnation of the halif-aUvered mirror to the index mirror.
Theae two screws have mUled heads generaUy, and may be turned by the
hand. The screw at the back of the index mirror D alters the inclination of
that mirror to the plane of the instrument. This screw has not a miUed
head, and must be tumed by a screw driver, for this reason, that it ought
to be meddled with as Uttle as possible.
When the instrument ia properly adjuated, both mirrors should be per
pendicular to the plane of the inatrument, and they should be exactly paraUel
to each other when the index B is at the zero of the graduated arc A C.
483 Adjustment qf the Half- Silvered Mirror. — Bring the index B to the
zero of the graduated arc, making it exactly coincident vrith the zero by
tightening the clamping screw T, and then using the tangent screw S.- Then,
holding the instrument by the handle, dfrect the telescope towards a distant,
weU-defined, smaU object, (it must be a distant object,) say, for instance, a
bright star. On lookmg through the telescope, the observer wfll see the star
double if the adjustments be not perfect, one image being formed by therays
which come through the unsUvered half of the nurror E, and ihe other by
the rays which fall on the mirror D, and are reflected by the sUvered half of
E to the telescope.
Let the observer now tum in succession the two screws which adjust the
mirror E, and he wiU perceive that one of these screws makes one of the
images appear to move at right angles to the plane of the instmment, and
the other in that plane. All that he has to do in order to adjust the mirror
is, to make the two images of the star exactly coincident with each other, by
turning one or both the adjusting screws, aa the case may requfre. When
he sees the star single, then the adjustment is complete.
484 Adjustment of the Index Mirror. — This adjustment should be done
by the instrument maker, and the observer ought to be careftil not to disturb
it by rough handling, or meddling -with the screw.
But, snould necessity requfre it, the adjustment of the index mirror is
effected by turning the screw (or screws) at the back of it, tUl the foUowing
condition is satisfied.
Let the observer hold the inatrument before bim in a horizontal poaition,
and in a level with his eye, having the index mirror D next his eye, and the
graduated arc ABC away from him. On looking in the index mirror, as he
thus holds the instrument, he wiU see the portion B C of the graduated arc
refiected ; he wUl at the same time see the arc B C iteelf. In fact, the arc
B C, and its reflection in the mirror D, wiU appear to unite at B, and form
one continuous arc. Now, the condition of perfect adjustment is thia. — The
arc B C and ita reflection must not appear bent or broken at the place where
they seem to unite, but they must appear to form one unbroken graduated
surface, so that the reflection of the arc B C may look as if it was reaUy the
continuation of the arc B C itself.
This condition being satisfied, the observer may be sure that the index
mirror is truly perpendicular to the plane of the instrument.
485 If this condition appears to be satisfied into whatever position we
move the index arm D B, the axia, round which the arm tums at D, must be
truly perpendicular to the plane of the instrument, and so far the instrument
must be a good one. It requfres a little practice, however, to see whether
this condition is accurately satisfled or not. But extreme accuracy is not
necessary in this adjustment,
486 Dark Glasses. — There are always a set of dark colom-ed glasses near
the two mirrors D and E, which may be placed before them or not at pleasure.
The use of these glasses is to destroy the excessive glare of the Sun, when it
is necessary to make an observation upon bim.

USES OF hadley's SEXTANT. 139

V, Uses of Hadley's Sextant.
487 Hadley's sextant may be used to observe the angular distance
between two heavenly bodies in the manner we have explained. Thus, the
Moon's distance from a fixed star may be observed, and the longitude thence
detennined, according to the method we haTe explained.
This is a pecuUarly Taluable method at sea, aa Hadley's sextant is the
only instrument that can be used for measuring angular distances on the
unsteady deck of a ship. The observer at sea often Ues on his back, in order
to manage the inatrument with greater ease and steadiness.
488 Observation of Altitudes by means of Hadley's Sextant. — If it be
necessary, as it continuaUy is, to observe the Sun's altitude at sea, the
observer dfrects the telescope of the sextant towards the visible horizon (that
is, the extreme boundary of the sea, where it appears to touch the sky,) hold
ing the instrument in the aame vertical plane with the Sun, as nearly aa he
can judge. He then makea the Sun appear in the field of view, and, by the
tangent screw, in the manner afready described, causes the image ofthe Sun
juat to touch tiiat of the sea. In this manner he finds the angular distance of
the Sun from the risible horizon — ^that is, the Sun's altitude above the visible
horizon. 489 But since the visible horizon at sea is a Uttle below the real horizon,
in consequence of the observer being at some elevation above the surface of
the sea, there must be an aUowance or correction to obtain the true altitude
of the Sun above the horizon. This correction is caUed the correction for
the dip of the horizon. The manner of making it is explained in treatises on
Nautical Astronomy.
490 Altitudes on land are observed by the aid of an artificial horizon.
(See Article 473.) The teleacope is pointed at the image of a heavenly body
seen by reflection in the trough of mercury, and the heavenly body itself is
brought into the field of view by moving the index arm, and made to coincide
exactiy vrith the image seen in the trouM of mercuiy by means of the tangent
screw. In this manner, the angular distance of the heavenly body from its
image reflected in the frough of mercury is determined, and half that angidar
distance ia the altitude of the heavenly body above the horizon, aa we have
explained in Article 472.
491 Determination of the Latitude of a Place by Hadley's Sextant. —
We have afready explained how the latitude of a place is found by observing
meridian altitudes. For this purpose, the graduated cfrcle with which we
obaerve muat be placed exactly in the plane of the meridian. Now, this we
cannot do with Hadley's sextant, inasmuch aa we hold it in the hand, and
therefore cannot be sure whether it is exactly in the meridian plane or not.
To obviate this difficulty, meridian altitudes are observed by means of
Hadley's sextant in the foUowing manner : —
The observer makes as good a guess aa he can at the position of the meri
dian, either by means of a magnetic compass, or the pole star, or otherwise ;
and he commences his observations on the heavenly body whose meridian
altitude he wishes to determine, a short time before it comes on the meridian.
He observes several altitudes of the heavenly body in auccession at short
intervals, which he finds to increase for a certain time, and then to diminish ;
for the heavenly body culminates, or attains its greatest altitude, when it
comes on the meridian. Hence, the observer has only to select the greatest
of the altitudes he has observed, and that cannot differ materiaUy from the
meridian altitude, if the obaervations have been made quickly one after the
other at the time when the observer perceives the altitudes to increase very
slowly and then begin to diminish.
There ia, however, a simple mathematical rule, caUed the Eule of Inter
polation, by which the observer may determine the exact meridian altitude,
and the time of transit acroaa the meridian, from a few altitudes observed

140 MATHEMATICAL GEOGRAPHY.
every five minutes or so about the time when the heavenly body comes on
the meridian. In this manner, Hadley's sextant may be used with consider
able accuracy to determine the meridian altitude and time of transit of a
heavenly body.
492 The greatest altitude of a heavenly body is easUy determined by
graduaUy turning the tangent screw, so as to keep the body and its reflected
image in contact as long as the body is ascending, and ceasing to turn the
screw as soon as the body appears no longer to ascend. The reading given
by the index wUl then be the greatest altitude of the body. It is important
to observe, that though the greatest altitude may be thus found with
tolerable accuracy, the time of the body's tranait over the meridian cannot
be found with any degree of exactneas in this way, as a Uttle consideration
wUl show.
493 Hence the time at any place may be determined by means of
Hadley's sextant, by obaerving tne time of teansit of the Sun, or any other
heavenly -body whose right ascenaion ia known. (See Article 454, &c.) Thus
Hadley's sextant may supply the place of a transit instrument ; it is not, how
ever, to be compared with a transit instrument as regards accuracy in deter
mining the time of transit.
494 We may observe here, that when we speak of the altitude of the
Sun, we mean the altitude of his centre, and therefore when we make the
Sun's lower limb appear just to touch the sea, we take the altitude of the
Sun's lower Umb, and not ofhis centre. It is necessary to correct this error,
which is often done by means of a table in the Ephemeris, or Nautical
Almanack, which gives the number of degrees, minutes, and aeconda, in the
Sun's apparent semi-diameter, which must be added to the altitude of the
lower hmb, in order to give the altitude of the centre.
Sometimes the altitudes of the upper and lower Umbs are observed,
lialf the sum of which wUl be the altitude of the centre.
495 The same remarks apply to the Moon, but, one side of the Moon
being generaUy dark and indistinct, the aecond method doea not always
apply, and therefore the altitude of the Moon'a centre must be found by
observing the altitude of the enUghtened limb, and adding or subfracting the
semi-diameter, according as the enUghtened Umb is lower or upper.
The apparent semi-diameter must be giTen in the Almanaci, because it is
a Tariable quantity, being greater or less according as the Moon or Sun ia
nearer or farther off. Befraciion.
496 We have alluded to the astronomical corrections in two or three
places already, and ejrplained in a former chapter the causes of some of them.
Two of them are optical, arising respectively from a real and an apparent
deviation of the Ught, which comes from a heavenly body to the eye, from ita
rectilineal course. Another correction arises from the observer's change of
position, which produces a corresponding apparent change in the positions of
the Sun, Moon, and planets, the stars being too far off to be affected by it.
Lastly, the correction for Precession and Nutation is due to the actual motion
of the Pole caused by the attractions of the Sun and Moon on the Earth,
whose deriation from a perfectly spherical shape, combined with its rotation,
caused the Pole by these attractions. We have only space to aUtide briefly
to one of these corrections — indeed, the fuU explanation of them would
requfre too much mathematical information on the part of the reader to
admit of saying much about them here.
497 We have afready explained tho manner in which the refraction of hght
takes place when it comes from a heavenly body to the eye, by the refractive
power of the atmosphere. This refraction always makes a heavenly body
appear higher up than it rcaUy is, and that iu a greater degree according as
the body is noai-cr to tho horizon. A body in the zenith is not affected by
refraction ; at 45° from Iho zenith it is olevalod about 1' bv refraction, and at

REFRACTION. 141
the horizon as much as 33'; so that the amount of refraction increases rapidly
towards the horizon.
498 The density of the atmosphere, aa is weU known, is continually
changing, in consequence of the continual variations of pressure and tempera
ture which, from various causes, are always taking place at the earth'a aur
face. The barometer is an instrument which meaaurea the preaaure of the
afr, and therefore its density, provided we take proper account of its tem
perature. Now, the refractive power of a transparent substance increasea
vrith its density, and the atmosphere is no exception to this rule. Hence,
the indications of the barometer must always be observed before we can make
a correct aUowance for the atmospheric refraction.
It appears that the refraction of the atmosphere mainly depends upon its
density, and that it varies very Uttle in consequence of changes of tempera
ture or humidity.
499 Since refraction always makes heavenly bodies appear to be higher
up than they reaUy are, the correction for refraction must alwaya be aub-
fracted from the obaerved altitude of a body in order to find its true altitude.
The foUowing formula givea the amount of the correction for refraction of
a heavenly body not far from the zenith : —
Let z be the observed or apparent zemth distance of the body, and r the
correction; then r = 57" X tan. z, _
and the true zenith diatance is z -\- r:
that is, in order to find the true zenith distance, aa far as refraction is con
cemed, multiply the tangent of the observed zenith distance by 57", and the
result added to the observed zenith distance wUl give the true.
This supposes the barometer to atand at its mean elevation, about 29|
inches, and the thermometer at the mean temperature, about 50 Fahr. If
this be not the case, we must multiply the above formula by the quantity
sg:^ to correct for the barometer, and moreover by the quantity . -„
to correct for the thermometer : b being the height of the barometer in
inches, and t the degree of the thermometer, (Fahr.) The formula for r vrill
therefore be — ,-»// b 500 , ,
^ = 57"X2g:gX^— ^Xtan,«.
Furthermore, if the body be not near the zenith, instead of tan. z, we
must put tan. (z — 230" tan. z) ; that is, the formula for r wUl be—
- = s7" X 2A X mh X *-• (^ - ^3*^" '^- '^
Thia formula is nearly coincident with one given by Bradley, only it has
230" tan. z, instead of 3 X 57" X tan. z, aa in Bradley'a formula.
The rule, then, for finding r is as foUowa :— Multiply the tangent of the
observed zenith distance (z) by 230", subtract the result from z, and find the
tangent of the remainder, which multiply by 57". The quantity thus obtamed
must be multipUed by the height of the barometer (b), and dirided by 29-6 ;
also, it must be multiplied by 500, and divided by the temperature (i),
increased by 450. The final reault thus obtained ia the value of r, which
muat be add.ed to z, and the tme zenith distance ia thua obtained.
This ia the only correction necessary iftbe heavenly body be a star ; butif
it be the Moon, another correction, eS\eA. parallax, muat be appUed: ofthis,
however, we cannot speak here.
For the sake of the reader who does not understand what a tangent is,
we give the foUowmg short table, in which the tangent for every degree is
given. By this table he may calculate the value of the refraction. Practical
men generaUy find the refraction, not by a formula, but by a table of refrac-
tiona, in which the value of the quantity 57" tan. (z — 230" tan. z) ia given

142

MATHEMATICAL GEOGRAPHY.

for all the values of* between 0° and 60°. "The angles are given in degrees,
and the tangents to three decimal places, which is sufficient for the present
purpose.

Angle.

Tangent.

Angle.

Tangent.

Angle.

Tangent.

1

•017

21

¦384

41

•869

2

•035

22

•404

42

¦900

3

•052

23

•42 i

43

¦933

4

•070

24

•445

44

¦966

6

•087

25

•466

45

1-000

6

•105

26

¦488

46

1-036

7

•123

27

•510

47

1-072

8

•141

28

•532

48

1-111

9

•158

29

¦554

49

1-150

10

•176

30

¦577

50

1-192

11

•194 i

31

¦601

51

1-235

12

•213

32

¦625

52

1^280

13

•231

33

•649

53

1-327

14

•249

34

•675

54

1-376

15

•270

35

•700

55

1-428

16

-287

36

•727

56

1-483

17

-306

37

•754

57

1-540

18

-325

38

¦781

58

1-600

19

•344

39

•810

59

1-664

20

•364

40

•839

60

1-732 1

CHARTOGRAPHY.

NEITHEE the nature of the present work, nor the space to which we
muat limit ouraelves, permita our treating in extenso of Chartography ; a
subject which, if fuUy developed, would of itself fiU a large vwume and
requfre a great many plates. We must accordingly confine ouraelves to a brief
notice, in which, however, we wUl endeavour to give aU the information we
can, consistently vrith a popular work Uke the present.
By Chartography, in its vridest sense, is understood the conatmction and
delineation of mapa, charts, and plans, no matter for what special purpose,
upon what projection, or on what scale. The dfrect object of maps is to
represent the whole or some portion of the Earth's surface; but as this surface
ia spherical, it is evidently impossible to reduce it, or any part of it, to a fiat
surface, without a greater or less distortion of its detaUs : whence it foUows,
that the only way in which the Earth can be accurately figured is by a globe ;
and even then the elevations of the surface cannot be shown in thefr proper
rehef, as the highest mountains wotild be less than the thickness of the paper
on an eighteen-inch globe.
Tbbsesteial Globe. — An artificial globe is a miniature representation of
our planet, with its grand dirisions of land and water, and on which all the
regions of the Earfli may be correctly laid down as regards position, form,
area, and distances. We do not mean to say, that even on the best globes
eveiything is mathematicaUy correct, for we are far from possessing the
exact latitudes and longitudes of aU placea on the aurface of the Earth, and
until we have theae, the position of many places, even on the most perfect
globes, must be regarded only aa approximationa to truth. But aa far as
positions are determined, they may be more exactly represented on a globe
than on any map. The ordinary size of globes, however, does not admit of
much detaU, and although very large globes have been conatructed, they are
rather objecta of ourioaity than of practical utility. Even a four-foot globe
takes up a great deal of room, and ia only fit for large Ubrariea or pubUc
teaching. In very large globea, again, any amaU portion of the surface has
so Uttle convexity, that if the country contained in such portion were pro
jected on the plane surface of a map, the forms would hardly be distorted,
and the relative distances of placea so near tbe tmth, that the globe, in such
case, would, as far as such country was concemed, offer no great practical
advantage. Globes are, nevertheleaa, very deafrable, both as conveying,
upon simple inspection, a much more correct notion of the true forms of
regions, and the relative positiona of places, than can be done by maps, and
aa enabling ua to aolve a great many intereating problems : the best adapted
for general use are of eighteen inches diameter.
The most accurate gtobes are those on which the detaUa of the surface are
drawn upon the globe itaelf dfrectly, and this is always done in very large
globea ; but such are, of course, very expensive. The usual mode ia to cover
the globe with a map conatructed and engraved emreasly for the purpose, in
a number of separate pieces or slips, caRed gores (in Viench, fiseaux), generaUy
twelve, fifteen, or twenty-four, bounded each by meridian lines, and termi
nating at the North and South Poles, or at the Arctic and Antarctic cfrcles, m
which latter case, two cfrcular pieces are requfred for the two frigid zones.
As each gore is a fiat surface, it can be made to coincide with the convex
surface ofthe globe only by the paper itself yielding or stretching, and it wfll
be easily conceived, that the pasting on of the paper, ao that each aeparate
gore ahaU exactly meet vrithout tearing^reaentmg folds, or overlapping, ia a
very difficult and delicate operation. When the paating is dry, the globe is
coloured and vamiahed, and then mounted. There are various waya of setting

144 CHARTOGRAPHY.
up a globe; the most usual is to fix it within a brazen meridian, set in a hori
zontal frame, caUed ihe wooden horizon, and as the mounting requires as
much care as is necessary for pasting the map, we are not to be surprised if
many globes are very imperfect, a fact of so much the more importance aa a
globe is useless unless it be perfect in aU respects. We therefore recommend
to every one who would possess a reaUy good globe, to examine it weU before
purchasing. The characteristics of a perfect globe are aa foUow:—
1. AU the meridional edgea of the sUps or gores must ioin so perfectly as
to form continuous fine cfrclea, neither overlapping nor failing to meet.
2. AU these cfrcles must be true, which is seen by bringing them
successively under the Brazen Meridian, vrith which they should correspond
aU the way round : if they do not, the fault may be either in them or in the
brazen meridian itself, wliich is not perhaps in a true plane,
3, When the poles are brought to the wooden horizon, in what is termed
the right position of the sphere, each meridian brought successively to the
wooden horizon, should correspond vrith it aU the way round.
4, The brazen meridian must be in a plane exactly perpendicular to that
af the wooden horizon, which it is, if, whUe any one meridian on the globe
corresponds with it aU the way round, the equator corresponds at the same
time with the wooden horizon aU the way round.
5. Every one ot the paraUels of latitude muat form continuoua and perfect
circles aU the way round, and, on turning the globe, must each of them
correspond in aU its parts vrith the same precise point on the brazen
meridian, 6. When the equator is made to correspond vrith the wooden horizon,
the two zero points of the brazen meridian must correspond exactly with the
upper surface of the wooden horizon, in which case, they wUl, of course,
also correspond exactiy vrith the equator on the globe.
7. AU the degrees on the equator, on the echptic, on the first meridian,
drawn on the globe, and those on the quadrant of altitude, when there is
one, must be exactly similar. In order to ascertain whether lliey are so, take
vrith the compasses any number of degrees from any one of these cfrcles, and
apply the measure to aU the other cfrcles, and see if it intercepte on them
all and everywhere the same number of degrees. In Uke maimer, the degrees
on the brazen meridian and on the wooden horizon must exactiy correspond
to each other,
8, The brazen meridian must sUde with ease through the notches cut to
receive it in the wooden horizon, but must not be so loose as to shake in it,
9. As the globe is turned round, every part of its surface muat be equi-
diatant from the brazen meridian and from the wooden horizon, and the
nearer the better, provided aU be so true that there is no danger of mbbing.
This is the true cnterion of a weU set globe.
10. The globe must be so truly balanced upon its poles, as to remain
quite motionless the moment you cease turning it, the poles being placed
horizontaUy. 11, In the right and in eveiy other position of the globe, except the
paraUel, the equator, on turning the globe round on ite axis, must correspond
to the same points on the wooden horizon, which pointe are at 90° from the
intersection of the brazen meridian with the horizon.
12. Every part of the polar and tropical cfrcles must correspond with
thefr known latitudes on the brazen meriaian.
With respect to the geography of the globe iteelf, it is necessaiy to see
that it contains aU the latest corrections of positions and discoveries of
importance, that no place of real note is omittedt that the names be weU and
diatinctly engraved, and that they be not too crowded, Lastiy, the wooden
horizon must be examined with reference to the several cfrcles marked upon
it, each of which must be properly graduated, and thefr several portions in
their true places, as regards the other circles and the globe iteelf.
Wo have spoken omy of the terrestrial globe, and of the more usual way

PROJECTION OF MAPS. 145
of setting or mounting it. There are various other modes,* but which our
limita wtII not admit of our detailing. As for the Celestial Globe, it is
destined for astronomical purposes, and is therefore foreign to our subject.
It is only by means of a globe, we have said, that the Earth's surface can
be correctly repreaented ; but as a globe is neither portable, nor capable, from
its amaU size, of exhibiting the details which are often required, we must have
recourse to maps, the great and indeed only disadvantage of which consists in
the impossibUify of truly representing a spherical on a flat surface.
Peojection of Maps. — Difi'erent methods haTe been derised for the
construction of maps, so that the real figure of the several regions of the
Earth ahaU be as Uttle distorted as possible. These constructions are called
Projections. We cannot here enter into the elaborate researches, the com
phcated analyses to which some of the greatest mathematicians haTe sub
jected the different projections and thefr modifications ; we wiU merely explain
the geometric construction of auch aa are most commonly employed.
There are Utc principal projections — namely,
1, The Orthographic,
2, The Stereographic,
3. The Globular, or Equidistant,
4. The Conical, and
5, The CyUndrical, or Mercator's,
In the orthographic, the stereographic, and the globular projections, the
plane of projection, or the flat surface on which the map ia drawn, is supposed
to pass through the centre of the globe ; but in the first, the orthographic, the
eye of the observer is auppoaed to be at an unmeasurable distance ; in the
second, or stereographic, it is presumed to be at the surface of the globe ; and
in the thfrd, or globular, it ia supposed situated at a point whose distance
from the surface of the globe ia equal to the aine of the angle of forty-five
degrees. In order the better to underatand how, in the aeveral casea, the picture is
formed upon the plane of projection, it is customary to imagine both that
plane and the globe to be transparent. Now, it is clear, that as we aee every
thing we look at through a pane of glass, as if it were drawn upou such plane
of glass, so in the above supposition, aU the details of the hemisphere on the
opposite side from the spectator would appear to him as though they were
drawn upon the transparent diaphragm or plane of projection. But unleaa
this supposition be limited, it is more likely to create a confusion of ideas than
assist the student in forming a right conception of the subject ; for whUe, in
considering the geographical position of any place on the Earth's surface, we
always refer to our own position as external, and thus say the east is to the
right when we face the north, it is evident that in a picture traced according
to the above supposition, we seethe objecta reveraed, so that what is reaUy to
the east appears to be to the west. The fact is, nothing of the surface of the
sphere is projected but its great and smaU cfrcles, and so far only as these are
concemed, is it safe to admit the imaginary transparency aUuded to. When
once the paraUela of latitude and the meridians are projected, the several
regions of the Earth are laid down upon the map in conformity with the
latitudea and longitudea of their aeveral parts.
The Oethogbaphic Peojection. — In this projection, the eye of the
spectator is conceived to be at such a distance from the plane of projection,
that the risual rays which traverse it in thefr passage irom different points of
the hemisphere beyond, are aU parallel and faU perpendicularly upon it,
whence it foUows that equal apacea on the hemispherical surface are represented
by unequal apacea on the plane of projection.

* A mode of mounting globea, far superior to that usually adopted, was proposed by Adams,
and executed with improvements by C. Covens : a description and plate of it will be found
in Malte Brun's Precis de Geographie Universelle. L

146

CHARTOGRAPHY.

Fig. 1

Thus, let A B C (fig. 1) represent a section of the
hemisphere divided into nine equal arcs, and A C
a section of its plane of projection. Now, if from
the several points on A BC, paraUel visual rays be
drawn perpendicularly through A C, it ia erident
the apacea intercepted between theae rays wiU be
unequal, whUe the points whence they proceed are
equidistant from each other. It wiU further be
observed that those nearest the centre approach
nearest to equaUty, whUe thoae farther removed
from it diminish in proportion to thefr distance.
As aU the parallels of latitude are in planes per
pendicular to the plane of projection, they will be
projected in straight Unes, wmle aU the meridians,
except the central one, vriU be projected in eUiptical
curves. The mode in which the orthographic projection
is graphicaUy constructed ia repreaented (fig. 2). A cfrcle N E S W ia drawn,
repreaenting the meridian bounding the plane of projection. Two diameters.

W C E and N C 8, are
next drawn at right angles
to each other : the former
being the projection of
the equator, and the lat
ter that of the central
meridian. The quadranta
of the cfrcle are then re
spectively divided into
spaces of ten degrees
each, marked 10, 20, 30,
&c., from the extremities
of the equator towards
the poles N and 8. From
these points draw lines
paraUel to the equator,
and theae wUl represent
the paraUels of latitude
for every ten degrees.
Now, from thefr extremi
ties, let faU perpendicu
lars upon the equator,
and through thefr points
of contact with it, draw
eUipses vrith N C S for a
common transverse axis.

Fig. 2

These

Thus,

and with CI, C 2, &c. respectively for half thefr conjugate axes.
curvea wUl be the projections of the several meridians.
The same projection may be effected on the plane ofthe equator.
(fig. 3,) describe a cfrcle to represent the equator, the cenfre ofwhich circle
will represent the pole. Then draw two diameters at right angles to each
other, and divide each quadrant, aa before, into nine equal parte. From these
points draw diameters to the correaponding divisions of the opposite quadrant,
and these Unes wiU represent the meridiana, any one of which being takeu for
the firat, the othera muat be numbered 10, 20, 30, &c., half way round on
either side, to 180. Next let fall perpendiculars from the divisions of one of
the quadrants on one of the radii, and tlu'ough the points of intersection 1,
2, 3, &c., describe circlea to represent the paraUels, marking them from the
outer to the inner with tho numbers 10, 20, 30, &c. for the degrees of
latitude.

THE STEREOGRAPHICAL PROJECTION.

147

Fig. 3

As aU the quadrUate-
ral spaces in figs. 2 and 3
represent ten degrees of
longitude and as many of
latitude, thefr simple in
spection ahows that, with '
the exception of such
placea as occupy the
cenfres ofthe projections,
the aeveral regions, parti
cularly those nearest the
cfrcumference, must be
most dreadfuUy distorted
in form, and diminished
in magnitude. The Steeeogeaphic
Peojection. — This pro
jection differs from the
former, in presuming the
eye ofthe speotatorplaoed
at the surface ofthe globe
and exactly opposite the
cenfral point ofthe plane
of projection, which, as
in the former case, is supposed to diride the globe into two halves, the farthest
ofwhich from the observer being that whose lines are to be projected.
From the proximity of the eye, the visual rays, instead of being paraUel,
aa in the former caae, aU converge from the hemisphere to the point of pro
jection, so that wbUe equal spaces on the hemisphere are stUl represented by
unequal spaces on the projection, the inequality is not near so great as in
the former case, and the spaces, instead of diminishing from the centre
_ tow^ards the cfrcumference, diminish
in the contrary direction — namely,
from the cfrcumference towards the
centre. This is rendered evident by
fig. 4, in which the visual rays, pass
ing from the equal spaces, into which
the hemisphere, represented in sec
tion by the arc ABC, is divided, in
tercept spaces in the plane of pro-
- — ::;";V;'-?S^ !?^ jection (of which A C is the section)
so much the larger as they recede
from the centre. This inconvenience,
however, is in part compensated by
the property enjoyed by this pro
jection of representing all the flgures
on the sphere' by similar figures,
and oonaequently aU the right-angled
quadrilateral spacea formed on the
sphere by the intersections of the meridiana and paraUela are projected into
simUar figures, so that the countries are not distorted in form, as is the case
in the orthographic projection.
The stereographic projection of a hemisphere on the plane of a meridian is
thus effected. Deacribe a cfrcle N E S W (fig. 5) repreaenting the meridian
that cfrcumacribea the plane of projection, and draw two diameters, N C 8
and WOE, the former to represent the projection of the central meridian,
andthe latter that of the equator. Then divide the quadrants from the equator
to the polea into 6 or 9 equal parts, according aa it ia requfred to have the
paraUela at 15 or at 10 degreea apart, (in the figure they are at 10 degrees),
l2

148

CHARTOGRAPHY.

Fig. 5

and number them successivelj- 15, 30, 45. &c., or, as in the fig., 10, 20, 30, kc.
From 8 draw lines to the several divisions, as S 10, 8 20, &c., and tbeir inter
section with the line WC E wUl be the points through wbich the circular arcs
representing the meridiana must be described. For the parallels, draw lines,
in like manner, from either extremity of the line W C E to the divisions of
the oppoaite quadrant, and thefr interaection with the central meridian wfll be
the points through which the area ofthe paraUels are to be struck.
The places of the centres from which the paraUela are described, depend
on the principles which determine thia projection ; one of which is, that the
distances of the centrea of the paraUels from the centre C of the projection,
are equal to the aecants of their distance from the pole, and accordingly, if
the length of these secants respectively be marked off from C on the prolon
gation of 8 C N, they wUl give the centres from which to describe the
paraUels. Thus, if a tangent N O be drawn paraUel to W C E, and lines drawn to it
from the centre C through the dirisions 80, 70, 60, &c., theae latter wfll be the
secants reapectively ofthe angular distances of theae paraUels from the pole:
C a the secant of 10 degrees, or the distance of the 80th paraUel from the pole ;
C b the secant of 20 degrees, or the distance of the 70th paraUel, and so on.
Transport theae distances successively from C on C N prolonged, and they
vriU give the centrea aought ; or, what ia the same thing in flieory, though
impossible in practice, draw lines from W through the divisions of the quad
rant on the same side of the central meridian, untU they meet the prolongar
tion of C N, and half the distance between these intersections and tne corre
sponding ones on N C wiU be the places of the centres.
Another principle ofthis projection is, that the distance of the centre of
projection of any great circle oblique to the plane of projection, is equal to
the tangent of tlie angle at which the cfrcle is incUned, and its radius ia equal

THE STEREOGRAPHIC PROJECTION.

149

to the secant of that angle. Hence the centres for describing the meridians
may be found by transporting the tangents of 10, 20, 30, &c. degrees already
found — ^viz., N a N b &c. to the line C E and its prolongation, as shown at
C a', C b', C c', &c., and from these points, with the secants, likewise found as
Ca, Cb, &o. for radu, describe the meridianal arcs. Or the centres for the
meridians may be found thua : from the divisions of the quadrant WN draw
diameters to the opposite quadrant, as A A', B B', &c. Through A', B', &c. draw
lines from S, and produce them tUl they meet the prolongation of W C E in
1, 2, 3, &c. ; then half the distances respectively between theae points, and the
intersections previously found of the line W C, wUl be the centres sought :
that is, the middle a' of the line 1, 10 wUl be the centre for striking the meridian
S 10 N, the middle b' of the Une 2, 0, the centre for 8 0 N and so on. It wUl
be observed that these points a' b' &c. are precisely thoae that were found by
teansporting the tangents N a, N b, &c. to C E.
The appUcation ofthis
projection to the plane of
the equator is exceedingly
simple. Thus, (fig. 6) de
scribes a cfrcle EQUA
to represent the equator ;
draw two diameters at
right angles to each other;
diride each of the quad
rants thus formed into
nine equal parts, and from
the divisions on E Q draw
linea to A; thefr inter-
sections with E P wUl be
the points through which
cfrclea muat be deacribed
from P, the pole, to re
preaent the paraUels ;
whUe radu drawn from
P to all the dirisions on
the equator vriU be the
projections of the meri
dians. As the globe may be
divided into two hemi
spheres in an inflnity of waya, so many difi'erent planes of projection may be
chosen, besides those on a meridian or on the equator, and accordingly
hemispheres are sometimes projected on the plane of the rational horizon of
some particular place, as on the horizon of Paris, as has been done by Lapie ;
on the horizon of London, as has been done by Mr. W. Hughes, &o. These
projections, caUed horizontal, (as thoae on the plane of a meridian are caUed
equatorial, and those on the plane of the equator are'caUed polar,) are ex
teemely interesting, but the constmction is somewhat complicated : we shall
explain it as appUed to the horizon of London.
Deacribe a cfrcle NES W, (fig. 7,) and draw two diametera, N 8 and
WE, at right anglea to each other. From N, mark off on the quadrant,
N W, a number of degrees equal to the latitude of the place, or height of
the pole above the horizon, (in the present case,) 51° 30', and P wiU be the
place of the superior pole. From it, draw the diameter P P', and P' wUl
be the place of the inferior pole. The eye being at E, draw E P, and its
interaection with N 8 in p vrill be the projection of the upper pole. Draw
also the Une, E P', and produce it tUl it meet the prolongation of N S in p',
then pp" vriU be the projection of the meridian PP'. Now aet off on either
aide of P aa many times ten degrees, or the ninth part of a quadrant, as there
are paraUels that diatance apart, between thc pole and aouthern part of the

150

CHARTOGRAPHY.

horizon, (in the present case twelve,)
and draw linea from these points to E,
the intersection of the ninth of which
vrith the Une N S, south of the pole p,
at Q, wiU be the point through which
the projection of the equator muat
pass, and the other intersections, the
pointa for the several paraUels, the
centres for which and for the equator,
wiU necessarUy be on N 8 and its pro
longation, and are determined by find
ing the middle point between the cor
responding intersections 80 and 80, 70
and 70, &c.
For the meridians, it must be re
membered that pp' represents the poles,
and the Une joining them, a meridian

Fig, 7

passing through the middle of the he
misphere, (the meridian, in fact, of
London, whose place is at L, in the
zenith of its horizon, NE 8 W,) and
accordingly, all the other meridians
must meet this one at the poles, under
angles equal to their difference of lon-
f itude from thia meridian. If then we
iaeot the diameter p p' in C, and vrith
C p for radius, deacribe the arc W p E,
it wUl be the projection of a meridian
at 90° from the meridian of London.
AU the other meridiana wiU have
their centres on the Une ACB drawn
perpendicularly to p p', and their places

THE GLOBULAR PROJECTION.

151

are found thus:-— -From p, as a centre, describe a cfrcle with any radius, say
p C, and divide it into thirty-six equal parta, beginning at C. Then from p,
through these dirisions, draw Unes tUl they meet the line ACB, and their
intersections with it vrill be the centres for d.eacribing the meridiana.
In the two figurea, 5 and 7, we have drawn only a few of the meridians
and paraUels, in order not to create confusion by the great multiplicity of
linea: it wUl be self-evident to the reader, that whatever constructive
operations are deacribed for one aide ofthe central meridian, must alao be
performed on the other in the opposite dfrection, in order to complete the
projection of aU the cfrclea. It is also vrith a view of avoiding too many
unes that we have not traced the polar nor the tropical rircles, but aa their
distance respectively from the poles and from the equator is known to be
twenty -three and a half degrees, nothing more is necessary for tracing them
than to set off those distances on the quadrant from the N and S points
of the cenfral meridian, and from the E and W points of the equator, and
then describe these cfrcles by the same processes as have been explained for
the paraUels.
The Globttlab Peo jection, — We have seen that, whereas in the
orthographic projection, equal spaces on the globe become very much con-
fracted towards the exfremities of the projections, they are, on the contrary,
greatly enlarged at thoae parta in the stereographic. In order to rectify
these opposite defects, La Hfre conceived that between the indefinite distance
at which the eye is supposed to be in the case of the orthographic projection,
and its position at the surface of the sphere in the stereographic projection,
there muat be a point from which they would be, if not whoUy compensated,
at leaat greatly reduced, and this point he determined to be at a diatance
from the surface of the sphere equal to the sine of the angle of 45°, or what
is the same thing, if the meridian N 8 (fig. 8) be 200 parts, it muat be
prolonged 70 of these
parta to S'. If, then. Fig. 8
viaual raya be dravni from
S' to the divisions of the
quadrant, thefr intersec
tion vrith C W wiU deter
mine apacea much more
equal than in the former
prgjectiona. Indeed, if
F D be the aine of 45°,
it ia evident that a Une
drawn from 8' to D vriU
exactiy bisect the radiua
C E in d, so that the
equal arcs E D and D N
are represented by equal
apaces E d and d C. AU
other arcs, however, wiU
not be so exactly repre
sented by equal spaces.
The geometrician. Pa
rent, found that by plac
ing the point 8' at only
59A parts from S, aU the
inequaUties of the spaces
on C E or C W would be
the least possible ; but in
order to have the zones
of the hemiaphere re
spectively proportionate
to those of^ the aphere.

s''

152

CHARTOGRAPHY.

the point 8' muat be placed at 110| parta from 8. StUl this projection, how
ever modified, is very defective, inasmuch as the paraUels and the meridians
do not intersect each other in it at right angles. It is, moreover, difficult
to construct, as aU the paraUela and meridiana are repreaented by ellipaea.
The Equidistant
Peojection. — We have
said that in the globular
projection, the spaces re
presenting equal arcs of
the sphere are nearly
equal; whenever, there
fore, this projection is
used, there is very httle
disadvantage resulting
from rendering them ex
actly equal, and when
thia is done, the projec
tion is caUed the Equi-
distant. Ita mechanical
constmction is as foUows :
Deacribe a cfrcle N E
SW, (fig. 9,) and draw
two diameters, N C S for
a cenfral meridian, and
WCE for the equator.
Divide each of the quad
rants into nine equal
parte, and each of the
semi-diameters, C N, CB,
&c. also into nine equal
parts. Then find on the prolongation of N 8 both ways, the cenfres of
circles whose arcs must pass through 80 a 80, 70 b 70, 60 c 60, &c., and these
arcs, described both on the North and onthe South ofthe equator, wiU be the
parallels. In like manner, find on the prolongation of W E both ways, the
cenfres from which to
strike the meridians, all ^'S 10
ofwhich muat join at the
polea, and paaa through
the pointa 1, 2, 3, 4, &c.
Having selected that
meridian which is in
tended for the first,
number the others suc
cessively 10, 20, &c. to
the right and left of it.
For a polar projec
tion, (fig. 10,) describe
the cfrcle A B D E ; this
wUl represent the equa
tor. Draw two diame
ters at right angles to
each other, A D and E B,
for two meridians at
ninety degrees apart.
Divide each quadrant
into nine equal parts,
and also each of the four
rp,du C A, C E, &c. into

THE EQUIDISTANT PROJECTION. 153
the fiame number. From the centre C deacribe circles passing successively
through the points 1, 2, 3, &c.; these wUl be the projections of the paraUels.
Now draw Imea from the several dirisions of the quadranta through the
cenfre to the dirisions on the opposite quadrants, and these diameters wUl
be the projections of the meridians. Place the numbers denoting the degrees
of latill^de 10, 20, 30, &c., upon the cenfral meridian from the equator towards
the pok, and from the same meridian place the degrees of longitude on either
sidehairroundtol80°. Having thus described the three principal projections employed for repre
senting the hemispheres, whether North and South, East and West, or those
bounded by the rational horizon of any place and of its antipodes, we will
now pause a moment to recapitulate their several defects and relative advan
tages; as to the defects, in some shape or other, they are unfortunately
irremediable. In the Orthographic projection — 1st. The parallels are projected in sfraight
lines, and the meridians m eUipses. 2nd. Equal spaces and distances on the
sphere are represented by unequal spaces. 3rd. The spaces lessen suc
cessively from the cenfre towards the cfrcumference of the hemispheres. The
. consequence is, that whUe the central parts are nearly in thefr correct pro
portions, those at a distance from the centre are terribly distorted in form
and diminished in magnitude.
In the Stereographic projection — 1st. The paraUels and meridians are all
projected in arcs of circles. 2nd. In thia, aa in the Orthographic projection,
equal spacea and diatancea on the sphere are represented by unequal spaces.
3rd. These spaces increase successively from the cenfre towards the cfrcum
ference, so that the parts near the circumference are much too large in
relation to those near the cenfre ; but as the paraUels and meridians intersect
each other at right angles, the forms oi ihe several regions are better pre
served than in the Orthographic projection.
In the GlobiUar and Equidistant projections (which differ chiefly in this,
that in the former aU the cfrcles of the sphere are projected in ellipses with
smaU eccentricity, whereas in the latter they are projected in perfect arcs of
circles) — lat. Equal apacea on the sphere are represented by equal or nearly
equal spaces on the projection, and accordingly the relative dimensions of the
several countries are more correctly obtained; but aa the rectangular apacea
on the sphere are not repreaented by simUar apaces on the projection, the
forms of the countries are greatly distorted, and the more ao the further from
the cenfre ; becauae the nearer to the cfrcumference, the more do the inter
sections of the meridians and paraUels differ from right angles. Nevertheless,
from the great ease vrith which the equidistant projection is executed, it is
very frequently adopted. As for the Globular, some geographers. La Croix
amongst others, give it the preference over the two other projections. We,
for our own part, prefer the Stereographic.
It is almost needless to observe, that the defects of theae aeveral pro-
jeetiona are equaUy sensible, whether they be equatorial, i. e. on the plane of
a meridian, or polar, i. e. on the plane of the equator. This wfll be evident
from simple inspection-of the figures ; though in the case of the Stereographic
projection, the enlargements affect the opposite regions in the equatorial to
what they do in the polar projection, so that, in some degree, the judgment
may be rectified by using both. In the case of the Equidiatant projection .
on the plane of the equator, it wiU be aeen that the degrees on the equator
and on the paraUels immediately adjacent, are much larger than the degrees
on the meridians, and accordingly, countries situated in the equatorial regions
must have thefr dimensions in longitude greatly exaggerated.
Upon the whole, as theae several projections are never used but for
planispheres, the defects we have endeavoured to point out are not perhaps
of any great practical consequence, particularly as this kind of map is omy
consulted vrith a view to having a general idea of the relative bearings and
positiona of the great diviaiona of the terraqueoua globe ; and certainly, of

154

CHARTOGRAPHY.

these projections the moat interesting and instructive are those on the plane
of the horizon of the capital of the country for which the map is designed.
It ia indeed matter of surprise that we see none such constructed on a
large scale. Unfortunately, but few map-makers vriU take the teouble to
construct them.*
A very useleaa custom stUl prevaUs with some map-makers of representing
on their planispheres and globes the tracks of the 'Endeavour' and 'Eeso-
lution.' Far be it from us to detract in the least from the merits of the
immortal Cook ; hia glorious achievements are too indeUbly impressed on the
national mind, and have had too great an influence on the commerce of our
country; have too largely contributed to its fame ever to be forgotten; but
we think that what was not only justifiable but highly proper at the time,
from the novelty of Cook's explorations and the wonders brought to light
by his circumnavigation, is no longer so, now that vessels of aU the great
maritime nations have foUowed in his track and made the tour of the globe,
and we hold that no map should contain a single feature that is unnecessary.
We come now to the other projections we have named. As the former
were, ao to aay, perapective repreaentations, thoae that remain to be apoken
of are more properly developments.
The utter impoaaibUity of fulfilling all the conditions of a perfect repre
sentation of a spherical on a flat surface by any of the means we have detailed,
led to the search for others less defective. It was considered that as cones and
cylinders are simple curves, suaceptibleof being developed or opened out, without
that operation effecting the slightest alteration of these surfaces, or the distor
tion of anything represented upon them, and that as these figures correspond
pretty nearly with portions of a sphere, the latter might be fransferred to the
former, whose development would then give nearly correct representations.
The Conic Peojection. — Let N E 8 W (fig. 11) represent a sphere, and
A B C a cone cfrcumscribed about it, so
as to touch it at the latitude of forty
degrees. It is evident, that at the pa
rallel of contact, the spherical and the
conical surfaces correspond exactly, and
this paraUel wUl be represented on the
development of the cone by a cfrcle,
drawn from its apex A, with the radius
A B. Consequently, any portion of this
paraUel on the sphere will be identical
with its corresponding portion on the
cone. Not so, however, with the paraUels
above and below it, as thoae of 20° and
60°. Here the aidea of the cone recede
from the sphere, and accordingly the
cfrclea representing these paraUels, and
drawn upon the cone from A, with A H
and A P as radu, wiU be somewhat too
large. The difference neTortheless is but
trifling, as the surface of the spherical
zone comprised between the given lati-

Fig. 11

* Mr. W. Hughes has published a very beautiful map of the world, in two hemispheres,
projected on the rational horizon of Loudon and its antipodes ; London being in the centre of
ono hemisphere, and a point a little to the S. E. of New Zealand in the middle of the other.
Concentric circles are dr.iwn round these centres at the distance of 1000 miles apart, and the
points of the compass being marked round tho borders, the bearing and distance of any place
from London are at once ascertained. It will ihrther be seeu by this map, that London is in
tho exact centre of all the land portion of the earth ; the opposite hemisphere being all water,
with the exception of the tail-piece of South America, and of Australia and its surrounding
islands. Tliis litile map is exquisitely engraved, and is highly interesting on every account.

THE CONIC PROJECTION.

155

tudes is nearly thc same as that of the conic frustrum H F G I ; the line H F
differing but Uttle from tbe arc a b.
In consfructing this projection, it is usual to make the cone coincide with the
cenfral or mean paraUel of the counfry it is intended to map, and accordingly,
aU the distances along that paraUel are as exactly laid down on the map as on
the sphere itself, whereas those on the extreme northern and southern paraUels
wUl be a Uttle too long, by an absolute quantity, howeTcr, so much the leas aa
the spherical zone is the more confracted in the dfrection of the latitude, and
vice versa.
There are, howcTer, other modes of conceiving the conic projection. Of
these, the best is that which was adopted by DeUsle de la Croyere for a general
map of Eussia. According to this method, the cone is suppoaed to be in
scribed instead of being circumscribed,
and it ia made to enter and leave the
sphere in such a manner that it co
incides vrith it at tioo parallels, each
of which ia intermediate between the
central one, and one of the exfremes.
By this means, the distances on the
map are perfectly correct along the
two paraUels, where the surface of
the cone coincides with that of the
sphere, as at C and E (fig. 12), whUe
at the intermediate paraUel D 50, the
distance is a Uttle too short, and at
the exfreme paraUela 30 and 70, a
Uttle too long. The errors are thua
more equally distributed over the map; and when the extent of lati
tude embraced by the map does not extend beyond thfrty or forty degrees,
the representation approaches very nearly to exactitude.
In the conic projections, strictly so called, the paraUels are always arcs of
cfrcles, and the meridiana straight Unea drawn from the common cenfre of
the cfrclea, the apex of the cone. This rule has, howcTer, been occasionaUy
modified in the way we shaU presently describe. The mechanical conatmc
tion of the pure conic projection is as foUows : —
When a hoUow cone is placed upon a sphere, the side of the cone forms a
tangent to the angle comprised between the axis of the cone and a perpen
dicular let fall from the point of contact of the cone with the surface of the
sphere to the centre of the sphere, and is a co-tangent of the complement of
that angle. Thus, in fig. 11, the side AB of the cone AB C, is the tangent
of the angle A O B, and co-tangent of the angle B O W. But the arc W B
expressea the latitude of the central paraUel B 40 C, vrith which the cone
coincides ; and as this holds good, whatever be the paraUel chosen, it foUows
that in determining the projection, in the case of a cfrcumscribed cone, the
side ofthe cone muat be made equal to the co-tangent of the latitude of the
middle paraUel. The absolute length must be found in degreea and minutes
of latitude thus : —
Draw an indefinite line A B (fig. 13) to represent the central meridian of
the map, and from any convenient point, say C, through which it is intended
to make the central paraUel (say that of fifty degrees) pass, set off above and
below, and at such mstance apart as shaU represent ten degrees of latitude,
according to the proposed scale of the map, the pointa through which the
other paraUels are to be drawn. This done, say — As tbe cfrcumference of a
cfrcle, or 3-1416, is to its diameter or 1, so are the 360 degrees ofthe cfrcum
ference to X degrees, the number contained in the diameter. This vrill be
found to be 114-591 degrees, and accordingly the radiua vriU contain the half
of thia, or 57-295; and this being multipUed by -839, the co-tangent of 50
degrees, (the latitude of the central paraUel,) gives 48-070505, or 48° 4' 13",
which, being taken from the marked off latitudes as a scale, and set off from

156

CHARTOGRAPHY.

Fig. 13

C towards A, determines the length of the
side of the cone or point O, from which the
paraUela through 60, 40, &o. are to be strack,
and to which all the meridians must converge.
Sfrike from the point O, thua found, an inde
finite arc through C; next find the angle
which the exfreme meridiana of the intended
map must make on either side with the cen
tral meridian O B. For this we must con
sider, 1st. That the number of degrees con
tained in two arcs of equal length is as thefr
radii, and that whUe any arc of the paraUel
C on the sphere has the cosine of its latitude
for radius, the corresponding arc of the cone
developed vriU have the side of that cone for
radius. Now, the side of the cone has been
shown to be the co-tangent of the latitude of
C. Hence, if we suppose the map to contain
forty degrees of longitude, the angle corre
sponding on a plane surface to that number
of degreea, in the paraUel of 50°, wUl be as
the co-tangent of 50° is to the coaine of 50°;
or, what is the same thing, as 1 (radius) : -766
(sine of 50°) : : 40° : 30° 38' 24", the angle
required. Set off half this angle on each side of O B,
and draw O D and O E for the exfreme meri
dians, they wUl intersect the indefinite arc in
d and e, the space between which wiU repre
sent, or be the development of the forty de
grees of longitude requfred for the map. Next divide C d and C e each into
two parta, the spaces thus obtained wiU be ten degrees of longitude each ;
through them draw the other meridians O F and O G. FinaUy, from O describe
arcs, concentric with d e, through the several points marked off at 60, 40, &c. on
the cenfral meridian ; then wiU the space contained between the exfreme
meridiana and parallels be the conic projection or development of a corre
sponding portion of the spherical zone, comprised between the latitudes of
thirty and seventy, and embracing forty degrees of longitude, and this
development wiU be a correct representation of the corresponding spherical
surface, except in as much as the paraUels above and below the central one
will be a Uttle too large.
A simpler mode of drawing the meridians is to take from a table the
number of mUes contained in one degree of longitude at the mean parallel,
(or find it by the rule — radius is to cosine of latitude as 60 is to x,) and
ten times this (taken from the scale which served to determine the degrees of
latitude on the cenfral meridian), aet off twice on each aide of C on the
indefinite arc, wiU give the points through which to draw the meridiana 0 F,
OG, OD, andOE.
In order to find the side of an inscribed cone, as at fig, 12, say — As 57-295
(tho degrees of the equator contained in the radius of the sphere) is to the
co-tangent of the central latitude, so is the coaine of the arc contained
between the cenfral latitude and either of the paraUels tiirough which the
cone ia to pass, to x. Tlus distance from the middle paraUel, measured on the
central meridian produced, wUl give the apex of the cone, from which to strike
the curvea repreaenting the paraUels.
With a view to obviate the errors in distance, measured on the outer parallels
as above aUuded to, Murdoch proposed, besides the inscribed cone already
mentioned, otiier methods of conic projection. Euler, also, and others, have
entered iulo profoimd rcsearclios, nud given directions for different modifica-

THE CYLINDRICAL PROJECTION.

157

tions of the projection we are now considering ; but as they only deprive it of
its simplicity, without effectually correcting its errors, we shall not deacribe
them, stUl less the method of Ptolemy which resembles the conic projection.
There is, however, one modification of Ptolemy's method, due originally to
Flamstead, but subsequently improved, which, being stiU employed, deserves
notice. It consists in the substitution of curvea for the atraight Unea repre
senting the meridians, and is thus effected : —
Having drawn, as before ex
plained, a vertical meridian N 8,
(fig. 14,) and described the central
paraUel with a radius equal to the
co-tangent of the latitude of that
paraUel, and also deacribed the se
veral other parallels as concentric
arcs, passing through thefr proper
points on the central meridian, mark
off (as many times as is necesaary
for the longitudinal extent of the
map) on each aide of thia meridian,
and on every paraUel, the length of
ten or fifteen degreea of longitude,
according to the law of thefr re
spective decrease, which for each
paraUel is as the cosine of the lati
tude to the radius. Then through
these points describe curvea for the several meridians. In our figure, the
paraUds and meridians are drawn at fifteen degreea apart, and the areas on
the globe are represented by equal areas on the projection, but as the forms
are dUated in proportion as they recede from the cenfre, distances can only
be measured along the paraUels or the meridians. This defect is still further
increased by the Uttle attention paid by the generaUty of map-makers to the
point from whioh they describe thefr paraUels, which, instead of being at the
distance of the co-tangent of the cenfral latitude, ia determined by the con
vergence of any two meridiana, arbitrarily taken. The distortion that results
is particularly aeen in the ordinary mapa of Asia.
The next and laat projection we shaU describe is —
The Cylindrical, oe Mbecatoe's Peojection.' — This projection being
destined solely for the use of mariners, and having comparatively little
interest in a geographical point of riew, might be altogether omitted in our
present enumeration, were it not that every atlas contains it, and that many
persons consult it in preference to the planispheres, when they would have
a more satisfactory idea of the relative bearings of those parts of the globe
whose contiguity is so awkwardly interrupted by the diverging cfrcumferences
ofthe two hemispheres.
The cylindrical projection was infroduced by Mercator, whose name it
beara, in 1556. In order to underatand the neceasity which existed for a
E rejection differing entirely from any of the preceding, it muat be remem-
ered that narigators requfre charts by which they may dfrect their course,
and lay it down with facility. So long as they have to saU due north or
south, east or west, the ordinary projections might answer their purpose, but
this is no longer the caae when the place for whioh they have to ateer Ues
between the cardinal pointa. If a vessel starting from any point of the
equator, for instance, were to steer a direct N.E. course, such vessel, if land
did not intervene, would describe a spiral round the northern hemisphere,
and arrive ultimately at the Pole* This curve is caUed the Loxodromic
hne. The way in which it is engendered is this. The meridians aU run due

• Mathematically speaking, it could never reach the pole, as for this, it must steer due north.

158

CHARTOGRAPHY.

Fig. 15

N. and 8., the paraUels E. and W., theae circlea cutting each other at right
angles ; but whUe the paraUels, aa thefr very name implies, are everywhere
at equal diatancea from each other, the meridians approach nearer and nearer
the higher the latitude. Now, as a vessel steering constantly N.E. must
move Song everywhere by a line 45° from the meridian, and aa the dfrection
of every meridian differs, so the veaael'a courae, after first starting from the
equator, wiU deacribe the spiral, or loxodromic, curve, and thia wUl be the
case on whatever rhumb the vessel may steer, for she wUl always have to
intersect the meridiana under the same angle, which ahe can only do by
describing the curve. Were ahe to proceed in a atraight line, ahe would cut
every meridian she passed under a diff'erent angle, and, consequently, never
make the port for which ahe waa bound. To render this sensible,
fig. 15 representa a portion of
the sphere projected stereo-
graphicaUy on the plane of
the equator, in which P is the
pole. Now it is erident that
if a vessel start from the point
A, and steer constantly in a
N.E. dfrection by compass,
her course mnst constantly
form an angle of 45° with the
meridian ; but aa every meri
dian forms an angle with the
one juat passed, so, in order to
form vrith them auccessively
the same angle, the vessd
muat in fact change her di
rection every inatant, and de
scribe a curve. If she were
to proceed on a straight Une, she would make with every meridian succes
sively a greater angle than 45°, tUl at length she would find herself at some
place due east of that from which she aet out; to effect which, however, ahe
would have to change her compass-bearing every moment.
For the facUity, therefore, of determining and laving down hia course, the
mariner requfred such a projection as would enable him, whUe steering by
his compass, to deal with straight lines only on his maps, and accordingly
Mercator, who had before infroduced the stereographic projection, invented
the cylindrical, as we shaU now describe it.
Let us suppose a cylinder to circumscribe a sphere in such manner that
the axis of the two shall exactly coincide, and the cyhnder be in contact with
the equator. If now the planes of the paraUels "be extended beyond the
surface of the sphere tUl they meet that of the cylinder, thefr intersections
with it vriU form a series of circles paraUel to each other and to the base of
the cylinder : and if, in like manner, tlie planes of the meridiana be extended
till they intersect the cylinder from top to bottom, the intersections wiU be
straight Unes equidiatant from each other. If, next, the cyhnder be alit open
in the direction of one of the meridians and laid out flat, it wUl repreaent a
cylindrical projection of the globe, in which aU the paraUela wfll be sfraight
linea, and the meridians also straight Unes perpendicular to the former.
But while the diatancea of tho paraUels from the equator would be the sines
of the latitudes, and accordingly so much the nearer to each other as they
approached the poles, the meridians would be everywhere equidistant ; that
is to say, the relation of the par.aUels and meridians would be the very
reverfe of wbat is requfred in order that the proper relative proportion
between thom bo preserved. For as the length of the degrees of longitude
diminish as the parallels approach the poles, whereas, on this projection, this
length is made equal on aU tho pai-tillela, it becomes necessary to lengthen, tho

THE CYLINDRICAL PROJECTION.

159

degrees of latitude on the projection in the same proportion aa the degrees
of longitude reaUy dimiiush on the sphere, to effect wiiich is extremely eaay
in practice, A hne A B, (fig, 16,) is drawn of the length requfred for the development
of the equator, according to the intended dimensions of the map. This line
being now dirided into 36 or 24 equal parts, for as many meridians at 10° or

SO is 0

Fig. 16
15 SO ii eo 78 90 loe 120 135 150 1C5 ISO 166 IBO 135 120 105 90 76 CO 45 SO

75

75
30 15
A 15
?o
15 ::15
I'l
60 7«
rs
30
15
15
0
46
A)
5
0 1
U5 1
0 1
J5 1
0 It
6 1
0 1
C6 1
50 1
J6 1
20 1
6
0 76 OO 46 30
15° apart, (in our figure we have taken 15° in order to have fewer Unes,)
draw the meridians perpendicular to A B. Now take from a table of
meridional parts the requisite distances of the several paraUels and of the
fropical and polar cfrcles from the equator, and set them aU off on the outer
meridians to the N. and 8. of the equator ; join these points and the Unes
are aU projected. Nothing now remains but to select the first meridian
according to cfrcumstances, and then to graduate the top and bottom borders
ofthe map in the usual way, E. and W. from the first meridian, and to indi
cate the degrees of latitude N. and 8, of the equator upon the two extreme
meridians. The meridional parts in the table just aUuded to, (and which is also caUed
a table of increasing latitudes,) are the number of minutes of a degree of
longitude at the equator comprised between that great circle and every
paraUel of latitude up to 89°. It would be foreign to our.object to enter here
into any detaU of the mode of calculating the table.
From the principles of the projection juat described, it wUl be evident
that the relationa of length and!^ breadth, that is, the figurea of the aeveral
conntriea, are perfectly accurate ; but that, as the lengtii of the degrees of
longitude and those of latitude are greatly exaggerated towards the poles,
the relative magnitudes of countries near them, as compared to those near
the equator, are grossly incorrect. But this, to the mariner, is of no conse
quence ; his object is to be able to lay down the route he has traversed, in
sfraight lines, and to see the stoaight-hne bearing of the point he is imme
diately bound for, so as to shape bis compass-bearing accordingly, and this
the charts on Mercator's projection enable him to do with the greatest eaae
and most unerring certainty. It is evident that, owing to the mequaUty of
160 CHARTOGRAPHY.
the degrees of latitude and longitude, no distance from one place to another
can be ascertained but by calculation.
We have atated that a Mercator's projection of the globe is often con
sulted by the geographer, and we are most desirous, for Ms purpose, that it
be always extended in longitude so as to exhibit both the Atlantic and Pacific
oceans 'in their integrity With this view we would not only carry the
longitude 180° east and west of Greenvrich, but repeat the last 80° of east
longitude on the westem side, reckoning back from 180° E. to 100° E. By
this means the continuity both of the lands and the oceans would be repre
sented in the most satisfactory manner. Mercator's projection, when
designed solely for charts, contains only the detaUs of the coast, islands,
soundings, and rhumb linea; but for geographical purpoaes, they should differ
in nothing from other maps, but in the mode of projection.
Having thua explained the nature and conatruction of the moat customary
projectiona, we will merely obaerve, that there have been proposed and
effected aeTeral modifications of them; but, generaUy speaking, if these rectify
errors in some particular respect, they increase them in others, or elae they
offer practical difficulties of^ execution, which are not compenaated by any
sufficiently important adTantage.
Choice of Peojections. — From what has preceded, it vriU be erident
that all the projections are not alike suitable for aU purposes. In order to
represent the whole surface of the Earth at one view, we must use either the
planispheres or Mercator's projections. As regards the former, we have
already stated our opinion that the 8tereographic projection is the best;
though, for our own use, we prefer a Mercator's projection to any map of the
two separate hemispheres. When the planispheres are used, the projection
is usually made on the plane passing through the twentieth meridian of West
longitude from Greenwich, by which arrangement the continuity of the great
continents, called the Old and the New Worlds, is uninterrupted. Aa maps of
the world are constructed for the purpose of exhibiting the relative posifions
of counfries, and the bearings of their principal ports and cities, the general
forma and extent in longitude and latitude of the grand divisions of the land
and of the water, &c., it follows that minute detaUs are not requfred. Maps
of the world, therefore, should contain nothing beyond the contour of the
land and water as correctly as possible ; the islands with which the ocean is
studded, the great sfreams, the great mountain-chains, the porta and har-
bom-a, the capitals and more important towns. Hence it is not necessary
that maps of the world should be large ; but we shaU freat of the scales of
maps presently.
In choosing the projections for the maps of the grand divisions of the
Earth, and for particular countriea, attention must be paid to thefr form and
their extent in latitude and longitude, in order that the defects of the pro
jection may, as much as possible, be thrown into those parts where they wifl
be of the least importance. With this riew, the conic projection has been
generally chosen, either pure, or in some one of its modified forms, according
to the taste or preference of different geographers and map-makers.
Map or Eueopb. — For Europe, the pure conic projection is unques
tionably the best. It is produced by the development of a cone, suppoaed to
intersect the sphere at the latitudes of 45° and 65°, these being intermediate
betfleen the mean latitude of Europe, 55°, and the exfremes, 35° and 75°.
On such a map of Em-ope, the diatancea on the two paraUela of 45° and 65°
are precisely the aame aa on the sphere, whUe the deficiency on the inter
mediate, and the excess on the extreme paraUels, being disfributed generaUy
over the map, and in themselves very frifling, are of no practical importance.
The rectangular spaces on the globe, formed by the intersections of the
paraUela and meridians, are represented by similar rectangular apacea on the
map, and consequently there is no distortion of form. FinaUy, distances
measured in sfraight hnea on the map, very nearly coincide with the shortest
distanoea as meaaured on the sm-face of the sphere. No other projection

MAPS OF ASIA AND AFRICA. 161
could combine so many advantages, and accordingly we find this projection
generaUy adopted for maps of Europe.
8ome geographers may perhaps be content with the development of a
circumscribed cone, tangent to some paraUel near the centre of the map. In
this case, we think the best would be that of 50°, by which means the greater
correctness would be found in the more important parts of Europe, while the
errors in excess would be thrown into tne comparatively little important
regions of the exfreme North on the one hand, and, on the other, over the
waters of the Mediterranean and the Black Seas, and the exfra European
counfries, as Asiatic Turkey and a portion of Northern Africa. The central
meridian of our maps of Europe generaUy passes through the twentieth
degree of East longitude from Greenvrich.
Map of Asia. — The same mode of proceeding, as that we haTe just
described for a map of Europe, may be adopted for one of Asia, making the
cone intersect the sphere at the paraUels of 25 and 60. It is true, that as
Asia embraces a greater extent of latitude than Europe, the errors of defi
ciency and excess on those parts of the map that are furthest remoTed from
the paraUels intersected by the cone, wUl be somewhat greater than in the
map of Europe. But if we exclude the Eastern Archipelago, we find that
the exfreme South latitude of Asia comprises only the Malayan peninsula,
the southern point of Hindostan and the island of Ceylon ; whUe beyond the
fifty-fifth paraUel of North latitude, there is nothing but the Uttle known frozen
steppes of Siberia. We cannot, therefore, see why the pure conic projection.
which offers so many advantages, should not be adopted in preference to that
distorting modification of it, which we have explained at fig. 14, in whioh the
meridians are projected in curves. It is certain that this method presents
upon the map areas equal to those on the sphere; but this advantage is
counterbalancpd by the impossibUity of measuring distances except along the
paraUels and meridians. The custom, however, is to make uae of Flamstead'a
modification. The cenfral meridian for a map of Asia is usuaUy that of 85°
East of Greenvrich.
Map of Afeica. — The position of Africa, extending, as it does, to nearly
forty degrees North, and aa many South of the equator, renders it impossible
to apply to it, as a whole, any modification of the conic projection. If it were
projected on two cones meeting by thefr bases on the plane ofthe equator, these
cones when developed would present parallels whose curvature would be in
opposite directions, those to tbe North of the equator being concave towards
the Nortii pole, and those to the South convex towards that pole ; whence it
foUows that the equator would be represented by two diverging curves,
touching only in a point, and the contiguity of the continent consequently
broken in a most unseemly and inconvenient manner. Northern and Southern
Africa are sometimes given separately, and in auch caae the conical projection
ia appUcable vrith advantage. But if, on the one hand, the conic projection
be not poaaible for Africa as a whole, so on the other, if the cylindrical were
adopted, it would exhibit aU the defects of a Mercator's projection, wliUe its
peculiar advantagea would have no application. A particular projection
therefore, ia employed, which so far resembles the Orthographic projection
deseribed by us at fig. 2, that aU the parallels are sfraight lines ; but while
the paraUels on the Orthographic projection approximate nearer to each
other as they recede from the equator, they are aU made equidistant in the
projection used for a map of Africa. The meridians are projected in curves
paaaing through points on the paraUels determined by the rale of decrease in
the degrees of loMitude at the different latitudes. The central meridian is
at fifteen degrees East of Greenvrich.
This projection haa been employed by J. B. Nolin for each of the four
quarters of the world ; its great objection is in the diafigurement ofthe forms
by the obhquity of the meridians in respect to the parallels, particularly
towards the extremities of the map, and which renders it impossible to
measure distances except along the paraUels. M

162 CIIARTOGRAPIiy.
Map of North Ameeica.— As this portion of the world, Uke that of
Asia, Ues between the fifth and eightieth paraUels, the map may be projected
exactly like that of Asia, either according to the pure conic, or to Flam
stead'a modification of it. If the first be chosen, we would say, that
upon the principle already aUuded to, of throwing the errors into those
parts of the map wher 3 thoy wiU be of the least consequence, it would be
advisable to make the cone intersect the sphere at the thfrtieth and fifty-fifth
parallels instead of the twenty-fifth and sixtieth, and for this reason, that
while the greatest amount of error in longitudinal distance would be removed
to the barren and little known regions of the North, on the one hand, and to
the very narrow portion south of the thirtieth paraUel on the other, the
distances along the broad and most important part of the region, comprising
the whole of the United States, and the settled portions of Canada, would be
more correct than if the cone intersected the sphere at paraUels more distant
from each other. Mr. William Hughes, whom wc have great pleasm-e in
mentioning as one of our most scientific geographers, and whose opinion has in
general great weight with ua, recommenda placing the northern enfranee of
the cone at the sixtieth parallel, but by the adoption, as we recommend, of
the fifty-fifth instead of the sixtieth, accuracy is brought atiU more within
the important parta of the map, while the errors in longitudinal distance wfll
stiU be but trifling at sixty degrees, beyond which, the nature of the country
renders the errors in distance of very little moment. Most geographers,
however, prefer Flamstead's modification for the map of North Amenea, as
for that of Asia. The central meridian for a map of South America ia that
of 100 degrees West of Greenwich.
Map of South Ameeica. — Aa by far the greater part of this continent
Ues to the South of the equator, the modified conic projection is sometimes
employed for it ; but the paraUels being very sUghtly curved, owing to the
great length of the radiua from which they are drawn, it posaesaes very Uttle
advantage over the atraight-line paraUels adopted for the map of Africa, and
accordingly the latter mode ia, by most map-makers, preferred for the map of
South Ameriea, The cenfral meridian is that of 60° West, and as the land
at the southern extremity of the continent extends but a short diatance from
this central meridian, the distortion arising from the difference in the
diagonals of the quadrangular spaces wiU not be great, nor indeed, if it were,
would it be of much importance, considering the little consequence of strictiy
correct general measurements of Patagonia.
From what has been said, it vrill be evident that the conic projection can
be appUed without any material practical disadvantage to the mapping of
Em'ope, Asia, and Nortii America. It is stUl better adapted to the lesa
extensive regions of the Earth's surface, prorided they be not situated imme
diately on the equator. And, moreover, that whenever the extent in latitade
does not exceed thfrty or thirty-five degrees, there is very Uttie diff'erence
indeed between the distances measured on the map and those on the sphere.
For countries on the equator, it is adrisable to employ the projection described
for the maps of Africa and South America.
In practice it wiU often be found, that the cenfre from which the paraUels
ahould be described are at auch a distance, that it becomes impossible to
strike the area in the usual way, and accordingly recourae is had to expedients
which answer the same purpose, and the details of which wUl be found in
works ad hoc.
It is customary with some map-makers to represent the islands of the
Pacific on a Mercator's projection, extending to forty or fifty degrees on
either side of the equator, and such is the minuteness of these islands
generally, that their forms and dunensions cannot be infiuenced by errors of
projection ; but thefr distances and beai-ings from each other are important,
and accordingly wo ourselves prefer employing for this great region the
projection recommended for the map of Africa.
Diffeeent kinds of Maps.— Ilie term Map is more particularly applied

DIFFERENT KINDS OF MAPS. 163
to representations of the land or land and water together, wliUe that of Chart
is lunited to the water surface only, including indications of currents, sound
ings, anchorages, rocks, shoals, buoys, Ughthouses, and other objects of im
portance to the mariner, for whoae use they are speciaUy designed.
Maps are of two kinds. Geographical and Topographical, and thc former
are eiiher general, such as the maps of the hemispheres, the four quarters of tho
world, and the great empfres and states, or particular, (oaUed also Chorogra
phical,) such as the maps of provinces, counties, &c. Topographical maps differ
from those caUed Geographical by their more numerous details. In order that
every feature, both natural and artificial, of the surface be represented, tho
scale of the map must be proportionably large, and hence topographical maps
usuaUy embrace a smaUer extent of coimtiw than geographical maps, though
there exist topographical maps of most European kingdoms. Generally,
however, they are confined to much smaller surfaces, as counties, parishes,
the enrirons of capitals and large towns, fields of battle, &o. Between thc
geographical and the topographical map there is an intermediate kind, termed
semi-topographical, which contains more detaU than the geographical, and
lesa than the topographical.
Besides the maps requfred for pure geography or for topography, there
are others constructed for special purposes, involving locality as an essential
element. These purposes may be political, ciril, mUitary, statistical, ethno
graphical, historical, physical, &o., and thefr several subdiviaiona : in the
present work, however, we muat confine ourselvea to geographical and
topographical maps.
As the diff'erence between geographical, chorographical, semi-topographical,
and topographical maps, consists not in the size of the mapa, but m the
amount of detaU they represent, so the possible amount of this latter
depends entfrely upon the scale to which the map is engraved.
On the Continent, it is the custom to state the scale of maps in propor
tional parts of nature. The scales of general and chorographical maps range
from a two-miUionth to a two-hundred-thousandth. The first, which is equi
valent to about thfrty miles to an inch, admits of the insertion of principal
mountains, rivers, great towns, and remarkable places, A scale of a two-
hundred-thousandth, or about three mUes to an inch, admits of the intro
duction of lesser towns and viUages, noted hUls, rivers, woods, marshes,
main-roads, &c.
Topographical maps range in scale from a one-hundred-thouaandth, or
1-5 iniles to an inch, to one-ten-thouaandth, or six inches to a mUe, which is
the scale of our Ordnance map of Ireland. This latter scale admits the
representation of the minutest detaUs ; every accident of the ground, every
hamlet, every smaU stream, every by-path, may be laid down on such a map.
Maps upon a larger scale than one-ten-thousandth are rather to be con
sidered as plans.
Whatever be the scale on which a map is engraved, it is generaUy a
reduction from original drawings on a much larger scale : sometimes from
regular surveys, laid down on so large a scale that the minutest topographical
detaUs are delineated. Maps of Uttie known counfries, that have never been
regularly surveyed, are either drawn and reduced from the rough sketches
of the routes of traveUers, and points laid down by them from distances and
bearings, or are protracted by the map-maker from the fraveUer's note-book.
GeneraUy speakmg, aU maps, as they now exist, (of extensive regions,) are
the result of a combination of asfronomicaUy determined positiona, of regular
surveys, and of fraveUers' routes and relations, and they are successively
improved as the spread of ciriUzation offers greater facUity for the exact
determination of positiona. When we compare any of our modern maps
with those of ancient construction, we are struck with thefr dissimUarity,
and the extraordinary distortion in the shapes of counfries as formerly laid
down, and we are apt to consider our modern maps as perfect. They
certainly come much nearer to the trath than the older maps, and it is
m2

164 CHARTOGRAPHY.
perhaps not too much to say, that, omitting the detaUs of certain coasts
little frequented, or stUl unexplored, the coast lines of the globe are pretty
correctly mapped aa to general outline. In Uke manner the latitudes and
longitudes of aU capital towns and ports are, perhaps, as nearly correct as
imperfection in instruments wUl permit. Some few are found to be incorrect
owing to the imperfect state of the instruments, otherwise good, with which
the Observations were taken at the time, ancl in some oases to want of
abiUty in the observera. Such incorrect positions, however, are becoming
every year fewer, as fresh observations are made vrith improved insfruments
and greater care ; and the time ia probably not far distant when every place
of note vriU be set down in its proper position on our maps as nearly as
possible. It is, however, far otherwise with the other details of some of
the most extensive regione of the earth. Thua, the interior of South
America, though, to the eye, weU filled in upon the map, offera but a
diatant approximation to truth ; and when, in after years, the axe ahaU have
cleared the aecular forests of that portion of the New World, .and the vast
regions that extend from the Andes to the Atlantic, shaU be covered with
the abundant harveata and the habitations of a dense population, the maps
of the country then constructed wUl, upon a comparison with those now
existing, show our descendants how wide of the truth were our maps in the
poaition of many places, and how totaUy different the true course of ita
rivers from what we now figure them with such show of accuracy. In like
manner, a great portion of North America, and the whole of the interior
of Africa, remain yet untouched by the astronomical observer and the
surveyor, and the same may be eaid of the greater part of Asia. Aa these
several regions become explored by the scientiflc traveUer, the maps of
them are improved. The greater part of Europe alone and of the United
States may be said to be correctly mapped from frigonometrieal surveys.
Indeed, if nothing were set down on the mapa of other parts of the earth
bnt what has been reaUy determined in a satisfactory maimer, the maps of
them would present, for the most part, so much blank paper. We have often
thought it were greatly to be desired that some enterprising and competent
geographer would pubUsh a set of maps in which the reaUy known, the
tolerably exact, and the merely presumed, should be distinctly marked ; it
would prevent the loss of time incurred by going oTer again what is known,
and would point out what yet remains to be done for tiie exact representa
tion of the earth's surface, and the correct setting down of man's various
habitations, Eeditction of Maps in geneeal, — We cannot go into fhe details of
the geodetic operations by which a counfry is surveyed. This belongs to
treatiaea on geometry and teigonometry ; suffice it for us to aav, that where
the materials exist, topographical maps are reduced from the plans frigo-
nometrioaUy surveyed on the ground. Chorographical maps are produced
by the assemblage and reduction of the topographical maps, and geographical,
or general maps, from the union aud reduction of chorographie, or particular
maps, and it is in these reductions from the larger to the smaller scale that
the detaUa incompatible with the latter are omitted. We wUl flrst state
briefly the mode in which these reductions are made, and then pass on to
the construction of maps of countries which have not yet been topographi-
caUy surveyed.
Having the original drawings of a topographical survey, the map to be
made from them may either be, as is sometimes required, on the same scale,
or on a reduced scale ; in the first case, aU that is requisite is, to unite the
aeveral parts ofthe survey into a whole, or iuto sheets, each of which is formed
of two or more portions of the actual survey. To effect this, each portion
of the survey must have at least two points in common with the portion
which is to join it, aud tbese poults may be made to coincide, either by joining
the two portions of the survey together, or by transporting the points on the
clean paper which is to receive the contents of the sheets to which they belong

TOPOGRAPHICAL MAPS. 165
in common. In this latter case, a line must be drawn through the two points,
and extending beyond them as far as requisite, and having, in like manner,
drawn Unes through the two points on each of the original sheets, similar
squares or other flgures, starting from one ofthe points m question, must be
dravm over the original survey, and over the clean paper to which it is to be
fransferred. The smaUer these squares or other figures are made, the more
exact the copy ia Ukely to be. If we would avoid covering the original dravring
with lines, a plate of glass, afready marked into squarea, may be applied to
the original, taking care that the squares on the clean paper correspond
exactly with them. AU that is now to be done, is to copy each square suc
cessively by the eye. Essential points, however, should be transported by
compass measurements. These operations must be continued till the whole
is completed, taking especial care, as we have said, that there be always two
pointa on each separate portion which correspond, or are repeated, on the
separate portions contiguous to it.
When a reduction is required, it is very simply effected by making the
squares or figurea to be fiUed up on the paper, though they must alwaya be
the same in number and disposition, amaUer in proportion to the extent of
reduction requfred, remembering that the reduction of the surface is inversely
aa the square of the Unear reduction. Thua, if the sides of the reduced qua-
drUateral flgures are half the length of those on the original drawing, the sur
face of each square wUlbe the quarter of the original. H the sides of the
reduced squares are one-thfrd, the aurface vrill be one-ninth, and so on.
In France the separate portions of a survey are at once transferred upon
the copper in the manner we have described, both when the scale of the
engraved map and that of the original drawing are the same, and when there
is reduction. It does not always foUow that, because the scale is reduced, any of the
detafls of the original survey should be omitted ; for the reduced scale may
stiU be such as to admit of their distinct representation. Sometimes it is
necessary to increase the scale of a map : but this is alwaya attended, more or
leas, with the disadvantage of magnifying any errors that may exist, whereas
the contrary operation of reduction diminishes, and sometimes wholly obUte-
rates them.
Of Topogeaphical Maps in paeticttlae. — The great advantage of
topographical maps consists in the numerous details they supply ; and, above
aU, in presenting the relief of the surface ; that is, the heights and depres
sions so necessary to be known for aU engineering and mUitary purposes. A
very great deal might be written on the modes of representing the mountains,
the hUls, and aU the minor undulations of the ground on the fiat surface of a
map, but our space wiU not aUow us to go fully into this subject. Various
modes of drawing and engraving the hUla have been, and stUl are adopted ;
but they may be classed under two principal heads. In the one, aU that is
aimed at is picturesque effect; in the other, a greater or less amount of
mathematical precision has been attempted. In both, the disposition of light
and shade is the mode by which effect is produced ; but whUe, in the one
case, the proportion ofthis light and ahade nas no other rule than the caprice
or taste of the draftsman and engraver, in the other it is aystematicaUy regu
lated. In both the arbitrary and the systematic modes, the Ught is some
times regarded aa faUing obUquely, and aometimea as faUing perpendicularly.
The foUowing tabular view wfll, however, best conTey an idea of the Tarious
modes adopted :—

166

CHARTOGRAPHY.

Aibitrary.

Systematic and
Arbitrary.

Systematic.

Arbitrary in direction.
. „ „ in length.
Etclied lines alone, J _^ ^^ j^ thickness, and
these being . • ¦ ) ", „ in distance apart.
The light falling at an angle of 45°.
Systematic in direction ; being the projections of
Etched lines alone, J the curves of greatest slope.
these being . . ) Arbitrary in all else.
The light falUng at an angle of 45 .
Systematic in the contour lines, wliich are at equal
altitudes, but the altitudes varying according to
Contour lines and the scale of the map and the nature of the
etched lines em- country.
ployed together. ) Arbitrary in the etched lines in everything but
This mode is . . their length, wliich is limited by the contour
lines, between which they are drawn.
The light falling at an angle of 45'.
Systematic, as in No. 8, the lines being drawn at ~
^ ,. , equal altitudes, but which vary according to
Contour lines alone . i ^^^ ^^.^^ ^^ ^^^^ ^^p ^^^ ^^^ ^^ture of the
, country.
' The contour lines as above.
Thicl^ness equal.
Spaces one quarter the co-tangent
Contour lines and of slope.
etched lines em- ¦( Etched J L No regard to light.
ployed together . lines. ) f P"'«f*i'">- > determined.
Length, i
Thickness proportional to the
sine of angle of slope.
Spaces as the cosines.
_ Light vertical.
^,. , . ,. , f Determined in" direction, length, thickness, and! ,
Etched Imes alone . | spaces. ' s j 7.
Besides the above seven modes there are several others, but which must
be all classed under the arbifrary, except one, which is mechanical, and of
which we shaU say a word presently. In some of these the effect is produced
by aquatinta shading, in others by stippUng. In some maps the nUls are
represented in perspective ; in some the shading is effected by etched lines,
straight and waved, and dots, and aU other modes which the engraver can
devise to produce effect.
Of the several systems above mentioned, we may observe that, where pic
turesque effect is aU that is wanted, the arbifrary modes are superior to the
systematic ; indeed, some maps executed according to this arbifrary method,
represent, in the most sfriking and satisfactory manner, CTcry undulation of
the soU, from the gentlest rise to the highest and most abrupt eminences.
They accordingly give a very perfect idea of the counfry, but are of no use
for the exact purposes of the engineer, or for the operations of an army.
This is easUy conceived. The engineer who has to construct a canal, a raU
way, or any other kind of road, to form reservoirs, to drain marshes, &c., can
be satisfied with nothing less than positive levels, and these the arbifrary
modes of drawing bUls,Tiowever effective they may be, do not supply. In
Uke manner, the general must be able to see upon his map where artiUery
and other wheel carriages can pass, where his cavafry can act, and where
none but his light infantry can advance ; what heights command or are com
manded, &c. ; he therefore, like the engineer, must know the positive amount
of the slopes, and must accordingly discard the more beautifiil, though to him
useless topographical maps, for tiiose where ho sees the actual slope and ele
vation of every foot of the ground.
As an example of arbitrary shading, we may mention the Ordnance map
of England, which can be scon at any time. In this topographical map the
cflcct is produced by etched lines ; thc light ia supposed to faU" upon the

TOPOGRAPIirCAL JVLAPS. 167
ground under an angle of 45 degrees, and on tho map to come from tho loft
hand upper corner ; the shading is regulated accordingly, the greatest depth
being given to the loftier and steeper eminences. Another and very beautiful
example oi arbitrary shading may be seen in the semi-topographical map of
Sardinia, lately executed by General Mai-mora. In both these examples the
shading is by etched linea. A map of very exceUent effect as regards the
bilk, and which I shall have occasion to mention for another reason, has
lately been executed at Vienna ; in it the hUls are in imitation of stippling,
and the effect is touly exceUent.
Of the systematic modes, we shaU mention only numbers 4, 5, and 7, of
our table ; and first, of the* method by contour Unes alone, or the representa
tion of the elevations of the surface by curves of equal altitude. This method,
admitting of a very near approach to geometric accuracy, has for engineering
purposes a decided advantage over eTery other, though in some respects it
IS not without its incouTcniences. As it has been much talked about lately,
and is again coming into uae, its history, and some detaUs respecting it, may
not be unacceptable to the reader.
The first idea of the contour system is attributed by some to PhiUp
Buache, but by La Croix to M. Duearla, who, he says, considering that if a
Une were drawn joining aU those points on a chart which are marked as having
the same depths of water, the contour thus fraced would be that of a section
cut off by a horizontal plane everywhere distant from the surface of the
water by so many fathoms, or feet, aa are marked by the soundings— con
ceived a means equaUy ingenious and satisfactory of geometricaUy representing
the elevations of the ground, or the relief oi a country. We shaU occa
sionaUy employ this term relief, because it ia both laconic and appropriate, and
because we have no other single word, as far as I know, that answers so well.
Whether it be to Buache or Duearla that we are indebted for the first idea
of the contour system, it was ffrst published by M. Dupin Triel, in 1 784. It
consists in projecting verticaUy upon the plane of the horizon, lines passing
through points equally raised above the level of the sea ; lines, in fact, which
would mark the limits of the ocean, if, by any cauae, it ahould rise to the
aeveral heighta indicated, in the same way as the Unes joining equal soundings
would become its succeaaive limits if it were to sink to the depths of those
soundings. The imaginary horizontal planes whose intersection with the elevations
of the ground form the curves projected on the map, rise one above the
other by equal quantitiea ; the actual amount of the rise, however, depends
upon both the nature of the ground and the scale of the map. It is indeed
self-erident, upon a Uttle consideration, that in the case of very gently
sloping groimd, if the altitude of the section be considerable, the curvea must
necessarily be very far apart from each other, whereas in elevations nearly
perpendicular, the projection of sections taken at the same height, one above
the other, would almost touch : those of a vertical cUff vrill in aU cases
coincide and form but one curve. Accordingly it is found convenient to increase
the vertical height of the sections as the hUls are more_ steep, and to diminish
it aa the ground is more gently undulating.
The neceaaity of varying the heights according to the scale of the map is
evident for a similar reaaon. For, if while the height of the aections remained
the same, the horizontal scale were enlarged or confracted, the aame incon
venience would be produced. The vertical diatancea of the horizontal sections
depend also upon the particiUar purpose for which the map is intended.
Thua, whUe on the plana intended for certain engineering works, the sections
may be from two to four or five feet of vertical altitude, in topographical maps
they may be much greater. The pure contour system may even be used in
general maps, but then the vertical heights are neceaaarUy very considerable.
In Dupin Triel's map of France, on a scale of about one-two-mUUonth, the firat
sections, beginning vrith the aea-level on the coast, rise by ten toises each, where
the ground is nearly flat; further inland, where it rises more rapidly, the curves

168 CHARTOGRAPHY.
indicate sections taken at twenty toises, then at fifty, then at one hundred.
The first are observed in the north-western portion of the country, and the
latter in the southern and south-eastern, where the more rapid slopes of the
Pyrenees and Jura occur. It is evident that whatever be the scale of the
map, contour linea alone caimot convey that expression of reUef that results from
shading, unless they be exceedingly numerous and close. On a scale of one-
ten-thouaandth, or about 6^ inches to a mUe, the reUef may be satisfactorily
figured by contour Unes alone. We do not, however, recommend their
adoption where effect is to be studied, they ahould be reserved for those
purposes that requfre exact levels, as for draining, canal and road makmg, the
defilement ol fortifications, &c., and in these cases the distances of the curves
from each other are much too considerable to picture rehef On the Ordnance
Survey the contours lately infroduced represent sections taken at the altitude
of twenty-five feet.
When contour Unes are drawn upon chorographical maps, it is erident
the sections have not been leveUed, that is to say, the horizontal planea of
equal altitude have not been determined by the usual process employed for
small distances. The curves are drawn through points whose altitude haa
been ascertained by baromefrical or trigonometrical meana, and the aections
are not flat paraUel planes, but portions of concenfric spheres, whose aurfaces
are paraUel with the convex aurface of the ocean. It is much to be regretted
that curves of equal altitude, such as those on Dupin Triel's map of France,
are not more generaUy appUed; they would throw great Ught on a vast
number of some of the most interesting problems of physical geography.
We have a map of Ireland, on the scale of ten mUes to an inch, on which five
successive curves are drawn at the heights of 250, 500, 1000, and 2000 feet,
and the belts between these curves being tinted, produce a very effective
picture of the positive and relative elevations of different parts of the
country. A map of Hong-Eong has also been contoured in a very successful
manner, the scale being four inches to a mUe, and the section one hundred
feet vertical. Indeed, the system we are considering is admfrably appropriated
for islands, particularly when they are smaU, for the whole coasfc-Iine forma
a closed curve, giving the lowest horizontal plane, or starting point, in aU
dfrections ; whereas in sectional mapa, that is, maps of a portion of eountry,
the rectangular edges of the map intersect many of the curves. This incon
venience is in part obriated by the addition of numbers to the curves ; the
same numbers denoting, of course, the same levels.
Cloaed curvea may represent depressions, as weU as elevations, and this is
one of the disadvantages of the system ; but if the curves are numbered, a
Uttle attention wUl suffice for determining whether the cloaed curves belong
to elevations or depressions. If the number on the innermost or smaUeat
curve be greater than that of the curve next to it, the curvea are thoae of an
elevation ; but if, on the contrai-y, the number on the innermost curve be
smaller than that of the curve next to it, the curves are those of a depresaion.
Captain Vetch, of the Eoyal Engineera, haa proposed to add to the contour
Unes, short etched lines on the side on wluch the ground falls, which
effectuaUy prevents aU ambiguity on the subject.
Upon the whole, then, the system of contour Unes alone ia by no means to
be recommended as a means of representing pietoriaUy the inequaUties or
the relief of the sm-face on maps ; but when positive levels ai-e requfred,
we know of no mode possessing equal advantages. It does not therefore
belong to maps constructed for general geographical purposes, but to maps
designed for special objects. We now paas on to the consideration of the
fifth system of our table.
The French, who attach much higher importance than we do to correct
representation of the inequalities of the surface in topographical mapa, have
at yarious times considered the subject in committees caUed^ together by the
Government, and composed of the heads of aU those scientific departments
for whoae piu-poses good maps are essential, such as the etnt-major, the corps

TOPOGRAPHICAL MAPS. 169
of engineers, civU and mUitary, the mining- department, the woods and
forests, the department of bridges and highways, aud the heads of the
several great schools, such as the Ecole d' Application of tho Geographical
Engineers, the School of the Etat-Major, that of the Mining Corps, that of
St. Cyr, &c. These committees have on aome occaaions aat for three or four
years, going most minutely into every detaU of the subject, and having tho
same portions of ground drawn and engraved upon a variety of scales, and
accordmg to every variety of mode.
We cannot, of course, enumerate all the opinions that were emitted by
these most competent persons, of the respective advantages and disadvantages
of the several systems, and their numerous modifications ; suffice it in this
place to aay, that no system has yet been devised that ia wholly unobjection
able; that, however, which waa at length adopted by the majority, and
which is at this moment aanctioned by the Government, is that which bears
the number 5 of our Uat.
This system is calculated to offer, as far as possible, the double advantage
of geometrical accuracy and picturesque effect. It is a combination of the
contour Unes with the liacliures or etched lines, these latter producing the
requisite tints of shade, which convey to the eye the effect of rehef, and
that with so much truer effect, as this very shading is subject to rule, and is
determined in strict relation to the contour Unes themselves. These latter
being detennined and drawn upon the map, the space between them ia fUled
up with etched lines, whose length is determined by the distance between
two contiguous contours, whUe thefr dfrection is perpendicular to the contour
lines ; they are accordingly the projections of the lines of greatest slope, of
those, in fact, wbich water, acted upon by gravity alone, would foUow in
running down the surface. The thickness of these Unes is not determined
by any rule in the syatem we are now considering ; but whatever it may be,
it ia imiform throughout, the tint of the ahading being effected by the greater
or less distance left between the strokes, and this is (except in the extreme
cases we shaU presently notice) invariably one-fourth of the distance of the
two contiguous contour lines, between which they are drawn. When the
vertical heights of the horizontal sections whose projectiona form the contour
linea of the map are equal, it is evident that the contour Unes wiU approxi
mate so much the closer as the slope of the ground is the more rapid ; and
aa the distance between the atrokes is regulated by that of the contour lines,
it ia clear that the nearer the contour linea, the closer will be the hachuves
(etched lines, or sfrokes of shading) to each other, and consequently the
darker the tint or ahade produced by thefr meana. Therefore, the steeper
the slope, the darker the shading, and that without any dfrect reference to
the way, either slanting or vertical, in which the Ught is supposed to faU.
When the contour linea are distant from each other, the strokes of shading,
being always one-fourth of the distance between the contour linea, wUl also
be far apart, which of course produces a very faint tint, such as is requfred for
the representation of a very gentle slope.
We have stated that, in exfreme cases, the rule qf one fourth of the
distance of the contour lines is not obaerved, and for obvioua reaaons. So
long as the contours run in sfraight, or nearly straight Unes, the strokes
which are perpendicular to one of them wUl also be perpendicular to the
contiguous one, and the distance of one stroke from another wUl be every
where the same. But when the contour Unes form curvea, the distance of
one fourth being taken on the upper line, and the sfrokes di-awn perpendi
cular to it, theae stookea naturaUy diverge as they descend, ao that at
their contact vrith the next curve their diatance is greater. If the distance
between theae curved contoura be not great, the divergence of the afrokea of
shading is of httle consequence ; but if the contours are wide apart, and the
sfrokes therefore long, the divergence becomes an object worthy of attention;
and accordingly, in such case, the distance of one fourth is taken, not upon
the contour lines themselves, but on one drawn for the purpose midway

170 CHARTOGRAPHY.
between the two, so that the strokes are brought closer together, and the
inconvenience of excessive divergence ia remedied.
The other extreme case is the opposite of the one just explained— namely,
when two consecutive contours approach nearer than two mUUmefres, (about
the -08 of an EngUsh inch). In this case, as it would be next to impossible
to draw four strokes of shading in so smaU a distance, the law of one fourth
givea place to an increased thickneaa in the afrokea themselves, by which the
very dark tint required for the shade of such rapid slopes as the contiguity of
the contours indicates, is equaUy weU effected.
Such, then, is an idea of the fifth system on our Ust, and which is that
generaUy adopted in France, and also in the United States, where they have
learnt it from the French ; and some of the topographical maps lately executed
at New York, according to this system, are exfremely beautiful. The sixth
syatem of our table, which is that advocated by Colonel Bonne, was sanctioned
by the French government, in 1828, for the Depot de la Guerre, more
eapeciaUy for such maps as were to be engraved. Tt differs from the fifth,
but they both combine the two great requisites of geometrical accuracy and
picturesque effect. The contours being preserved, are easfly fraceable by
breaks in the continuity of the shading afrokea or etched linea ; every grada
tion of level is marked for engineering and mUitary purpoaea, while the
shading figures at once the undulations of the surface and pointa ont the
several degrees of incUnation of aU the slopes of the ground. Let us now
pass on to the seventh system of our Ust.
In Germany and aome other countriea, the mode of representing the
inequaUties of the sm-face in topographical maps, diffiers eaaentiaUy from the
French ayatems we have juat noticed. That generaUy adopted, though
sUghtly modified in different places, is known as Lehmann's, or the Saxon
method. In it there are no contour Unes ; the slopes or inequaUties of the
surface are represented by etched Unes, or hachures, alone, but then the thick
ness of these, and thefr distances apart, are regulated according to scale, ao that
a determined proportion is maintained between the rapidity of the slopes and
the intensity of the shading by which they are represented. The dfrection of
the sfrokes is that of the greatest slope ; thefr thickness and distance apart is
determined as follows : —
The Ught is conceived as faUing verticaUy upon the ground, and, accordingly,
the different parta of the aurface wtU be more or less iUumined as they are
more or less inclined to the supposed vertical raya of the sun. A horizontal
surface receiTing the fuU effect of these rays, vml, in nature, be the Ughtest,
and is therefore represented on the map without any shading ; whUe a highly
inclined cUff, receiving few of the vertical rays, will be very dark in nature,
and is accordingly represented by a very dark shading on the map. To deter
mine a regular gradation, however, between the most and the least iUumined
surfaces, the foUowing system was determined on.
The angle of 45° was regarded as the greatest natural slope of the ground,
and this was supposed uniUumined. Irom this incUnation down to the
horizontal, aU intermediate slopes were supposed to be Ulumined inversely as
the angles of elevation, and hence the angle of any slope less than 45°, and
its supplement, or what it wants of that number, wcre considered as the
proportional terms of Ught and shade on any declivity. Thus the proportion
of light and shade on a declirity of 5° was said to be as 40 to 5, or 8 to 1 ; —
on a decUvity of 10° as 35 to 10, or 3| to I ; — on a decUrity of 15°, as 30 to 15,
or 2 to 1, &c. These suppositions, — viz., that a slope of 45° is the greateat
natural slope of the ground — that auch a slope receives no vertical light — and
that the quantity of light received by aU slopes of leaa inclination than 45°
is in proportion to such incUnation, are pcrfectfy gratuitous, the facta being —
1. That 60 is the gi-eatest natm-al slope of the soil; — 2. That a slope of 45°
receives a very considerable quantity of vertical light; and— 3. That the amount
of vertical light received by auy slope whatever is exactly m proportion to
the cosine of thc angle of sueh slope. Hence it is clear, that though the

TOPOGRAPHICAL MAI'S. 171
Saxon method of representing the relief of the ground bo syatomatic, it is by
no means natm-al : it is, in fact, a conventional syatem, whose practical
execution is thus effected : —
All slopes of 45° and upwards are represented on the map by absolute
black. All alopes below this, down to the horizontal, arc represented by
graduated tints of shade growing Ughter aa the decUvity ia leas, tiU, at the
horizontal, the paper is left perfectly white. As it would be impossible to
represent every minute difference of incUnation from 45° to horizontaUty,
or to paaa from absolute black to perfect white, so that the eye could at once
detect the difference between contiguous shades, the tint is effected by nine
diflferent grades of shading, each indicating a difference of 5° in the slope.
The mechanical means employed to produce these nine different tints is by
hachures drawn in the dfrection of the greatest slope, and the thickness of
these hachures, or etched Unes, bears the same proportion to the white space
left between them that the angle of the slope to be represented bears to what
it wants of 45°. Thus—
Angles Hor. 5° 10° 15° 20° 25° 30° 35° 40° 45°
T, ,. „ r Black 0123456789
Proportion of | ^^^e 9876548 2 10
If the slope to be represented be one of 30°, ita complement, or what
it wants of 45°, is 15°, wliich being the half of 30°, the black Unes vriU be
twice as thick as the white spaces left between them, and as 45° is repre
sented by perfect blackness, and from this to perfect whiteness ia divided
into nine grades of shades, it is clear, each of these grades becomes Ughter
than the other by one ninth ; 45° having the whole nine parts black, 40 wUl
have eight black and one white — 35° wUl have seven black and two white —
30°, six black and three white, and so on, as in the above table ; whence it is
seen that, whUe the shading for a slope of 30° is produced by hachures whose
thickness is to the space between them as 6 to 3, or 2 to 1, that of a slope
of 15° is produced by hachures whose thickness is to the white space between
them as 3 to 6, or aa 1 to 2, The tinta thus become successively Ughter as
the rapidity of the slope diminishea, and although the progression is not a
natural one, it is invariably determined by a conventional scale, so that, if
strictly adhered to in practice, not only the relative ateepneaa of the hUls is
picturesquely represented so as to produce the sentiment of reUef, but the
positive amount of the incUnation is shown ; and farther, as the length of
the slopes on the maps is the horizontal projection of such slopes, it is evident
that tMs, the Saxon, or Lehmann, system, suppUes the means of obtaining as
correct a profile of the ground as the contour system of the French. Unfor
tunately, however, the practice of this method does not answer to the theory.
In the first place, it is exceedingly difficult in execution, No draftsman,
whatever skUl he may have acqufred, or however careful he may be, can keep
sfrictiy to the thickness of the afrokea, and to the distance between them,
required by the scale, and without the most perfect accuracy in this respect,
the system loses its chief advantage. The labour of drawing such myriads
of smaU atrokea fatigues the eye, and diminishes its faculty of discriminating
the thickneaa of the atrokes and the breadth of the spaces between them ;
the hand becomes unsteady, the pen wears thicker, the ink evaporates whUe
you are working, and thus, insensibly, you are drawing a slope of 5°, 10°,
or 15° greater steepness than you should do ; and even supposing the
most favourable case of very exact and clever draftsmen, there is seldom
uniformity between the several parts of the same map when executed by
different persons ; the engraver also may falsify the whole ; and if we addf,
that when the slopes are not taken in the field with instruments, but
merely by the eye, they cannot be mathematicaUy correct, and that, accord
ingly, a profile drawn from the map, may give heights very different from
what they are in nature — it wUl be evident that the German method, though
ingenious, though systematic and beautifid when carefully executed, is

172 CHARTOGRAPHY.
Uable to so many defects in practice, as stiU to leave room for something
more perfect, more easy of appUcation, less tedious, lesa expensive, and more
readily understood by the pubUc at large, for whom, after aU, mapa are
made. Various moifioations of the method just described have been
attempted, but with little success. To detaU them, and a variety of other
syatema, would requfre a great deal more apace than we can devote to the
subject. Nevertheleaa, we muat say one word on anaglyptography aa apphed
to maps. The perfect resemblance of reUef which is obtamed by this art,
ia well known in the case of medala and coina. But the firat idea of its
application to the purpoaes of geography seems due to Mr. Greenongh.
At a meeting of the British Aaaociation at Briatol, in 1836, that gentleman
expressed, in the Geological Section, a hope that the process in question inight
be appUed to the delineation of mountams ; and at the meeting of the same
body at Liverpool, in the foUowing year, Mr. Dawson, one of the ablest
draftsmen employed in the ordnance survey, having acted on Mr. Greenough's
suggestion, exhibited a small map produced by the anaglyptographic process,
and representing a portion of Wales. Subsequently, a much more perfect
specimen waa executed by the dfrection, we beUeve, of Colonel Colby. Mr.
Lowry (the father) executed for Profeaaor PhiUips a smaU anaglyptographic
map of the Isle of Wight, and other maps have since been done, particularly
one of a portion ofthe Pjrrenees infour sheets. In producing the appearance
of relief, nothing can equal the process we are speaking of; but there are two
cfrcumstances which wUl ever prevent its appUcation to maps becoming
general. In the first place, a correct model of the country must be ffrst
produced, for it is by applying the inatrument to a model that the engraving
is produced. Now, it is at once evident that the expense and time required
for modeUing, not only a whole country, but any large district, muat ever
preclude the appUcation of the anaglyptographic proceas for mapa of auch
extenaive surfaces. Secondly, the very perfection, strange to say, of the
effect produced is against ita uae for maps. It is weU known, that if an
intagUo receives the light from the left, it has the appearance of a rehevo
Ughted from the right, and, in Uke maimer, a reUevo, in certain cfrcumstances,
aaaumea the appearance of an intagUo. Now, the anaglyptographic process
gives so true and beautiful an effect of rehef, that it is sometimes necessary
to pass the hand over the surface, in order to be convinced that it is flat. But
from this very perfection it foUows that, unless the Ught faU upon the map in
a manner conformable to the shading of the map, aU the hoUows become
reliefs, and the reUefa hoUows ; ao that, seen in certain positions, the vaUeya
assume the appearance of sharp ridged chains, with aU the rivers and sfreams
running along their summits. This very remarkable effect ia most striking in
the anaglyptographic map of the Pyrenees. Such mapa, therefore, have the
great inconvenience, that they can only be looked at in one dfrection as
regards the light, and when they are to be suspended, they can be so, only
on one particular side of the room as regards the light. In aome cases,
we beUeve, mapa executed by this process have had engraved upon them,
directions as to the way of looking at them. Theae, then, are inconveniences
which cannot be got over, and accordingly the mode of engraving we are
considering wUl never become general, and need not therefore engage ua any
longer. We cannot here go further into thia subject, nor is it necessary in a sfriotly
geographical point of view that we shouid; for whatever be the system
employed for representing the reUef of the ground, and whatever interesting
detaUs topographical maps may exhibit, they must all be rejected when these
maps are reduced for the construction of geographical mapa. Some few of
the principal featm-es, such as the most prominent elevationa of the ground,
the high roads, &c., are retained iu what are termed the aemi-topographical
maps, which hold a middle position between the topographical and the
geographical map. The former also contains nU the amaUer towns, and even

CHOROGRAPHICAL AND GEOGRAPHICAL MAPS. 173
the viUao-es, which, in geographical maps, eaunot be set down, by meana of the
smallness of the scale. , • i ¦, mi
Mapa are conatructed in an order tho reverae of their details. Thus, a
topographical or a semi-topographical map is a reduction from the actual
survey; a chorographical map is a reduction and assemblage of topographical
maps, and a geographical map, a reduction and assemblage of chorographical
maps, and aU details which a diminished scale renders too minute to be easUy
appreciable or correctly expressed, are necessarUy omitted.
Of Choeogeaphical Maps. — We have afready explained the process for
assembhng and reducing the several portions of a survey, to form from thema
topographical map, but when we would assemble and reduce these latter, in
order to construct a chorographical map, we have, moreover, to subject the
operation to the projection we adopt. For this pm-pose ; having projected the
permanent paraUels and meridians of the mtended map, and traced as many
mtermediate ones as may be deemed necessary, draw upon the topographical
maps, and in thefr true dfrection as regards the north, straight parallels and
meridians perpendicular to each other, and corresponding with those of the
projection ; then copy what is contained in the aquarea of the topographical
map into the corresponding quadrUateral spaces of the projection. As the
aquarea ofthe one do not exactly correspond with the quadrUateral apaces of
the other, we muat, if great accuracy be required, ascertain the distance of the
point to be set down, from the aides of the square within which it ia placed in
parts of a degree of latitude and longitude, and then take simUar parts from
the paraUels and meridiana on the projection.
Of GEOGEAPHICAL Maps. — The passage from the chorographical map to
the geographical, is simUar to that just deacribed for the consfruction of the
former. It must be observed, however, that as errors may have been com
mitted either in the original topographical maps, or in the reduction of these
to form a general map ; it is adrisable to check such errors by marking at
once on the projection, whether it be for a chorographical or a geographical map,
a certain number of important points in thefr true astronomicaUy determined
positions, ao that if the intermediate spacea and objects as they exist on the
maps to be reduced and copied, are either too proximate or too remote, the
distances may be extended or shortened, so as to bring them to thefr proper
hmits, and by spreading the errors over the whole surface, diminish their
individual importance. There are different ways of effecting this correction,
but we are compeUed to refer for such detaUs to works treating expressly on
the practice of map-making.
What has just been said applies only to maps of such countries aa have
been trigonometrioaUy surveyed; but as thia is the case for a very smaU portion
of the Earth's surface, other means must be resorted to when regions less
perfectly known are to be mapped.
CoNSTEUCTiON OF Maps FEOM Vaeious Mateeials. — It is in the con
struction of mapa from a variety of different materials, aU more or lesa imperfect,
that the talent, the knowledge, and the critical acumen of the map-maker are
most conspicuous. We use the term map-maker, insteadpf that of geographer,
adrisedly ; for in our estimation they are by no means synonymous. The geo
grapher is not merely conversant with the positive and relative positions of tbe
several objects on, and features of, the Earth's surface, but he is also acquainted
with tbe particular character of the several regions of the globe, as regards
climate and productions ; he understands the physical laws by whieh the several
phenomena are regulated, and the influence of the soU and aspect in modi
fying the meteorological action, &c. Now, the mere map-maker has no such
knowledge, nor ia it perhapa, strictly speaking, absolutely necessary that be
should possess it, not but what it would be aU the better, nay, infinitely
better, if he did. We could, it is true, name one or two, who, in addition to
the practical knowledge they possess of map-making, add an extenaive
acquaintance with aU that a geographer ahould know, but they form the
exception, not the rule : nor do we make the observation in disparagement of

174 CHARTOGRAPHY.
the talented and conscientious map-maker; his merit is great, hia duty
arduous, and, if well performed, hc is justly entitled to the best thanks, not
only of the pubhc, but of th e geographer himself, for whose studies he supplies
indispensable materials. Alas ! that there should be so few, so very few
good map-makers. Of aU those who supply the public and cater to their
appetite for maps, how many are there who produce anything of their own?
Not one in ten — not one in fifty. Nor is this aU, Not content with embodying
in their productions the labours of others, (a plagiarism, by the way, tolerated
by usage, and without which we should have but three or four names to aU
our modern maps,) they do not even copy correctly. Indeed, the carelessness,
not to say the want of common honesty, with which some maps are got up and
sont out among the public, is a crying evU ; but — and we regret to say it — so
smaU is the amount of knowledge possessed by people in general of this
department of science, that if not one map in ten be good for anything, there
is not one person in a thousand capable of detecting the errors, or discovering
the discrepancies of the maps they purchase. If there were sound critics in
this matter, map-makers would perhaps be more careful, and find it better for
thefr reputation, if not more to their interest, to publish less in quantity and
superior in quaUty. When we shaU have explained what is requfred of a good
map-maker, it wiU soon be seen how far it is possible to beUeve that anything
like care can be bestowed upon those maps which are issued to the pubhc
with a kind of raUway precipitant, so soon as any particular interest is
attached to any particular region. But to return.
The construction of the map of a country that has never been trigonome
trioaUy surveyed, requfres the use of a great variety of materials, and a
profound knowledge of thefr respective Talue. These materials are the
existing maps, the positions, as deduced from the use of Ephemerides, the
measurements and relations of traTeUers ; and where aU these differ, as they
invariably do, more or lesa, much knowledge, much time and labour, and
great sagacity are required in arriving at even an approximation to the truth,
through such a mass of conflicting documenta. Suppose the longitude and
latitude of a place to have been determined by eight or ten different persons
at different times, and that none agree. It will not do, aa is sometimes
recommended, and is the almost invariable practice, to take a mean of the
several determinations, for this may give a position far vrider of the truth
than some of those already laid down. If, of the twelve different positions
assigned to Mexico vrithin the last century, a mean had been taken between
the extremes of longitude, the position, instead of being rectifled, would be
set down about two hundred mUea to the West of its proper place, and
further removed from the truth than any one of the twelve positions assigned
to it, except two ; and a mean of the e.xlTeme latitudes would place it further
North than any, but one. The same may be said of an infinity of cases,
eapeciaUy of those in which the errors, as is frequently the case, Ue aU one
way. The conscientious map-maker, therefore, vriU ascertain how the several
positiona wcre respectively determined — if asfronomicaUy, how, when, and
by whom. As to tho how, some methods give more correct results than
others : aa to the when, what inatruments could the observer have had at the
time ; they may, nay, in most cases, must have been very defective compared
with those of the present day : what asfronomical tables existed at the time,
from which the observers could make their calculations, and how far could
theae Ephemerides be depended on ? As to the observers themselves, were
they known as exact and able, or were they persons who, from want of
education and capacity, were entitled to no confidence P If the longitudes
were determined by the transport of time, what amount of reliance can be
placed on tho watches then in use P and how far ean the place to which the
time was referred, be regarded aa accurately laid down— or if incorrect, are
the amount and direction of the error ascertained ? If the positions were
determined by itinerary measures, ^hat were they, and is thefr frue Talue
positively known P Sometimes the only measure has beeu days' journeys on foot.

MAPS FROM INPORMATION OV TRAVELLERS, 175
or estimated by the pace of the horse, the camel, &c. Was the route, in thia
case, hflly or level ? How were the bearings taken, &c. f Nor is it enough
that the map-maker satisfy himself by a first process of the confidence he
can place on any of thefr several methods. It may happen that the very
results which differ most widely, have been arrived at by means entitled to
most credit. Then must he have recourse to coUateral arguments derived
from other sources, before he come to a conclusion in favour of the one or the
other, and is perhaps obUged, after aU, to spUt the difference.
Now it is clear, that this sifting of contradictory evidence is no easy task,
and impUes extensive information, great patience, and intense application. It
wfll not always do to cut the matter short, by taking the latest observation as
probably the most correct. The position of Mexico as laid down by Velasquez
and Gamma in 1778, was correct in latitude, and only about fifteen miles too far
to the West, whUe Arrowsmith (the elder), in 1803, placcs it about tlifrty-
three mUes too far North, and forty-five too far West, and the Connoissance des
Temps for 1804, whUe it givea the latitude nearly correct, placea it in longitude
a whole degree too far West. We repeat it, then, Uttle reUance can be
placed on any maps, but such as are pubUshed by inteUigent, painstaking,
and conscientious map-makers; thefr number ia very Umited, and they are
entitied to the gratitude of all who have a just notion of the great importance
of correct maps. But a map may be correct, and stiU not be a good map
in every sense of the word, aa we shaU presently explain.
We have hitherto spoken of the construction of maps from regular surveys
from the assemblage and reduction of other maps, and from various sources,
stUl including the use of afready executed maps. We have now to say a word
on mapping from the mere information of fraveUera,
Mapping feom the Infoemation op Travellees. — The deUneation of
countries that have not been surveyed in any way, depends entirely on the
relations, the notes, the information received, and the sketches made by
fraveUers, From these sources of knowledge the flrst detaUs of a country
are laid down, and from them the map becomes fUled up, and corrected as
fresh information is acquired, A few years since, the map of Australia
presented one great blank ; but the Sturts, the Eyres, the Leichardts, the
Mitchells, the Sfrzeleokis, and other adventurous, indefatigable, and weU-
quaUfied fraveUera have, by thefr moat hazardous and difficult explorations,
enabled our map-makers graduaUy to lay down some important ieatures of
that vast island, and consequently increase our knowledge of that singular
and even yet Uttle known region. We could also point to Sir K, Schomburgk's
toavels in Guayana, and Dr. Beke's in Abyssinia, and indeed many others, as
examples of the enrichment and correction of our maps by the mere researches
of fraveUera in the abaence of regular surveys.
The value of the information suppUed by explorera ia not alwaya tho
same ; some possess greater acqufrements than others, and some have better
or more extensive opportunities than othera of applying thefr ability. It can
of course be the lot bnt of very few to unite the varied knowledge of a
Humboldt, and bring home as the result of their travels, new facts gleaned
from every department of nature, and throw new Ught upon the questions
relating to the several races of mankind, thefr language, arts, customs, and
institutions. Almost every fraveUer is remarkable for some speciaUty, and,
according to the bent of his incUnation, dfrects his principal attention to this
or that particular object ; but we have here to deal chiefly, if not exclusively,
with his abUity as a topographer.
If the traveUer be possessed of good instraments for observing the
latitudes and longitudes of the several remarkable points of his exploration,
and knows how to uae them properly, this gives very great value to his
indications ; for, if his observations can be rehed upon, they not only serve
to check the data afforded by hia hearinga and itinerary distanoea (if he has
noted these), but enable us to lay down the points with precision without the
aid of any bearings and distances, and of assigning to them their proper

176 CHARTOGRAPHY.
places on a conic or any other projection, without those reductions that are
indispensable when the distance of points otherwise ascertained is such, that
the spherical surface of the earth must be taken into account.
If the traveUer be not supplied with the requisite instruments for the
astronomical determination of his latitudes and longitudes, or is unacquainted
with the use of such instraments, hia pointa muat be laid down by bearings
and distances. This is a very common mode in rapid exploration, and the
result vrill be the less incorrect, aa the croas bearings have been more multiphed
and taken with the greater care, and according as the itinerary measurements,
whatever these be, are properly reduced with regard to the nature of the
ground traversed. A long route thus laid down can hardly be esteemed
tolerably correct, unless it terminate at aome spot whose position is pretty
weU known ; in this case, its more glaring errors may be compenaated. fri
Uke manner, if the traveUer return to his starting point by another route, the
one wiU serve to correct the other. If, subsequentiy, another fraveUer start
from some very diff'erent dfrection from the first, and come to any point laid
down by him, thia new route fumiahes an additional meana of corroboration
or correction, and thus by degrees the map is improved, and tolerable accuracy
ia at length obtained.
As the fraveUer proceeds, he does not confine himself strictlyto hia dfrect
route ; he often leaves it to explore to his right and left. He notes the
remarkable hiUs and other objects he sees around him, judges more or less
correctly of their distances, and sets down thefr bearings. He notes the rivers
he passes, thefr direction, their depth, and breadth, and the sfrength of their
currents, marking carefuUy the day and hour of aU his observations. He
gleans, moreover, all the information he can from the natives, carefnUy stating
his reasons for beUeving or discrediting thefr assertions. Sometimes the
traveUer maps his route himself, and this greatly assists the professional map-
maker's labour. But it too often happens, not only that notes are aU the
traveUer brings home, but that, either through inadvertence on his part, the
notes are incorrect, or he may have neglected aome important feature, snch as
a river, or may have stated the direction of it to be the very reverse of what it is,
or he may have set down as a fact what he heard from natives, who may,
through ignorance or design, have made a false statement. One part of tine
traveller's notes may be directly confradicted by another ; indeed, the sources
of error are numerous, and yet it is from such materials that the map-maker
is often called upon to protract a fraveUer's route through an unknown region,
and lay down topographical features where there waa only a blank before.
Great discrimination is therefore required of him, and it is only the rare few
who are able and vriUing to bestow upon thefr maps that great amount of
labour, which, in so many cases is indispensable, and which, after aU, only
assures an approximation to truth.
Having thus far initiated the reader into the art of mapping, which, as we
have before stated, cannot here be fr-eated of in extenso, we shall explaiti what
we meant by saying that a map might be correct, and yet not be a good map.
A CoEEEGT Map not always a good one.— a great error prevSls almost
universaUy in respect to maps — ^namely, the desfre of making them answer aU
sorts of purposes at once. Most persons expect to find on a map every place,
no matter how insignificant it may be ; and if thefr own hamlet or the vdlflge
where they reside be not set down, are inclined to look upon the map as
incomplete. Then, again, they would have all the poUtical dirisions and
subdivisions, and as many of the physical features as possible, as also historical
and statistical indications, &e. Now, there cannot be a more Ul-conceived
exigence. We have already stated, that a geographical map should contain
nothiug beyond tho capitals, principal towns, ports, harbours, capes, and other
prominent features ; the general chains of mountains, and principal rivera, and
high-roads, and the limits of empires and state.'!. Anything beyond thia tends
only to confusion. We eould mention a striking example in the case of a
modern chorographie map, whieh we have every reason to believe very

SCALE OF MAPS. 177
accurate ; we know it to be beautifuUy executed ; but the publisher, from a
desfre to meet the ridiculous wishes of his numerous patrons, has inserted
every hiUock in the land, every petty glen and fillet of water, the projected
raihoads, as weU as those executed, the celebrated battle fields, the light
houses dong the coast, the merest viUages, and even gentlemen's seats, &c. ;
and aU this on a map of no greater sc3e than twelve mUes to an inch, pro
ducing altogether a mass of grey conftision, a crowd of names, many of them
inaignificant, and which can hardly be read vrithout a glass. This, therefore,
though a correct, is not a good map.
Scale op Maps. — The scales of maps muat naturaUy vary with the particular
nature of the maps, and should be determined by that alone. Such is the
case with all maps constructed in France under authority. But, in our own
country, where there exists an exaggerated aversion to cenfraUzation, no
matter for what purpose, and where the government are too glad of such an
excuse for leaving undone many things which they alone could effectuaUy
accomplish, everytiiing appertaining to maps is left entfrely to the discretion
of map-makers, publishers, and vendors, who, in perfect ignorance for the
most part of the importance of the scales of maps, do not give the matter so
much as a thought ; with them the scale is nothmg, the aize everything, and
this is regulated with a riew to mere convenience, by the dimensions of the
paper they think proper to employ in each indiridual case, whether for single
maps or atlases. So almost invariably is this the case, that when the writer
once made inquiry of several map-makers, reapecting the scales generaUy
employed by them, of which he requested to be favoured vrith a Ust, the
answer received from all was to the effect, that to give a Ust of the several
scales they had employed, would be to give a Ust of aU the maps they had
published, as they md not beUeve they had ever iasued two on the same scale,
though they had made several of the aame size.
Thia is the fault ofthe publishers much more than of the map-makera ; the
former employ one ofthe latter to prepare a map or an atlaa. I want it, say
they, to be on a sheet of so many inches by so many, or we want a quarto
atlas, an imperial quarto, an oblong quarto, a large foUo, a smaU folio, an
imperial octavo, &e. The map-maker, thus resfricted to size, has to consider
how much margin he vriU leave, and this, with the given dimensions of the
paper, determine the aize of the engraving ; within thia aize the counfry must
be crammed, whether it contain fifty or only ten degrees of latitude or longi
tude, and accordingly, in no case is there any relation between the length of
the degreea and any definite scale. Thns, for example, an octavo aflas is
ordered ; the size of the map within its border is 9^ inches by 7| (the maps
being folded in the middle). Now, a map of England and WsUes, reduced to
theae dimensions, wUl be on a scale of 44^8 miles to the inch. Europe, in
the atlas, muat be brought within the same dimensions, and here the scale wUl
be 347 mUea to an inch, and so of aUthe other countriea and regions included
in the atlas, no twq of which vriU be onthe same scale, and not in a single case,
perhaps, reducible to even an arbitrary scale of inches, vrithout fractions,
much leas bearing any regular proportion to nature.
The inconvenience of different scales, even, when they are Umited and
defined, is almost unavoidable in the case of an atlas ; but the number of
scales may be greatly reduced, aa in the better system lately adopted by Mr.
Sharpe, of whose atlas we ahall say more preaently.
The larger the scale of a map, the greater the number and variety of the
details it may admit. But it doea not foUow that because the scale of a map
be large, the map must necessarily contain much detaU ; some very large
maps contain much leaa than aome very amaU onea.
Class maps, or those intended for the instraction of classes in schools, for
lectures, &c., are executed on very large scales, in order that such features
and names aa are fraced upon them may be sufficiently distinct to be aeen at
a distance, and with the same intention they scarcely contain any but the

178 CHARTOGRAPHY.
more remarkable featurea of the region, and no names but those of the most
important places and objects.
Library Maps, that is, such of them as are intended to be suspended upon
roUers, or otherwise, are usually on a large scale, and, generaUy speakmg, are
aemi-topographical mapa. Their use being for general purpoaes, they are
more full in respect to places than geographical maps, but as they represent
large regions they cannot exhibit topographical details. _
County Maps are topographical, and accordingly their scale muat be large.
Such mapa are chiefly employed for suspending in town haUs and in wie
board-rooms of the local magisfracy, &c.
Boad Maps, Uke library maps, are, or should be, semi-topographical, bnt
thefr scale is usuaUy determined by the extent of country to be drawn on a
portable size for the use of fraveUera ; for portabUity being a desideratum,
it ia erident that a road map of aU Europe muat hardly take up more room in
a fraveUer's baggage, or be less convenient for constant reference, than a road
map of our island.
The scales of maps then must vary with thefr nature and objects ; but,
unless in a few exceptional cases, the scales best adapted for the different
kinds of maps should be regulated upon a principle, and not be lefl to fhe
arbitrary determinations of any compUer of maps.
One of the great advantages of mapa ia thefr pictorial nature, the eye
readUy receives, and the memory easUy retains particular forms, and thus a
person who only occasionally consults maps, can immediately recognise a
country by the general form of its outUne, without the assistance of any
name, while a person stUl more conversant with maps, knows at once where
to place his finger on any remarkable town, by remembering its diatance
fi'om, and position in reference to, some particular portion of the general
outline, &c. But these advantagea are greatly lessened by the indiscriminate
use of all sorts of scales. Every one must have experienced, whenever, in the
course of his researches, he has to consult difi'erent maps of the same country,
the puzzUng effect of different scales, and the loss of time in finding out the
spot he is looking for, and to which his eye woiJd immediately have guided
bim, if the scales had been the same, or even some aUquot part of each other.
Thus, if after looking for VaUadolid on a map of one scale, we go to anothermap
on a very different scale, the probabiUty is, that we shall be aome Uttle time
in finding it. We may very weU know that this city is on the Esgueva, near
to ita confluence with the Piauerga, but it wiU be aa difficult to find these
tributaries of the Douro as the towTi itself. Whereas, if the second map
referred to were on the same scale with the fitrst, we should put our finger on
Valladolid at once. Or, if the aecond map bore some definite proportion to
the first, we shoidd be greatly assisted in our search by knowing what that
proportion was. Again, it ia very desfrable to have a correct idea of the
relative size of different counfries, and nothing tends more to falsify our
conceptions on this aubject than the multipUcity of arbifrary scales in use
among us.
The Ddpot de la Guerre, in France, have determined that general maps,
i. e. those of the four quarters of the world, shaU be on a scale of one-two-
mUlionth, or that two mUlions of metres on the ground shaU be represented
by one metre on the map, and aU other maps on scales determined by succes
sive decimal reductions, or aUquot parts of this. Thus, a degree of latitude
of the general map being taken as unity, a degree of any other general map
is -5, '2, or '1 of auch unity ; by which meana a regular proportion ia main
tained throughout the whole aeries.
If we were to adopt a aysteA aimilar to that of the French, the radius
of" the earth would be represented by ten feet aix inches, a duodecimal
dirision of which might afford a series of convenient scales for aU our mapa.
We have atated tbat, iu Mr. Sharpe'a Atlas, the number of scales has
been greatly reduced, and we gladly had thia as a step in the right direction.
The mapa of this Atlas are called by the author. Corresponding Maps

SCALE OF MAPS. 179
There are in aU fifty-four, consfructed upon only fom- different scales, and
accordmg to these scales, the maps are designated by the names of Conti
nental, fritermediate, Dirisional, and Enlarged. Of the first kind there are
ten; of the second, seven; ofthe thfrd, twenty-seven; and ofthe fourth, six;
besides whioh, there is one, that of Switzerland, whose scale ia much larger
than the rest— two hemispheres and a Mercator map of the world. The
hnear scale of the Intermediate maps is twice that of the Continental ; that
of the Dirisional, five times that of the Contmental; that of the Enlarged,
fifteen tunes that of the Continental, or three times that of the Dirisional.
The arrangement ofthis Atlas results in a somewhat different distribution of
countriea and regiona from what ia customary, and which, if it has its
advantages in aome casea, ia, perhaps, inconvenient in othera. Ofthe general
accuracy of the Atlas we are not prepared to speak, nor would this be the
place, under any cfrcumstances, to enter into ita detaUs. We observe that
the latest discoveries are inserted, and therefore presume that the compila
tion has been carefuUy made. We merely notice thia Atlaa on account of
its pecuhar featurea, of which there are two othera, besides the smaU
nimmer of scales. Thus, instead of two hemispheres, as usual, we have here
four equal aectiona of the earth's surface ; an arrangement not new, though
seldom adopted, and which has both ita advantagea and ita defects ; the
former consisting in greater accuracy as to the form of the several regions
of the earth than is possible according to the usual projection, whUe its
defect is the interruption of continuity of the great eastern continent. In
the present case, however, thia is not, perhapa, of much consequence, the
separation being at the fifty-fifth meridian, cloae upon the confines of Europe
and Asia, northward of the Caspian. It is true Persia is cut in two, and a
shee of Arabia scinded. The next particular feature of the Atlas is in the
adjustment of the scale of EngUsh mUes to every separate map.
When the earth is considered aa a perfect sphere, aU the great cfrcles
are of the same extent, and accordingly one degree of a meridian is of equal
length with a degree of the equator. But the case is otherwise when the
true figure of the earth, which is somewhat flattened at the poles, is taken
into consideration ; for then the meridians are no longer arcs of cfrcles but
of eUipsea ; the arcs, having less curvature aa they approach the polea, are
area of larger cfrclea, and oonaequently a degree of latitude near either pole
is larger than a degree of the equatorial arc, so that if a degree of the latter
contain 6915 British mUes, the degreea of the eUiptical meridian wUl differ
from thia, and be so mueh the longer aa they are nearer the poles. With a
riew, therefore, to greater accuracy of admeasurement than is customary,
Mr. Sharpe has given upon each map the exact number of British mUes
contained in a degree of its middle latitude. This effort at increased accuracy
is praiseworthy, as denoting what we so much wish to see, a desfre on the
part of map-makera to make thefr maps as perfect as possible. But, at
the same time, when we consider that the very element of the calculation
for the number of British mUes in each degree of latitude — viz. the amount
of depression at the polea, ia still matter of dispute, b^g variously given,
'^ TCi> tIt' sYs' ^"-i 3^'i that, in any caae, the fractional difference for a
degree amounts only to a few hundredths of a mUe, and lastly, that measure
ments on a map can never be exact, — we do not aee that, any very material
advantage ia gained by the ayatem here adopted. Nevertheless, we repeat
our conviction that the reduction in the nuniber of scales ia an important
point effected, and in so far is an example worthy of imitation.
In cases such as that of the Atlas just mentioned, we think it would be a
great improvement if the smaUer scaled maps were made to serve as indexea
to thoae on the larger acalea, by drawing faint lines on the former to ahow
the boundariea of the latter, with corner numbers of reference.
Whatever be the scale ofa map, it ia much to be deafred, for more reasons
than one, that auch scale be invariably stated. In the first place, it saves the
time and trouble of finding out the scale by meaaurements ; secondly, when
N 2

180 CHARTOGRAPHY.
we know the scale, we can carry it pretty correctly in the eye, so as at a
glance to have a tolerable idea of the distances of places from each other;
thfrdly, it enables us at once to add the scale to the other details in making
a descriptive catalogue of maps, and such a catalogue, vrithout the scales
being given, is imperfect in one of its most important items.
Be it, moreover, observed that, though most maps have scales affixed to
them, they seldom announce any definite proportion ; that is, they say, for
instance, geographical mUea, Britiah mUes, &c., of each of which the scale
contains a certain arbifrary number, and the smaUer divisions are sometimes
units, aometimea fives, or tens, or fifteens, &c., and if an inch measure be
taken in the compaaaes and appUed to the acale, it faUa in with none of its
subdiviaiona. In order to aupply this deficiency of our maps, the writer has
consfructed a Chaetometeometee, which, by merely applying it to the
central meridian of any map, indicates (with sufficient accuracy for aU prac
tical purposes) the scale of the map in number of geographical and of British
mUes to an inch.
With reapect to these Britiah or rather EngUah mUes, it may be weU to
remark, that cUfferent map-makers state them differently. Thus, in one Atlas
we flnd on some of the maps 69 English mUea to a degree ; on others, 69-1,
and 69-12. Another Atlaa has aimply ' scale of British miles' without stating
how many of them go to the degree. Another, again, has everywhere 69 British
miles to the degree ; whUe a fourth has 69-2 ; a fifth, 69-5 ; and Sharpe's
Atlaa, aa we have just aeen, states the number of British mUes to a degree
differently on the different maps. Geographical freatises also give the pro
portions variously. In the midst of this conftision it is not easy to say who
is right ; the probabUity is, that not one is strictly correct ; for, admitting that
our standard measure of length be weU determined, the measurements of
various arcs of meridians are not so perfectly correspondent as to comprise
any exact or invariable number of EngUsh mUes. The differences, however,
are too trifiing in amount to be of any practical importance in such measure
ments aa are made upon maps ; for even if the amount of depression at the
polea were exactly aacertained (which it is not, being variously stated, as we
have shown, at yj^, g-^r, yjt, &c.), and if the number of British mUes to a
degree of latitude in (Ufferent parts of the eUiptical meridian were most accu
rately determined, stUl sfraight-lihe measurements on a map can never be
exact by reason ofthe distorting effects of projection. A more or less close
approximation to trath is aU that can be obtained, and, indeed, is aU that
need be aought ; and whUe the scales of British mUes vary in two different
maps, as, for instance, 69 mUea to a degree on map A, and 69-5 on map B,
the probabUity ia that m some one dfrection, or in some particular part of
map A, the scale of map B is nearer the truth than that indicated on map A
itself, and vice versa. It must be borne in mind that we are here aUuding only
to the smaU fractional differences in the several statements of the number of
British miles to a degree, and that when we assert that these differences are
of little practical importance, we are by no means to be understood aa aaying
that the scale of mapa is a aubject of indifference; on the confrary, we have
endeavoured to ahow that it ia a aubject of great importance in many respects,
Geaduation of Maps, — The graduation of maps ia Uttle less arbifrary
than their scales ; in one point, however, uniformity prevaUs, it being the
practice to divide the meridians and parallels in the same manner. These
divisions themselves vary: — thus, the paraUela and meridians are drawn
sometimes at every degree, at other times at every second, every fifth, or
every tenth degree. This is a matter which, of course, depends much upon
the scales of the maps. When the scale is smaU, the paraUels and meridians
may conveniently be drawn at every tenth degree, on a medium scale at every
fifth degree, and on larger scales at every single or every second degree, and
this seems to be the general practice ; but that it is arbifrary is evident from
the fact of maps by different compilers being differently graduated, though
on the same, or nearly the same scale. When the "division is by tenth

CONVERSION OF LONGITUDES. 181
degrees, then each of these grand dirisions, on the borders of the map, may
be subdivided into two portions of five degreea each, and each of theae again
into five parts or single degrees. When the division ia hj fives, each niay be
Bubdirided into five single degreea, and theae again into halvea, or 30 minutea
or geographical nulea. When the paraUela and meridiana are drawn at eyery
second degree, then, on the borders of the map these may be divided into
two portions, representing each one degree, and these again subdivided into
three parta of 20 minutea each, or into aix parts of ten mmutea each. When
the dirision is into single degrees, these may be subdivided into six for 10
minutes each, or into twelve for 5 minutes each.
The object of graduation is the finding of the longitude and latitude of
places on the map ; but unless in caaea where the paraUels and meridians are
both sfraight Unes, (as in a Mercator projection,) it anawera but very inef
ficiently the purpoae intended. When the paraUela are afraight Unes, aa in
most maps of Africa and South America, the latitude is easUy found by
placing the edge of a ruler (sufficiently long to reach from the place to the
nearest border of the map) against the place and everywhere equidistant from
the nearest paraUel, when the graduation on the border, at the point inter
sected by the ruler, ahows the latitude.
In the Conical Projection, even when the meridians are straight lines, the
latitude cannot be taken from the border of the map, for as this intersects
the paraUels under very different angles from what the meridians do, the apace
compriaed between any two paraUels on the map is much greater at the
border than elsewhere ; indeed, the exact latitude can hardly be found but by
drawing an arc concenti-ic vrith the paraUels on the map, and passing through
the place; but in order to do this, the common cenfre of the paraUels must be
found, which it is always difficult and often impossible to do.
The longitude may be approximately found on the conic projection, when
the meridians are straight, by placing a ruler of sufficient length close upon
the place, and in such wise that it may intersect the same degree of longitude
marked on the top and bottom borders of the map. In those maps where
both the meridiana and paraUels are curved, the border graduation of the
map only suppUes the means of a very rough measurement or guess at tbe
longitude and latitude of any place. It would be a decided advantage if the
cenfral meridian of all maps were graduated for the latitude, and tms might
very easUy be effected without the sUghteat inconvenience or diafigurement
of the map ; and when the other meridiana are curved, the graduation for
longitude should be marked on some convenient part of every paraUel,
between any two contiguous meridians. By this meana, and with the aid of
a pafr of oompaases, the latitude and longitude of any place might be found
pretty exactly.
CoNVEEaioN OF LoNGiTtTDES. — In the graduation of maps, the longitude
unfortxmately is not always reckoned from the same meridian. Thus, Ptolemy
fixed hia first meridian at the Fortunate Islands (the Canaries), as being
the most westerly country known in his time, though the precise point is
stiU doubtful. -b r ±-
Louis XIII, ordered that the firat meridian ahould hie drawn through the
Island of Ferro, the westermnoat of the Canaries. Deliale had made out the
longitude of Paris twenty degrees to the eastward of thia ; but subsequent
and better information gave 20° 5' 50" for the longitudinal difference of the
two places. The first meridian waa accordingly shifted 5' 50" to the East, ao
that, at the present day, the meridian of Ferro is quite conjectural, and
paasea by no remarkable place.
By the Dutch the first meridian was made to pass over the Peak of
Teneriffe. Gerard Mercator chose for the first meridian that which passes over the
island Del Corvo, one of the Azores, becauae, in hia time, the needle there
showed no variation.
At the present day, however, almost every country considers as first

182 CHARTOGRAPHY.
meridian that which paasea over ita own capital or obaervatory. Thus, the
French reckon from Paris, the EngUsh from Greenwich, the bpaniards fi-om
Cadiz or Toledo ; the Ruaaians have hitherto, Uke ourselves, reckoned from
Greenwich, though occasionaUy from Ferro; but it is probable, now that they
possess a magniffcent observatory at Pulkova, near St. Petersburg, they will
reckon their longitudes from that place. The Anglo-Americans reckon fi'om
Washington, the Venezuelans from Caraccas, and, as M. Jomard observes,
the AustraUans may perhaps ere long have thefr own first meridian.
The foUowing table wUl show the longitudes of the principal first
meridiana with reference to Grreenwich : —

Toledo .
Cadiz . .
Ferro Del Corvo
Caraccas .
Washington 77'

3°

59'

7"\

6°

17'

22"

18°

9'

37"

31°

3'

00"

66°

44'

37"

77°

2'

1"J

Gfreenvrich

EAST.

Paris . .

. 2°

20' 23"

Pulkova .

. 30°

29' 38"

When to this diversity be added, that some geographers reckon the longi
tude eastward aU the way round the equator from 0 to 360, whUe others
count both eaatward and weatward, 180 degreea each way, and that some
deduce thefr longitude from aome particular meridian not considered as the
firat by any people, it wUl be easUy conceived what confusion exists in this
matter. Indeed, the perplexity is often great when we would know the
longitude of any place, as reckoned from different meridians, or in different
ways from the same meridian. Some map-makers (and this is a great over
sight) do not even state upon thefr maps from what first meridian the
longitude is reckoned. When the first meridian and the mode of counting are
known, a calculation is necessary whenever we would refer the longitude
given, to what it would be if reckoned in a different way, or from some other
first meridian.
The longitude reckoned aU the way round is caUed the GeograpMcal
Longitude ; that which is reckoned only half-way round. East and West, is
caUed the Nautical Longitude, and accordingly, as we have to deal with the
one or the other, the mode of reduction is different.
In the first caae, (that ia, reckoning the longitude aU the way round,)
when we would find, from the longitude as given trom any particular first
meridian, what it would be reckoned from any other first meridian, the
rule ia —
Take the difference of the two first meridians, and if the one from whieh
we are desirous to count be to the westward of that given, add the difference
to the given longitude ; but if it be to the eastward, subtract it.
1st Example.— The given longitude of Calcutta is 271° 32' East of Paris,
Query— what is its longitude from Greenwich?
Greenwich is 2° 20' 23" West oi Paris, consequentiy 271° 32' 4-2° 20' 23"
 97Q° f;2' 23".
~ 2nd Exampie.— Moscow, given longitude from Ferro, 55° 14' 45". Query
—what is its fongitude from Paris ?
Paris is, 20° 30' Eaat from Ferro; accordmgly 55° 14' 45" — 20° 30'
= 34° 44' 45",
If after the addition, the whole be more than 360 degrees, which may
often happen, tiien the rule is—
Suitract 360 degrees from the larger sum, and the remainder wiU be the
longitudo sought. Thus— _
3rd Example.— Madrid is 353° 57' 40", Geographical Longitude, East of
Paris. Query— what is its longitude, counted after the same method, from
Ferro P
Ferro is 20° 30' West from Paris. Then 353°57' 4O"-)-2O°30'=374°27'40"j

CONVERSION OF LONGITUDES. 183
this is more thau the whole cfrcle; accordingly 374° 27' 40"— 360°= 14° 27' 40",
the geographical longitude from Ferro.
Again : if the given longitude be less than the meridianal difference to be
subfracted, the rule is —
Add 360 to the longitude, and then subtract the difference.
4th Example. — The Island of Gomera is 32' from Ferro. Query — what is
its longitude from Teneriffe ?
32'-|-360°=360° 32', and the difference ofthe meridians being one degree,
360° 32'— 1°=359° 32', which is the geographical longitude of Gomera from
the Dutch first meridian of Teneriffe.
In the case of Nautical Longitude to be reduced to Geographical Longitude,
we may observe, that when we reckon from one and the same first mericUan,
the geographical and the nautical longitudes are the same aa far as 180°
East. Ll the case of West longitude, the rule is —
Subfract the given West longitude from 360, and the remainder wiU give
the geographical longitude. Thus —
5th Example. — Icy Cape is 161° 30' West of Greenwich. Query — what is
its geographical longitude ? 360°— 161° 30'=19S° 30'.
It is self-evident that by the inverse operation, geographical longitudes
above 180° may be turned into nautical longitudes by subtracting them from
360. Thus—
6th Example. — The geographical longitude of Icy Cape ia 198° 30'. Query
— ^what is its nautical longitude ?
360°— 198° 30'=161° 30', West.
But if the caae regarda two different ffrst meridians, or atarting pointa,
then the rule ia —
See ffrst whether the meridian to which we would refer the longitude be
to the East or to the West of that from whioh it ia given ; then subtract the
difference of the meridians, when they are of the same name, and add when
they are of contrary denominations. Thus —
7th Example. — Constantinople is 29° East of Greenwich. Query — what
is its longitude from Paris ?
Now Paris is 2° 20' 23" East from Greenvrich ; therefore
29°— 2° 20' 23"=26° 39' 37".
Sth Example.— Cape Horn is 67° 21' 15" West from Greenwich. Query—
what ia it from Paris ?
67° 21' 15" -I- 2° 20' 23"=69° 41' 38" West.
It sometimes happens that the place whose longitude is to be reduced lies
between the meridian given and the one to which we would refer it ; being to
the East of the one, and to the West of the other. In this case the rale is —
Subtract the longitude from the difference between the meridian given,
and that to which the place is to be referred, and change its denomination.
Thus— 9th Example. — Dover is 1° 18' 30" East from Greenwich. Query — what
is ita longitude aa referred to the meridian of Paria ?
The difference of the two meridiana of Greenwich and Paris is 2° 20' 23",
therefore 2° 20' 23"— 1° 18' 30"=1° 1' 53" West from Paria.
What happena in reference to placea situated between the meridian given,
and that to which a place is to be referred, may alao happen in reapect to thefr
oppoaite meridiana. Thus, when instead of subfracting, we have to add to
the given longitude the difference between the meridian from which it is
reckoned, and that to which we would refer it, we sometimes find it greater
than 180 degrees. In this case the rule is —
Subfract the sum from 360°, and change the denomination. Thus —
10th Example. — Tortoise Island is in 177° 57' West longitude from
Greenwich ; what ia its longitude from Paris P

184 CHARTOGRAPHY.
As in this case, the difference of longitude between Paris and Greenwich
is additive, 177° 57' -|- 2° 20' 23"=180° 17' 23", which being more than half
the equatorial cfrcle, must be subfracted from 360°. Thus —
360°— 180° 17' 23"=179° 42' 37" East longitude from Paris.
From the above examples it wUl readily be seen, how very desfrable it is that
some one first meridian be adopted by aU nations ; this desideratum has been
frequently and loudly insisted upon by the most eminent geographers of
Europe, but it is to be feared, alas ! that absurd national prejudices wiU ever
stand in the way of so desfrable a reform, as it does in that of many other
important changes.
Details or Maps. — A very great deal might be said on the details of
maps, such as the choice and aize of the character uaed for the names of the
several objects ; the limitation of the double Unes of rivers to the extent of
thefr navigation ; the modes of indicating the mountain chains, &c. The
colouring of maps ; the kind of paper best suited to maps of different kinds ;
the best methods of mounting, arranging, and cataloguing them, and many
other matters ; but to go into theae detaila would be to lengthen the present
article far beyond the hmits to which we muat of neceasity restrict ourselves.
For the aame reason, we have been unable to give any history of the progress
of map-making, or to aay anything of ancient mapa, auch as the Catalans,
the Portulans, &c. Indeed, as we stated at the commencement ofthe present
chapter, the subject of Chartography, fuUy freated, would of itself fiU a large
volume, and requfre to be Ulusfrated by many and expensive platea.
We cannot, however, cloae the preaent article without proteating against
the general want of attention to the orthography of mapa. Surely aomething
like greater uniformity in our manner of writing foreign namea might be
effected. The Eoyal Geographical Society have long aince eatabhshed a rule
for the orthography of Oriental namea, which ia both aimple and judirioua,
and if adhered to in mapa, in hooka of eaatern fravels, and in geographical
works, would go a great way to diminish the confusion of which every one so
justly complains. The system to which we aUude is as foUows : —
GEOGEAPHICAL Oethogeapht. — The orthography, as far as possible, is
reduced to a fixed standard, each letter having invariably its corresponding
equivalent. The consonants are to be sounded aa in English, the vowels as
in ItaUan. The accents mark long vowels, and the aposfrophe the letter
'ain; gh and kh are stoong gutturals; the former often Uke the Northumbrian
r, the latter Uke the Scotch and Welsh ch: a as in far ; e as in there ; i in
ravine ; o in cold ; u in rude, or oo in fool ; ei as ^ in they; oa as oa) in fowl;
ai as i in thine ; cA as in chUd,
What has thus been done for eastern namea, mirfit in like manner be
effected for those of the Slavonic nations, Russia, &c. But to expect improve
ments of thia kind, would be to look for an amount of zeal and industry on
the part of our map-makera for the real interests of the science, which we are
not likely to find.
We must now conclude this brief memofr on mapa, which, imperfect as it
is, vriU, we hope, prove acceptable to our readers.

PHYSICAL GEOGRAPHY.

PART I.
OF THE EARTH'S SURFACE.

CHAPTER I.
INTRODUCTION.
§ 1. General outline ofthe subject. — 2. Divisions ofthe subject. — 3. Planetary condition ofthe
earth. — 4. Elemental conditions of matter. — 5. Mechanical conditions of matter, and divi
sions of science thence resulting. — 6. Advantage arising from the study of Physical Geography.
f~1ENEBAL Outline of the Subject. — If, in a syatem of geography it is
yjT thought necessary to explain in detaU those facts which bear upon the
occupation of the earth by man, it is not leaa important to communicate a
general view of the various mutual relations of the inorganic and organic
bodies met with onthe Earth's crust, however these may aometimea have been
neglected by writers whoae views were limited to the more technical part of
the subject dfrectly before them.
Such general views and discussions it is the object of Physical Geooeaphy
to furnish, and to this the science thus designated ia properly hmited. It
regarda the human race in its relations with external nature. It has, however,
no concern with human history ; nor doea it directly introduce thoae important
commercial intereste which bind together different branches of the great
human famUy. It deals not vrith artificial boundaries of nations, or with the
poaition and relative importance of thoae localitiea where men congregate in
multitudes. It makea no reference to the habita of men, or the distinction of
races, except when theae, in thefr turn, affect the general grouping of organic
beinga on tiie globe.
The acope and objecta of thia acience are, however, sufficiently interesting,
and bear in no trifling degree on the most important interests of men.
Physical geography is the history of the earth in its whole material
organization; — as a planet, inasmuch as it affects, and is affected by, the other
planets of our solar system, and aU other bodiea in space ; as a masa of
matter, whoae external cruat exists in various mechanical conditions acting
on and affecting each other ; as the seat of organic Ufe, consisting of certain
tribes of vegetMiles and animals adapted to its present state ; as subject to
certain mechanical and chemical changes which modify the conditions of
organic existence ; and, lastly, aa containing and exhibiting in ita aohd portion
a history of itself in former states, and when inhabited by different organic
beings, thus affording memorials of events and changes that have occurred at
and near its surface during the lapse of a vast period of time, if not from the
very commencement of its existence as a planet.
2 Divisions of the Subject. — The fundamental knowledge requfred 'to
comprehend the science of physical geography consists, then, of many and
varied facts concerning — 1st, the planetary conditions of the globe ; 2nd, the
nature, properties, and chemical and mechanical conditions ofthe portions of
matter which make up the Earth's crust ; 3rd, the general form and manner
of distribution of the sohd, fluid, and aeriform parts whioh are presented for
observation at and near the surface ; 4th, the nature and distribution of

186 PHYSICAL GEOGRAPHY.
existing racea of vegetables and animals ; and Sth, the former gronjiing of
these organic bodies, as determined from thefr remains existing within the
Earth's crust, and discoverable by investigation and inference.
3 Planetary Condition of the Earth. — The material universe comprises
a vast but unknown multitude of bodies, made evident to our senses by their
power of emitting or reflecting Ught, but connected together also by the
universal action of one great law — that of gravitation. AU these bodies,
although at immense diatancea apart, act upon each other in very important
waya. They are coUected into groups, ofwhich the one to which our Earth
belongs consists of a central body, the Sun, which is self-luminoua, and a
number of amaUer bodiea, the planets, revolving round it, and only reflecting
Ught ; but themselves, in many caaea, the centres of motion of others, stifl
smaUer, caUed moons or aateUltea. The group altogether is not remarkable
amongst the heavenly bodies, and our Earth offers no pecuUaritiea of impor
tance either with regard to magnitude, poaition, or other essential quaUties,
The Sun, the central body of this syatem, ia of great magnitude compared
vrith any of the bodiea revolving round it, and it aeems to be the only one of
the whole number which is capable of emitting any considerable amount of
light and heat. Although many times larger than aU the members of our
system together, it is not so dense aa most of them, and in consequence of the
external surface being luminous in a high degree, it has not been found possible
hitherto to do more than measure its dimensions, distance, and relative density.
Of the other bodies, most of the planets revolving round the Sun in various
periods appear to possess many analogies with each other and with onr Earth;
while the sateUites or moons, of which the Earth has one, revolve round the
planets, and appear to differ from them in some respects. Comets are
wandering bodies, apparently aelf-luminoua. They revolve in eUiptic and
irregular orbits round the Sun, and are ao extremely anomalous, that little has
hitherto been determined ooncerning them except that they are probably
gaseous. The stars appear to be self-luminous, but thefr distances are far too
great for ua to be able to determine anything with regard to thefr mechanical
and chemical condition, leaving us only to assume thefr vast magnitude and
the extent of the systems to which they belong.
Thus, then, the Earth, unimportant as it is as an individual member ofthe
countleaa hosts of heaven, becomes to us, its inhabitants, not only important
as our dweUing-plaoe, but as the only object in space concerning which we
have the means of minute investigation ; for however the distant riews of other
bodies may communicate trae general notions of thefr real state, we can
observe and investigate only those things presented to us here and capable of
dfrect and experimental handling. Thus it is that our ideas ofthe conditions
of matter are limited to those commonly presented to our senses, and our
notions of forms of Ufe are simUarly confined, nor does it seem altogether
possible for us to imagine other conditions or other forma without running
mto extravagant and even ridiculous exaggeration. It is not, however,
reaUy essential to the existence of a planet, and it may not be needful for
organic existence, that matter should be invariably presented in the ways in
which we are accustomed to aee it. The conditions that obtain on our Earth
may not be universaUy met with ; the ultimate elements of which another
planet is composed may be different fi-om those here found ; the proportiona
m which thoae elementa are combined in the moat abundant and characteristic
materials are stiU more Ukely to be different ; the proportion of Ught and
heat, the extent and nature of chemical and elecfr-ical action, may be capable
of infinite variation ; and when the Umits of one planet are passed, the forms
so famiUar to us as to seem esaential to matter may entirely alter, and new
and unimagined contrivancea appear, producing results not less perfectiy and
beautUuUy adapted to existing circumstances.
4 Elemental Conditions qf Matter. — In order to understand how this
may be, it is necessary to be famUiar vrith the true actual conditions of matter
and life on our globe ; and thus arise, at the outset, various considerations

INTRODUCTION. 187
concerning the materials of which the earth is built up, the ordinary and rare
combinations of the material elementa, their mutual action, the cauaes of
internal change and modification that oan be traced amongst them, and the
mechanical condition of the various kinds of material, and their mechanical
action on each other.
So soon, then, aa we commence investigations of this kind, we flnd our
selves, in fact, launched on an inquiry which includes within ita wide embrace
two special sciences of immense extent and vast importance. Chemistet, in
ita highest sense, and Mineealogy are requfred at the starting point, and
must form the basis of all accurate knowledge of the Earth. These teach us
that the materials of the Earth's crust are combinations of various aubatances,
and that the cause, aa far as we can discover, of thefr pecuUar condition is
connected with the presence of an imponderable agent, which, whether caUed
by the name of light, or heat, or electricity, or chemical force, is not less con
nected with, and derived from, other bodies of the universe, than are the
known effects of that great law of gravitation, which knits together into one
group aU material bodies.
lius, the result of the very first inqufry is to compUcate the problem, and
refer us back to those very bodies concerning which we know so Uttle. But
it is altogether in harmony with everything yet discovered in nature that
there should be these mutual relations, and no real isolation. The same kind
of mutual influence is met with everywhere, and appears to form a chain of
eridence erincing a marvellous unity of design in the whole creation.
5 Mechanical Conditions of Matter, and Divisions of Science thence
resulting. — When, however, by a reference to aU that is known of the laws
of chemical force, and the nature of chemical combinations, and when, by
careful examination of those substances whioh are most abundant and moat im
portant in nature, we have obtained a knowledge of the materials which form
the Earth's crust, we are next introduced to a ^enomenon of the mechanical
condition of these aubstancea, which is of the most singular interest, and is
productive of the most essential characteristics of organic existence, and also
of a constant modification ofthe Barth's crust. In consequence of the nature
of the combinations, and the actual temperature of the Earth's surface, the
three mechanical conditions of solid, fluid, and aeriform are assumed by different
kinds of matter, the result being that we have a solid crust of frregular form,
the irregularities being partly occupied with water, and the whole invested
with a transparent veU of afr. The mutual action of theae is the source of a
freat multitude of phenomena to be deacribed under various distinct heads.
he science of Meteoeology, or the phenomena of the atmosphere; Hydeo-
logy, or the phenomena of water, including not only the sea and rivers, but
all other portions of the aqueous covering of the globe ; together vrith a
description of the modifications of the existing aurface by varioua causes,
thua require minute attention amongat the facts of physical geography. The
actual distribution of land and water on the globe, the configuration of con
tinents, islands, &c., the description of the mountain ranges, and the river
systems, the great plains of the Earth, the vaUeya, and other sfriking pheno
mena of form and configuration, these complete another ofthe main branches
ofthe subject.
The intemal structure of the Earth, and the reaction caused by the con
ditions of matter beneath the aurface — ^involving much of the past history, aa
well as the present statei of our globe — is another department of the subject ;
whUe the generaUzationa obtained by an accurate and detaUed atudy of every
organic body that comes under man's observation, whether actuaUy now
endowed with Ufe, or having existed only in distant ages, and long since
extinct — aU these together make up the physical history of the earth, or, in
other words, the science of physical geograpihy.
6 Advantage arising from the Study of Physical Geography. — The study
of such phenomena as those here aUuded to may be regarded not merely as
promoting the interests of man in reference to his material wants, but also

188 PHYSICAL GEOGRAPHY.
as greatly affecting his general inteUectual advance. This has been weU re
marked by Alexander v on Humboldt, whose knowledge of external nature is,
perhaps, greater than has been acqufred by any man of our own or former
ages, and who, in the infroduction to his Cosmos,h3.s admfrably touched upon
the advantage of such knowledge and the objections that have been raised to
it. I shall not hesitate to avaU myself of the ^pressions of so adnurable a
writer to iUustrate thia part of my subject. He remarks that, 'it ia the
intuitive and intimate perauasion of the existence of theae relations which at
once enlarges and elevates our views and enhances our enjoyment. Such
extended views are the growth of observation, of meditation, and of the spirit
of the age, which is ever refiected in the operations of the human mind, what
ever may be their direction.
' Special accounts of districts, and minute statements concerning those
portions of external nature presented for our investigation in a single country
are, no doubt, the most available materials for a general physical geography;
but the most carefcd successive accumulation of such descriptions would be aa
far from affording a true picture of the general conformation ofthe irregular
surface of our planet and the general conditions of matter at, above, or beneath
its surface, as a Ust and account of aU the species of plants or animals found
in different districts wotdd be from communicating knowledge conceming the
general geography of plants or animals.'* This latter aubject, the geography
of plants and animals, involves the grouping of organic beings — ^the exfracting
from minute individual accounts that vvhich is common to them aU in regard
to their cUmatic distribution — the investigating the numerical laws, or the
proportion of certain forms, or particular famiUes, to the whole number of
species — ^the assigning the geographical position of the district, where in the
plains each form reaches its maximum number of species and ita highest
organic development. So, alao, the final aim of phyaical geography is to
recogniae unity in a vast variety of phenomena, and by the exeroiae of
thought, and the combination of observations, to discern that which is con
stant through apparent change.
If, however, we would comprehend existing nature, we muat not separate
the consideration of the present state of things from that of the successive
phases through which they have previously passed, and thus we have the word
history fitly infroduced vrith reference to nature, and the phrases ' natural
history' or 'history of nature' sfrictiy adapted to descripfrons such as we
contemplate. The organic world — that portion of nature endowed with the
mysterious principle of Ufe — is, as every one is aware, constantiy exposed to
change, so fer as the individual is concerned ; and a careful study of the rela
tions that exist amongst organized bodies shows that this principle of change
extends also to those natural groups of simUar individuals, which we deno
minate species. But it is not only in the organic world that matter is con
stantly undergoing change, and becoming resolved into its elements, in order
that these elements may enter into new combinationa — such is the case, also,
vrith the inorganic materials, which are never permanentiy in repose, and
which have undergone many and important mo(Ufications, evidenced by the
condition of those sfrata of sedimentary rocks which compose a large part of
its crust, and which also contain numerous early forms of organic life now
totaUy lost, but originaUy aaaociated in groupa which have successively
replaced each other.
Vast, therefore, and compUcated in a high degree are the phenomena, and
grand are the generalizations with which we have to deal in considering fully
the subject before ua. It is founded on absolute facte, and on the observation
of what actuaUy takes place and exists, but it involves the expression of many
phenomena co-existing in space, and an account ofthe simultaneous action of
numerous and confUctmg natural forces. A view of the effects of tune, and

• See Humboldt's Cosmos, Col. Sabine's translation, vol. i. p. 47.

FORMS OF INORGANIC MATTER. 189
the analogy of the effects of time and space with regard to the disfribution of
organic bemgs, together with a general history of aU terrestrial phenomena
m thefr mutual relations, render it at once a uniform and comprehensive
science. , , , i ¦ j.-,
Littie haa hitherto been attempted on the plan proposed m the present
work, to present in one view the principles of geographical science, and afford
means of studying this acience on its true basis. Many important facta of
physical geography have, however, been accumulated by various authors, and
have lately been arranged, both in Germany and England ; and whUe in the
present outUne the plan and method are altogether distinct, including also a
wider range than has hitherto been thought necessary, the author has been
indebted to his predecessors, and to the works of many naturaUsts and
fraveUers, for the substance of what is given. The Cosmos, and other works
of Alexander Von Humboldt, Johnston's Physical Atlas, Hof&nan's Phy-
sikalische Geographie, and in some cases Mrs. SomerriUe's Physical Geo
graphy, as well aa several admfrable articles in the Penny Cyclopcedia, will
be found freely quoted, though generaUy not vrithout acknowledgment.

CHAPTEE II.
FORMS AND MODIFICATIONS OP INORGANIC MATTER.
5 7. Limits of our knowledge with regard to the earth's structure, and importance of heat as an
agent of change. — 8. Forma of matter. — 9. Forces affecting matter, and effect of change of
temperature. — 10. Sources and causes of heat. — 11. Chemical action. — 12. Polarity. —
13. Material substances usually in combination at the earth's surface. — 14. Elementary
substances. — 15. Oxygen gas, and its important combinationa. — 16. Combustion. —
17. Nitrogen, hydrogen, and chlorine, with their combinationa. — 18. Non-metallic solid
elements. — 19. Metallic elements the bases of earths. — 20. Metals. — 21. Mutual action of
various forms of matter. — 22. Terrestrial magnetism.
ZIMITS of our knowledge with regard to the Earth's Structure, and
importance of Heat as an Agent of Change. — The knowledge that haa been
acquired with regard to the Earth is very limited in some important reapecta,
but involvea much interesting detaU in others : it teaches much, but leaves also
very much untaught ; part of which ia at present beyond our comprehenaion,
and part we can never hope to learn.
We know, for example, the form of our Earth and the denaity of the
maas, we can compare this density with that of matter at the surface, and we
can also determine the absolute weight ofthe whole globe. AU these conditions
exhibit direct reference to temperature ; and we learn by observation, that
whUe the temperature at the Earth's surface varies at different parts, haring
relation to the aolar rays, the temperature at a certam depth below the
surface is in aU parts of the Earth uniform ; whUe below this stratum of uniform
temperature, there ia an increaae of heat with increaaing depth, not altogether
Tegular and uniform, bnt sufficiently so as to render it highly probable, that
at a considerable distance down the heat is sufficiently intense to produce
fusion of even the most refractory subatancea met with at the aurface. The
increase being about one degree of Fahrenheit's thermometer for every
fifty-five Enghsh feet of depth at all known depths, this, if continued in the
aame arithmetic ratio, would produce the melting point of granite at a depth
of about twenty mUea below the aurface.
When, too, we remember that the temperature of the aurface ia ao greatly
affected by the position of the Earth with regard to the Sun, aa to admit of
innumerable climatal peculiarities, especially of thoae periodical changes we

190 PHYSICAL GEOGRAPHY.
caU Seasons ; when we further consider the effect of light, and the important
relationa of light and heat with electricity, galvaniam, and magnetism, the
vast importance of the aubject of heat wUl be underatood, and the reaaon for
devoting some space to a consideration of the forms of matter, and their
relation with this and other imponderable agents, vriU be fully recogniaed.
8 Forms of Matter. — In the general views that may be taken of natural
substances, certain relations appear which afford the meana of arranging
them in distinct classes, each diatinguiahed by certain aenaible and obrious
qualities. The ffrst class consists of Solids, under which form most of the known
part of the globe is presented. When in amaU masses, soUd bodiea retain
whatever mechanical form may be given them: — thefr parta are separated
with difficulty, and cannot be made to unite readUy after aeparation. Some
(caUed non-elaatic) yield to pressure, and do not recover their former figure;
others (called elastic) regain thefr form, after losing it by pressure. They
differ from each other in degrees of hardness, in colour, fransparency,
and weight, and when having definite crystaUine forms, in the nature of
these forma.
The aecond class consists of Fluids, oi which there are fewer varieties.
These, in smaU masaea, assume the apherical form: their parts poaaess freedom
of motion; they differ in degreea of density and tenacity, in colour and
degreea of tranaparency. They are uauaUy regarded aa incompreasible. They
are contained in or repose on soUds, and assume the form of the vessel in
which they are placed.
The third class includes Elastic Fluids or Gases, which may either exist
free in the atmosphere, or be confined by soUds and fiuida. Their parts
are highly moveable, they are compreaaible and expanaible. They are all
transparent, and very rarely present colour. They differ materiaUy in density.
It has been auppoaed by some natural phUosophers that there exists also
a fourth kind of matter, which has been caUed Ether, occupying the spaces
between those aggregations of matter which form suns, planets, comets, and
satelUtes. The phenomena of Ught, heat, and electricity, and thefr relation
to the Sun in our syatem, have been thought to requfre the existence of some
intervening material substance in order to admit of the action of forces or
powers recogniaed under those names.
9 Forces affecting Matter, and effect of Change of Temperature.— AH matter
is subject to the law of gravitation, by which one portion is atfraoted to
another in proportion to its mass, and inversely aa the aquare of the distance
intervening. Matter existing at the Earth'a surface exhibite also the action of a
force called cohesion, which preserves the form of soUds, and gives globularity
to fiuida. This force is, therefore, a prime cause of the permanency of the
arrangements to which we owe the aurface of the globe.
When any aubatance in a state which occaaiona the sensation of heat to
our organs, is brought into contact with another body which has no such
effect, the result of thefr mutual action from the difference of these conditions,
is that the hot body contracts and becomes cooler, whUe the cold body
expands and becomes warmer.
The effect of heat is, therefore, generaUy to cause the particles of bodies
to separate from one another, and heat is communicated either by actual
contact, or by means of rays fransmitted from the one body to the other.
As, however, there ia nothing to affect the weight of bodiea in the com
munication of heat to them, and they occupy larger space, after being heated,
than they did before, they muat then become leaa dense. . ,
In the case of matter in the liquid or aerial form, the communication of
heat ia found by experiment to take place by cm-rente, or particles actually
moving amongst each other. How far currents may be induced in bodies in
a aohd atate ia not easy to decide. Tbe effect of cfrculation thus produced
is easUy recognised in the atmosphere, since the unequal heating of the
Earth by the Sun produces wind ; and it ia seen also in currents produced m
the ocean.

FORMS OF INORGANIC MATTER. 191
When a substance in a fluid or sohd state is exposed to the action of heat,
a change of condition takes place, the solid becoming at ffrst fluid, and then
assuming the aerial or gaseous state. When, on the other hand, fluid or aerial
bodies are made to part with thefr heat, they aasume in most cases a soUd
form. Thus most of the gases become fluid, water becomes ice, &c.
Generally, when a change of condition takes place in conaequence of the
addition or abafraction of heat from varioua bodiea, the addition of heat pro
duces expansion, and the subtraction of it confraction ; but the amount of
change of volume is different for different substances, and material bodies
change thefr states at very different temperatures. Owing to this it is that
the matter at the earth's surface assumes the form of solid land, vrith a watery
ocean floating on the surface and fiUing up inequaUties, whUe the atmosphere
floats evenly over the whole. We have here exemplified the three conditions
of sohd, fimd, and aerial.
Although, however, generaUy the alteration of volume in different bodies
IS uniform dm-ing similar changes of temperature — that is, although bodiea
generaUy contract regularly whUe heat ia being regularly taken from them,
and expand regularly during simUar increase of temperature, thia ia by no
meana invariably the case. There are many exceptiona, but one is of vital
importance to every organized being on the Earth, and has had much to do
with the general constiinition of the Earth's crust. Water contracts regu
larly as it cools down to a certain point ; it afterwards expands slowly as the
heat is farther reduced, and aa it congeals or assumes the solid form, it ex
pands considerably, so that ice, instead of being heavier, is hghter than
water, and floats on its surface. Were it not so, the sea in cold latitudes
would become graduaUy frozen into a mass of ice, which the bright and warm
sun of summer would have Uttle effect upon. In point of fact, however, water
congeals only at the surface, where it is liable to be acted on by the sun and
by warm currents of afr, which tend to restore it to the fluid state. When
the water in a lake, or in the sea, approaches near the freezing point, it
• begins at once to descend, diminishing m volume and becoming, therefore,
hearier, ao that no ice can be formed tiU the whole of the water haa been
cooled to the point where it posseaaea greatest density. When the ice is once
formed, it increases in thickness very slowly, the soUd form of water being a
very bad conductor of heat.
IO Sources and Causes of Heat. — The cause of heat is by no means clear,
and there are many modes of producing it beaidea exposure to the sun's rays.
A piece of Indian rubber extended and suffered to confract rapidly several
times, becomes hot ; a naU is made red hot by hammering ; the axle of
a carriage takes fire by rapid motion, when the friction ia not diminished by
grease ; the sudden compression of fluids and gases also produces heat ; and,
on the other hand, when by the afr-pump a receiver is rapidly exhausted of
part of ita air, the sudden expansion of the remainder produces a considerable
diminution of temperature. All these facts prove that one immediate cause
of the phenomena of heat is motion.
Since matter may be made to fiU a smaUer space by cooUag, it is evident
that the particles of matter must have apace between them It ia also pos
sible that the particles themselves may be actually smaUer than the inter
vening space in the ordinary condition even of soUds, and thus in all cases
currents of theae particles may be produced during the transmission of heat
and the action of other imponderable agents.
1 1 Chemical Action. — The various material substances met with in nature
are not only in different mechanical conditions, but are also variously acted
upon by each other, If, for example, we take the three substances, oU, water,
and soap-lees, it is eaay to show that the oU and water wiU not mix or act
upon each other ; the oU wiU separate itaelf from the water and arrange itaelf
according to its weight, the two fiuida not in the least combining. On the
other hand, the soap-leea wUl mix intimately with the water, having none of
its properties altered. But if the oU and aoap-lees are mingled, they wUl

192 PHYSICAL GEOGRAPHY.
unite, forming a soft solid substance, which is, in fact, a species of soap, and
differs materially from either of ita conatituent parta. Many substances in
nature have thus what ia caUed affinity for each other, combining intimately,
and the kind of attraction exhibited when two bodies have this affinity is
called chemical aeiion.
Different bodies, however, unite with different degrees of force, and
one body ia capable of separating others from certain combinations, so that
mutual decompositions of different compounds take place under favour
able circumstances, and new combinations and new compounds are formed.
Thia has been caUed double affinity, and it involves a kmd of preference of
one body, or set of bodies, over another. It is thus often deacribed as
elective affinity.
Now, it is very important to understand the difference in kind, of those
two forces whioh have been caUed respectively atfraction and chemical affinity,
Attracticn, whether that of gravitation, cohesion, or what has been eaUed ad
hesion (Ulustrated by the holding power of glue, mortar, &c.), never in any
case effects a change in the properties of bodies. On the other hand, when
two substances that have aflmity are brought into close approximation, and
the affinities come into play, great and decisive changes take place in the
two bodiea, and a new aubatance ia formed, which may be altogether dif
ferent in aU its esaential characteristics from either. Thia action ia beat effected
when the particlea are moat free to act on each other, and thua the addition
of heat or fluid often facUitates considerably changes ofthis kind. The order
of affinity is a matter also of great importance and interest.
12 Polarity. — There is yet another force exerted on bodiea, andtendiM
to produce the condition of things observable at the aurface of the earth E
ia best described by the word polarity, and is exemphfied by that form of
polarity exhibited m a bar magnet, which tends to place iteelf (when sus
pended freely) in a certain position vrith reference to Iwo opposite ideal points
m space — the north and south pole — ^near the exfremities of the ideal axis
round which the earth revolves. Tbe magnet also atfracte to itself at one
end, and repels from the other, the exfremity of a simUar piece of fron also
magnetized. Chemical polarity, however, involves much more than ordinary
magnetic action, and must in the preaent atate of science be understood to
include electricity and galvaniam, as weU as magnetism, if not light, heat, and
chemical affinity. The form known as galvanism is that which exhibits most
of the pecuUar results of this force, while that caUed magnetism ia not less
interesting, as showing in some respecte the most fammar, as weU as dia
tinctly marked phenomena of polarity, preaented in a moderately simple
form. Electrical atfraction and repulaion are equaUy atriking, and not less
simple in iUustration,
Electric or galvanic action is generaUy connected either with the evolu
tion of heat or chemical decomposition, and is excited by heating or rubbing
certain soUd aubatancea, and by the contact of others of different kind when
immersed in certain fluids. Changes of temperature at the Earth's surface,
however, eUcit magnetic and elecfric currents, and theae again produce results
which are among the most interesting that are met with on the globe. The
Earth itaelf may be regarded as a magnet, and terresfrial magnetism may thus
be ascribed either to inequaUties in the temperature of the globe, or to those
galvanic currents which we regard as elecfricity moving in a cfrcuit. Scarcely
any important change can taie place in the atmosphere vrithout the dis
turbance of elecfric equUibrium.
13 Material Substances usually in combination at the Earth's Sulfate.
—The intimate action of these forces, if they are diatinct, or the varioua modes
of action of thia one moat varied force, if indeed there is but one, have pro
duced those combinations which are presented at the Earth's surface, and
have formed this variety of condition which is there recognised. Thus it is
that some aolida are conatantly on the verge of change, under ordinary con-
ditiona, while others are so permanent as to yield scarcely, if at all, to the

FORMS OF INORGANIC MATTER. 193
most exfreme action of this force that we can bring to bear upon them.
WhUe, also, some bodies are occasionaUy permanent in the fluid form, others
can hardly be preserved in that form when very aUght changes of temperature
occur, and some of the aerial or elastic fluids are so Uttle affected by the ab-
sfraction of heat or increase of pressure, as not yet to have yielded to the
greatest efforts tbat have been made, although others are readily altered and
made to assume the Uquid form. Some decompositions also are easUy
effected, whUe others are so only with exfreme difficulty ; so that the chemiat,
whoae object it is to determine the ultimate constituents of matter, is often at
a losa to know whether, after all hia laboura, he reaUy obtains an elementary
body, or has to account for effects produced by assuming the admixture of
portions of a body whose properties are not yet even imagined.
Notwithstanding this doubt of the ultimate elementa, aince it is necessary
for the purposes of science to have certain principles and generaUy acknow
ledged facts from whieh to proceed, it has been found convenient to regard aU
those bodies which no art has yet been able to decompose as elementary.
Thus it is usual to speak of a considerable number of elementary substances,
many of which, however, may be reaUy compounds, and many are so extremely
rare in nature, or present in auch small quantities, that in general descrip
tions they may almost be neglected.
14 Elementary Substances. — Of the ao caUed elementary aubatances,
several are abundant and weU known, and others are highly important in
combination, though of themselves rarely or never aeen. They are of two
very distinct kinds — those which are metaUic, and those non-nietaUic. The
whole number certainly known at preaent is fifty-nine, of which forty -three
are metals, and five gases ; but of this number only about thirteen are abun
dantly present in the rocks that make up the mass of the Earth's crust. The
rest are chemical or mineralogical curiosities, or else occur in quantities so
smaU as not greatly to affect the whole mass, however useful and important
to man. The thirteen elementary (?) substances most abundantly distributed are
the foUowing : —
Four gases — oxygen, hydrogen, nitrogen, and chlorine ;
Three non-metalUe soUd elements — silicon, carbon, and sulphur ;
Five metals, important as alkaline bases — calrium (basis of Ume),
sodium (basis of soda), potassium (basis of potash), magnesium
(baais of magnesia), aluminum (basis of alumina, the ingredient
of clay) ;
One true metal — iron.
15 Oxygen Gas and its important Combinations. — Oxygen gas is beyond
aU comparison the most abundant material present at the Earth's aurface, for
although not met vrith in a free state, it is found mixed with nitrogen forming
the atmosphere, with hydrogen forming water, and vrith sUicon, calcium,
sodium, potassium, magnesium, aluminum, constituting various subatancea
known aa aUica or flint, lime, soda, potash, magnesia, and alumina. It also forms,
with fron and other metals, a vast number of the moat abundant of the ores
and minerala. On the whole, aa much as one-half by weight of the materials
ofthe Earth's crast consists ofthis gas. Oxygen gas is colourlesa, and a Uttle
hearier than atmospheric afr. It may be made to unite with aU the othel
elementa except one (fiuorine), and in many caaea its combination, atom for
atom, vrith another element, forma what is caUed an alkaline base, while a
larger proportion of oxygen produces the aubatances caUed acids. Other
proportiona of this gas with other elements produce neufral bodiea (those
which are neither acid nor alkaline), of which the most remarkable instance
in nature ia water, a mixture of oxygen and hydrogen. A number of other
combinations, under the name of salts, alao derive their important propertiea,
and many of thefr most intereating pecuUaritiea, from the preaence of oxygen,
16 Combustion. — The phenomenon of combustion is one which it is
O

194 PHYSICAL GEOGRAPHY.
chiefly the province of the chemiat to conaider in reference to the various
elementary bodies, but it is also very essential that we should have a general
idea of its nature, in order to comprehend the mutual relations of light, heat,
and chemical action. The combinations of oxygen vrith other substances are
attended with an alteration of volume and the evolution of heat, and oflen,
but not always, by a considerable amount of Ught; and in common language,
when a body combines with oxygen, it is said to be burned, and instead of
undergoing oxidation, is said to suffer burning, whUe a body which can com
bine with oxygen and emit heat is caUed a combustible. It ia important to
remember, that no loas whatever of ponderable matter occurs in combustion,
and that the matter formed may always be coUected and thua proved to have
the weight of the oxygen gaa added to that of the combuatible, which has
either been reduced to an aah, or haa entered into new combinationa during
the process. There is no such thing as annihUation discoverable in nature.
1 7 Nitrogen, Hydrogen, and Cldorine, wiih their Combinations. — Nitrogen
gas is a singularly inert substance. It is tasteless and inodorous, and is hghter
than atmoapherio afr, of which it forma four-fiftha, and in which it aeems chiefly
to act as a dUuting medium. Forming so large a part of our atmosphere, it is
necessarUy a very important and abundant material, but it mixes with few
elementa, and its properties are chiefly negative. In many respects, it is
remarkably contrasted with the thfrd mghly important gas, hydrogen, wliich,
indeed, haa been compared to metals, in its relation to other elements,
although it is the lightest substance known in nature, and is highly
inflammable. Water — a substance universaUy distributed at the Earth's aurface, and
preaent there in large quantities — is the result of the combustion of hydrogen
and oxygen gases. It is eminently a neufral body, and is to a remarkable
extent capable of diaaolving varioua proportions of other substances — a quaUiy
which is well Ulusfrated in the composition of sea water, whose density is
greater than that of pure water, by the addition of 3J per cent, of saline
matter. It is probable that, at high temperatures, water ia capable of holding
in aolution a portion of almoat every aubatance in nature. It is chiefly
the remaining gas, chlorine, combined with soda, which makes up the saline
matter present in sea-water.
i8 Non-metallic Solid Elements. — Amongst the substances presented m
a solid form under ordinary atmospheric conditions at the Earth's surface,
carbon, silicon, and sulphur are highly important, exfremely abundant, and
widely distributed. They are aU of them also without those peculiarities
which characterize metals, iu the ordinary acceptation of the term. It wiU
be as weU to describe the more usual forms of these elemente.
Carbon occurs in three very different forms in nature, being crystaUized
in the diamond ; existing in a state of partial crystallization, but of a very
different fundamental form, in graphite or plumbago (the common black lead);
and in a very different atate again in the varietiea of mineral coal. It appears
to be quite infusible at any temperature, or under any circumstances to
which it has yet been exposed by the chemist, and aeema to offer itself under
thia variety of aapecta, according to the structure ofthe aubstance from which
it ia derived, and the mode of ita preparation, when obtained artifieiaUy.
Carbon is abundantly preaent in aU organic substances, and is a principal
ingredient in the carbonates, of which limestone (carbonate of lime) ia the
moat widely distributed, and the largest in quantity.
Sulphur is Ukewiae an elementarv substance, occasionaUy found native and
pure, but more commonly combined with other elementa. This ia especially
the case with regard to the moat important metals, which are, vfith few
exceptions, found associated with this substance. The metal arsenic, and
another rare metal caUed selenium, exhibit very remarkable analogies with
sulphur in their mixtures with metals.
Silicon is the name given to an elementary aubstance derived by removmg
its oxygen from pure sUica, which in the state of flint or siUceous earth is one of

FORMS OF INORGANIC MATTER. 195
the most abundant of aU the matters that compose the Barth's crust. This
mineral constitutes sand, all the different varieties of sand-stone and quartz
rock, and, combined chemioaUy with alumina, it forms a very large propor
tion of aU flays. In its pure and elementary state it is of Uttle interest,
but in consequence of tho number and importance of its combinations, it is
beyond aU comparison the most remarkable of the non-metaUic elements.
Combined vrith line, potash or soda, magnesia, or alumina, and often with
fron, it forms nearly all the other mineral ingredients of granite, mica-slate,
volcanic rocks, shales, sandstones, and various aoUa — in other words, of aU
rocks, with the exception of pure limestones.
19 Metallic Elements the Bases of Earths. — The metal calcium mixed with
oxygen (with which it combines so readUy as not to be preservable, if exposed
in contact with any known aubstance containing that gas) forms the substance
caUed lime, and this again combined with carbon and an additional supply of
oxygen (carbonic acid), is the ingredient of aU marbles and Umestones, in
cluding under that name chalk and other calcareous bodies of whatever kind.
Combinations of other elements with lime are also abundant in nature, and of
these sulphate of lime (gypsum or alabaster) is one of the most interesting.
Alumina, derived from an obscure metal, just as lime is derived from
calcium, is rarely met with in nature, except as a very hard and precious
mineral, called the oriental sapphire, which exhibits its true crystaUine form.
It is aa sUicate of alumina or clay that this material is most interesting in
reference to the Earth's crust. In that form, however, it is universaUy and
abundantly disfributed.
Soda and Potash are two other substances which are very widely dis
tributed; the former in sea water with chlorine, the latter in nifre (saltpetre).
Magnesia, in Uke manner, is very plentiful, although the quantity is not so
great as in the case of aome other substances whioh may be regarded as
proximate elements.
20 Metals. — Iron is the only metal which is at once so universal and so
abundant as to be worthy of a rank among the principal ingredients of the
globe. It is not found native in the Earth, though fragments are met with
on the surface, containing this metal in association with other metals, but its
ores are numerous, and its presence is everywhere recognised. It ia quite
unnecessary to define and describe a substance ao universaUy known.
These various aubstancea, the remaining elements, and numeroua combina
tions of these and other elements, amounting, however, in aU to a comparatively
amaU number, are mixed together in certain definite proportions, and thus
form what are caUed minerals, groups of which in mass are designated rocks.
Minerals, in most cases, are capable of assuming definite forms, and become
crystaUized into certain recognisable shapes, the study of which, and of thefr
relationa with each other, forms the basis of the science of mineralogy. The
consideration of those masses of minerals which we have described as rocks,
the earths, clays, Umestones, aandstonea, &c., the various kinds of granite and
slate, and aU other great and vridely-spread coUections of Uke minerals, forms
one department of geology, and is more immediately interesting in the study
of physical geography.
21 Mutucd Action of various Forms of Matter. — Reverting to the obser
vations made in the beginning of the present chapter, it will be under
stood that the dirision of aU matter preaent at the Earth's aurface into three
parts — namely, soUd, fluid, and aerial — ^has its origin in certain conditions of
temperature and certain chemical combinationa. It is not, as we have now
seen, an essential condition of matter that there are theae various states, it ia
rather what may be caUed an acridental condition, but at the aame time one
particular state seems much more consistent than any other with the known
properties of some of the elements, and also of aome of their combinationa.
These various conditions, however, involve many modifications, chiefly
mechanical, and the fact that air and water are capable of retaining small
quantities of each other, and of various elements in aolution and auapension,
o 2

196 PHYSICAL GEOGRAPHY.
without chemical change, cauaes some very important and highly interesting
reaulta. The crust of the Earth is greatly affected by the passage over it of
air and water ; these latter aubatances also greatly affect each other, and the
whole mechanical sfructure ofthe crust ia, in fact, due to the action of air and
water, and air mingled with water, aa modified by the changes of temperature
resulting from the partial incidence of the sun's rays on the aurface, and the
more or less favourable condition of the atmosphere for franamitting light and
heat, aa weU aa of the Earth'a aurface for receiving them. Thus, it is that
Meteoeology and Hydeology become part of Physical Geography, and that
the sciences relating dfrectly to afr and water require to be considered as
portions of a more general acience, whose object it is to describe general
terrestrial phenomena, Thua alao it ia that Chemistey ia to a certain extent
required for the same end, and that the laws affecting thoae forcea which
modify the material elementa, muat be in some measure explained and under
stood, before we can proceed to consider either the surface or structural
phenomena of our globe.
22 Terrestrial Magnetism. — There is yet one more subject to be con
sidered before passing on to the material phenomena of the globe. The
researchea of natural phUosophers, chiefly of our own day, have brought to
Ught a vast group of facts concerning the magnetic condition of the Earth,
and have shown that which is now designated ' terrestrial magnetism,' must
be regarded aa one of the moat important, if not absolutely the most important,
of aU the imponderable agents. We have afready aUuded to the phenomena
of magnetism, commonly so caUed, and have said that the tendency of a
magnetic needle to arrange itself in a certain dfrection, ia connected with a
subject of great extent and high interest. The Earth, in fact, exhibits a
certain amount of magnetic force, and this is manifested at the surface by
three classes of phenomena: varying intensity of the attraction; varying
declination, the needle not always pointing to the aame spot or pole on the
Earth's aurface ; and varying inclination, or amount of departure of the needle
from the horizontal plane. Thia latter variation is caUed the dip of the mag
netic needle, and the declination is commonly spoken of as the variation of
the compaaa. In other words, when a compass is referred to, in different
parts of the Earth, or at distant periods, the needle wiU not be found always
to arrange itself so quickly in its position of rest ; it wiU not always point to
the aame point, and it wUl not, if auapended, freely repoae in a horizontal
plane, or at the aame angle to the horizon. In Uluafration of thia, it may be
mentioned, that whUe in the year 1657, the needle pointed due nortii in
London, thia was not the case in Paris tUl twelve years afterwards, notwith
standing the smaU difference in longitude between the two cities. At the
present time, the whole of Europe, except a smaU part of Russia, has west
dechnation, whUe in Asia the declination is east.
But the most remarkable fact with regard to this constant shifting of the
dfrection ofthe needle, is that there is an hourly change of position dependent
on the apparent course of the sun and the lapse of time between the observa
tions. The hour of the day may in this way be known between the fropics,
and the movements of two small bars of magnetized steel suspended from a
thread, even if they are suspended at depths beneath the Earth's surface, wfll
measure accurately the distance which separates them. There are also parts
of the Earth where the mariner, who has been enveloped many days in fog,
seeing neither sun nor stars, and having no means of determining time, may
know with certainty, by an observation of the magnetic inclination, whether
he is to north or south of the port which he desires to enter.
The hourly changes of dechnation of the needle seem to be govemed
by the sun, whUe that luminary is above the horizon of any spot, but they
also have reference to the actual position of the spot on the globe, and its
distance from the magnetic polea. Throughout the northern hemisphere the
mean movement of the north end of the needle from 8| a.m. to 1^ r.A, is
from east to west, and in the southern hemisphere, at the same time, from

FORMS OF INORGANIC MATTER. 197
west to east. Thus, along a Une near the equator there is no horary variation
in declination. The name of magnetic poles has been applied to those pointa on the Earth'a
aurface where the horizontal force disappears. Of theae there are two in each
hemisphere, not far removed from each other, or from the true poles of the
Earth, but unequal in the amount of their attractive force. The focus of
greatest intensity in the northern hemisphere is in North America, near the
south-west shores of Hudson Bay, in 52° N. latitude. The corresponding
weaker focua is in Siberia, about 120° E. longitude from Greenwich.
It is known that the forces which attract the north end of a magnet and
repel the south end, preponderate in the northem hemisphere, while in high
latitudes, in the south hemisphere, the converse is the case. There is, there
fore, in addition to the Une of no decUnation, near the equator, another line
of no preponderance of the northern or aouthern force, and it is found that
both hnes are exfremely frregular.
The intensity of the magnetic force is measured by examining the oacU-
lation of a auapended needle, and ia determined with very great accuracy.
The intensity increases towards each pole, and thus we have a line of least
magnetic intensity near the Earth'a equator, in addition to those Unes afready
mentioned, and quite distinct from them.
Intimate relations have been discovered between the state of elecfricity
of our atmosphere and the magnetic condition of the Earth, and it is known
that whUe a conductor of elecfricity is rendered magnetic by the passage of
an elecfric current through it, so also magnetism gives rise by induction to
electric currents. The identity of electricity and magnetism is thus fuUy
made out.
The importent discoveries of Faraday on the condition of matter with
regard to magnetic influences — ^magnetic force affecting aU bodies as necessa
rily and dfrectly as the force of gravitation, — ^haa given new interest to this
subject. According to the reault of hia experiments, aU aubstancea arrange
themaelvea into two great divisions — the magnetic, in which the substances
tend to place themselves paraUel to the dfrection of the magnetic needle, at
the spot where the experiment is performed; and the diamagnetie, where
the tendency is to assume a dfrection at right angles to that of the needle.
By far the greater portion of the materials which compose the Earth's
crust ijelong to the latter, or diamagnetie class; for even as respects the rocks
and mountains, the quantity of magnetic matter needed to counteract the
diamagnetie tendency is very large, and the ocean, lakes, rivers, and atmo
sphere exert thefr effect as diamagnetics, almost uninfluenced by any magnetic
matter. Mr. Faraday has suggested the possibUity of magnetism being, in
fact, generated in the atmosphere by Ught proceeding from the sun, and
passing rapidly through the air, but he vriaely suspends any theoretical con
siderations until experiment has given a sufficient groundwork for them.
However this may be, there can be Uttle doubt that for aU practical purposea
we must regard the magnetic force as resident only on the surface, or rather
just vrithin the oxidised crust, which ia all that we actuaUy know of our
globe. The Earth is not, aa was once imagined, an inert mass, having, by
some unimagined means, a pecuUar power to attract fron towards its two
poles of rotation. It is a masa of matter, every part ofwhich is affected by
magnetic force, and which ia, throughout its external crast, hard and immove
able aa that may seem, exposed to changes and modifications of the most
exfraordinary kind, and of great extent.

198
CHAPTEE III
METEOROLOGY.
23. Constitution ofthe atmosphere. — 24. Its chemical condition. — 25. Its chief importance in
Physical Geography. — 26. Its relation to light generally. — 27. Twilight. — 28. Mirage. —
29. Colour. — 30. Atmospheric meteors exhibiting colour. — 31. The phenomena of sound.—
32. Motion of the air — Winds. — 33. Land aud sea breezes. — 34. Trade winds. — 85. Mon
soons. — 36. Hurricanes. — 37. Eelations ofthe atmosphere to water. — 38. Dew. — 89. Mists
and fogs. — 40. Clouds. — 41. Kain. — 42. Distribution of rain. — 43. Snow. — 44. Glaciers.—
45. Hail. — 46. Climate, and distribution of heat. — 47. Conclusions.
CONSTITUTION of the Atmosphere.— ^^e proceed now to consider that
KJ portion of the material universe preaent in an aerial form at the Earth'a
aurface, and which haa long been known under the name of atmosphere.
The atmosphere is highly elastic, and therefore more dense near the Earth's
surface than in its upper portions, where there is less pressure ; but notwith
standing its great elasticity, there can be no doubt of ite terminating abso
lutely at a small elevation compared vrith the magnitude of the Earth. The
real extent of this gaseous veU has not indeed been very satisfactorily deter
mined, and has been variously estimated at from forty to a hundred nules ;
but as the diameter of the Earth is eight thousand miles, the largest estimate
does not assume it to be more than one-fortieth part of the radius, and there
is no reason to suppose that it is nearly so much.
The weight of the whole atmosphere can be accurately determined, and
the degree of preaaure at any point is alao a fact which offers Uttie difSculty
in determining. By depriving of afr the closed upper exfremity of a tebe
filled with mercury, whioh opens below into a cistern also fuU of mercury,
the pressure of the whole column of the atmosphere may be measured against
that of a column of mercury, and thus the pressure is found to be equivalent
to about fifteen pounds on every square inch of aurface.
The conatituenta of the atmosphere are as foUow. Of every 10,000 parts
of afr in the ordinary state with regard to moisture, there are —
Oxygen  2,100
Nitrogen  7,750
Aqueous vapour  142
Carbonic acid gas  4
Carburetted hydrogen  4
10,000
There ia alao a frace of ammoniacal vapour.
It waa formerly aupposed, that in whatever part of the Earth it is taken,
at whatever depth or height above the mean level of the surface, or under
other peculiar cfrcumstances, the constitution of the atmospheric air was
exactly the same. Although this is not quite frue, it is very nearly so, the
quantity of oxygen varying sUghtly, but perceptibly, in different seasons of
the year, and over the sea, or in the interior of contmente. So mueh change
by oxidation is constantly going on at the Earth's surface, that it would be
strange if this were not the case ; but the absolute quantity of this gas com
pared with the surface and the materiiJs exposed to its action, is far too great
for the change to be readUy perceived.*

* It may be interesting to repeat here tho diiTcrent localities from which the atmospheric
air has been chemically examined, to show how little tlie proportion changes. The air from
the Alps was analysed by the younger Saussure; from Spain, by De Marti; fi-om France and
ligypt, by BerthoUet ; from England aud tho coast of Guinea, by Davy ; fi'om the Peak of

METEOROLOGY. 199
In addition to the materials afready mentioned, there are also traces of
ammoniacal vapour and even of some other gases in the atmosphere ; but
these, although important in their influence ou organization, are not to be
considered as afi'ecting the general physical condition of the afr. It has also
been supposed that the atmosphere contains, diffused through it, minute por
tions of the vapours of aU those substances with which it is in contact, even
including earths and metals. Although, however, unknown ingredients may
be occasionaUy mingled with the atmosphere and impart to it deleterious
properties, auch ingredienta being of too subtle a nature, and present in too
smaU proportion, to be discovered by our imperfect instruments, it yet ap
pears that a limit exists to the production of vapour of any tension by bodiea
placed in auch a medium aa the atmosphere, and that beneath auch limit they
are perfectly fixed.
24 Its Chemical Condition. — Two views have been entertained of the
nature of the union that exiata among the elaatio bodies forming our atmo
sphere. It has been generaUy supposed to be a chemical compound, because
the proportions are very nearly fixed, and the ingredienta do not tend to arrange
themaelvea according to their different specific gravities. It ia, however,
more probable that the mixture ia, after aU, mechanical, the various elastic
fluids not having any atfraction or repulsion towards each other beyond that
of the simple action of the law of gravitation, and each of the ingredients
exerting its own separate pressure, and behaving as if it were itself free, and
formed a distinct atmoaphere.
The most important and valuable investigations in the science of meteor
ology, have been founded on the assumption that there are two distinct
atmospheres, one of dry air, and the other of aqueous vapour, and that
these are inixed mechamcaUy together; and alao on the conclusion that
the relations of these to heat are different, and thefr states of equUibrium
incompatible with each other. Thus are produced those changes of^condition
consequent, aa we know, upon changea of temperature, and also thoae other
changes resulting iu what la caUed climate.
25 Its chief Importance in Physical Geography. — The atmoaphere may
be chiefly regarded aa important in Physical Geography in its relationa vrith
Ught and aound ; vrith heat, aa the means of distributing temperature ; with
water, as the meana of distributing moisture over the Earth; and with
electricity, as connected with the mode of action of thia force in aU ita varioua
forma. The motion that takes place in the atmosphere, and which we deno
minate wind, is thus a matter of vital interest, since it aids in these diafribu-
tions, and affects also very directly many operations of man. The optical
and acoustical phenomena of the afr being, to a certain extent, independent of
its motion, though not uninfluenced by it, may first be considered. We may
then study the pnenomena of the winds, and afterwards proceed to conaider
some points connected vrith the distribution of heat and water.
26 Its Belation to Light. — In its relations to Ught, our atmoaphere plays
a very important part, and greatly affects the action of several forms of the
imponderable force; and whatever its origin or trae nature may be, it is
capable of teansmission through certain bodies, thence aaid to be transparent,
of which the atmosphere is one.
It is found that in being transmitted or passed through a fransparent
body, a change of direction ofthe ray of Ught takes place whenever the sub
stance througli which Ught pasaea becomes of different denaity, or when Ught
passes from one medium to another of different density. Thus, when a stick
IS placed in water, and is not vertical, it wiU appear to an eye looking down

Teneriife, and near the summit of the Andes, by Humboldt ; and from the still loftier elevation
ot 22,000 feet, (attained in a balloon,) by Gay Lussac and Thenard ; and all these gave results
approaching as nearly as possible to each other. The observations of Lewy are those refen-ed
to as showing a slight difference in different parts ofthe Earth.

200 PHYSICAI, GEOGRAPHY.
upon it as if it were bent, for the water is more dense than the afr, and the
body ia aeen only by meana of the raya of Ught which proceed from it ; and
thus, also, if Ught pass through afr of different density, the rays are bent at
an angle or curved. A part only of the Ught, however, ia tranamitted, part
of it being actuaUy lost, part of it reflected, and a part dispersed. It is im
portant to remember that, in proportion as light pasaea through a greater
thickneaa of matter, as for example, of afr of varying density, it becomes less
and leas in quantity, being graduaUy absorbed, dispersed, and reflected.*
It is usual to apeak of the bending of light in its passage from one medium
to another of different denaity, imder the term refraction, whUe the throwing
back of light from a surface ia caUed reflexion. A ray faUing on a body ia
aaid to be incident. The part fransmitted is r^r acted, and that thrown
back, reflected.
The courae of a ray of light in ita progreas to the earth ia, therefore, as
foUows : — The ray faUa on the uppermoat limits of the atmosphere, and meets
there an elastic fransparent fluia : at thia point it is turned aside or refracted,
a small part of it being, however, reflected back into space, a part dispersed,
reflected, or distributed into the surrounding atmosphere, and a part abso
lutely lost. As it proceeds through the afr towards the Earth, it passes
continuaUy into a denser atmosphere, because the pressure increasing, and
the afr being elastic, the dimensions diminish, and at each instant the ray
becomes therefore more and more deflected, whUe more and more of it is
absorbed, and more is also diapersed and reflected. The portion that reaches
the Earth varies in quantity according to the extent of atmosphere passed
through, and its density, and is therefore not constant; but whatever the
amount be, this portion ia refiected back from the surface of opaque bodies,
or fransmitted, vrith atUl further loss, through fransparent ones, and so again
and again tUl it is completely dispersed or desfroyed.t
Diminished splendour, and the false estimate we make of distance, from
the number of intervening objects, lead us to suppose the sun and moon to be
much larger when in the horizon than at any other altitude, though their
apparent diameters to the eye when measured are then somewhat less. These
and a number of other effects are results of refraction and the partial loss
of light in passing through a great thickness of atmosphere.
In consequence of the dispersion of Ught by meana of the atmosphere, we
obtain aU thoae varietiea of half shade which alone enable ua to make use of
organs of vision constructed aa oura are. If it were not for thia, we ahould
constantly have either fuU broad and dazzUng Ught, or deep black shadow
and impenetrable darkness. The objecta from which Ught is emitted are few,
and, with the exception of the sun, are rarely avaUable, except by artificial
means, so that in countries where the sun is often long absent, or where the
clouds obscure its face during a large part ofthe day or year, the inhabitants
would, in the caaea aUuded to, be in total darkness. A large quantity of hght
being, however, dispersed and reflected from particles of vapour in the afr,
there can hardly be found at any hour of the night, or at any season, a total
abaence of Ught, and there are no sudden and abrupt franaitiona to affect our
deUcate organs of vision.
27 Twilight. — During a fine, clear, calm day, in our northern latitudes,
it may be observed, that as the sun approaches the horizon, the sky in the
west asaumea a yeUow or red tint ; towards the zenith, or dfrectiy overhead, it
becomes whitish, and the sky is less clear ; untU just as the sun has fairly

• See ante, p. 76 .
t The quantity oflight that passes through the atmosphere in different states may be thus
estimated :— Of 10,000 rays falling on the surface of the Earth, 8123 arrive at a given pohit if
they fall perpendicularly, 7024 if the angle of direction be 60°, 2S,?1 if it be 7°, and only flve
rays arrive through a horizontal stratum. In consequence of so large a proportion Of light being
sometimes lost in passing through the atmosphere, many celestial objects may be altogether
invisible from a plain, and yet be visible fl-om elevated situations.

METEOROLOGY. 201
sunk below the horizon, a red colour is seen in the east opposite to the
setting sun. This is the commencement of the phenomenon called twilight,
and is ovring to the existence and properties of the atmosphere, and chiefly to
the light being reflected from its higher portions. It depends, however, on
the position ofthe Earth with respect to the sun, and also the condition of
the atmosphere at the time, how long this phenomenon shall continue ; since,
in the fogs of winter, darkness comes on almoat immediately after aunaet,
whUe, on a clear summer evening, the broad Ught of day continues for more
than an hour little diminished. A simUar phenomenon of twiUght occura in
the morning before sunrise.
Investigations concerning the absolute limits of our atmoaphere have been
greatiy aaaisted by careful observations on the duration of twUight, but the
subject is one of great intricacy, and the results which have been hitherto
obtained are not absolutely conclusive.
, 28 Mirage. — It is not only the rays of Ught that proceed from a lumi
nary vrithout the Earth, but also those emanatmg or reflected from bodies at
and near its surface, that are refracted by the unequal density of different parts
of the atmosphere. The phenomenon of ordinary refraction, as it occura in
fluids of equal density throughout, is exceedingly simple, of whatever kind the
fluids may be, when once the principle of refraction is understood ; but this is
not the case with some curious appearances connected with unusual and irre
gular refraction producing optical iUusions, and not unfrequently assuming aU
the appearances of direct reflection. The word mirage has been appUed by
the French to such phenomena, and as there is no satisfactory English trans
lation, we must be content to adopt it.
The Ulusions of mirage differ according to cfrcumstances, and they are
aometimea exceedingly afrange and almoat atartUng in thefr character, pre
senting an image of what reaUy exista, but ia entirely out of the range of
ordinary vision. Sometimes, also, they exhibit parts of objects, broken, dis
torted, and out of place ; sometimes they confuse in a singular manner the
true outlines of objecta, and occasionaUy they present a gorgeous and fairy-
Uke spectacle — superb palaces, vrith then- balconies and windows resting on
the boaom ofthe broad ocean, lofty towers near them, herds and flocks grazing
in wooded vaUeya and fertUe plains, armies of men on horseback and on foot,
with multipUed fragments of buUdings, such as columns, pUasters, and arches.
All these may be aeen again repeated in the afr above, and fringed with red,
yeUow, or blue Ught.
Phenomena so sfriking can be explained only by a reference to the condi
tion of the atmosphere when in an unusual state vrith regard to moisture as
weU as density, and they may be conveniently arranged under one or other of
the three foUowing clasaea : vertical reflection, lateral reflection, and s uspenaion.
The moat aimple example of vertical refiection is that often observed in hot
sandy deserts, and occurring after the soU haa become heated by the presence
of the sun. In auch caaea, the prospect seems bounded by a sheet of water,
and underneath each object, as the viUages which in Egypt are generally
buUt on smaU eminences, the apparent refiection is aeen as if in water. A
singular effect of thia kind is described as haring been noticed in India, where
Captain Maunday states, ' A deep, precipitous vaUey below us, at the bottom
of which I had seen one or two miserable viUages in the morning, bore in the
evening a complete resemblance to a beautiful lake. The vapour, which
played the part of water, ascending nearly half-way up the sides of the vale,
and on ite bright surface trees and rocks were distinctly refiected,'
In horizontal reflections the image is presented sideways. In this manner
Dover Castle has been seen from near Ramsgate, as if an intervening hUl,
which under ordinary vision cuts offa part of it, were actuaUy removed ; and
in this way, too, the French coast has been seen distinctly, and in aU its
detaUs, from near Hastings, although the distance is sufficiently great to
render it invisible by ordinary refraction.
The phenomenon of suspension is not less remarkable, and is caUed in sea

202 PHYSICAL GEOGRAPHY.
language, looming. It consists in the representation of an object immediately
above its true place, either in its true position or reversed. Thus, Captain
Scoresby describes that he on one occasion diatinctly recogniaed hia father's
ship at sea, by its inverted image fri the afr, although the distance between
the two ships was aa much as thirty mUes, and the ship was therefore far
below the horizon of that from which it was observed,
AU these phenomena, and their different modifications, depend on the dif
ferent density of the lower strata of the afr, and as thia difference of densitv
may be occasioned both by heat and moisture, and aa heat may be reflected
from a mountain side as weU as from the horizontal surface of a plain, and
from the sea as well as from the land ; and further, as contiguous vertical
columns of afr, as weU as horizontal strata, may be of different densities, itis
easy to understand why mfrage may be aeen in very different situations, and
why it presents auch varied appearancea. It wiU also be erident that any
cause which re-estabUshes the equUibrium of density in the different portions
of the afr must cause the Ulusions of the mfrage to vanish. Calm in the
atmosphere is almost essential to the phenomenon in question, and it has been
remarked that thisperfect cahn is often the precursor of a tempest.
29 Colour. — The ray of white Ught proceeding from the sun, and whose
course we have traced through the atmosphere, has been found to consist, in
reaUty, of several rays, some ofwhich communicate to our eyes the notion of
various colours, whUe others seem chiefly important in producing heat or
chemical action. It is found, alao, that these rays are differently affected by
paaaing through, or being reflected from the same substances, aome being
more readUy absorbed and loat than others. Thus, the impression on our
senaea in looking through the clear atmoaphere, ia that of blue, whUe the
aetting sun communicatea red or golden light to clouda, according to the cir
cumstances under which the Ught faUs.
The colours which, being combined, make white light, are three, and are
called blue, red, and yeUow, but several weU marked modifications of these
exist, and it ia uaual to speak of seven primitive coloura — ^viz., red, orange,
yellow, green, blue, indigo, and violet.
All aubstancea known, however opaque, aUow some portion of Ught to
pass through them, and aU, however transparent, absorb and deafroy some
rays. The coloura of bodies are derived from thefr power of absorbing
certain raya more readUy than the reat, and thus giring forth light, which, in
atead of being a mixture of coloura in the proportiona of white light, have
some colour in exceaa, the idea of which they communicate to the eye. When
light also passes through a transparent medium, auch as a priam, a glass
sphere, or a drop of water, it becomes decomposed, and in this way are pro
duced some of the moat atriking meteoric effects in which colour appears.
Bodies that refiect aU the rays in the same proportion appear white, those
that absorb all are black ; a violet refiects the violet rays alone, and absorbs
the rest ; while a leaf reflects the blue and yeUow rays, absorbing the red,
and produces by a mixture of the two the compound colour known as green.
Very careful observation has shovm that there are dark Unes in the image <rf
the sun received on a screen after the transmission of a ray of hght through
a prism, and these by thefr permanence and uniformity appear to show that
certain raya are abaorbed in paaaing from the sun, or perhapa in traversmg
the solar atmosphere.
30 Atmospheric Meteors exMbiting Colour. — The rainbow, one of the
most striking ofthe common but occasional meteors, is the first that requires
notice. It is a circular arch of variously coloured Ught, risible in the heavens
when tho sun or moon is shining, and when at the same time a shower oj
rain is faUing, — the spectator bemg placed with his back to the sun, and
observing the falling rain. Besides the principal bow, a aecond bow with
inverted colour ia often aeen outside the principal one. Both consist of con-
t'entric bands of the prismatic colours, arranged aa they have been deacribed to
occur in the solar spectrum. Thc lower edge of the mterior bow is violet.

METEOROLOGY. 203
It is not very difficult to comprehend generaUy the cause of the rainbow.
A ray of sunUght entering a drop of water as it is falling to the earth is
refracted as it enters, and the refracted ray is subsequently reflected from
the inside of the drop on its opposite side, and then emerges and proceeds
towards the eye of the spectator, placed as has been described. But the rays
of colour being refracted to different points, and becoming a Une of coloured
light as they issue from the drop, a part only wUl reaUy reach the eye of the
spectator, and from one drop he will see one colour. The same will happen
with aU the other drops, and the eye wiU only be aenaible of a band of coloured
light having an apparent breadth about equal to four and a half timea the aun's
apparent diameter in the case of the inner bow, and an outer band about half
as large again.
The appearance sometimes observed around the sun and moon, and termed
halo or corona, is caused by the refraction of light by particles of water
floating in the afr. Parhelia — repetitions of the sun near the trae place of
that luminary, and athelia or falae auna, are referred to the refraction of Ught
by floating prisms of ice. These and a number of rarer results of the action
of those laws which affect Ught, produce thefr effect in consequence of the
pecuhar condition of our atmosphere, its occasional and irregular contents,
and ita unequal denaity.
31 The Belation of the Atmosphere to Sound. — If the atmoaphere were
removed, and our organs of hearing remained as they now are, a death-like
sUence would appear to us to pervade nature ; for aU sound ia connected with
ribrationa of particlea of the air, producing wavea throughout the whole maaa,
though each individual particle does not move far from ita atate of reat. The
appearance of a field of ripe corn when agitated by wind, offers a good Ulus-
fration of the condition of the atmosphere when fransmitting soimd, the only
difference being, that each ear of corn ia aet in motion by an external cauae,
and ia uninfluenced by the motion of the rest ; whereas, in afr, which ia com
preaaible and elaatic, when one particle begina to osciUate, it communicates
ite ribrations to the surrounding particles, which transmit them to those
adjacent, and so on continuaUy.
The velocity of sound is uniform, and quite independent of its loudness ;
but whatever increases the elasticity of afr, must accelerate the rate of the
vibration, so that sound travels faster in warm weather than in cold. The
speed at the temperature of 62° Fab. is 1143 feet per second, whereas at
freezing temperature, sound only fravels 1089 feet in the aame time. It is an
interesting fact that the rate of speed of sound is faster than would appear
from theory, unless the reault 01^ the compression of the afr in the trans
mission of the wave is taken into account. It has been already said that
compression of an elastic fiuid produces heat, and we have juat seen that heat
quickens the rate of transmission. Thus the actual rate at which aound
travela is about one-sixth greater than it would ha,ve been, if the temperature
remained unaltered during the compression of the atmosphere.
The franamiaaion of sound, therefore, aa weU aa the ten thousand other
changes going on about ua, are themselves engaged in originating stiU further
changea, and caUing into action powers and forces at first Uttle suspected.
All fluids and soUds transmit sound, and most of them far more rapidly
than afr. Water, for example, conveys vibrations of this kind four times,
and aome kinda of wood neariy seventeen times, as rapidly aa air. StUl, air ia
the only means on which we can depend, for without this, our auditory
apparatus would be useless, or only available by the actual contact of material
bodies in the soUd or fluid atate.
32 Motion ofthe Air. — Winds. — So long aa the density ofthe afr remains
the aame, there ia nothing to disturb the equiUbrium of the atmoaphere, but
if from any cause the equUibrium ia disturbed, a movement results, which we
cahwind. If, for example, at any point of the Earth's surface the temperature
is increased and the afr above it heated, a displacement occurs, the warm air
rising, and cold air rushing in from aU sides to restore the balance. These

204 PHYSICAL GEOGRAPHY.
currenta of air play a very important part in nature. They purify the air ot
towns ; they modify and improve extremes of heat and cold ; they disperse
clouda, and they aaaiat, by the diatribution of poUen and seeds, and by a
constant agitation of the different parta of plants, in preserving vegetation ma
healthy atate, and ensuring its continuance.
Winds are generaUy denominated from the quarter from which they blow.
Thus, we speak of a north-easterly wind or a south wind, but there are also
names given to some winds that are locaUy prevalent, or that exhibit any
peculiar characteristics. Such are the trade vrinds, the monsoons, and others.
The wind blows not only from various quarters, but vrith every degree of
force and rapidity, from the moat gentle zephyr to the most destructive
hurricane. The diff'erent kinds of winds in respect of quicknesa and force are
spoken of under the terms breeze, gale of wind, and tempest or hurricane,
respectively. The dfrection of winds is determined by reference to an arrow or weather
cock placed on an elevated position, and where there are no adjacent buUdings
at so great an altitude to disturb the trae dfrection of the current. The
intensity of force is measured by an inatrument caUed an anemometer, the
principle of which ia that of a smaU windmill, whose saUs are moved more or
less rapidly as the wdnd ia more or leas powerful.
However apparently varioua the cauaes of winds may be, they are
almoat all referrible more or less directly to changes of temperature. The
Barth is constantly presenting a different portion of its surface to the direct
rays of the sun, and is consequently exposed perpetuaUy to alterations of
temperature. These aU affect the atmosphere, and produce an inflnity of
minor currents, influenced, however, by certain main currente, consequent
upon the general regularity of the change undergone.
The winda which it is important to notice, aa belonging to a general riew
of physical geography, are these : the land and sea-breezes, which occur daUy
on the coast and in the islands in fropical regions, certain periodical winda
prevaUing in aome parts of Europe, some irregular winds observed in districts
offering remarkable physical features, the trade winds, the monsoons, atorm
winds, hurricanes, and whfrlwinda. Thoae frregular winds which blow from
various quarters in temperate latitudea are not aufficientiy referred to general
principlea to admit of description in this place.
33 Land and Sea-breezes. — The winds caUed land and sea-breezes are
derived from the unequal action of the sun on the land and water, combined
vrith the tendency of the atmosphere to preserve a state of nearly tmiform
denaity. Duriug the day, iu hot countries, the steady shining of the sun,
especiaUy when nearly vertical, heats the land much more than the adjacent
ocean, and thua the atmosphere above the land becomes more rarefied, and
from about nine a.m. the air from the sea flows towards the land, to occupy
the partial vacuum produced. As the heat of the land goes on increaaing,
the force of the breeze increases also, and this continues tiU two or three, p.m.
After that time, the temperature of the land diminishes, decreasing much
more rapidly than that of the water, so that about sunset the breeze from the
sea ceases. During the night, the sea and the afr over it retain thefr tem
perature, but the land and overlying air become cooler, and the breeze then
seta in from the land, the warmer and Ughter afr being again diaplaoed by the
cooler and hearier. Thia breeze from the land augmenta in force tUl near
aunriae, when the temperature of the earth begina to increaae once more,
untu about nine a.m., when the sea-breeze sets m. Theae breezea are not
confined to the coast, as they converge and diverge in every dfrection, and
extend far inland, but they must stUl rank as local phenomena.
There are some periodical winds lasting for very limited periods, and
occurring in varioua parta of tho Earth. In the eastern part of the Mediter
ranean, for example, a current aets in from the north-east, and blows every
day from about the middle of July till the end of August, commencing at
about nine a.m., and dropping afc sunset. SimUar winds blow in Spain and

METEOROLOGY. 205
also in Asia from the eaat, but are of shorter duration. Such vrinds are
probably caused by the rarefaction of the air under the tropic of Cancer, in
consequence of the heat of the sun at the setiaon during which they blow.
The most important of the atmospheric movements observed and referred
to regular laws occur within a zone, whose general limits are the thirtieth
Cillel of latitude above and below the equator; although beyond these
ts, some of the prevailing winds which there take their origin are often
found to extend.
34 Trade Winds. — There are two regions in which the trade winds
prevaU ; the one is north of the equator, reaching from latitude 10° north to
the tropic of Cancer, and extending in the West Indies to near 30° north
latitude, the other commencing a few degrees south of the equator, and
extending generaUy to the fropic of Capricorn ; but in the Pacific Ocean,
reaching a little further to the south. Between these regions is a zone of
variable winds and calms.
The zone of variable winds and calms, situated close to the equator, is a
convenient point of departure in describing the periodical and regular winds.
Although generaUy characterised by calms and Ught westerly breezes, sudden
atorma and squaUs are not unusual, and vast quantities of ram faU there.
The general result of the rotation of the Earth on its axis, from west to east,
and the greater influence of the sun near the equator, cause the atmospheric
covering of the globe to be, as it were, left behind, producing apparent winds
near the equator. These, and the polar and equatorial currents that set in,
and affect chiefly, and at first, the higher parts of the atmosphere, appear to
produce the singular zone juat referred to. It is situated entfrely north of
the line, owing, no doubt, to the pecuUar form of the land in the northern
hemisphere, and the great preponderance of land there.
The trade winds are perpetual winds occurring in the open fropical seas,
north and south of the zone of calms, and are so caUed because they greatly
promote navigation and frade. To the north of the equator, these winds blow
in the eastern parts of the ocean from the north-east, but further to the west
they become more easterly, and sometimes even blow from a little south of
east. South of the equator they blow in the eastern parts of the ocean from
south-east, but become more nearly due east towards the west. They
blow vrith less force and steadinesa in the eaatern than in the western seas,
and are only experienced at a distance from land and in the open ocean. They
are generally stronger in the hemisphere where the sun is not vertical, and
are also there less easterly. The weather is generaUy fine when the trade
winds are blowing, but, aa has been afready observed, the intermediate belt
of sea is remarkable for the quantity of rain that faUa there.
The frade winda occur both in the Atlantic and Paciflc Oceana, but vary
conaiderably both in extent and force in theae two great diriaions of the water.
In the Atlantic, they are found to have a wider range on the American
than on the European side, and on that side they blow from due east, whUe
near the Old Continent the dfrection is north-east. Of the two regions
affected by these winds, the northern is less regular than the aouthern, and
towards its northern boundary is less boisterous and capricious. The latter,
or southern region, also ranges much further north, commencing a Uttle north
of the equator, so that the northern district of the trades ia even sometimes
encroached on by it, and the winds meet.
In the Pacific, the frade winda are by no meana so weU determined as in
the Atlantic, nor are they ao extensive in proportion to the much greater
breadth of open aea, or so much to be depended on. They appear to blow
permanently only over that part of the ocean extending from about the
meridian of the Galapagos to the Marqueaaa, or from longitude 91° to 130°
W., afterwards becoming periodical wmds, or monsoons. In the Indian
Ocean, from the coast of Madagascar to the ahorea of AuatraUa, the aouth
trade winds prevaU, but the northern do not exist. Aa in the Atlantic Ocean,
the aouthern perpetual winds extend north of the equator, when the sun is

206 PHYSICAL GEOGRAPHY.
in the northern hemisphere, haring been met vrith as far as 3° 30' TS. lat. in
the month of July ; but in the oppoaite aeason, they recede to one or two
degrees south of the Une. The north-eaatern frade wind ia described as being
more regular than in the Atlantic, and its northern boundary leaa variable.
The region of calma in the Pacific ia little viaited, and leaa known. It is
certainly north of the equator, but probably nearer to the line than in the
Atlantic. The boundary of the trade winds in the temperate zone, in both hemi
spheres, and in both oceans, varies with the seasons — ^the difference being
considerable : and thus there occur regions, several degrees of latitude in
width, alternately exposed to the sway of frade winds and of variable winds.
The actual termination of the zone of frade winds ia generaUy marked by a
sudden change of wind Thia region of variable winds in the Pacific, and
especiaUy in the southern hemiaphere, ia generaUy much more uniform than in
the Atlantic.
The frade vrinds are confined to the ocean, but regular and constant
easterly winda alao occur between the tropica in aome countriea, which pro
bably owe thefr origin to the same cauae. Such winda, however, do not
extend beyond extenaive level plains. Examples are seen in the easterly wind
which blows aU the year over a great part of the Sahara, or Desert of Afnca,
and a aimilar wind always blows on those vast plains of South America
which are drained by the Amazon, and on those in the lower course of
the Orinoko.
The cause of these winds is generaUy considered to be the constant rare
faction of the afr between the fropica, where the aun exerte so much more
power than in the temperate and frigid zones, and the consequent rushing in
of currents of cold afr, from the north and south, towards the equator. If
the winds moved vrith the rapidity of the Earth, the currents would of course
be north and south, but as this is not the caae, and the Earth moves far more
rapidly from west to east, the winds are left behind, and appear to blow
from other points. Thus, they blow from the north-east in the northem
hemisphere, and from south-east in the southern, whUe near the equator,
and where influenced by land, they occasionaUy blow from due east, or
nearly ao.
35 Monsoons. — These winds differ from the fradea, in being only
periodical, whUe the latter are perennial. They occur chiefly in the Indian
Ocean, but prevaU also in the seas between AusfraUa and China, which may,
indeed, be considered a portion of the Indian Ocean. They are produced by
the pecuUar conformation of the land in that portion of the Old World, and
by the predominance of land there, combined with the difference of tempe
rature constantly existing between it and the sea in its ricinity.*
The monaoons nearly occupy the place of the northern trade winda in the
diatrict above defined. Between the southern trades and this fract of ocean,
there are occasional calms, often interrupted by winds, which, when the sun
is in the northern hemiaphere, generaUy blow between south-west and
north-west, and during the other six months between south-east and north
east. These are sometimes caUed the north-west and north-east mon
soons, but they are not to be classed as monsoons in the proper sense of the
term. The proper monaoons occur north of this region, and consiat of
a north- eaat vrind blowing from November to March, and a south-west
wind from the middle of April to the end of October.
The north-east monsoon extends a Uttie south of the line. It becomea
regular near the coasts of Africa sooner than in the middle of the sea, and
near the equator sooner than off the shores of Arabia. It is most regular
and powerful in the month of January, especially in the northernmost angle
of the Indian Ocean. It ia not aeoompaniea by ram on the Indian coaat, but

Periodical winds, called monsoons, occur also on the const of Mexico, blowing north
westwards along tho coast from May to December, nnd south-eastwards from Deeembor to
March. Othera occur on f.lm n,.n..;iin,, .,.,....*

March. Others occur on the Brazilian coast.

METEOROLOGY. 207
blowing over a large fract of warm sea, it produces the ramy season on tho
eastern coast of Africa.
The south-west monsoon begins a Uttle north of the equator, and aooneat
off the coaat of Malabar, Its infiuence is felt on land along the course of the
Indus, At sea it is a serene wind of moderate force, but it brings very heavy
rain to the coast of Hindostan,
The change of the monsoons takes place between the latter part of March
and September, and the early part of AprU and October ; in some places a
week or two earUer than in others. The change takea place gradually, and is
accompanied by storms and tempests. On the wind ceasing to blow in one
dfrection, the clouds in the upper atmosphere are at once observed to take an
opposite course, but some weeks may intervene before the change is felt at
the Earth's surface.
36 Hurricanes. — These are storm-phenomena that occur from time to
time on most parts of the Earth's surface, but certain districts are remark
able for exhibiting aU the phenomena of atmospheric disturbance on the
grandest and most destructive acale. Under the names Typhoon, Sciroceo,
Tornado, &c. are sometimes designated storms having certain pecuUaritiea
depending on local conditiona.
Hurricanes often fravel far from the spot in which they originate, and
thefr path is marked by desolation, although thefr consequences are often
not unfavourable to health, by entfrely changmg and purifying the air in those
districte exposed to them.
Hurricanes occur most frequently within the tropics, or rather near the
verge of the fropics, and in the ricinity of continents and islands. In the
northern hemisphere, the West Indian islands, and in the southern, the
ialanda of Mauritiua and Rodriguez, aeem to be the foci of the moat violent
and deatructive storms. In the former disfrict these commence near the
Leeward Islands, and fraveUing first W.N.W., pass out into the Atlantic
round the shores of the Gulf of Mexico, and are lost between the Bermudas
and HaUfax. Near the Mauritius the hurricanes come from the N.E., travel
S.W. by S., and return again to the east ; whUe in the Bay of Bengal they
some from the east and travel westward.
The period of hurricanes in the West Indies is from August to October,
md early in June and July. In the Indian Ocean, these storms occur from
December to AprU, and sometimes, though rarely, in November and May.
The range of theae atorms in the Weat Indies is from latitude 10° to 50°
aorth, and longitude 50° to 100° weat. In the Indian Ocean they extend
over a tract of 3000 mUea in length.
The motion of the afr during a hurricane is by no means simple, and has
induced the name of whirlwind to be given to some casea when thia motion ia
recogniaed. It ia produced by a mixed rotation on an axis and progression in a
curved line, so that a kind of spfral results, the storm often seeming to return
again a second, or even thfrd time to the same spot, having in each of these
returns a different and often contrary dfrection, whUe in places not far distant,
there is not the smallest apparent disturbance of the equUibrium of the
atmosphere. One of the results of this kind of motion is, that although the
violence of the vrind, in the active part of the hurricane, is sufficient to desfroy
houses, and tear up the largest trees by the roots, the rate of progress of the
whole storm, from point to point, on the ocean is not greater than that of the
ordinary atmospheric currents, varying, that ia, from aeven to fifteen mUes
an hour. The atorm aeems, therefore, to be a violent local disturbance of
the equilibrium of the atmosphere conveyed along the Earth's surface, inde
pendently of, andin addition to, its own proper motion, which is round an axia.
The hurricanes of the coast of China are caUed typhoons, or tyfoons, and
occur only, on an average, about once in three or four years, whereas not less
than thirty great hurricanes have been recorded as occurring in the West
Indian seas aince the commencement of the preaent century.
There are aome remarkable local storms also well worthy of notice. The
simoon is one of theae ; it blowa only in abort gusts of unequal duration, and

208 PHYSICAL GEOGRAPHY.
originates in the vaat sandy plains of Northern and Cenfral Africa. It makes
its appearance during strong south-western winds, but only between the
middle of June and the twenty-first of September. The gusts are burning
hot, and have a putrid and sulphurous smeU and suffocating feeling, occa
sioning profuse perspfration, difficulty of breathing, and often death, to those
exposed to them.
The har7nattan is a wind extending along the western coast of Africa, from
Ca} e Verde to Cape Lopez, and its period of occurrence is from December
to Febraary. It blows from the side of the Great Desert, and is exfra-
ordinarily hot and dry, but not unhealthy. /
These grand disurbanoes of the atmosphere are intimately connected with
electric changes, and are often accompanied by the most magnificent exhibi
tions of atmospheric electricity. Important reaults connected with terrestrial
magnetism are also found to be involved with these appearances.
37 Belation ofthe Atmospliere to Water. — It is manifest to every one in
the latitudes in which we Uve, that the condition of the atmosphere with
regard to moisture is constantly undergoing change, the afr sometunes being
so dry that the soU cracks and vegetation is parched, whUe at other timea
torrents of rain pour down and deluge the whole country. These conditions
are, however, variable in every sense of the word, and different counfries are
verydifferently acted on by atmospheric changes.
Whatever be the sensations of dryness commimicated by the afr, there is
always present a certain quantity of aqueous vapour, but this quantity ia
capable of great increase, and especiaUy when the temperature ia heightened.
An atmosphere of steam is thua alwaya mixed vrith the dry atmoaphere of
oxygen and nitrogen gas, and this steam atmosphere is sometimes suddenly
and considerably increased, sometimes very rapidly diminished : sometimes it
is made visible by audden changes, while at others it continues so perfectly
mixed as to be inrisible to the eye. In these various stages of visibihty, we
speak of afr as containing mist, fog, or cloud — ^mist and fog being conditions
ofthe atmosphere when vapour is visible at the Earth's surface, wlule clouds
are the visible masaea of vapour of aome definite form, and at a diatance from
the Earth.
There is a certain limit beyond which afr of a given temperature wfll not
hold aqueoua vapour in perfect auapenaion, so that changes of temperature
may cause the deposit of vapour previously held suspended and invisible,
thus producing important alterations in the transparency find clearness of the
atmoaphere. It is important also to consider that water in aaauming a different
mechanical condition — that is, in passing from the fiuid state into the sohd or
aerial — involves very considerable electrical changes. The fluid water in ita
usual condition passes into the gaseous state at all temperatures ; even when
it ia solid, this process goes on very readUy; and since a large proportion
of the globe is covered with water, the changes thus involvea become con
siderable, and the equiUbrium of the atmosphere is constantiy undergoing
disturbance from thia cauae alone. Perhaps, indeed, the mutual action oi
afr and water produces many of the most marked and importent atmospheric
phenomena. The evaporation of water is accompanied with the apparent
losa and temporary disappearance of a large quantity of heat, which ia thence
said to be latent, or concealed, and the conversion of steam into water and
water into ice, reproduces or renders sensible this concealed heat.
To underatand, therefore, the nature of aqueoua meteora, it muat be
remembered that every change of condition of water involvea changea to a
great extent both of temperature and electricity. The most remarkable of
the meteors are dew and hoar frost, mist and fog, clouds, rain, hail, and
snow. With these are connected changes in atmospheric condition, made
known and studied by tho hygrometer, the thermometer, the barometer, and
the magnetic needle. We shall here only very briefly explain the nature
and cause of the phenomena themaelvea.

METEOROLOGY. 209
38 Dew. — ^Dew is the moisture deposited from the air, in minute globules,
on the surface of various bodies, when that surface is colder than the atmo
sphere. This occurs chiefly at night, more especiaUy in Spring and Autumn,
out generaUy on clear, serene nights, when the difference of temperature
oetween day and night produces a marked variation in the quantity of water
whioh the afr is capable of retaining in a atate of perfect solution. When
the vapour is made visible, the afr ceases to be clear, and mists or fogs ariae,
but these are very different from dew both in thefr nature and appearance.
The deposit of moisture is then only caUed dew when the water is precipitated
on soUd bodies and the afr retains ite fransparency.
Since the formation of dew depends on the difference of temperature of
the afr and solid bodies with which it is in contact, and as solid bodies part
with temperature with very different degrees of rapidity, it is clear that there
ought to be a larger quantity of dew on those bodies which radiate heat
reSUy than those which are slow in undergoing change ; and this is indeed
the case; for the poUshed surface of metals receives scarcely any dew, whUe
wool, or any animal substance, or glass, radiating heat rapidly, receives large
quantities. So also the interposition of any aubstance, auch as a cloud, very
sensibly affects the quantity of water deposited in this form, for it both
interferes vrith radiation and reflects back again some heat. The dew is
mainly deposited near the ground, since the radiation of heat from the
Earth's aurface in the evening and night producea there the greatest amount
of cold. When the cold at the aurface ia below the freezing point, the dew
freezea as it is formed, and thus are produced the beautiful appearances of
hoarfrost. The presence of a considerable quantity of vapour in the air,
indicated by the deposit of large quantities of frozen dew, or hoar frost, after
a clear night, has often been remarked aa indicative of change of weather,
and ia not Ukely to be aucceeded by steady and long-continued froat.
39 Mists and Fogs. — These phenomena are frequent results of a small
change in the condition ofthe atmosphere near the ground, in those countries
in which the soU is occasionaUy damp and comparatively warm, whUe the air
ia damp and cold. The damp afr in contact with the Earth, on a cahn
morning, chiUed by the colder air above, parts with its moisture, or, at leaat,
the moiature assumes the form of risible vapour. Where there are vast
multitudes of minute particles of carbon floating in the air, as in the neigh
bourhood of large cities, these mix with the vapour, and form those thick and
almost opaque fogs so weU known in London and other places. Thus, also,
are formed thick mists in Newfoundland and on the eastern coast of North
America, when the melting of icebergs, stranded on the great bank of New
foundland, chiUs'the air, and causes it to part with a large portion of the
moisture it had before held in a fransparent state.
40 Clouds. — Mists forming on mountains, either immediately or after
being removed by drifting winda, often become true clouda, but clouda are
dot only formed in contact vrith the Earth, but often very high in the afr ; nor
are they left in thoae placea where they firat appear. Clouda alao assume an
infinite variety of form, and, by decomposing or refiecting Ught, produce
beautiful effects of colour ; and they are no less remarkablfe for thefr combi
nations vrith each other, and the changes thua induced, which, aa rain, haU,
or snow, or electric and magnetic atorms, are of very great interest in refer
ence to the general sfructure and conditions of the Earth's crust : as in aU
cases the change of condition from visible water or ateam to inviaible vapour,
or the converse, produces great alterations of temperature and elecfricity
and these again react upon the rest of the atmosphere.
The clouds that are formed or fioat in the atmosphere, are coUections o£
minute globules of water, preserved in equiUbrium at a certain height above
the Earth's surface, either because of the croaaing of currenta of afr differently
capable of retaining water, owing to differences of temperature, or becauae
ascending currents of afr prevent the further descent of vapour having a
very smdl degree of density. During the day, the surface of the Earth gene-
P

210 PHYSICAL GEOGRAPHY.
raUy receives a sensible addition of heat, which it parts with by radiation at
night, and thua it ia not unusual to see the clouds rising higher in the air as
the day advancea ; whUe in the evening, after aunset, they descend and often
deposit moiature.
Clouda differ ao much in thefr appearance, thefr position, and thefr in
fluence on weather, as to require consideration in some detaU. They have
been described under different names, in three groups, which appear tolerably
distinct. There is a group of clouds often aeen in the upper regions of the atmo
sphere, and frequently in the finest weather. They are of tbe most deUcate
forma, and are known by various names to mariners and othera who study
the appearances of the aky. Thua mare's taU, mackerel sky, and other names,
indicate thefr sweeping and fretted character, and they are aeen also in long
ranges, apparently radiating from the north magnetic pole, particularly during
or after the phenomena of the Aurora, and when any great change in the
magnetieal condition of the atmosphere ia going on.
These clouds originate from three to four mUea above the aea level, and
reach even to higher altitudea than thia in mountain countries. They are
common in the finest weather, and show the most distinct and sharpest forms
when the air is driest. The technical name for such clouda ia cirrus, or curl-
clouda, and when wet weather approachea, they pass into horizontal sheets,
descend lower, become denser, and lose much of thefr picturesque character.
When seen in motion, they rarely agree in dfrection with that of clouds and
air currents nearer the Earth.
The cumulus, or heaped cloud, is generaUy of much denser atrudure than
the cirrua, and much nearer the Earth. Clouda of thia kind convey large quan
titiea of moisture to great distances, and act avery important part in modifying
the effects of the sun'a raya, often forming during the day and dispersing at
night. In fine weather, they are of moderate elevation, varying from one to
two mUes, and they are then also of moderate extent, exhibiting weU-defined
roundish outUnes. Before rain, they increase rapidly, sink nearer to the
Earth, become fleecy and frregular, and pass into another form.
The clouds oaUed stratus reat generally on the surface of the Earth or
water, and thus resemble or replace mists. They are essentiaUy night-clouds,
and often pasa into cumulus after sun-rise, but are greatiy mixed with cumuli,
forming in that caae banks and ranges of cloud. It has been obaerved, that
although these clouds and the combinations of them increase very much, and
put on the most rain-Uke appearance, they do not actuaUy rain so long as
they retain a definite character and a separate existence.
41 Bain. — Rain is the deposit of moisture from clouds, in drops falling
through the air ; but before rain takes place, the clouds nndergo a change,
and pass into the state caUed nimbus. This is best seen in stormy weather,
when the cumuli rise first into mountain-Uke maaaes, and afterwarda change
into those sfratiform masaea of vapour, which, occupymg a middle state
between cumulus and rain, are so commonly seen in changeable weather m
our climate. Long ranges of delicate clouds m horizontal sfreaks occupy the
summits, and ultimately form a crown, extending from the top in tufts, and
the sudden union of such clouds immediately precedes, and is accompanied
by a shower. Rain faUs also occasionally, but rarely, without clouds.
When, as sometimes happens, a very large quantity of rain falla in a short
Eeriod of time, it may aeem (Ufficult to comprehend exactly the phyaical cause,
ut generaUy the mingUng together of great beds of afr of unequal.tempera-
ture, and in different electrical states, may be referred to as sufficient, because
in the admixture of such beds of air, fhe united volume is not by any means
capable of retaining the same quantity of water as the two separate beds had
done. It is not, however, the case tliat admixture of air neoesaarily involves
a fall of rain.
42 The Distribution of Bain. — Rain falla upon the Earth in exceedingly
variable proportiona ; in aome places the faU being periodical, in others almost

METEOROLOGY. 211
constant, and in others again, so rare as to be scarcely known, while in our
counfry and many parts of both temperate zones, it is so variable and irre
gular aa to induce ua to aasume the weather as the type of inconstancy. The
quantity of rain that faUa ia also very different for different districts, at
various seasons of the year, and in different years ; depending much on local
peculiarities, such as the insular or continental position of any particular spot,
the mean annual temperature, the extremes of temperature, the prevailing
winds, the form of the land, and its height above the sea level.
Speaking generaUy of that part of the habitable globe known by actual
observation, we may refer to the northern and southern temperate zones as
districts m any part of which rain may or does faU every day of the year,
(thence caUed zones of constant precipitation,) and the torrid zone, where one-
half ofthe year is characterised by extreme moisture, and the other by extreme
drought. The northern zone of constant precipitation is the one of which the
phenomena are best known, but many important observations have also been
made in the corresponding southern zone, aa well as between the tropica.
On the whole, the quantity of rain ia greateat at or near the equator, and
diminishes towards the poles ; but too Uttle ia yet known of the mean annual
rain-faU in exfra-European districts, to admit of any general conclusion
being drawn, or accurate comparisons made. There appears to be a much
larger quantity of rain in the fropical region of the western than the eastern
hemisphere, and a larger quantity in the northern than the southern zones of
constant precipitation. More rain also faUs on islands and coasts than in the
interior of continents, on the slopes and summits of mountains than on the
plains adjacent, and on the western than the eastern side of continents.
In Europe, and generaUy in the north temperate zone, winter is the wettest
season, and summer the driest; whUe on the east coast of AusfraUa, the
autumn and summer include the chief rain months.
Within the fropics, the rainy aeason foUowa the apparent courae of the sun,
and the rain is both most frequent and most abundant in the narrow zone of
variable winds, afready described as extending a Uttle north of the equator,
where also there are frequent thunder atorma. Most ofthe 1-and withm this
zone is the scene of almost incessant rain-faU ; whUe in the open sea, north
and south, when the frade winds are blowing, rain is extremely rare. In
India, however, the monsoons greatly modify the order of the seasons, the
western coagt being watered by the south-east monsoon, between AprU and
October, and the eastern by the south-west monsoon blowing from October
to AprU. Between the coasts and in the interior of the peninsula of India,
the raina are sometimes occasional through the year, and the cUmate partakes
of that of both the east and weat coaat.
There are large fracta, forming a belt round the globe, in which rain is
either never known to faU, or occasionaUy falls, but only in small quantitiea,
and at long intervals. The moat extensive of these districts includes the great
Sahara, or desert of Africa, the deserts of Arabia and Persia, and that of
Beloochistan. It occupies three miUions of square miles. The great table
land of Thibet is a aimUar district, occupying near two 'TnUUons of square
mUes, and the table land of Mexico exhibits me same pecuharity over half a
million of aquare mUes. AU theae extensive regions are not, however, hope
lessly barren, aa might be expected from the absence of rain ; for in many of
them, the large deposit of moisture in the form of dew renders vegetation not
only possible, but luxuriant.
43 Snow. — When moisture is precipitated from the union of atmospheric
volumes of unequal humidity and temperature, it frequently happens in the
temperate and frigid zones, that the temperature of the air ia below the
freezing point of water, and thia may ariae either from absolute cold or (at
high altitudes) from greatly diminished atmospheric pressure. In these cases,
the moisture wUl become frozen, and form into flakes of snow, each of which,
when examined under the microscope, is found to be composed of a great
nmnber of separate and transparent crystala of ice. It ia in intenaely cold
p2

212 PHYSICAL GEOGRAPHY.
weather that these are most remarkable, and many of the most interesting
forms are only met vrith in the Polar regions. During the faU of snow, it ia
not unusual in temperate cUmates for the thermometer to rise considerably.
In aU parts of the Earth, the rarefaction of the afr at a certain height
above the aea is sufficient to produce a temperature at which water exists in
the solid form, but thia limit of perpetual anew variea exceedingly with lati
tude and local position, rising withm the tropica to upwarda of 17,000 feet,
and in the Polar regiona deacending to the aea level. The moat remarkable
instance of the elevation of this line occurs in the Himalayan chain, the
loftieat in the globe, where the anow limit ia lower by aeveral hundred feet on
the northern than on the aouthern side of the mountains, although from the
position and the latitude, it might have been expected that the confrary would
have been the case. The proportion of the absolute aurface of the Earth
covered with perpetual snow has not, we beUeve, been yet determined ; and
in consequence of the form of the land, and the position of the high moun
tains on the Earth, many of the most remarkable elevations do not reach the
limit, wbUe others, far leas important, are more or less included in it. The
foUowing tabular statement wiU be found interesting, as giving an approxima
tive view of the poaition of the snow-line in various latitudes.
limit of Perpetual Snow.
Andes  15,000 to 20,000 feet.
Hmialaya  12,000 to 16,000 „
Alps  about 8600 „
Norway  „ 5000 „
Patagonia  „ 3000 „
Iceland  „ 2000 „
Mount Erebua, in the South Polar land, rises 12,000 feet dfrectly fixim the
sea, covered with perpetual snow from its base to its summit.
44 Glaciers. — Glaciers are masses of ice, often commencingin such moun
tain valley a aa are above the hmita of perpetual snow, and reaching to consider
able diatancea inthe plainsbelow. Theyhavebeen described as icicles descending
from a snow-covered roof; and as thefr mass and extent arise from the
difference between the quantity of snow sinking into the vaUey in a year, and
that of ice melted during the same time, they are dependent on the form of
the vaUey, and the amount of shelter it affords, together with the mass of the
snow above, and the facilities for descending the gorge, and may thus descend
considerably below the snow-clad mountain tops, and advance far into retired
and fertile valleys.
The most remarkable and extenaive glaciers are those of the Alps, Norway,
Iceland, Spitzbergen, Western Patagonia, and the shores of the Antarctic
continent. The best known are those of the Alps. Except in Patagonia, the
great chain of the Andea preaents no glaciera, and in the Himalayan moiin-
taina there are but few, and those not extensive. The extent of glaciers in
the Alps is estimated at about 14,000 square mUes, and thefr number aa 400.
45 Hail. — Thia phenomenon, which conaists of the faU of frozen drops of
rain, and occurs usually when the weather ia warm, haa often atfracted
attention. Connected as it ia with great electrical disturbance of the atmo
sphere, and often with thunder atorms, there can be no doubt that the main
cauae of the formation of lumps of ice in the afr is the result of cold, produced
by very sudden and rapid evaporation. The descent Of haU, at leaat in some
countnes, appeara limited to particular aeasona and certain hours m the day;
the chief haU atorms having also very definite and narrow limits. Had
rarely faUs on mountains in temperate cUmates, whUe in the equatorial
regiona it is equally rare for it to descend so low as 2000 feet. In some
extreme cases, haUstones have been noticed meaauring more than a foot in
circumference, and weighing upwards of half a pound. These are occasionally
romid or polyhedral, but sometimes flat and angular, and there is great
difficulty in accounting for the formation of auch large maases.

METEOROLOGY. 213
The disturbance of elecfric equUilyium is accompanied by storms of
thunder and lightning, as weU as heavy rain, hail, and strong -wind, Theae
atorma often take place very high in the afr, having been aeen in the tem
perate zone at a meaaured vertical elevation of 26,650 feet ; but on the
other hand, the sfratum of cloud in which thunder takes place, is sometimes
not more than 3000 feet above the plains,
46 Climate, and Distribution of Heat. — By climate, in a general sense,
we understand aU those states and changes of the atmosphere which sensibly
affect our organs, Theae include temperature, moisture, variation and amount
of pressure of the afr, calmness of the afr or the effects of prevalent -winds,
electricity, purity, and fransparency of the afr, and serenity and clearness of
the aky, AU auch causes influence the human frame, and greatly affect the
development and health of aU organic beings.
Questions of temperature that affect climate must be considered on the
average of a long penod of time, and very different averages are obtained,
according as we take the mean temperature of the whole year, of the summer
months, or of the winter months. It has been found convenient to bring toge
ther the results of observation with regard to each of these points in different
disfricts, connecting by lines the places where the same temperature obtains.
In this way are formed those imaginary lines upon the Earth, known respec
tively as isothermal lines (Unea of equal mean annual temperature), isotheral
lines (thoae of equal mean aummer heat), and isochimenal Unes (those of
equal mean winter cold). Other Unea have alao beeu determined, which assist
greatiy in determining, a priori, the climate of disfricts not previously
known, amongst which are isobares (lines of equal mean height of the
barometer at the sea level), but we consider only, in this place, the aubject
of temperature. Owing to the poaition of the Earth with regard to the sun, different
quantities of heat are received on different zones of the surface, varying
according to latitude or distance from the equator. If the surface were
uniformly level, and everywhere of the same conducting and radiating power,
paraUels of latitude would be at once isothermal, isotheral, and isochimenal
Unes, but aa this ia not the caae, and aa every unevenneas of surface and
every difference of material produce, both directly and indfrectly, a difference
in respect of temperafrire, it reaulta that places, in the same latitude, rarely
receive the same amount of heat in the year, and, even when they do, hardly
ever have it simUarly distributed. Examples ofthis are innumerable, and will
at once preaent themaelvea to the reader's memory. The mean annual tempera
ture of Quebec, in latitude 47° N., is nearly the same as that of Trondjem, on
the coast of Norway, in latitude 63°. The temperature at Nain, on the coast of
Labrador, is about 20° Fahrenheit lower than that of parts of Scotland in the
same latitiide, whUe the limit of perpetual ground-frost (32° Fahrenheit) in
the northern hemisphere, rises in the Greenland sea five degrees of latitude
above the Arctic cfrcle, and on the sea of Okhotsk sinks no less than twelve
degrees below it. So also the mean vrinter temperature of Pekin (in a
lafrtude south of Naples,) ia more than five degreea (Fahrenheit) below the
freezing point, whUe that of Paris, 700 miles further north, is more than aix
degreea (Fahrenheit) above the freezing point ; the mean temperature of the
month of Auguat in Hungary is nearly 70° Fahrenheit, wmle in DubUn,
situated on the aame iaothermal, it ia barely 61°. The winter temperature of
Dublin, however, ia more than 3^° higher than that of Lombardy, although
its mean annual temperature is more man 4^° lower than that of the towns
in the latter country. Thus, it ia clear that the same mean annual tempe
rature may be distributed in a variety of waya, in the different aeasons of the
year, whUe, owing to local influences, places on which the sun shines for the
same number of hours during the year, may receive very different amounts
of heat. It is found that, in the northern hemisphere, there are two poles
of cold, round which the curves are grouped ; the Western, or American pole,
being in 80° N. lat., and 260° E. long., with a temperature of 85° below zero of

214 PHYSICAI. GEOGRAPHY.
Fahrenheit, (351° below the freezing point of water,) while the eaatern, or Sibe
rian pole is in the same latitude, but in 95° E. long., with a temperature of
one degree of Fahrenheit, being thus five and a half degrpes warmer than
the other. The isothermal lines round theae two poles, and thefr inosculation
have not been accurately determined.
On the whole, the foUowing table seems to give the most useful general
idea of the disfribution of heat on the globe ; the different regions in the
two hemispheres being distributed into zones according to thefr mean
annual temperature -. —

DesigiiatioQ.

Limits.

Mean Annual
Temperatnre.

Hot or equatorial zone .
Warm zone ....
Mild zone ....
Cool zone .
Cold zone 
Frigid or polar zone .

Between isothermal corves 77° both hemispheres
77» and 59°
„ 69° and 41°
41° and 32o
32° and 6°
Within isothermal curve of 6°

¦f 79°-70 Fah.
-t- e8°-oo
+ ,50°00
+ 86°'50
¦i- I8°-50
-^¦ 3°-20

It has been attempted to determine also the mean temperature of large
portions of land. Thus, the temperature of the tropica generaUy, near the
coast, is estimated at 81^° Fahrenheit, but in the interior is much higher.
The mean temperature of the whole Earth has been recently estimated by
Dove to amount to 58-2° Fahrenheit, being about 54° in the month of Januaiy,
and 62° in July. Many interesting conclusions are obtained from the study
of this branch of Meteorology.
As among the remarkable results shown by the recently published maps of
Profesaor Dove, we may also here mention that the mean temperature of the
northern hemisphere is nearly 60°, and that of the southern only 56° ; that
the mean vrinter temperature in the former is, however, less than 49°, and in
the latter 53|°, whUe the aummer temperature in the northem hemisphere ia
71°, and in the southem only 59^° ; the limits of deviation in the one case
being 12°, and in the otber only 6°. These tables are deduced from observa
tions extending over a series of years at as many as 900 stations.
The changes of temperature above referred to are assumed and described
throughout, if possible, for the level of the sea ; but as we have afready seen
that on the higher slopes and summits of many mountain disfricte, in various
parts of the world, snow not only falls, but there is a limiting plane above
wlUch it never melts, it is clear that there must also be gradual changes
of temperature on the sides of mountains, and at aU considerable altitudes.
This is, indeed, the case ; and elevation even to a very moderate extent often
produces considerable modifications of climate.
It ia a general rule, that the actual temperature of any part of the Earth'a
surface depends, partly on the mean annual temperature at the sea level, as
determined by the isothermal line passing through it, and partly on the
elevation above the sea, or the greater or lesa column of air that the solar
raya paaa through, the temperature diminiahing one degree for about three
hundred feet of vertical elevation. Many important local exceptions pre
vent thia from being a calculation to be depended on, in any apot not yet
determined by actual measurements ; but, as a general nUe, it ia appUcable
between the tropics. Thua, many citiea aituated on elevated plaina are cooler
than would appear from the iaothermal line paaaing through them, and thus
also on the slopes of mountain chains, within the fropics, we find all varieties
of climate, sometimes within two days' journey.
The winda whioh blow over a country pasa sometimes over very large
areas of warm soa, sometimes over cold seas, and aometimea over ice, whUe,
in aome cases, also, they have just proceeded over extenaive rangea of land,
oitlier heated by tho suu's rays, or cliiUed by the presence of perpetual snow.
It is therefore evident tiiat the chmate wUl bo verv much moified by the

METEOROLOGY. 215
nature of the winds that blow, inasmuch as these not only affect the tem
perature, but also very greatly influence, and even bring with them, the
amount and regulate the diatribution of moiature. The obaervationa already
offered on the aubject of winda and rain, together with those which wUl be
given when considering the phenomena of the ocean, have reference to cUmate,
and the general conditiona which render a counfry fertUe or habitable.
It is commonly known and felt that both cold and heat are more intense
when the sky is clear than when it is overcast with clouds, and thus it arises
that those countries where the winda bring large quantities of moisture, and
are met by others differently constituted in this respect, and where, con
sequently, clouds and mists are frequent, the climate wUl be essentiaUy
different from that of countries in which the same mean annual temperature
is accompanied by a clear aky. England and HoUand are examplea of thia
difference. 47 Conclusion. — The meteorological portion of Physical Geography,
which we are now bringing to a conclusion, shows that the various processes
going on in the vast aerial ocean, are so intimately connected, that each
separate meteorological process is at the same time modified by all the rest.
This compUcation of causes and effects renders it very difficult to interpret
ftdly and clearly the different phenomena, and almost prevents any such
prediction of atmospheric changes as is requfred or demanded for agriculture
and narigation, or even for the oonveniencies of life. Those, therefore, who
look only to an immediate result and power of prediction, may beUeve that
this branch of science has made but Uttle progress. But the results of
science are not always in this way immediately and positively applicable, and
although many facta and lawa of extreme practical intereat have been made
known afready in the purauit of meteorology, the main value of the science
must stUl be placed in the knowledge of the phenomena themselves, and the
extent and truth of thoae partial generalizationa whioh have been auggeated,
and which have yet to be examined and verified.
Among these general results it appeara that considerable deviations from
the mean distribution of temperature are rarely local in their occurrence,
but extend uniformly over large areas, reaching thefr maximum at some
determinate place, receding graduaUy untU its limits are reached, and then
when these are passed, extending into great deviations in the opposite
dfrection. It appears, too, that simUar relations of weather extend more
often from aouth to north than from eaat to weat, but there is no reaaon for
auppoaing that a severe winter wUl be foUowed by a hot summer, or a mUd
winter by a cool summer.
With regard to inatrumenta, it is important to remember that the baro
meter indicates to us what takes place in upper and distant regiona of the
atmosphere, whUe the thermometer and hygrometer give purely local results;
but as important changes of weather do not usually arise merely from local
causes situated at the place of observation — thefr origin occurring rather in
disturbances of the equiUbrium of the currents of the atmosphere and
elecfrical changea begun afar off — various and long-continued observations,
and a careful comparison of resulte, are absolutely requfred for accuracy in
meteorology.*

* The recent introduction of the aneroid barometer, an instmment for measuring the pres
sure of air by means of a partial vacuum — avoiding the column of fluid hitherto employed — ^is
worthy of some notice in this place.
At the present time, and judging from the instruments hitherto made, there seems no
probability of the ordinary mercurial barometer being superseded, but the application of the
aneroid principle to improved machinei-y promises to be ultimately very important, on account
of the convenience of form and faciUty and safety of transport. For these reasons, the aneroid
may be carried by the traveller to measure the height of mountains, and obtain much other
nseful and desirable information, which the inconvenient form and fragile nature of either the
common or mountain barometer render difficult to procure.

216

CHAPTER IV.
ON THE FORM AND DISTRIBUTION OF THE LAND.
§ 48. What is meant by 'land.' — 49. Distribution of land. — 60. Continents. — 51. Islands.—
62. Inequalities of the surface of land. — 63. Low plains and steppes. — 54. Deserts. —
66. Silvas. — 66. Llanos. — 67. Pampas. — 68. Savannahs, or prairies. — 59. High plains,
table lands, or plateaux of the Old World. — 60. Table lands of America. — 61. Mountain
systems of the earth. — 62. General connexion of the mountains of the Old World. —
63. Mountain chains of the New World. — 64. Mountains of Australia.
TTTHATis meant by Land. — Under the term land, is included every variety
rr of mineral substance and rock formation usuaUy existing in a soUd form
upon the Earth, and not covered constantly by water; and it is matter of fami
liar knowledge that the surface of the Earth thua presented, is exceedingly
irregular in outline and elevation, being coUected mto aome extenaive conti
nental masses, and a vaat multitude of smaUer areas, caUed islands. The form
and position of the contuienta — thefr extent both in magnitude and dfrection —
the poaition of the several portions of thefr surface with respect to the sea-
level — the nature, extent, and dfrection of thefr elevationa above, and depres-
siona below, thia general level — together vrith the position, the mode of
grouping, and the irregularities of surface of the different insular areas —
these are aU points of interest with reapect to the land, and together they
involve a description of the phyaical pecuUaritiea of this portion of our
globe. 40 Distribution of Land. — The land is very unequaUy distributed in the
two hemispheres separated by the Earth's equator ; the proportion of land to
water on the northern side being very much larger than on the southem ; so
also the absolute quantity of dry land on the eastem side of the Atlantic is
much larger than on the western ; and if an observer were stationed vertically
above a point in England, not far from the Land's End, in ComwaU, and
could thence see one half the globe, he would have before him almost aU the
land ; whUe, on the other side, would be acarcely anything but a few islands
and a portion of AusfraUa and Patagonia visible above the water.
Many facts have been noted in reference to this subject. The whole area
of land on the Earth has been estimated at about 51| mUUons of square Britiah
statute mUes, and of this quantity more than three-fourths lie to the north of
the equator. Only about one twenty-fourth of the whole area of land con
sists of islands (Australia being excluded). If we compare the north with
the south temperate zone, we find the proportion of land nearly as thirteen to
one ; whUe, on the equator, about five-sixths of the cfrcumference is water. It
appears also that only one iweuty-seventh ofthe existing land has land dfrectiy
opposed to it in the opposite hemisphere.
50 Continental Land. — Of the whole area of land, that portion which,
being connected together and continuous, is caUed continent, consists of two
principal portions, one on the eastern side, containing Europe, Asia, and
Africa, sometimes caUed the Old "World, or the great continent ; and the
other the westem, including the two Americaa, and known under the name of
the New World.
The principal direction of the old continent is from east to west, or, more
precisely, fi-om north-east to south-west ; w hUe the westem continent extends
from north-north-west to south-south-east. Both continents are terminated
towards the north at about tho seventieth pai-allcl of latitude, and both run
into pyramidal pomts towai-ds thc south, having submarine prolongations

FORM AND DISTRIBUTION OF LAND. 217
indicated in South America by islands, and in Soutii Africa by shoals. The
area of the greater (the old) continent, together with its adjacent islands, ia
about thfrty -three miUions of square mUea ; that of America, only fourteen
miUiona and a half; and Ausfraha, with the Polynesian Archipelago, barely
four. Of the portiona of the old continent, sometimes caUed separately con
tinents, Asia forms one-half, Africa three-eighths, and Europe only about
one-eighth of the whole.
The pyramidal termination, southwards, of aU the principal land on the
globe, is a very remarkable fact ; and it has been observed, that the southern
exfremities of Africa, AustraUa, New Zealand, and South America, form a
regular gradation, each reaching nearer the South Pole, in the order here
expresaed, aud the projecting points are as nearly as possible in the same
meridian in the two hemispheres. Pyramidal terminations obtain also in the
peninsulas of Arabia, Hindostan, IVfalacca, and California, and in the chief
masses of land in the Mediterranean, as Italy and Greece.
The form and indentation of the coast Unes are phenomena of considerable
interest, eapeciaUy as they bear on commercial enterprise ; and the existence
of those peninsnias and irregular projecting tongues of land, or detached
islands, which abound chiefiy on the coasts of Europe, Eaatern Aaia, and
Eastern North America, ia worthy of notice, in reference to the progreaa of
the civilization of mankind. AU the ahorea of Europe are deeply indented
by bays, and there are also a number of inland seas of very considerable mag
mtude, ao that our continent haa a greater proportion of maritime coast than
any other diatrict of the aame magnitude. The European coaat line meaaurea,
indeed, nearly twenty thouaand mUea. The coaat of Aaia also exhibits large
seas, bays, and gulfs, which are sheltered by a chain of islands, rendering
navigation dangerous. The whole length of Asiatic coaat amounta to about
thirty-three thouaand mUea. The coast of Africa measures nearly fifteen
thouaand mUea in length, and is little indented except along the coaat of
Guinea and in the Mediterranean. The American coast is very different in
different parts, and ita whole length ia upwarda of forty thouaand mUea. The
shores ofthe Icy Ocean are very compUcated, and other parts of the eastern
coast, as far as Mexico, exhibit a considerable number of gulfs and inlets,
but the shores of South America are very entfre, except at the southern
exfremity. On the whole, the result of investigation on tbia aubject shows
that the western coaat of the Old World, in Europe, ia the moat deeply and
frequently indented, and the beat adapted of any on the globe to the wander
ing habita of mankind.
5 1 Islands. — The islands, or portions of land separated by water from
the great continental areas, vary in character very greatly, some being
arranged in diatinct groupa and series, having common peculiarities, othera
being related rather to the adjacent mainland. These may be conaidered to
form two principal seta — riz., the elongated or continental islands, generally
belonging to the nearest considerable mass of land, and the round or pelagic
slanda, forming aystems, generaUy occurring in the open ocean, and apart
from continental landa. The former are generaUy in aeriea, and appear in
some places to give indication of extensive submerged continental lands, as
in the long suite of islands which, beginning to the south of New Zealand,
sweeps round the east and north sides of New HoUand, including New
Caledonia, the New Hebrides, the Solomon Islands, New Zealand, New
Guinea, &c., and the yet more remarkable islands beginning vrith the PhiUp-
?ine8, extending northwards through Formosa, the Loo-Choo and Japanese
slands, and ao to the Kurile Islands. The chain of islands of which the
Moluccas, Java, and Sumatra form the principal in point of magnitude, the
important island of Madagascar, off the coast of Africa, the main chain of
West Indian Ialanda, in the Gulf of Mexico, and the long rangea of islands
on the northem coast of North America, are farther examples in diatant
countriea ; whUc in Europe, the chains of islands on the coast of Scandinavia,
the Britiah islands, the eUiptic islands between Italy and Spain, the ialanda

218 PHYSICAL GEOGRAPHY.
on the east coast of the Adriatic, and the islands of the Greek Archipelago,
complete the series of this class of insular land.
The principal islands belonging to the second or oceanic group are, the
Friendly, the Society, the Marquesas, the Sandwich, and other groupa in the
South Pacific ; the Canary lalands, the detached islands in the Indian Ocean,
the Galapagos, and, generaUy, the multitudinous group of single volcanic
ialanda in various parts of the world ; and also the groups of coral islands.
These form two groups, distinguished by thefr origin, and generaUy not less
diatinct by thefr vertical elevation.
Perhaps, the general plan and nature of these different kinds of islands
win be best understood if we consider them as due in the first case (conti
nental islands) to the slow elevation or depreaaion of large masses of land on
a Unear axis, by the tUting up of one edge of a plane. The other two cases
are also understood, if we conaider the one as reaulting from the local eleva
tion of certain amaU areaa on a point of upheaval, and the other aa the conse
quence of slow depresaion of areaa of broken land without much tUting, and
whUe cfrcumatances were favourable for the rapid increase of growth of marine
animals. The facts connected with the actual horizontal configuration of the land
are perhaps more important in Physical Geography than haa often been
thought, and the evidencea derived from the obaervations on island distribu
tion are not the leaat remarkable. The linea afready aUuded to, one extend
ing from New Ireland to the New Hebridea, and the other to the Sandwich
Islands, each range north-west, vrith perfect paraUeUsm, for 2000 mUea, at a
distance of 3500 mUes apart, and indeed this same dfrection (north-west)
obtains to a greater or less extent through the world, not only in islands, but
in thoae higher elevationa above the mean level which come under the deno
mination of mountain chaina. The phenomena connected with these we ahaU
describe presently.
g2 Inequalities ofthe Surface of Land. — Not only is it the case that the
land, whether continental or uiaular, offera various pecuUarities of horizontal
configuration, but each masa of land alao presente some distinct features of
inequality of level. Occasionally, but very rarely, large tracts may be
observed extending in every dfrection, at nearly the same level, and removed
but little above the surrounding water. Much more frequently there occur
undulations in every extensive area, and also different degreea of absolute
elevation above a mean level. Such varieties produce the phenomena
which are described under the names of plains or table lands, and these are
rent asunder by vaUeys and gorges, or pierced through by mountain chains,
and broken into picturesque forms of hUl and dale.
These general inequalities of surface are exhibited in thefr most typical
and characteristic form in those districts where thefr details ean be studied,
and their origin therefore be-made the subject of speculation; but they are
often mingled together with more or less of indistinctness, and thus thefr
true characters become concealed or lost. It is only in large fracts of land
that they are seen in aU thefr grandeur : in islands and small parts of conti-
nenta, where more than one prevaUs, the great force of the phenomenon is
not appreciated.
There is much mutual relation amongst these varieties of vertical profile,
and also much reference in aU of them to the structural pecuUarities of the
Earth's aurface. Thua, they requfre careful consideration, and the different
facts that have been recorded concerning them, possess dfrect interest, not
only as afiording examples of the physical outhne of our globe, but also in
thefr bearing on those conditions which affect man as its chief inhabitant.
S3 Low Plains and Steppes in Europe and Western Asia. — A very large
quantity of the land is distributed as low plains near the sea level, and often
not far from a coaat line. These occasionally present bills of moderate alti
tude, in most casea not reducible to any general syatem. Sometimes these
hills arc long waves or undulations, nnd often perfectly uniform in sfructure

FORM AND DISTRIBUTION OF LAND. 219
for many mUes. Under the name oi plains, are designated the k.w flat lands
of Northern Germany and Russia, and of Lombardy ; the flats of Tartary are
caUed steppes; those occupying the central parts of Northern Africa are
deserts; those in the northern part of Southern America, silvas, or forest
deserte ; those of other parts of South America, llanos and. pampas; and those
of Nortii America, prairies, or savannahs. Many are the pecuUarities of these
districte, but they have in common the important physical feature of vride
extent, uniform general level, and smaU elevation above the sea.
These fracts of fiat land may be conaidered as including several distinct
areas. In the northern part of the Old World they are traceable from the
ahorea of the German Ocean, through Holland and North Pruasia into
Russia, thence into Siberia, and so at intervals, only broken by low eleva
tions, to the coast of the Pacific in Behring's Sfraite. Within these Umits,
they occupy an area of not less than four and a half millions of square miles,
and while on the one side HoUand would be overfiowed by the sea if it were
not for its dykes, so on the other, near Astrakan, the plains sink stUl lower,
and the country around the Caspian Sea and the Sea of Aral, forms a vaat
carity of 160,000 aquare mUea, aU considerably below the bed of the ocean : the
surface of the Caspian Sea itself, at the lowest point, being depreaaed 348 feet.
Towards the eastem exfremity of Europe, the great plains assume the
peculiar character of a desert, consiating of level wastes destitute of trees.
These steppes begin at the river Dnieper, and extend along the shorea of the
Black Sea, including aU the counfry north and eaat of the Caspian and Inde
pendent Tartary, and passing between the Altai and Ural mountains, occu
pying aU the low landa of Siberia. Hundreda of leagues may be traversed
eaatwarda from the Dnieper without variation of scene, and a dead level of thin
but luxuriant pasture, bounded only by the horizon, fatigues the eye of the
fraveUer day after day by the same unbroken monotony. So long as the
vegetation remains, horses and cattle beyond number give animation to the
scene, but winter comes on in October, and the whole area then becomea a
fracklesa field of apotless snow. Fearful storms rage, and the dry snow is
driven by the gale vrith a violence which neither man nor animal can resist,
whUe the sky remains clear, and the sun shines cold and bright above. The
aummer's sun ia aa severe in its consequences in these wild regions as the
vrinter's cold. In June, the steppes are parched, no shower faUs, nor does a
drop of dew refresh the thiraty earth ; the aun riaes and sets Uke a globe of
fire, and during the day is obscured by a thick mist. Thus, in some seaaona,
the drought ia exceaaive, and the afr is then fUled vrith dust and impalpable
powder, the springs become dry, and the cattle perish in thousands. Death
friumphs over animal and vegetable nature, and desolation fracks the scene
to the utmost verge of the horizon.
Of the whole extent of these plains, a very vride range is hopelessly barren ;
the country from the Caucasus, along the ahorea of the Black and. Caspian
Seas (a dead flat, twice the size of the Britiah ialanda) being deaert, and
destitute of freeh water, while between the Caspian Sea and the Lake of Aral,
there is, for the moat part, an ocean of shifting sands, often driven by appal
Ung whfrlwinda.
The Siberian or Asiatic portion of the great northern tract of low land in
the Old World, occupies more than seven mUlions of square mUes, and is
rarely visited except along its outer boundary. Parts ofthe tract are occupied
by a rich black mould, covered vrith grass and trees, but other and larger
portions are hopelessly and desolately barren.
To the lowlands belong almost the whole of Northern Asia to the north
west of the volcanic chain of the Thian-schan ; the steppes fo the north of
the Altai and ofthe Sayan chain ; the counfries which extend from the moun-
taina of Bolor, or Bulyt-Tagh, (' cloud mountains,' in the Uigurian dialect,)
which foUow a north and south dfrection7 and from the Upper Oxus, whoae
sourcea were found by the Buddhistic pUgrims, Hiuen-thsang and Song-yun,
in 518 and 629, by Marco Polo in 1277, and by Lieutenant Wood in 1838 ;

220 PHYSICAL GEOGRAPHY.
in the Pamer Lake, Sir-i-kol, (Lake Victoria,) towards the Caspian ; and from
Tenghir, or the Balkhasch Lake, through the Efrghis Steppe, towards the
Sea of Aral and the aouthern extremity of the Ural mountains. As compared
with high plains of 6000 to 10,000 feet above the level of the sea, it may weU
be permitted to use the expression of ' lowlands,' for flats of Uttle more than
200 to 1200 feet of elevation. If the word plateau, so often misemployed in
modern works on geography, is to have its uae extended to elevations which
hardly present any senaible difference in climate and vegetation, the indefi-
niteness of the only relatively significant denominations of highlands and
lowlands, wUl deprive phyaical geography of the means of expreaaing the
idea of the connexion between elevation and climate, between the proffle or
reUef of the ground and the decrease of temperature. Humboldt, to whom
we are indebted for the above information on this subject, remarks, ' When I
found myself in Chinese Dzungarei, between the boimdary of Siberia and
Lake Dsaisang, at an equal diatance from the Icy Sea and from the mouth of
the Gangea, Imight well conaider myaelf in Cenfral Asia. The barometer,
however, soon taught me that the plains through which the Upper Irtysch
flows are hardly more than from 800 to 1200 feet above the sea. Further to
the east, the Lake Baikal is 1420 feet above the sea.'*
The low lands on the south-side of the great back-bone of mountains,
running eaat and weat through the Old Worid, are of very different kinds,
in aome respects, from those already described. They exhibit a more fropical
character, and are strikingly confrasted in thefr different parte, — either rich
in aU the exuberance that heat, moisture, and soU can produce ; or covered
by wastes of barren and burning sands : — some of them being in the most
advanced state of cultivation, and othera in the wUdest garb of nature.
The Great Desert of Northem Africa forms, perhaps, the moat atriking
example of one of theae conditions. The aUuvial plains of China confrast
this perfectly, and are paraUeled in some respecte by the vast and rich low
tracts near the mouth and lower valley of the Ganges and Brahmapootra, and
the plains of Hindostan. The latter are rich and highly cultivated, offering
little that ia extraordinary beyond the fact of thefr wide extent. The former,
or desert lands, require more detaUed notice.
54 The Sahara, or great African Deaert, oecupiea the cenfral part of
Northern Africa, reaching from the rocky country confining the NUe vaUey
to the very ahores of the Atlantic. Ita length is upwards of 2500 mUes, and
ita greatest breadth 1200 mUes. Its area has been steted to amount to two
and a half milUons of square mUes, and it runs out into the Atlantic, being
continued by extensive aand-banka far beyond the coast.
For the most part, the tract is level and low, but is broken occasionaUy by
atony ridges, more than one of which crosses it in 15° E. long., and by the
presence of a Uttle clay theae admit of vegetation. The deaert ia thua dirided
into an eaatern and weatern part — ^the eaatern, or Lybian Deaert, being the
smaUer, and the most favoured. For the most part, ite surface is not covered
with sand, but formed of hard horizontally bedded sandstone rock, perfectly
smooth and level. At intervals, smaU spots occur watered by sprmgs and
enlivened by the presence of vegetation. Theae are generally depressions
below the surface, and are caUed Oases. The largest is nearly a nundred
mUes long, and from one to fifteen mUes vride, but tiie others are much
smaller. The western portion of the Sahara contains some narrow tracts along its
northern border, adapted to ciUtivation, but the rest of the district is almost
entfrely unfit for any kind of agricultural or horticultural employment. The
soU is sometimes of fine sand, on which low ridges appear hke the waves of
an agitated soa, but in other places it is much harder, and more graveUy —
though stUl perfectly and hopeleaaly barren. In aeveral spots, beds of salt

* Humboldt's Aspects nf Nature, vol. i. p. 76.

FORM AND DISTRIBUTION OF LAND. 221
occur, three of which are known and have been described, and there are also
brine springs, and thick incrustations of salt on the ground, produced by
evaporation. On theae interminable sands and rocks no animal — not even an insect —
breaks the dread silence, nor is a tree or a shrub to be distinguished during
days of incessant travel. In the glare of noon, the air quivers with the heat
reflected from the red sand, and the night ia chiUy, under the clear aky
sparkling with ita host of stars. In these plains the traveller is frequently
deceived by the deceptive appearance of water produced by mirage.
55 Silvas of the Amazons. — The plains of America differ distinctly from
those of the Old World, and are known under varioua names, each referring
to some physical peculiarity. Commencing with the northern or tropical
part of South America, we find there a range of low land covered with
foreat, (thence caUed Silvas,) occupying more than a mUUon of square mUes,
and drained by the most gigantic river on the Earth, the Amazons. This
fract ia ao subject to inundations, that probably not leaa than 200,000
square miles are annuaUy laid under water, but the whole is covered with
exceedingly thick wood, rendered perfectly impenetrable by brushwood and
innumerable creepers. The amount of rain faUing duriug the year, the
intense heat of a tropical cUmate, and an inconceivably rich soU, here
produce an exuberance of vegetable and animal Ufe, which actuaUy offers a
bar to civUization, not less effectual than the gloomy sterility of the African
deserts. The native Indians seem irredeemable, and sunk in the most
wretched barbarism, and there appeara no prospect whatever of any im
provement in the diatrict, aince man can find no apot on whioh to commence
his operations.
50 Llanos. — These are fropical plains, situated chiefly on the left bank
of the river Orinoco, and they are continuations northwards of the forest
plains of the Amazons. Thefr area amounts to near 350,000 square mUes, or
about twice the extent of France, and although a smaU portion forming the
delta of the Orinoco is wooded, the remainder of the whole region is entirely
destitute of frees.
One portion of these plaina, the Llanoa Altoa, riae gradually from the
banka of the river, but so gently tbat the rise is imperceptible to the eye,
amounting only to an elevation of five hundred feet in a distance of more
than one himdred mUes. At this point fiat low banks arise, elevated only
five or aix feet, but extending at a dead level for about thirty or forty mUea,
and forming a water shed. On the other side, the plains descend towards
the Caribbean Sea, somewhat more rapidly than to the aouth, but atUl
imperceptibly. The summit forms a very low table-land, consisting of sand
mixed with calcareous rock, and is barren, vrith the exception of a few hardy
fraaaes, the rain that faUs not forming into pools and fertUizing the land,
ut ainking into the aand to aome beds of impermeable argUlaceous rocks,
and then mnning off in springs or rivulets to the plaina below.
The larger and more level portion of the Llanos Ues along the base of the
rocky elevations, which commence the chain of the Andes, and extend from
9° N. lat. to the equator. These, though further from the ocean, are much
lower than the Llanos Altos, the lowest portions being only two hundred and
twenty-four feet above the aea, (from which they are distant five hundred
mUea,) and riaing to the aouth and west to the height of five hundred feet.
Theae plains are so nearly level, that the currents of two rivers in their lower
course are imperceptible, and the waters flow back towards the sources, when
the wind blows sfrongly in that dfrection, or when the Ormoco, to which they
are fributaries, becomes swoUen. In these plains, no rock, no stone, not even
a pebble is seen ; there are no inequalities, except some low hills of sand,
riaing a few yards above the common level, and some slightly elevated
grounds, having an area of one hundred square mUes or more, which can only
be (hscovered' by a practised eye, and whoae surface is completely flat. The
soil is a mixture of aand and calcareoua rock, with aome mould. Grass grows

222 PHYSICAL GEOGRAPHY.
everywhere, but there are no frees, or even bushes, except a few isolated
palm-trees, at great distances from each other, and some bushes on the banks
of the rivers.
57 Pampas. — The Pampas are treeless plains, which extend from 22° S.
lat. to the most southem Umits of the American continent, occupying a total
length of two thousand mUes. The breadth, throughout this vaat diatance,
is very varioua, rarely however leaa than two hundred and forty milea, and
between latitudea 26° and 38° amountmg to nearly double that. The area,
eatimated rouglily, ia about 750,000 square mUea, or nearly four times the
whole extent of France.
There is necessarUy great difference in climate, and also in the nature of
the surface and the vegetable productions, in plains extending thus through
thirty degrees of latitude, (one-sixth of the half great cfrcle from pole to pole.)
The aouthern portion is caUed the Pampas of Patagonia, and preaent the
appearance of a number of atep-like terracea, running north and aouth, each
alightly rising to the south, generaUy very aterile, but occaaionaUy clad with
verdure. The surface is diversified by huge bouldera, tufta of brown grass,
low bushes armed with spinea, brine lakea, white snowUke incrustations of
salt, and black lava platforma Uke plaina of fron. The plains are, here and
there, intersected by a ravine or a atream, but the watera do not fertihze the
soU. The transition from heat to cold is rapid and exfreme, and piercing
winds rush in hurricanes across the disfrict. Towards the north, the Pampas
of Buenoa Ayrea are separated from thoae of Patagonia by aeveral ridges of
table-land, and present an extensive surface of ground, not without irre
gularities, though these are too alight to be denominated hUla. A large
portion of the aouthern part of this diatrict is occupied by swamps and fens
abounding in lagoona and wide-apreading saUnes ; one of the swamps or
lagoons alone (that of Ybera) occupying one thousand square miles, and being
entfrely covered by aquatic plants. These swamps are greatly swoUen by
the annual floods of the rivers, which inundate the Pampas, desfroying vast
numbers of cattle, but leaving behind thick beds of fertilizing mud.
Beyond the river Salado, the face of the country changes, the swamps
ceasing, and being succeeded by very sUghtly undulating and dry plains,
covered with luxuriant grass, and occasionaUy by thistles eight or ten feet
high, used as fuel. Further to the west, there occurs an extensive pastoral,
and also an agricultural disfrict, separated by a Une drawn on the meridian of
66° W. long., the pastoral disfrict being to the east. The surface of the
latter is almost everywhere a dead level, but large shallow salt lakes occur in
very smaU depressions, one of them being fifty mUes long and twenty mfles
wide. The aoU is good, consisting of a dark friable mould, without a pebble :
no trees occur, and there are no permanent water-com-ses. The district
affords admirable feeding ground for horaes and cattle, which were infroduced
by the Spaniards, and have replaced the Uamas, the indigenoua ruminating
qjiadrupeda of the counfry. It is calculated, that there are a million of
horned cattle, and three mUlions of horses fed on these plains.
The weatern or agricultural district is less level than the pastoral ; the
soU, consisting of loose sand impregnated with saUne matter, being entirely
imfitted for the growth of grass, although when frrigated it is exceedingly
fertUe, and particularly adapted for the growth of fruit-fr-ees. Thia ti-act is
succeeded to the north by a salt desert, consisting of a vride plain, extending
about 200 mUes from east to west, and 140 mUes northward, which ia level
and smooth as a fioor, and snow-white with superficial salt, sfretching its
treeless and shrublcss wastes ou all sides to the horizon, unbroken by any
object save a few stunted, straggling, nnd leafless bushes. Throughout the
whole district no grass grows, and tiiere is a great scarcity of water. Eain
has been known not to faU for eighteen months, and aews are entfrely
unknown. 58 Savannahs, or Prairies. — The prairies, or, as they are sometimes
caUed, savannahs, are vast fracts of plain country of inconsiderable elevation,

FORM AND DISTRIBUTION OF LAND. 223
occupying the central part of North America, estimated by Humboldt to
amount to nearly two and a half millions of square mUes, and extremely
varied in climate, in character, and in productions. They have been divided
mto three classes— 1. The heathy or bushy ; 2. The dry or rolUng, generally
destitute of aU vegetation but grass, and by far the most common and exten
aive ; and 3. The aUurial or wet prairie, abounding in poola, and the frequent
resort ofthe wapifr and other deer, and of wUd horaes.
The vast savannahs on the banks of the Mississippi are covered with long
grass ; and in the aouthern disfricts, as weU as on the banks of streams, are
occasionaUy clothed with frees, but these are rare exceptions to the general
monotony. A salt efllorescence is often exhibited on thefr surface, and they
frequently possess a deep rich soU.
Many of the plains of North America are covered by foreat vegetation,
but thia has been greatly cleared in the United States, as the white man has
advanced. The forests are not throughout of the same character ; sometimes
consiating of a rich variety of magnificent trees, whUe over many hundreds of
square mUes there extend vaat monotonoua tracta of aand, clothed only with
gigantic pines, and charaoteristicaUy denominated pine-barrens.
59 High Plains, Table-Lands, or Plateaux of the Old World. — A very
considerable portion of the dry land upon the globe consists of land extend
ing for great distance at a conaiderable elevation above the sea. Such land
often presents a greatly varied surface, and is generaUy connected with
important mountain chains. An example of such table-land in Europe is seen
in the central plateau of Spain, consisting of a tract of nearly 100,000 square
mUes, elevated from 2000 to 3000 feet above the sea, and nearly surrounded
by mountains. Other plateaux of enormously greater dimensions, occur in
other parts of the world.
Tbia table-land of Spain ia varied by mountain ridges, (sierras,) some of
them of considerable height. There is a want of cultivation in many parts,
owing to the smaU quanfrty of rain that faUa ; and the whole area may be
deacribed as monotonous and naked, although com and wine are produced in
abundance in some places, whUe others serve for pasture. This table-land is
more fertUe on the Portuguese side.
The bigh land of Spain is continued, though at a much lower elevation,
through the South of France, but chiefiy by hUl and low mountain ranges.
The table form being rather characteristic of the eastern than the western
portion of the great continent, first begina to exhibit the peculiar and striking
features of such fracts in the Balkan range of mountains, which rises very
abruptly from the ahores of the Adriatic, and is everywhere rent by deep
and fremendous fissures, fransverse to the principal dfrection of the high
land. From thia point an elevated plateau ia continued, with few intervals,
across Asia, as far as the Pacific Ocean ; its breadth graduaUy expanding till
it amounts to 2000 mUes. It is interrupted in some places by lofty mountain
chains, and ite altitude varies greatly, but is throughout considerable.
The western portion of this vast fract forms the table-land of Persia, and
extends from the shores of Asia Minor, nearly to the riglft bank of the Indus.
It oecupiea an area of 1,700,000 square mUea, and ia generaUy 4000 feet above
the sea, but in aome placea riaea to 7000 feet. The eastern portion is very
much larger, (amounting to 7,600,000 aquare mUea,) and in aome placea
attains an elevation of 17,000 feet.
It muat not be underatood that theae high lands present generaUy an
absolute level, or resemble in this respect the steppea, deserts, or savannahs,
already described. They are often bounded by mountain ranges, and the
highest mountains of the world rise out of them. They occaaionaUy alao
exhibit in thefr wide extent many mountain featurea.
Among the westernmost portions of the great Asiatic table-land may be
obaerved the cold, treeless plains of Armenia, 7000 feet above the sea, and
the great salt desert, and adjacent sandy deserts of Irak and Kerman, in

224 PHYSICAL GEOGRAPHY.
Persia. Throughout this vride area, there is scarce any cultivation, the brick-
red sand being drifted about by the vrind into wave-like hUla, or the soU bemg
covered vrith a thick efflorescence of common salt and nifre.
The oriental plateau of Thibet is separated from that of Persia by a spur of
the Himalayana, and from the plaina of Hindoatan by the main chain of the
Himalayana, rising in some places to the height of 28,000 feet. The Altai
mountams separate the district from Asiatic Siberia, while on the eaat they
are cloaed in by the almoat unknown mountain chains of westem China. The
height of this vast plateau above the sea varies from about 4000 feet in the
northern portion to as much as 15,000, or even in aome places 17,000 feet
near the Himalayana, and the district is fraversed by three mountain ranges.
A plateau of considerable, but very unequal elevation, haring the names
of Gobi, Scha-mo, (aand deaert,) Scha-ho, (aand river,) and Hanhai, runa in a
S.S.W., N.N.E. direction, with Uttle intermption, from Eastern Thibet
towarda the mountam knot of Kentei, to the south of Lake Baikal. Thia
sweUing of the ground is probably anterior to the elevation of the mountain
chains by which it is intersected ; it is situated, as already remarked, between
79° and 116° longitude from Paris, 81° and 118° east from Greenwich.
Meaaured at right angles to ita longitudinal axis, its breadth is, in the south,
between Ladak, Gertop, and H'laaaa, the seat of the great Lama, 720
geographical mUea ; between Hami, in the Celeatial Mountains, and the
great bend of the Hoang-ho, near the In-schan chain, hardly 480 ; and in the
north, between the Khanggai, where the great city of Karakhomm once
stood, and the chain of Ehin-gan-Petscha, wliich runs north and south in the
part of the Gobi fraversed in travelling from Kiachta, by Urga, to Pekin, 760
geographical mUes. The whole extent of tins sweUing ground, which must be
carefuUy distinguished from the far more elevated mountain range to the
east, may be approximately estimated, taking its inflexions into account, at
about three times the area of France.
No portion of the so-caUed Desert of Gobi (parts of which contain fine
pastures,) has been so thoroughly explored in respect to differences of eleva
tion, aa the zone of nearly 600 geographical mUea in breadth, between
the aourcea of the Selenga and the Great WaU of China, and it has been
determined that the mean height doea not amount to more than about 4000
feet, instead of double that elevation, aa was at one time supposed. It
appears also that Thibet is not at aU an unbroken plain, or table-land, but a
district intersected by mountain groups, belonging to distinct systems of
elevation, and containmg but few plaina, whUe the loftiest of them are not
more than 13,340 feet above the sea level, and the mean elevation of tho
plateau is not more than 11,510 feet.*
Table-land is not unfrequently characteristic of islands as weU aa conti-
nenta, and on the coast of Europe the Faro Islands, situated due west from
Norway, exhibit this feature, rising at once 2000 feet, and presenting nearly
the same elevation over a great part of the group. The north-western part
of Scotland and the central portion of Ireland ^so, partake of aimUar character,
but the elevation ia not so conaiderable.
Africa exhibits moderately elevated teble-land, over the whole, or nearly
the whole of its southern portion, but the greater part of that continent is aa
yet unexplored by white men. North of the Cape of Good Hope, the land
rises to about 6000 feet, and the continent haa recentiy been crossed by
Dr. Smith, on the tropic of Capricorn, and by some native travelling mer
chants about 12^° further north. At the Cape, the breadth ia about 700
miles, and in the last-mentioned latitude about 1600 miles, and within these
limits the table-land appears unbroken by any lofty range of mountains,
although frequently rent by precipitous, deep rarines.
The southern portion of Aj"rica ia aomewhat better known, and presents

Aspects of Nature, ante oit., vol. i. p. 79.

FORM AND DISTRIBUTION OF LAND. 22.5
some lofty plains, projecting into the lower flat ground, like promontories.
One of theae terminates with the Table Mountain, at the Cape of Good
Hope. 60 Table-Lands of America. — The table-lands and plateaux in the New
World are not so extensive as in the old, but a wide and lofty tract occupies the
f -eater part of Mexico, extending also to CaUfornia. It begins at the Isthmus of
ehuantepec and reaches northwards for 1600 miles, expanding towards the
north to a breadth of about 360 mUes. The most easterly part of this plain
is 7500 feet above the sea, and it rises towards the west tiU it becomes 9000
feet high in Mexico, whence it diminishes graduaUy to 4000 feet. In CaUfornia
it is about 6000 feet above the sea. It is throughout torn by narrow, deep
caritiea, and the descent to the low lands is on aU aidea (but especiaUy the
east,) exceedingly precipitous.
South America is not without table-landa of aome importance, though
more remarkable for great altitude than extent. One of the moat extraor
dinary, that of Deaaguardero, has an absolute altitude of 13,000 feet. Its
breadth varies from 30 to 60 mUea, and it sfretches 500 mUes along the top
of the Andes. The whole area includes 150,000 square mUes, and presents
a considerable variety of surface. The city of Potosi stands on this plain,
at an elevation of 13,350 feet, and lofty mountains rise on each side of it.
The table-land of Quito is another remarkable instance of extensive high
ground. It is 200 miles long and 30 mUes wide, at an elevation of 10,000 feet
and is bounded by a range of the grandest volcanoea in the world. Mexico also
afforda extensive plains several thousand feet above the sea, and in North
America the gi-eat plains graduaUy rise towards the north and west tUl they
assume the character of plateaux.
Of these plains some portions are generaUy fertile, but very large tracts
afford no fraees of natural vegetation, and offer Uttle promise. In some cases,
rain ia exceedingly rare.
61 Mountain Systems of the Earth. — The most elevated portion of the
Earth'a crust consists either of lofty ranges exhibiting a serrated or aaw-liko
summit of jagged edges, riaing dfrectly from plams; of elevated ridges
flanking table-lands; of ridgea subordinate in height, having, notvrithstanding,
important physical characters; or of isolated peaks, or cones, not connected
by intervening high ground. It is important to imderstand the term
' mountain chain' as being independent either of absolute or relative height
either above the sea level, or with respect to adjacent plains, for there may
be ridges of very low elevation which are in the strict sense mountains,
and there are, on the other hand, many rangea of hUla which are properly so
caUed, although far more lofty than many mountain chains,* the mountain
character not depending on absolute height above a fixed level, but rather
on distinct physical features. Mountain chains also may and do extend
far out to sea beyond their prominent and lofty ridges, and in this and many
other ways are highly important and very distinct features of the Earth,
greatly affecting its condition as the habitation of organic beings.
Strictly speaking, there are but two great systems of mountains on the
globe, one in each great continent, although there msfy also be traced a
multitude of others, aome paraUel to, and some making angles with, the
principal dfrections. The mountain chain of the Old World, or Eastem
Continent, haa its main axis running east-north-east and west-south-weat,
whUe that of the New, or Weatem Continent, ia north-north-weat and
aouth-south-east. The length of the former is about 9000 mUcs, and that
of the latter 10,000 mUes. The one rises in its highest part to not less than
28,000 feet, whUe the other nowhere attains a greater elevation than about

* It is also important to remember that a mountain range is not necessarily a water-shed,
nor does a water-shed require mountain country. Q

226 PHYSICAL GEOGRAPHY.
25,250 feet. The height of the elevated land thus beara some general pro
portion to the whole maas of land above the sea level.
There are certain features common to aU mountain chains, which it may
be weU to consider before passing to the particular ranges themselves. They
are rarely simple, but consist of distinct and often short ridges of high
ground, running in the same dfrection, and nearly paraUel to each other,
rising at intervals to culminating peaks by the union of several convergent
or radiating ridges. They exhibit also from time to time narrow fransverse
branches, or spurs, often of very great altitude, and forming, in fact, frans
verse mountain chains, which stretch far into the plains beyond.
The two sides of great mountain chains generaUy differ much in the rate
at whioh they are inclined to the horizon, the one side being much more pre
cipitous than the other. In the mountain chain of the Old World, for
example, the aouthern aide ia generaUy scarped, and the northem side sloped,
whUe in the Andes, the westem aide descends almoat precipitoualy to the
Pacific, whUe towards the Atlantic the slope is comparatively slow.
The masa of land, aa meaaured by the relative elevation of different
portiona above the aea, has been made tbe groundwork of calculations whose
object is to determine the mean height of various continental and other areas,
and an enumeration of the effect of the various parts on the whole, as
exhibited in the way of adding to the mean elevation, ia one meana of
ascertaining the relative importance of mountain chains and other elevated
districts. The position ofthe mean height of aU the soUd parts of the Earth's crust
above the sea, has been estimated by Humboldt at about 1000 feet ; that of
aU Europe, 671 feet ; of Asia, 1132 feet ; of South America, 1151 feet ; and
of North America only 748 feet.
The effect of the plateau of Spain on aU Europe, meaaured in thia way, is
eatimated at 36 feet, whUe that of the whole chain of the Alpa is only 20 feet.
In Asia, the great central plaina are estimated to contribute 120 feet of
elevation. Theae reaults are, of course, only approximate.
62 The General Connexion of tlie Mountains of the Old World. — The
great mountain ayatem of the eaatern hemiaphere may now be described a
little more in detaU. Commencing with the westem boundary of land at the
Atlantic, we find the Atlaa chain in Africa, the cenfral Spanish mountains and
the Pyrenees in Europe, nearly paraUel to each other, and each connected with
very lofty ranges further east, but aU at length uniting' and forming the
commencement of the great Asiatic range, of vvhich the Himalayan chain is
the central and loftieat portion.
The Atlas range is lofty, complicated, and important, and forms a broad
belt, having three principal divisions, which occupy the whole interval
between the Sahara and the Mediterranean. The loftiest portion ia the most
inland, and forms, in Morocco, a mountain knot 15,000 feet high; the other
portions are less elevated. The crest of the range is composed of granite and
crystaUine rocks, but the fianks are of stratified depoaite of newer date.
The Spanish peninsula is almost entfrely occupied by the teble-land already
described, and parallel ridges of serrated mountain peaka, terminated north-
wards by the Pyrenees ; the latter being a chain of considerable elevation, the
mean height of whose summit Une is about 7000 feet. On the whole, thia western
extremity of the great mountain system of the Old World is remarkable for
its great breadth and for the way in which it projecta into the Atlantic,
rather than for ita altitude above the sea level.
The Pyrenees are continued eastwards at first by inconsiderable elevations
and low table-landa, but these soon connect themselves with the westem
extremity ofthe Alpa, whence the ground ascends rapidlv by successive chains
of mountains, commencing with the lofty range of which Mont Blanc and
Monte Rosa are culminatmg points, extending through the various ranges of
the Oberiand, the Tyrolese, the JiUian, tho Noric, and other Alps, mto the
Balkan, and atretchmg southwai-da by very unportant spurs, of whioh the

FORM AND DISTRIBUTION OP LAND. 227
Apennines and the mountains of Dalmatia are the most considerable, but of
which other traces are also seen in the islands of Sardinia and Corsica.
The aubaidiary ranges, whether parallel to or diverging from the principal
chain of the Alps, include between tnem a somewhat extensive tract of low
ground, and also a certain amount of higher table-land, but the position of thc
mountain chains, and thefr height above the sea, are the only points to which
we now refer. These mountain chains consist, not only of those already men
tioned, but also of the Jura (a aomewhat fransverae chain, subsidiary to the
Alps,) and the Carpathians, which, turning southwards, partly complete the
range towards the east, and partly connect the European mountain system
with that of Asia. This communication is effected by the elevated land of
the Crimea, conducting the Carpathians to the Caucasus ; by the Balkan,
paaaing into Asia Minor ; by the mountains called Anti-Taurus ; and also by
the Taurus chain, which, by distant though appreciable links in Sicily, Crets
and Greece, connecta the south Spanish mountain ridges with thoae of Aaia
Minor. In this way there appear to be in the European system three prin
cipal and nearly paraUel rangea, the northern one being the loftieat. There are
alao several important subsidiary ranges, and one principal transverse range,
that ofthe Scandinavian chain, running north and aouth, but of conaiderable
altitude compared with the Alps and other lofty mountain chains. There are
four principal and parallel chains that intersect the interior of Asia, foUovring
with tolerable regularity an east and west direction, and coimected by trans
verse elevations at a few detached points : these are the Altai, the Thian-
schan, the Kuen-lin, and the Himalaya. There are also four or more running
north and south, ofwhich the Ural, the Bolor, and the Ehingan, are three,
and the fourth is Chinese.
63 General Outline of the Mountain Chains of the New World. — The
mountain systems of the westem continent are fewer, more aimple, and more
readUy fraced than those of Europe, Asia, and Africa. The mass of land
being much longer in proportion to its area, and the outline of the land on
the whole less broken, no doubt contribute to this, but the comparative sim
plicity of geological structure is not without an important bearing on this
condition. The Rocky Mountains, which begin on the shores of the Arctic Ocean,
nearly under the 70th paraUel, commence the American system, and connect
it by islands with that of Asia. They continue south-eastwards in an
unbroken line, separated only by the plains near the north end of the Gulf of
CaUfornia, from the high plateau of Mexico. These lands, themselves very
lofty, support alao some high ridges and peaks, occupying the country aa far '
as the Isthmus of Panama, where hUls of low elevation, piercing through low
plains, intervene before the commencement of the Andes.
Tlie Andes. — This great chain may be considered as commencing with
the plains of Mexico, at the point where the Rocky Mountain system ceases
to be fraceable, and passing through the narrow sfrip of land wmch separates
the two Americas by means of the volcanic range of Guatemala. The chain
enters South America at the Isthmus of Panama, and continues in a steady
and almost unbroken line of high elevation, forming successively the Andes of
Colombia and Quito, of Peru and BoUvia, of ChUe, and of Patagonia, sinking
down into the ocean beyond the southern extremity of Tierra del Fuego, after
haring fraversed the whole continent from north to south, a distance of 4500
mUes. The general character of the Andes is that of a number of paraUel moun
tain chama of great elevation and smaU breadth, often uniting into knots, and
often containing between them plains of vast elevation and considerable
extent ; but this character is not seen so strikingly in the southern as in the
northem portion of the country, so that for 2000 inUes, or from Cape Hoorn to
the paraUel of 20° aouth, the chain is single, narrow, and uniform.
Beaidea the main and continuous chains of the Rocky Mountains and thc
Andes, there are also in North America the Alleghanies, or Appalachian
<42

228 PHYSICAL GEOGRAPHY.
chain, and in South America those of Guiana and Brazil, which appear to be
independent ; besides tbat of Venezuela, which is an eastern branch or spur
of the principal range of the Andes.
The Appalachian, or AUeghany Mountains, consist of a series of low
undulations of nearly uniform elevation and paraUel to each other, rarely more
than 3000 or 4000 feet high, extending under various namea in a north
easterly dfrection. from about 35° north latitude to the mouth of the St.
Lawrence and the coast of Labrador. The eastem range is known, in its
course northwards, under the namea of the Blue, the CatskUl, and the Green
Mountaina, respectively. The breadth of the range is generaUy from 100 to
150 milea.
Aa subsidiary mountains of South Ameriea we must mention here the
great system of Parime and that of BrazU. The former of theae ia a group
of not lesa than aeven chains of low mountain elevations, rising generally to a
moderate height above the plain (which is 2000 feet above the sea), but haring
some much loftier elevations, of which an inaccessible peak. Mount Marivaca
(10,500 feet high), is the moat remarkable. The BrazUian mountains, so far
aa they are known, conaiat of rangea running north-east and south-west, of
which the highest peaks rarely attam to the height of 6000 feet, and which
average only from two to three thousand.
Between the two Americas, and in the Une of the principal islands known
as the Great AntiUes (Cuba, St. Domingo, and Porto Rico), there is an im
portant mountain system, running west-north-west and east-north-east,
parallel to a aimUar range of leaa elevation, riaing above the sea only in
Jamaica. Of theae, the mountains of Cuba rise to the height of 8000 feet, and
those of St. Domingo to 9000 feet, whUe the elevationa in Porto Rico are less
considerable. The Jamaica mountains form a very sharp east and west ridge,
running across the island at an elevation of from 5000 to 6000 feet, whUe some
of the transverse spurs are as much as 7000 feet high.
64 Mountain Systems of Australasia. — It now only remains to deacribe in
a few words the chief physical pecuUarities exhibited m the mountain aystems
of the vaat group of ialands in Australasia. AusfraUa itaelf, the chief mass of
land in this district, exhibits apparently the same characters of table-land that
are presented in Africa ; where the extent of the land is large, the elevation
tolerably uniform, and the coasts Uttle broken into deep and narrow inlets.
In other words, it presents sudden and precipitous mountain ranges towards
the coast, which are not repeated inland, but slope graduaUy towards the
interior. Thus, in New South Wales generaUy, and especiaUy in the sonth-
" eastern part ofthis disfrict, there is a north and south mountain range, which
seems to be situate about 100 mUes from the shore, and which rises to a
height varying from 3000 to 6000 feet and upwards. In South AustraUa there
is a simUar range near Adelaide fraced for some diatance. The mounteui
ayatema in other parts ofthe Archipelago are littie known, except tbat in New
Zealand there is a range nearly paraUcl with that of New South Wales.
In addition to the great mountain systems fraceable for conaiderable
diatauces on the Earth'a aurface, there are in many placea detached mountains,
or groupa of mountains, chiefly volcanic, either rismg directiy from the aea,
or from extensive fiat and often elevated plains. These being aU connected
with that reaction of the interior of the Earth on its exterior, which it wfll be
convenient to consider under a distinct head, are for the present neglected in
the account we have given of the plan of arrangement of those distinct raoun
tain groups, which project in ridges above the general surface ofthe Earth's
craat in a given diatrict, whether that aurface be above or below the level of
the sea.

229

CHAPTEE V,
HYDROLOGY.
{ 66. General phenomena ofthe ocean. — 66. Action ofthe wind on the ocean. — 67. The tides. —
68. The Atlantic Ocean. — 69. The Pacific Ocean. — 70. The Indian Ocean. — 71. The Arctic
Ocean. — 72. Marine currents. — 73. Whirlpools. — Calms. — 74. Inland salt seas. Bays, and
golfs. — 76. Springs. — 76. River basins. — 77. River systems of the Atlantic group. —
78. River systems of inland seas of the Atlantic. — 79. Rivers of the Asiatic system. —
80. River systems ofthe Paciflc Ocean. — 81. River systems of the Indian Ocean. — 82. Rivers
not communicating with the ocean.
/^ENEBAL Phenomena ofthe Ocean. — The principal part ofthe water on
\jr the globe occupies large depressions on the soUd surface, known under
the name of Oceans. These are connected together by comparatively narrow
passages, and are therefore reaUy united, forming one vride and continuoua
expanae of aea. The different parta are, notwithatanding, known by distinct
namea, the moat important being the Atlantic, Pacific, Indian, and Arctic
Oceans. There are also aome intemal seas, or laies, of considerable extent, as
the Mediterranean, the Baltic, and others, which are almost entirely enclosed
by land, and are fiUed with salt water, besides the great gulfs and bays of
North America, and others better known, but far less extensive in Europe.
It appears by calculation, that the actual surface ofthe globe being reckoned
at about 197,000,000 aquare British atatute mUes, as much aa 145,000,000
square mUes are covered by the waters of the ocean. It appears further, that
out of about ninety milUons of square mUes of surface in the South half of
the torrid zone and the South temperate zone together (the space between
the equator and the Antarctic cfrcle), nearly seventy-seven miUions of aquare
mUea (almoat aeven-eightha) are water, whUe in the North temperate zone,
the quantity of land is nearly equal to that of water. It is, therefore, erident
that a great frregularity prevaUs in the distribution of land, and no reason
has been suggested why this particular arrangement, rather than any other,
has resulted. One consequence of thia diafribution of the water wUl be seen
when we conaider the phenomena of the tidal wave.
The depth of the ocean variea exceedingly, and ita bed is broken, Uke the
surface of the land, into plateaux, forming shoals, and ranges of mountaina as
well as isolated mountaina, appearing above the aurface in islands, and groups
of islands. The structure also of the land ia often continued into the sea,
beyond the exfremities of continents, aa in the Agulhas bank beyond the
south exfremity of Africa, and also the ialands of Tierra del Fuego. In
other caaea, there is a rapid and very complete termination of the high
ground on the coast in the course of a very amaU diatance. Many parts of
the ocean have been fathomed, but in some placea a line, whoae length
nearly equals the elevation of the loftiest peaks of the Himalayan chain, has
faUed to reach the bottom. Around our own coast the depth is very variable,
not amounting to one hundred feet over great part of the German Ocean,
while towards Norway, where the shore is bold, the depth is more than
five thousand feet at a very short distance from the coaat. The deep water
oommencea also at a short distance from the shores of Ireland.
The ocean, over aU parts of the Earth, contains a certain proportion of
salt, which is not the same, however, for different seas, and even varies in
different seasons and at varioua deptha. The proportion la generaUy about
three or four per cent., but is larger in the southern than the northern
hemisphere, and in the Atlantic than the Pacific. The greatest proportion in,

230 PHYSICAL GEOGRAPHY.
the Pacific is in latitude 22° N. and 170° S. of the equator, and the smaUest
is in the Polar Seas, where the saltness is affected by the melting of the
Polar ice. The surface is often less salt than the deeper parts of the sea,
owing to the flowing into the ocean of large quantities of fresh water from
rivers. In this case, the fresh water being lighter, floats on the surface for
a long distance before becoming thoroughly mixed. Deep seas are generally
more aaline than thoae that are shaUow, and inland seas than the open ocean,
but this is not invariably the caae, aa it depends on the proportion that the
river-water flowing into the aea bears to the evaporation from its surface,
and alao partly to the influx of salt water. Thus, the Mediterranean, espe
cially in the deeper parts, is much more salt than the open sea, but the Baftic
is much lesa so.
The temperature of the water is generaUy different from that of the
atmosphere above it, and is greatly affected by depth and local cfrcumstances.
The temperature of deep water is constant, and m most parte of the ocean,
within the temperate and torrid zones, is much lower than that of the
surface.* The temperature diminishes, however, very irregularly in different
seas, being ao unequal, that one degree of the thermometer (Fahrenheit)
answers sometimes to seven, and at other times to fourteen, fathoms depth,
and even more. StiU it has been considered, that in general the temperature
decreases six times aa rapidly in the sea aa in the atmosphere, and thus we
much sooner arrive at the sfratum of invariable temperature (a limit wliich
corresponds to ' the anow line' in aacending into the atmoaphere). Under the
equator thia atratum ia at the depth of 1200 fathoma — ^thence it riaea towarda
the aurface, and reaches it in the southem hemisphere (where the water is
moat open) in latitude 56° 26', and then graduaUy deacenda again to latitade
70°, where it is 4500 feet below the surface. The temperature in the latitude
mentioned is 39° 5' at aU depths. At the equator, the water at the surface ia
at 80° Fahrenheit, and therefore much above that of the afratum of inva
riable temperature ; but at the pole, on the other hand, the water is much
colder at the aurface than at the depth mentioned above. Submarine currents
aetting from the pole to the equator, retuming at a higher level to the pole,
are concemed in the production of thia condition.
66 Action of Wind on the Ocean. — The aea ia constantiy imdergoing a
certain amount of movement, produced by various causea, aome of which,
and these among the most remarkable, are external to our planet, although
producing results upon it of the greatest possible importance. Others are
connected with the mere surface action of the atmosphere when disturbed,
and moving rapidly over the water, sfriking it at an angle. These reaults,
producing what are caUed wind and storm waves, have been weU described
m a recent work on Physical Geography by Mrs. Somerville, and as she has
expressed in a few worcfe aU the moat striking phenomena on this subject at
present known, we cannot do better than borrow her words : —
' Raised by the moon and modified by the sun in the equatorial seas, the
central area of the two oceana ia occupied by a great tidal wave, which
oscUlates continuaUy, keeping time with the retums of the moon, having its
motion kept up by her attraction acting at each return.
' The motion of the wind, however, combines with the tides in agitating
the surface of the ocean, and, according to the theory of undulations, each
producea its effect independently of the other ; wind, however, not only
raises waves, but causea a tranafer of auperficial water alao. Attraction
between the particles of afr and water, as woU as the pressure of the atmo
sphere, brings ita lower sfratum into adhesive contact with the aurface of the
sea, If the motion of the wind be paraUel to the surface, there wiU atiU be

* This, however, Is not everywhere the case, for Humboldt observed, in crossing from
Corunna to Ferrol, that the surfncc water viiried from 64j° to 60° Falirenheit, while the deep
ivater was 00° to 60.^°, aud the atmosphere 66°.

HYDROLOGY. 231
friction, but the water vriU be smooth aa a mfrror ; but if it be inclined, in
however small a degree, a ripple wUl appear. This friction raises a minute
wave, whose elevation protects the water beyond it from the wind, which
consequentiy impinges on the surface at a smaU angle : thus, each impulse
combining with the other, produces an undulation which continuaUy advances.
Those beautiful aUvery atreaks on the aurface of a tranquil sea, caUed cats-
paws by aaUors, are owing to partial deriation of the wind from a horizontal
direction. The resistance of the water increasea with the atrength and
incUnation of the wind. The agitation at first extenda little below the
surface, but, in long-continued gdes, even the deep water is teoubled ; the
bUlows rise higher and higher ; and as the surface of the sea is driven before
the wind, thefr ' monstrous heads,' impeUed beyond the perpendicular, faU
in wreathes of foam. Sometimes several waves overtake one another, and
form a sublime and awful sea.
' The highest waves known are those which occur during a north-west
fale off the Cape of Good Hope, aptly caUedthe Cape of Storms by ancient
'ortuguese navigators ; and Cape Hoorn seems to be the abode of the tempest.
The sublimity of the scene, united to the threatened danger, naturaUy leads
to an over-estimate of the magmtude of the waves, which appear to rise
mountains high, aa they are proverbiaUy aaid to do. There la, however,
reason to doubt if the highest waves off the Cape of Good Hope exceed
forty feet from the hoUow frough to the summit. They are gaid to rise
twenty feet off AusfraUa, and sixteen feet in the Mediterranean. The waves
are short and abrupt in small ahallow seas, and on that account are more
dangerous than the long roUing bUlows of the wide ocean. The undulation,
caUed a ground-sweU, occasioned by the continuance of a heavy gale, is
totally different from the toaaing of the bUlowa, which are confined to the
area vexed by the wind, whereas the ground-sweU ia rapidly tranamitted
through the ocean to regiona far beyond the direct influence of the gale that
raised it, and it continuea to heave the smooth and glassy surface of the
deep long after the wind and the bUlows are at reat. A sweU frequently
comes from a quarter in dfrect opposition to the wind, and sometimes from
various pointe of the compass at the same time, producing a vast commotion
even in a dead calm, vrithout ruffling the surface. Wavea are the heralds that
point out to the mariner the distant region where the tempest has howled, and
they are not unfrequently the harbinger of its approach.
' In addition to the other dangers from polar ice, there is always a aweU
at ita margin. Heavy sweUs are propagated through the ocean, tUl they
graduaUy subside from the friction of the water, or tiU the undulation is
checked by the resistance of land, when they roU in surf to the shore, or dash
in spray and foam over rocks. The roUers at the Cape de Verde Ialanda are
aeen at a great diatance, approaching hke mountaina. When a gale ia added
to a ground sweU, the commotion is great, and the force of the surge
fremendous, tossing huge masses of rock, and shaking the cliffs to their founda
tion. The riolence of the tempest is sometimes so intense as to queU the
biUows and blow the water out ofthe sea, driving it in a heavy shower, called
spoon-drift by saUors. On such occasions, saline particles have impregnated
the afr to the distance of fifty mUes inland. The effect of a gale deacends to
a comparatively smaU diatance below the aurface ; the sea is prpbably tranquil
at the depth of 200 or 300 feet : were it not so, the water would be turbid and
aheU-fiah would be deafroyed. Anything that diminishes the friction ofthe wind
smoothes the aurface of the sea : for example, oU, or a amaU sfream of packed
ice, which suppresses even a aweU. When the afr is moist, its atfraction for
water is dimimshed, and, consequently, so is the friction ; hence the sea is not
60 rough in rainy as in dry weather.'*
67 The Tides. — We have already mentioned the fact of the existence of
a great tidal wave osciUating continuaUy, and produced by the periodical

Somerville's Physical Geography, 1st edition, p. 239.

232 PHYSICAL GEOGRAPHY.
movements of our satellite the moon. If the Earth presented a uniform.
globe, with a belt of sea of great and uniform depth encfrcUng it round the
equator, thia wave would be perfectly regular and uniform. The sun carry
ing with it one such wave, and the moon another, there woiUd be four tides,
so modified, however, as to produce two principal ones compounded of the
four. The actual case ia, however, very different from this imaginary condi
tion, so that the heights of successive tides vary, indeed, in some proportion
to the way they would do in the simpler case, but the dfrection of motion
and the state of high water are exceedingly various. It is very difiScult to
form an adequate notion of tidal phenomena, vrithout elaborate tidal charts,
the materials for which have only been partially accumulated ; but we may
by description give some idea of the true case. Looking at a globe or map of
the world, we observe no uniform belt of sea round the equator ; but on the
contrary, the great continents croas the equator at nearly right angles, the
Atlantic Ocean remaining as a comparatively narrow basin, whUe the Pacific
ia greatly intercepted by coral reefs, islands, and sunken continents. In point
of fact, the great reaervofr of water in which regular tidal action occurs, is not
only in the southern hemisphere, but nearer the Antarctic cfrcle than the
equator. The source of the tides is therefore to be sought in the expanse of
sea occurring within the south temperate zone, where the great cenfral
agitation seems to commence, and whence on aU sides it appears to flow
northwards. The Atlantic thus receives from the south ite great wave of
tide, wluch graduaUy becomes a curve, whose convexity is more and more
northwards, untU after passing the tropic of Cancer, the advance of the wave
is so greatly retarded on the coast by the narrowness of the chaimel, that a
portion of it has reached the latitude of the southem extremity of Greenland
by the time that another portion has scarcely passed Cape Blanco on the
African coast, and Cuba in the Weat Indies. The great wave of tide passing
northwards, in this narrow channel, thus forms an enormous sfream tide on
the shores of Britain and North America, but it has, by this time, become so
complicated, that it is difficult to trace its relations with the moderate and
regular undulation produced originally by the attraction of the moon. So
also in the Pacific, the tide is so checked by the sub-marine frregularitiea of
aurface, that for a conaiderable part of that vast ocean, there is acarcely any
wave of the kind exhibited. In the Indian Ocean, on the other hand, the
tide wave, little interrupted by such cauaes, makes its way in an frregular
curve to the shores of India, and there dirided by the pyramidal form of the
peninsula of Hindostan, one portion proceeds up the Bay of Bengal, and the
other towards the Persian Gulf; the former having no eacape, and not dis
sipated by irregularities in the form of the land, graduaUy increases in height
as the bay narrows, and finally reaches the mouth of the Ganges, where it
expends its force on the ahorea in the fbrm of the weU known and terrific hore
of the Hooghly. In point of fact, therefore, the tides, although formed
entirely by the attraction of the sun and moon, by no means foUow the
apparent course of those bodies after thefr original genesis. Afler the wave
has once entered the canal of the Atlantic, it moves continuously northwards,
with very various velocity, but at first at the rate of nearly a thousand milea
per hour. In the firat twenty-four houra, it haa brought high water to Cape
Blanco on the west of Africa, and Newfoundland on the American continent.
In tho morning of the second day, thia great wave having been driven east
wards, reaches the western coast of Ireland aud England. Passing round the
northern Cape of Scotland, it reaches Aberdeen at noon, fravelUng in pre
cisely the opposite direction to that of its ffrst progress, and also opposite that
of the sun and moon. StUl proceeding onwards, at mitlnight of the second
day, it reaches the mouth of the Thames, and on the morning of the thfrd
day brings the merchandise of the world to the port of London. It thus
takes more time to roach Loudon from Aberdeen than to pass over an arc of
120°, (8000 miles,) between 60° soulh latitude and 60° north. Tho velocity
of tho progress of tins wave is greatest where tho water is deepest, aud where
ihc configuration of the shores ofl'ers the fewest obstacles.

HYDROLOGY, 233
68 Tlie Atlantic Ocean. — We must now consider those phenomena that
are peculiar to the different parts of the great Ocean. The Atlantic, although
its boundaries are not completely marked by nature, is yet perfectly distinct
and easUy described. It is that area of water occupying the space between
the western shores of the Old and the eastern shores of the New World, and
reaching from the Arctic circle to the icy shores of the Antarctic land. The
limit to east and west beyond the land of the two continents to southward (in
latitude 34° and 55° S. respectively,) is considered to be a continuation ofthe
meridian of longitude of the Cape of Good Hope and Cape Hoorn, (20° E. and
70° W. from Greenwich). This ocean, includmg its inland seas, covers about
tliirW mUUons of square (British statute) mUes.
Extending thus for nearly 140 degreea of latitude, the breadth of the
Atlantic will be aeen to be comparatively smaU. The two continenta which
form ita ahores approach nearest one another between Greenland and
Norway, in latitude 69° — 71°, and are there only 800 mUes apart. Widening
gradually, but then again contracting, the breadth about 5° S. ofthe equator,
between BrazU and Sierra Leone, in Africa, is stiU only 1500 miles. At 30°
N. latitude, where ita breadth ia greateat, (between Florida and the coast of
Africa,) the width is 3600 mUes.
The elongated vaUey form of this ocean long since atfracted the attention of
Humboldt, who observed that not only do the projections and protube
rances of one coaat correapond with receaaea on the other, but that the
nature of the mountaina and plaina also corresponds. This is chiefly the case
with regard to Africa on the east, and the northem part of South America on
the west. There are few mountains in the bed of the Atlantic, or, at least,
few that show themselves as islands above its surface. The principal of these
form volcanic islands and groups, and, except those in the northem part and
the West Indian group, are placed near the ahorea of Africa, and are
probably the last indications westward of the great mountain system crossing
the Old Worid.
The depth of the Atlantic is in some parta very considerable. In latitude
27° 26' S., longitude 17° 29' W., it was sounded by Sfr James Ross, and
found to be 14,550 feet ; 450 mUes west of the Cape of Good Hope it was
16,062 feet, (332 feet more than the height of Mont Blanc ;) whUe in latitude
15° 3' S., and longitude 23° 14' W., a Une of 27,600 feet faUed to reach the
bottom. The form of the land on the northem shores of the Atlantic is worthy of
notice, having a tendency to linear extension, not only in the several islands
of Nova Zembla, Spitzbergen, and Greenland, but also the main land of
Norway, which ia spUt as it were into shreds by deep inlets (jjords).
Scotland exhibits, in its northern and western islands, a similar pecuharity of
form. The shores of this ocean are also very deeply indented by large seas,
of which the Baltic and the Mediterranean are the most remarkable.
In consequence of the contorted and complicated Une which the shores
make, the length of coast enclosing the Atlantic is very considerable, and
is indeed much more so than that of the Pacific, notwithstanding the far
greater magnitude ofthe latter ocean. The eastern coast Ine ofthe Atlantic
IS 32,000 mUea in length, and the westem, or American, 23,000 miles, making
a total of 55,000 mUes.
The Atlantic receives the rivers of a certain portion of the land enclosing
it, and the area of each river basin includes aU that land the water of which
naturally flows into the river. In Europe and Africa, there are no rivers of
first-rate magnitude emptying themselves dfrectly into the Atlantic, since the
Rhine, the Eirgest of them, has a course of only 700 mUes, while the NUe,
the Danube, the Dnieper, the Rhone, and others, run into the Mediterra
nean, the Volga into the Caspian, and the Elbe and Oder into the Baltic.
On the American side numerous gigantic rivers pour directly into the
Atlantic a vast body of water, draining almost the whole of the New World.
There are aeveral exceedingly important currenta in the Atlantic, but
these wUl bc best considered after we have described the phenomena of the

234 PHYSICAL GEOGRAPHY.
Pacific and Indian Ocean. The winds of the Atlantic have been already the
subject of aome notice in speaking of atmospheric influences.
A very extensive area of the Atlantic, extending from 19° to 36° N. lati
tude and from 30° W. longitude to the Bahama Islands, (occupying in all
360,000 square mUes,) is covered at intervals vrith a species of marine plant,
(fucus natans,) called sometimes the sargasso, or gulf-weed. The quantity
of marine vegetation, and consequently of animal life, in this vast range,
eapeciaUy in two principal fielda near the termination of the Gulf Sfream, and
where two portions of the sfream meet, ia truly astonishing. The real
origin of this accumulation is not known, but in its results it is sufficientiy
intereating, aa it afforda food and shelter to a multitude of marine animals.
The Atlantic Ocean is divided by geographers into two portions — one north,
the other south of the equator, and caUed, therefore, respectively the North
and South Atlantic Ocean. There is no natural division corresponding to
this artificial arrangement.
6p Paciflc Ocean. — The Pacific Ocean covers more than half the
surface of the globe, and its area may be roughly eatimated at ninety
miUions of aquare miles, occupying the space between the shores of America
on the one side, and the coasts of Aaia and Ausfraha on the other. Ita
northern boundary is Behring's Sfraits, which, between East Cape, in Asia,
and Cape Prince of Wales, ia not ao much aa forty mUes wide; but from this
point the coasta rapidly diverge, and at 54° 30' N. latitude, between the
peninaula of Alashka and Kamtschatka, are more than 1200 mUea apart.
Continuing to diverge, the breadth from California to the coMt of China,
on the fropic of Cancer, ia 8500 mUes ; and this remains pretty constant as
far as the south tropic, where the diatance from Sand Cape in Auafralia to
the coaat of ChUe ia 8200 mUea. Towarda the southem exfremity, the limits
of the Pacific are understood to be the meridians of longitude passing
through Cape Hoorn and South West Cape, in Tasmania, and the ocean
terminates, as the Atlantic does, at the icy shores of the Antarctic land.
The Asiatic border of the Pacific is fringed in a very remarkable manner
with islands, almost enclosing a range of seas, or small basins, which corre
spond vrith and replace the deep inland seas ofthe Atiantic. Long peninsulas
also project from the main land, and these, aa weU as the ialanda, (and the
coaat itaelf where they do not occur,) are dotted at intervala vrith active
volcanoea, of which a very large proportion of the whole number known on
the globe are there placed. Although, however, the Asiatic and North
American coasts are much broken, the South American is for the most part
bold and rocky. The total length ofthe coast line, including that of the whole
Indian Ocean, is eatimated at 47,000 mUes, about 8000 mUes leas than that of
the Atlantic.
WhUe the south-western and westem portions ofthe Pacific are so thickly
strewn with islands that the number of them is not at aU known, even approxi
mately, the eaatern, northern, and southern portions are singularly free from
islands, the sea for fifty degrees of longitude west of the American coast
(exceeding very greatly the whole Atlantic in extent,) having only one group of
any importance, (the Galapagos,) and that exfremely smaU. Of the island
diatrict, which extends chiefiy between the fropica, and reaches from the weat
boundary of the ocean to longitude 135° W., there are two principal groups,
the one consisting of fiat, low ialanda, in groupa more or lesa connected with
sunk coral reefs, often of great depth, and the other of high and volcanic
islands, occasionaUy surrounded with a fringe of shallow coral. A space extend
ing more than 1000 mUes in length nnd 600 in breadth, south of New Guinea,
and between tho north-eastern coast of Australia and the New Hebrides
group, is remarkable for the innumerable multitude of coral reefs, islands, and
banks it encloses, and this may possibly be the laat remaina of a sunken
continent, of which the eastern part of AusfraUa, New Guinea, and other
islauda formed a part, but which has now almoat entirely disappeared overs
large portion of its area. The Pacific woiUd appear to possess a depth
corresponding in some degree to its vast area.

HYDROLOGY. 235
70 Indian Ocean. — That portion of the great ocean which extends
southwards from Asia to the Antarctic Cfrcle, and eastwards from Africa to
Ausfraha, thus occupying the interval between the Atiantic and Pacific, is
caUed the Indian Ocean. Including the Red Sea, Peraian Gulf, Bay of
Bengal, &c., it occupies an area of about 23,000,000 of square mUes, and is
thus nearly as large as the Atlantic itself It mcludes several very large and
important islanda, aa Madagascar, Borneo, Sumatra, Java, Ceylon, &c., and
aome important aystems of islands, and it receives the drainage of aeveral of
the principal river-baains of Asia, as the Ganges, Brahmapootra, Indus,
and Euphrates. The chief points of interest coimected with tnis ocean have
reference to its currents.
71 Arctic Ocean. — The fract of sea vrithin the Arctic Cfrcle, bounded by
the northem coasts of Europe, Aaia, and America, includes an area of about
3,000,000 of square mUes, and is called the Arctic Ocean, or Icy Sea. It is
connected with the Pacific by Behring's Straits, and with the Atlantic by the
wide sfrait between Greenland and Norway. The corresponding tract of
ocean at the opposite pole is caUed the Antarctic Ocean, and is estimated to
occupy about 2,000,000 aquare nules. Its exact limits have not been very
aoem-ately determined, as the ice extends much further from the aouth than
it doea from the north pole.
72 Marine Currents. — The water of the aea ia not only constantly kept
in motion by the atfraction of the sun and moon, producing the tidal waves,
and by occasional disturbances the reault of winda, but there are also large
bodiea of water, aa weU in cloaed seas as in the open ocean, which are con
tinuaUy moving onwards in a fixed and constant direction, some of them
depending on causes not less permanent than the globe itself, and others,
alinough originated bythe form of land and local infiuences, remaining constant
for periods of time far longer than any records of man can reach. There
are also periodical currents of greater and less importance.
Of these various currents, aome are merely superficial, slow in their motion,
easUy turned aside by natural obstacles, such as sand-banks, projecting head
lands, &c., and resulting generaUy from constant winds ; others are deep,
broad, and sometimes even rapid ; thefr temperature is different from that of
the ocean through whioh they make thefr way, and they proceed like rivers
through a great continent, keeping a course which sometimes extends for
thousands of mUes. The former are caUed drift currents, the latter
stream currents. The most important of the atream currents are those
which occur in the Atlantic, or, at least, it may be considered that, as these
are best known and most affect narigation, they requfre the moat extended
notice. Many of these currents, however, commence in other seas, and
thua connect the watera of different parts of the great ocean. Thus,
the Gulf Sfream, perhaps the moat important of aU, muat be regarded as
originating in the Indian Ocean or even in the Pacific, and the Arctic currents
bring ice and cold water far into the Atlantic from the Arctic Ocean.
Oinitting, for the present, thoae currents which have their origin in the waters
which pour into the sea from the great rivera of the Earth, we wiU consider
now the principal marine currents in thefr relation with one another.
Commencing in the northem part of the Bay of Bengal, a current sets
aouthwarda for some distance, and passing round the south of Ceylon, tums
weatwarda to near the coaat of Africa. This current, however, depends upon
the monsoon, being a northerly current during the south-west monsoon, from
February to October, and southerly during the reat of the year. Between
Madagaacar and the mainland of Africa there sets another current, which,
under the name ofthe Mozambique Current, continuea close along the African
coast in a south-westerly dfrection during the whole year. A little farther
south it becomes a tme southerly current, having near the coast a mean
velocity of from 18 to 20 mUes per day, which at some seasons is greatly
exceeded, a caae haringbeen known ofa ahip drifted by thia current 139mUea
w 'j*"^''®' * velocity only paraUeled in the maximum of the Gulf Stream.
JNear Algoa Bay, and ofl" the Agulhaa Bank, this current pasaea mto the Cape

236 PHYSICAL GEOGRAPHY.
Current, which is formed, indeed, of its junction with the currents from the
seaa aouth of Madagascar. A part of the Cape Current is deflected by the
Agulhas Bank, and passes round by the Cape of Good Hope into the Smith
Atlantic Current, but the main portion tums southwards in latitude 21° to 24°,
and then, passing eastwards, forma an important counter-current, mixing vrith
the South Atlantic Counter Current.
The Cape Current ia from 90 to 100 mUea broad, and m different parts of
its courae flows at the rate of from 60 to 100 mUes per day. Outside the
Agulhas Bank the temperature has been observed to be about 80° above that
of the ocean. The counter current running eastward has a breadth of from
200 to 240 mUea, and a velocity of 50 milea per day.
The South Atlantic Current ia a continuation of the Cape Current towarda
the north and north- weat, along the toast of Africa. In latitude 10° aouth it
haa ceased to be traceable at the surface, and then commences the Main
Equatorial Current. Thia important part of the sfream currents of the
Atiantic may be distinctly recognised off the coast of Africa, alittle south ofthe
equator. It runs nearly on the equator, and paraUel vrith another (the
Guinea Current), which terminates a Uttle to the north, near the mouth of
the Niger ; and for a distance of more than 1000 mUes these two currents
exhibit the remarkable phenomenon of paraUel streams in contect with each
other, flowing vrith great velocity in opposite dfrections, and having a differ
ence of temperature of 10° or 12°. The Main Equatorial Current proceeds
on both aidea of the equator to 22° west longitude, and then sends off the
North-west Branch Current, and, declining to the aouth, runs paraUel with
the coaat of South America beyond the ta-opic of Capricorn. At Cape St.
Roque, however, a portion of the stream runs paraUel to the northem coast
of South America, tiU it disappears near the mouth of the Amazons, being
covered and crossed by the volume of fresh water proceeding from that river.
The north-west branch of this current flows at fu-st north-westwards, and
afterwarda towards the north, till, in about 30° north latitude, it merges in a
drift current ; its breadth varies from 200 to 300 mUea. The length of the
Main Equatorial Current, meaaured from the coaat of Africa to its termination
near the Caribbean Sea, is about 4000 mUes ; and that of the Brazil Current,
its southem portion on the coast of America, ia nearly 1000 miles ; ite breadth
at the commencement is about 160 mUes, at about 5° west longitude it has
increased to 360 mUea, and at the point of aeparation ofthe north-west branch.
amounts to 450 mUes. The mean velocity ofthe whole course ofthe current
may be reckoned at 36 mUes per day, but between 10° and 16° west longitade
in the summer aeason, it varies from 44 to 78 mUes, and has even been
recorded at 90 miles per day. The velocity of the north-west branch is much
less, commencing at from 20 to 24 mUes per day, and graduaUy diminishing.
Throughout ita course to the Caribbean Sea this ia a cold current, the average
temperature being from 4° to 6° below that of the ocean ; ite nortiiern portion
paasea into what la oaUed the Guiana Current, which extends about500 mUes,
with a velocity varying from 10 to 36 miles per day. Thia current enters the
Caribbean Sea, and is there lost sight of.
In addition to the currents afready described, and uniting them between
the Cape of Good Hope and the coaat of BrazU, ia the Southem Connecting
Current, which ia but little known, and flowa chiefly to eastward about 150
milea south of the Cape of Good Hope, into the Indian Ocean. We have seen
thus that a great body of water proceeds acrofes the Atlantic from eaat to west,
spreading out northwards and southwards as it approachea the great barrier
of land presented by the continent of America. The form of this land, the
vast recesses ot the Caribbean Sea and the Gulf of Mexico, separated from
the main ocean by the chain of the West Indian islands and the peninsula of
Florida, conceal the fm-ther progreaa of those currente. But an important
and very considerable ciirroiit has been traced, aetting round the Campeche
Bank intotbe Gulf of Mexico, and assisted by the river current of the Misaia-
sippi paasing out iuto the Atlantic between Florida and Cuba. Running
within the Bahama Bank, the water thus issuing into the open ocean con-

HYDROLOGY. 237
tinues paraUel with the coaat of North America, tiU it meeta the St. George
and Nantucket banks, when ita courae is directed eastward. After passing
the southern exfremity of the bank of Newfoundland, it continues in the
same dfrection to about 38° west longitude, between 35° and 43° north lati
tude, and at this point it turns to south-east and south, and, paasing the
westernmost of the Azores, is soon afterwards lost in the Atiantic. This
remarkable and important sfream-current is weU known under the name
of the Gulf Stream. It extends on the whole upwards of 3000 mUes, and
occupies 78 days in its progreas, thus averaging a daUy rate of 38 mUes,
but the velocity varies greatly, amounting to 120 mUes per day at the
end of the Gulf of Florida, and not more than 10 miles per day in
the ricinity of the Azores. The maximum temperature of the sfream
is in the sfrait of Florida, and is then 86° or 89°, conaiderably above
that of the ocean in the aame latitude ; 10° farther north, it is stUl as
much as 84°; and, although both temperature andvelocity decrease aa the afream
progreasea, the temperature remains constantly very much above that of the
ocean outside the current. It is the influence of this stream upon climate
that renders the British islands green and fertUe, while the shores of
Labrador in the same latitude, or the shores of America, are fast bound in the
fetters of ice ; its influence is not therefore confined to the Une of its dfrect
course, but is felt along the shores of Europe even as far north as Spitz
bergen. The Gulf Stream must be considered to terminate, as we have said,
in about the 25th meridian of weat longitude, but two other currents are
fraceable onthe westem coast of the Old World ; one caUed Bennel's Current,
commencing near Cape Finisterre, running northward along the coaat of
Spain, and thence along the west coast of France. After croaaing the EngUsh
and Irish channels, and the south coast of Ireland, this current enters the open
ocean, and joins the other, or North African Current, which runs first south
wards, foUowing the coast of Africa, but then, continuing parallel vrith the
shores of that continent, it turns eastwards, and forms that remarkable con
frast to the Equatorial Current afready aUuded to. Rennel's Current has a
velocity of about a mUe an hour, in certain winda, and the North African
Current about half that velocity in the northern part of ita courae, but after
wards a rate of as much as 50 mUes per day.
The remaining Atlantic currents are two, the Arctic Current, and that
which, paasing round Cape Hoorn, may be regarded as an Antarctic Current.
The former is understood to originate in the ice which surrounds the North
Pole ; it seta aouth-weatwards, from between Iceland and Greenland, and
arriving at Newfoundland, divides into two branches, the main afream paaaing
between the great and outer bank of Newfoundland intotbe Gulf Sfream, and
afterwarda again dividing, one portion fiowing aouthwarda to the Caribbean
Sea, whUe the other forma the United States Counter Ci/rrent, which extends
between the Gulf Stream and the coast to Cape Hatteras and Florida ; thia
current conveys southwards enormous masaea of ice, bringing with them
immenaequantitiesof stoneand earth, which are sometimes stranded in shaUows
or on banks, and sometimes,melting graduaUy, pass down into low latitudes, and
temper the heat or cbUl the afr of those countries along whose shores they pass.
The Cape Hoorn Current is an easterly current along the southern extremity
of America and the Falkland Islands, but it has originaUy proceeded from the
Antarctic Polar Sea, and thus brings with it very large quantities of drifted
ice, Ita velocity appears to vary very greatly, from 12 to about 56 mUes per
day, and it probably mixes vrith the waters ofthe southem connecting current.
The currents of the Pacific Ocean are not so weU known as those of the
Atlantic, nor do they appear to be by anymeans so considerable or so important
in narigation. The most interesting is that which, commencing as a drift
current from the Antarctic Pole, near the newly discovered Victoria Land,
becomes a coast current of cold water between latitude 40° and 50° south,
and then runs northwards along the western coast of South America, lowering
the temperature of the land, and apparently producing an effect exactly the
converse of that wbich the Gulf Stream produces on the coast of Europe. At

238 PHYSICAL GEOGRAPHY.
the surface this current is slow, often not amounting to more than a third ofa
mile per hour ; but at the depth of from 12 to 15 fathoms it is more considerable
and in the same direction. In aome part of its course this current mna at the
rate of 14 to 18 mUea per day, and it ia traceable along the coast from Val
paraiso almost to the equator, when it turns weatwarda into the open ocean of
the Pacific, but remaina sensibly affecting the temperature to a distance
of several thouaand mUes ; the chfference in temperature between the cur
rent and the mean annual temperature of the atmosphere ia throughout
considerable. 73 Whirlpools. — Calms. — Whfrlpoola are produced by opposing tides,
winds, or currenta, but the former most generally. They are rare m aU seas, and
not by any means so destructive now as they seem to have been in ancient
timea, when the principlea of navigation were less understood.
Although the greater part of the ocean is disturbed constantly by these
various causes, there are not wanting very extensive areas, especiaUy within
the tropica, and far from land, when dead cahna prevaU, and the aea remaina
for daya in a atate of unruffled stUhiess. The low flat tidal wave ia then so
large, and so regular in its heaving, that it seems loat, and thus an appear
ance of perfect quiet is presented.
74 Inland Salt Seas. — Bays and Gulfs. — Although we have afready had
occasion to allude to thoae deep inleta of the aea that occur in various parts
of the world and form inland seas, it is stUl necessary to refer to them again
in some little detail, to give an idea of thefr comparative dimensions and
importance. Of the inland seas connected with the Atlantic, the Mediterranean ia the
largeat and the most beautiful. It occupies 950,000 square mUes, but is
nearly dirided into two seas by the projecting land of Italy, continued by
shaUows to the opposite coast of Africa. The temperatnre of the water is
higher by 10° or 12 than that of the Atlantic, and the evaporation is exces
sive. It ia one conaequence of thia and of the comparative amaUness of the
river drainage emptying itself in the Mediterranean, that ite watera are as much
as four timea as salt aa the ocean. Many parts are exceedingly deep.
The Baltic ia a long narrow inland sea, occupying about 200,000 aquare
miles in the cenfre of northem Europe, and receiving the drainage of more
than a fifth of the whole continent. Its depth nowhere exceeds 115 fathoms,
and is generaUy not more than forty to fifty fathoms. It is one-fifth less salt
than the ocean.
The Black Sea, the Sea of Azof, the Caspian, and the Aral, together
form one depreaaion, which is only partly fiUed with salt water. The whole
area of water in the two former lakes is near 250,000 square miles, and in
the Caspian 180,000 square miles. The watera are brackish; the depth,
especially of the Caspian, is considerable, but decreases towards the ahorea
gradually, and in terracea.
Baffin's Bay, twice the aize of the Baltic, and Hudson's Bay, also of vast
dimenaiona, penetrate the North American continent at Davis' Straite, whUe
the Gulf of Mexieo, occupying 800,000 square mUes, and the Caribbean Sea,
whose area ia more than a miUion and a quarter miles, are stUl more extensive
indentations nearer the equator, shut in by islands, and resembling in this
respect the YeUow Sea, the China Sea, and the Sea of Japan, on the east coast
of Asia. 7.5 Springs. — A glance at the disfribution of water upon the Earth wiU
show that there are two very distinct parts of the subject, one of which we
have already considered — namely, the phenomena of the great mass of salt
water forming the ocean and ita branches, — whUe the other, relating to fresh
water, stUl remains to be considered. 'This aecond group of phenomena ia
alao twofold, including thc aourcea whence the ft-esh water upon the Earth ia
derived, and alao the brooks, streams, and rivers which convey the water across
the land, and pour it iuto tbe sea. Lakes of fresh water, and other accumula
tions dependent on tho form of land, alao require somo consideration.
The firat commencement of running T\-ater upon tho Earth's surface is

HYDROLOGY. 239
generaUy from springs, which issue occasionally from hUl sides, sometimes from
crevices in the Earth of no great magnitude, but sufficient to allow of the
out-pouring of a large body of water, and sometimes from large natural
cavities in very considerable quantities. However little these diflerent
sources may seem to have reference to the rain falling on the surface of the
Earth in thefr vicinity, they are, in fact, with very few and unimportant excep
tions, thus derived. It is only a part of the rain that runs oil directly from
the surface into sfreams and rivers, and thus manifestly sweUs thefr magni
tude; and although no doubt this quantity is increased by that portion
which, falling as snow, and coUected on mountain-tops in the colder parts of
the year, is graduaUy melted in the warmer seasons, there stUl remains a very
large proportion. A portion of this again is soon received into the atmo
sphere by evaporation, but a very considerable quantity sinlcs down within
the crust of Earth, and is conveyed along underground, re-appearing in the
springs afready aUuded to. The absolute quantity of rain faUing upon the
Earth is, as has been afready stated (see arite, p. 210), exceedingly great, and
that portion of it which runs off to the sea by means of rivers in the west
of Europe, is aupposed not to exceed one-third, although doubtless very
much greater in climates where the rain faUs more heavUy. The proportion
that amka beneath the surface, and re-appears at a distance, must also be
large, so that, on the whole, the actual cfrculation of fresh water upon
the globe, evaporated fr-om the ocean, conveyed through the afr in clouds,
and falUng upon the land as rain, is important, not only as affecting the
fertiUty of the Earth, and its adaptabUity as a habitation for organic beings,
but also absolutely in its effect upon the physical features of the Earth. This
latter subject wUl requfre careful consideration in a separate chapter.
76 Biver Basins. — It wUl be at once e-rident that so far aa rivers depend
for thefr suppUes on the dfrect acceaaiona they obtain from aurface water, the
whole area of the land may be divided into districts, each of wluch, in con
sequence of the form of the enclosing high ground, conveys aU the water that
falls upon that diatrict, either into a depreaaion within its area forming
a lake, or into a channel which conducts the water to the ocean. The whole
Earth may thus be divided into ocean beds and river baaina. Almoat aU the
running waters or rivers of the globe of considerable importance, commu
nicate dfrectly or indfrectly with the ocean, sometimes, indeed, passing through
and being apparently lost in lakes, but ultimately fiowing mto that graud
receptacle which has suppUed the water, and which must again receive it.
This is not, however, invariably the case, and thua we have oceanic and
continental systems of river baaina. These are both so important that we
must now proceed to consider them in some detaU.
It ia a weU known fact, frequently determined by actual experiment, that
a much larger quantity of rain, cceteris paribus, falls on hUls and high plains
than on the lower plains, and hence it arises that the high table-lands and
mountains of every district are even more dfrectly concerned in the natural
drainage than might at first be supposed, and thua it also reaulta that the water
shed, or that line along high ground which determines the ultimate direction
of the rain that faUs, is an important element in su«h considerations as
those we are now entering upon. If we look upon a map of the world, or a
good globe, we find there must be natural divisions forming those groups or
basins to which we have aUuded, and which, as we have already remarked,
are of two kinds, one communicating immediately with the ocean, iuto whieh
the rivers empty themselves, which may therefore be caUed oceanic river
systems, including each of them a number of rivers ; and another, including
what may be caUed continental river systems, forming large basins, in which the
drainage is confined entfrely or chiefiy within continental fracts of land, without
proceeding to the ocean. In every case, the springs, brooks, and rivulets whose
waters confribute to the formation of a single river, and the land whioh is
drained by theae various water-courses, form the area of drainage, and the
line inclosing this area forms the water-shed.
We proceed now to conaider the principal river basina in various parts of

240

PHYSICAL GEOGRAPHY.

the world, and these we may regard aa forming eight diatmct groups— namely,
the groups of the Atlantic, Pacific, Indian, and Arctic Oceans ; those of the
Black Sea, the Mediterranean, and the Caribbean inland seas, the latter
including the Gulf of Mexico; and the great contmental groups, of which the
chief is m Central Asia, where a number of rivera empty themselves into the
Caspian Sea, the Lake of Aral, and the lakes in the eastem part of Cenfral
Asia, in the desert of Gobi, without reaching the ocean.
77 Biver Systems in the Atlantic Group. — The Atlantic group includes
a considerable number of river systems of great importance, both in Europe,
Africa, and America, and the foUowing table gives a connected view of the
extent and relative importance of those amongst them which are beat known.
Peincipal Rivee Systems in the Atlantic Geoup.

Names of Rivek Systems.

Extent of
river basin in
square iniles.
(Greographical.)

In Geographical Miles.

Direct dis
tance of
river from
source to
mouth.

Extent of
development of stream.

Extent of
windings of
stream.

I. EuBOPEAN RiVEES.
Neva 
Rhine 
Vistula 
Elbe 
Oder 
Loire 
Dwina 
Niemen (Memmel) .
Douro 
Garonne ....
Seine 
Tagus 
Guadiana ....
Guadalquiver . . .
Weser 
Minho 
Pregel 
Thames 
II. Ameeican Rivees.
Maraiion (Ajnazons)
La Plata ....
St. Lawrence & Lakes
Tocantins .
Orinoco . .
St. Francisco
Paranahyba
Essequibo .
Delaware .
Connecticut

67,200 P
65,28056,640
41,860 39,04033,94033,44032,180
29,250 24,450
22,620 21,76019,36015,04013,120
11,840 5,9205,000

1,512,000 886,400297,600284,480
252,000 187,200115,200 61,650 8,7008,000

315?360
280344280320280240
260200220360210 180
200 108 60
112

1548
1028 860990

i?

872560350180
231

440? 600520681
480520560
460440320340
480
420 260280 192100
192

308019201800112013521400 744420265270

128
240240340
200200
280220 180120
120 120180 808056
40 80

1562 892
940 130
984 528 184 70 8539

ini-^frt^^riin^-, ""i™ °^ development ofa stream, is meant its length from source to mouth,
Z, v^^^rt M,„ ™"f '"f "n'j turnings. This, compared with the direct distance between thc
fXn.n tL^w^ !• """"" ^^^ ''°"""" "*¦ "'^ windings, and enables us to determine the
nolonlv T/r i„r,„.^''™/ f,^^™^ 0° "8 district. But to understand this, we have to consider
uot only tho length of the princ.pul channel, but also Uie surface extent of its tributary

HYDROLOGY. 241
Of the rivers mentioned in the above table, the Bhine takea its rise in the
Alpa from two principal aources ; one of them on the north aide of the St.
Gothard, from a glacier at the height of 7650 feet, the other from the
Rheinwald glacier, near St. Bernardin. The river has a rapid decUvity to
the Lake of Constance, on emerging from which, its bed is suddenly depressed
at the celebrated falls of Schaffhausen, and the river then runs weatward
to Basle, whence, turning northwards, it is navigable to the German Ocean,
being interrupted only in passing through the narrow defiles between Bingen
and the town of Bonn. The chief tributaries to the Rhine are the Mosdle,
the Maine, the Necker, and the Meuse.
The Elbe rises on the westem slopes of the Riesengebfrge, from upwards
of thirty springs, one of which has an elevation of 4500 feet, but the greater
part of this river mns through a very flat country, and its estuary is encum
bered by sand-banks.
The Neva is, with the exception of the Rhine and Rhone, the only im
portant European river wbich is connected with considerable lakes. It riaes
m the hUly disfrict extending between the Volga and the Dwina, and thence,
imder various namea, proceeda northwards to the lakes Onega and Ladoga,
entering the Gulf of Finland at St. Petersburgh. Although ita river basin
is of great extent compared with that of moat of the European rivers, the
Neva preaenta few points of interest in Phyaical Geography. The remaining
European ayatems are also not remarkable for any physical peculiarities, and
vriU be again aUuded to in the Descriptive part of this work. The rivers of
the British islands drain only smaU river basins, those of the Severn and
Thames being somewhat smaller than that of Pregel ; they also are chiefly
interesting in reference to Descriptive and PoUtical Geography.
It wUl be at once observed, on reference to the above table, that the river
baaina in the New World are enormously larger than those in the Old. The
Maranon, or Amazons, alone, has for its area of drainage a disfrict nearly
three times as large as that of all the European rivers which empty them
selves into the Atlantic ; this vast river, the largest on the globe, is, m some
E laces, six hundred feet deep, it is navigable more than two thouaand mUea
rom ita aource, and is nearly one himdred mUes wide at its mouth. More than
twenty superb rivers pour their waters into it, and the torrent that rushes
from it into the ocean ia borne along upon the surface in nearly a dfrect line,
in spite of the currents that cross its course at right angles, its stream ren
dering the water perceptibly less salt than that of the ocean, at a distance of
more than three hundred mUes from the shores of America.
Although no river approaches in magnitude the gigantic Amazons, the
river Plata, the fourth largest in the world in tbe extent of its river basin,
and combining two important rivers, the Parana and the Uruguay, is stUl
worthy of more than passing notice. Like the Amazons, it receives at its
affluence rivers which, in extent and magnitude, axe of the firat class. At
Buenoa Ayres, two hundred mUes from its mouth, and along its whole course
from that river to the sea, its breadth is never lesa than one hundred and
seventy mUea. It is aubject to dreadful inundationa, the Parana, after the rains,
rising every season and covering not leaa than 36,000 aquare miles of land. The
water ia exceedingly muddy, and can be traced in the Atlantic to a distance
of two hundred mUea from the coast of America.
The five next river systems of greateat importance in South America, the

channels. Thus, the direct distance ofthe Ehine is shown by the table to be 360 miles, or 80
miles more than the Vistula ; the development of its course is also 80 miles greater than the
Vistula, but its windings are less, notwithstanding that the area drained by the former is much
greater than that by the latter river. This table, and the deductions here expressed, as well
as other tables of like nature %vhich succeed, are given on the authority of Mr. Johnston's
edition of Berghans's Physical Atlas. The measurements are in geographical miles, of which
sixty are reckoned to a degree of latitude. The geographical mile contains 6086 feet, and the
British statute mile 5280 feet. B

242 PHYSICAL GEOGRAPHY.
Tocantms, the Orinoco, the Paranahyba, the Francisco, and the Essequibo, do
not together drain a greater area than the Plata and its tributaries. The
Orinoco ia, however, intereating for another reaaon than ita extent, as it
exhibits in the upper part of its course the very rare example of a natural
canal, uniting it with another great river system. This canal, called the
Casiquiare, connects the Rio Negro with the Orinoco. Its length is 120
mUes direct diatance, or 176 including the wmdinga, and ita width ia 100
yarda where it branchea from the Orinoco; but on approaching ita junction
with the affluent of tbe Rio Negro, which forma the connecting Unk of the
two systems, it amounts to nearly 600 yards. In addition to this curious
network complicating two great and diatinct river systems, the Orinoco in
its detours follows such a direction that the course ofthe stream is apparently
turned, and although the general dfrection of the stream is north-east, its
mouth ia found almost in the same meridian as some of its sourcea.
The largeat of the North American river aystema communicating dfrectly
vrith the Atlantic (tbat of St. Lawrence,) is much more remarkable for the
great chain of lakes through which it pasaea than for any other phenomenon
it preaents. Of the 297,600 square miles which it drains, no less than 94,000
are covered with water, and the river runs through these lakes, bearing
different names, and resembling rather a series of lake sfraits than any
continuous stream. Of theae lakes, the largest is Lake Superior, whose
length is 400 mUes, and mean depth 900 feet, and the smaUest (with tho
exception of Lake St. Clafr) is 100 mUes in length and 500 feet deep. The
Lake Superior is the westernmost of the whole chain, and is the largest body
of fresh water in the world. It discharges its waters through the sfrait of
St. Mary into Lake Huron, whieh receives also the waters of Lake Michigan,
the next in magnitude to Lake Superior. The waters of Lake Huron (which
is 240 miles long and 100 feet deep,) pass into Lake Erie, and thence, by the
Niagara River, into Lake Ontario, forming in its course of 33J nules the
celebrated FaUa of Niagara. The River St. Lawrence, which draina aU these
lakes, ia not known by that name tiU after paasing Monfreal, but then,
forming a broad estuary, it enters tbe Gulf of St. Lawrence, at Gasp^ Point,
by a mouth more than 100 mUes in width. The other principal rivers of
North America, belonging to the Atlantic group, offer nothing especiaUy
worthy of remark in this place.
The depression occupied by fresh water in the great lakes of the St.
Lawrence system in North America is a phenomenon of conaiderable
importance in the physical geography of this part of the globe. The principal
lakea, Lake Superior, Lake Michigan, and Lake Huron, have a mean depth
of nearly 1000 feet, and cover an area of 75,000 square mUes; thefr surface
is considerably less than 600 feet above the sea, and thus thefr bed has a
mean depth of more than 400 feet below the level of the ocean. Lake
Ontario, whose elevation above the sea is only 230 feet, but whose depth is
500 feet, presents to ua another area of 6300 square miles, 270 feet below the
sea level. This remarkable depression is paraUeled by one other simUar case,
that which has been observed to the east of the Mediterranean, where the
Dead Sea occupies a hollow more than 1000 feet below the sea level, and the
whole interval between the Caspian Sea and the Lake of Aral is a depression
from which the ocean has been recently drained.
In addition to the rivers already described aa emptjdng themaelvea into the
Atlantic, we have also aeveral on the coast of Africa. There are aome of
them more important, and connected with larger river basms than the
largest of those occurring in Europe, but they are much less completely known.
The largest of them is the Quorra, or Niger, which, though not so extensive
aa the NUe, has, in aU probabUity, a more extensive river basin. It ia
suppoaed to riae in about 9° N. latitude and 9^° W. longitude ; but there
are probably more aources than one of ao extensive a stream. It fiows along
a courae of as much as 2300 mUea, and receives many very large affluents.
Ihe current ofthe river ia moderate, and offers no impedimenta to narigation.

HYDROLOGY.

243

and the river flows through more than one considerable lake. The Senegal,
850 mUes in length, which draina two lakes and an extensive disfrict, is the
next largest river on this coaat ; and the Gambia, whose course is eatimated
at 600 mUes, is also connected vrith a river basin of great extent. The
Gareep, or Orange Biver, near the thirtieth paraUel of S. latitude, has a long
course through the table-lands of South Africa; and the Zayre, or Congo
Biver, is a very important afream. Both the latter are, however, too Uttle
known, either with regard to the length of thefr course, or the extent of the
country they drain, to enable us to offer tabular statements resembling those
given above of the European and American sfreams.
78 Biver Systems qf Inland Seas opening into tlie Atlantic. — Let us next
consider those river systems which empty themselves into the great inland
seas of the Atlantic Ocean. The general facts conceming them are given in
the annexed table : —

Namt. of ErvEB.

Area of the
river basin in
square miles.

Direct dis
tance of river
in miles.

Extent of
development of river.

Extent of
windings.

Mediteebanean Geoup.
NUe 
Po 
Rhone 
Ebro 
Euxine Geoup.
Danube 
Dnieper ....
Don 
Dniester ....
Geoup of the Gule
OF Mexico and
Caeibbean Sea.
Mississippi-MissouriEio del Norte . .
Magdalena . . .
Motagua ....

520,200 29,95028,16025,100
234,080 169,680 168,420 23,040
982,400 180,000 72,000 7,040

1320 232
248268 880548408 360
1412
1220 560 196

2240 352
560
420
14961080 960 440
3560184« 828260

920 120
352 152
616532 552 80
2148 620268 64

Of the river systems of the Mediterranean group, that of the Nile is by
far the most remarkable, from the great regularity and importance of the
annual inundations in the lower part of its course, wmch fertUize Egypt. The
absence of permanent sfreams aa affluents for the last 1200 miles of its
progreas to the Mediterranean ia alao a remarkable fact. At ita enfranee
mto the Mediterranean, thia noble river expanda into a delta, which has been
for a long period rapidly and steadUy increasing. The sources of the NUe
have been the objects of research to scientific traveUers, and it would seem
that one of its two principal head-sfreams rises in the table-land of Abyssinia,
but the other is supposed to take its origin in the Mountains of the Moon.
As it entera Egypt, the NUe runs in nine or ten cataracts or rapids, over a
auccession of terraces ; but these cataracts of the principal stream are not
so remarkable as thoae of the Tecazze, one of ita tributaries.
The Po, draining a very considerable area of Northern Italy, is chiefly
remarkable for its torrents and the delta at its mouth. It rises on the eastern
b2

244 PHYSICAL GEOGRAPHY.
side of Monte Viso, about 6000 feet above the sea, and is a rapid and irre-
gular stream.
The Bli07ie riaes in the Rhone glacier, 5500 feet above the aea. After
passing through the Lake of Geneva, it enters France, and paaaes southwards
into the Mediterranean. It is a very rapid stream, fiowing at the rate of 120
feet per minate.
The Danube riaea in the Black Forest at an elevation of 2850 feet above
the sea, and running through the plains of Bavaria, it receives the two
important rivers of the Isar and the Inn, proceeding from the Tyrolese Alps.
For a considerable part of its course, it fiows in a narrow vaUey, between two
mountain ridgea ; but, after passing Vienna, it proceeds through open flat
plains, except where in the celebrated defUe of the iron gate, it crosaes the
eaatern continuation of the great Alpine chain. It entera the Black Sea by
no less than aeven mouths, passing through an extensive swampy district,
forming a delta.
The Dnieper and the Don, as well as the Dwina and the Volga, have
thefr sources in low, flat districts, and present nothing remarkable in their
course. The D7iiester rises on one of the declivities of the Carpathians, and
after running with a rapid current, and vrith a considerable body of water
during the whole of its course, enters the Black Sea by a smaU delta.
The American rivers emptying themselves into the inland seas ofthe Atlantic
are, Uke those which enter directly into that ocean, far more important in thefr
magnitude and the extent of thefr drainage, than thoae of the Old World.
The Mississippi, taken with ita fributaries, forma the largest river syatem in
North America, and one of the greateat in the world. The parent sfream
receives in its course two rivers, the Missouri and the Ohio ; the ifrst of
which, coming in from the north-west, greatly surpasses the Mississippi
itself, whUe the other is alao a gigantic river, and the largeat of ite eaatern
affluenta. The Misaouri riaes in two branches within a mUe or two of the
sourcea of the Columbia, and runs for 3000 mUea before it joina the Mia-
sissippi ; it ia a very rapid river in the whole of ita courae, and itself receives
several important affluents. The average velocity of its current may be
estimated at 4j mUes per hour, but in times of freshets, ia accelerated to h\
mUes per hour. The Mississippi has its source in two smaU lakes, about
1500 feet above the level of the sea, in latitude 47° 10' north, and longitede
96° west. It runs through Lake Winnipeg, and flowa with great velocity,
forming several smaU faUs. Before the waters of the Missouri mingle with it,
it receives the St. Peter's river, the Wisconsin, the Illinois, and other sfreams,
and its vaUey is bounded by high bluffs, intersected by deep ravines. After
the junction of the Miaaouri, the courae of the united sfream becomea gentle,
and the vaUey more open ; and in ita progreaa towarda the Gulf of Merico, it
continuea to receive veiw important rivers, of wluch the Arkansas and the
Red River are those which have the longest courae ; the moutha of the
Mississippi project far into the Gulf of Mexico, in a long and very remarkable
delta, on which is buUt the city of New Orleans. Near ite mouth, this vast
river becomes a rapid, desolating torrent, loaded with mud. Ite violent
floods, produced by the melting of snow in high latitudes, sweep away whole
foreata, rendering the navigation very dangerous ; and the frees matted
together in masses many yards thick are floated down, and at length
deposited over the delta and in the Gulf of Mexico, in an area of many
hundred square miles.
The Bio del Norte is the largest of the Mexican rivers, but is too fuU of
rapids to permit of any kind of navigation for a great part of ite courae. It
rises in 40° north latitude, near the aourcea of the Arkansas, and of the Rio
Colorado. Like many other of the great rivers of the world, it is subject to
occasional freshets, but these do not extend to ita lower com-ae.
The Magdalena and the Motagua drain, the former, the north-western
extremity of South America, the latter, the promontory of Yucatan. The
Magdalena riaea in tho central chain of the Andes, and receives several

HYDROLOGY.

245

sfreama in its course ; the Motagua rises in the mountains near Guatimala,
and flows into the Gulf of Honduras.
79 The Biver Systems ofthe Arctic Ocean. — The foUowing table expressea,
as far as they are known, the important facts connected with the Arctic
system of rivers : —

Direct dis

Extent of
tance of
Extent of
Extent of
Names of Eiver Systems.
river basin in
rivers from
development
windings of
square miles.
source to
mouth.
of streams.
streams.
Asiatic Rivees.
Obi 
924,800
1276
2320
1044
Yenesei
784,530
1228
2800
1572
Lena
594,400
1280
24flO
1004
Kolyma
107,200
440
800
208
Dwma .
106,400
380
864
484
Indigfrka
86,400?
560?
908?
348
Olenek .
76,800
600
1000
400
Anadfr .
63,360 P
...
...
Petchora
48,800
360
600
240
Mesen .
30,580
...
...
N. Ameeican Rivees.
Mackenzie ....
441,600
964
2120
1156
Saskatchevan . . .
360,000
924
1664
740
ChurchUl ....
73,600
668?
848
180
Albany 
52,800
380
560
180
Of the Asiatic rivers that empty themselves into the Arctic Ocean almost
aU are, as wdU be seen, of great magnitude and extent, but the nature of the
country over which they pass, consiating for the most part of dreary plains,
and the northern decUvitiea of extensive table-land, conspfrea to render them
almost useless for the support of vegetation, and therefore for the abode of
man. The Obi and the Irtish, forming together the largest river of the Old
Continent in the extent of its drainage, if not of its development, has so
smaU an absolute elevation when it leaves the Altai mountains, from which it
takes its rise, that for a distance of one thousand two hundred mUes it has a
faU of only four hundred feet, and although the bed of the river ia very deep,
the current ia necessarUy alow, and ita banka are readUy and constantly over
flowed, forming immense marahea characterising a large part of Siberia.
. The Obi is the moat westerly of the three great rivera of Siberia, and the
Yenesei, which draina the district to the east of the basia of the Obi, is Uttle
inferior in the magnitude of its basin, and has even a greater extent of
development ; some of its branches, wbich are numerous, have a very rapid
course, but below Irkuktsh the current graduaUy decreaaea in rapidity. At
ita mouth, this river enlarges into an estuary twenty mUes wide, and more
than two hundred mUes long. In its upper course, it pasaea through the Lake
of Baikal, the largeat and most remarkable of aU the mountain lakes.
The Lena, the most easterly of the Siberian river systems, takes ita rise
from mountaina a Uttle to the weat of the Lake of Baikal, and thence proceeds
first in a north-easterly and then in a northerly dfrection to the sea. It is
narigable for a considerable part of its courae, receiving a number of impor
tant tributariea, and terminates in an extensive delta fraversed by several
arma of the river, three of which are navigable. Both it and the Yeneaei are
frozen near thefr mouths for nearly nine months of the year. The other
246

PHYSICAL GEOGRAPHY.

rivers of Asia, emptying themselves into the Arctic Ocean, are of inferior
extent and importance.
The Mackenzie is the largeat river system which contributes its watera to
the Arctic Ocean in the weatem hemiaphere. It ia formed by the umon of
several smaU streams, each designated by its own name, which rise on the
eastern alopea of the Rocky Mountains, and after passing through Athabasca
Lake, form Slave River, which again on lea-ring Grreat Slave Lake is caUed the
Mackenzie. The Saskatchevan rises vrith two branchea in the Rocky Mountains, and
these uniting at a diatance of four hundred and fifty mUes from thefr aources,
run through Lake Winnipeg, and thence continue under the name of the
Nelson River, into Hudson's Bay. The Churchill is another stream nearly
EaraUel, passing through and draming aeveral lakes, and at length terminating,
ke the Saskatchevan, in Hudaon Bay.

80 Rivee Systems

OF THE Pacific.

Name of Eivee.

Extent of river
basin in square
miles.

Direct dis
tance of
rivers.

Extent
of development.

Extent of
windings.

Asiatic Rivees.

Amour ....
Yang-tae-Eiang . .
Hoang-Ho ....
Tche-feiang . . .
582,880 547,800537,400 99,200
120015501150 480
23802880 2280 960
1160
13121160 488
Ameeican Rivees.
Columbia ....
Colorado ....
194,400169,200
576 512
1360 800
784
288
The river aystems of the Pacific Ocean are, as wUl be seen, of very great
extent and importance in the drainage of Asia, but mnning through a
territory so jealously guarded as China, very httle is known of the country
through which they pass. The Hoang-Ho and the Yang-tse-Kiang have thefr
sources and thefr mouths in very cloae approximation, both riaing in the
extensive terraces on the eastem slope of the table-land of Cenfral Aaia, and
emptying themaelves into the aea between latitudes 32° and 35° N. These
rivers are tidal to the extent of four hundred miles from thefr mouths, but
they bring down with them a vast quantity of mud, which they deposit chiefly
at the entrance of the YeUow Sea. They are separated during a great part
of thefr course by a mountain ridge, which serves as a water-shed for a
distance of several hundred miles.
The Amour, the thfrd important river of Asia, empties iteelf into the
Pacific by the Sea of Okhotak. It riaes in the Russian dominions, but runa
for the greater part of its course through China ; and there passes through a
number of lakes, receiving many unknown and hitherto unnamed rivers,
whith take their rise from the edge of the great table-land of the Gobi. The
Tche-Kiang ayatem draina the fract of country aouth of the Yang-tee-Kiang,
and ita moat important afream is best known under the name ofthe Cambodia
river. This river, after traversing elevated plains, where it is narigable,
rushes through the mountain barriers which border tliese plains, and crossing
a wide valley, enters the Gulf of Siam by three principal arms.
The only important river of North America which contributes its waters
to the Pacific Ocean is the Columbia, or Oregon, which rises in the most
rugged steeps of the Rocky Mountains. It forms many rapids and cataracts,
and ia only navigable aa far as Point Vancouver, a distance of about one
hundred mUes, to which pomt the tide reaches. The Colorado descends from
HYDROLOGY.

247

the aouth side of the water-shed in latitude 41°, from the north side of which
many of the tributaries of the Columbia take thefr rise, and after a consi
derable course enters the Gulf of California, teaversing a country almost
entirely unknown. 8i RivEB Systems of the Indian Ocean.

Extent of

Direct dis

Extent

Extent of
windings of

Name of Eiveb.

river basin
in square

tance from
source to

of develop
ment of

miles.

mouth.

streams.

aLretiiusi

Ganges, including "I
Bramahpootra . J

482,480

824

1680

856

Irawady ....

331,200?

1100

2200

1028

Indus 

312,000?

900?

1960?

864

Menam 

216,000?

620?

940?

320

Euphrates ....

195,680

600

1492

892

Godavery ....

92,800

540

748

360

Bastna 

81,600

440

688

228

Of these rivers it may be steted generaUy, that although the Gangea and
Bramahpoofra drain the largest area, the Irawady, which waters the Birman
empfre, and falls into the Bay of Bengal, and whose sources are in the same
chain of mountains with those of the Bramahpoofra, has both a longer dfrect
distance and a greater extent of development. Ita course, however, for the
first eight hundred mUes, is through countries not familiar to Europeans,
although it is known to pass through a noble and rich plain, containing no
less than four capital cities. From the city of Ava to its delta, which is very
extensive, and presents fourteen principal channels, the river is more than
four mUes broad, but is encumbered vrith ialands. It receives several
important affluenta.
The Ganges and Bromialipootra form a remarkable double syatem of
rivera, -^^hoae aources are at great distances, but which converge to a
common delta at the head of the Bay of Bengal. The Ganges commences
at once in a very rapid stream, not less than forty yards across, proceeding
from a huge cavern, in a perpendicular waU of ice. Thence it flows in a
south-easterly dfrection through the plains of Bengal, receiving in its course
a multitude of tributaries, of which no lesa than twelve are more conaiderable
than the Rhine. The Bramahpootra takea its riae in the north of the
Birman empfre, probably from the eastern extremity of the Himalayan chain,
and after winding for five hundred mUes through Upper Aaaam, it enters the
plains of Bengal and unites with the Ganges, about forty miles from the
coast. The united delta of the two sfreams commences two hundred and
twenty mUes in a dfrect line from the Bay of Bengal, and gxtends for more than
two hundred miles along the coast. The volume of water discharged by the
Bramahpootra during the dry aeason is not less than 150,000 cubic feet per
second, whUe that discharged by the Gangea, in the aame time and under
aimUar cfrcumstances, is only 80,000. The quantity of mud brought down
by the joint sfream through the delta, in the wet aeaaon, is not less than
600,000 cubic feet (20,000 tons) per second, and the Sunderbunds, an
innumerable multitude of river islands, forming a wUderness of jungle and
forest frees, mark the extent to which auch aUuvial mud has been accessory
in producing the preaent appearance of the moutha of these rivers.
The Indus and the Sutlej tate thefr rise in the Snowy Mountains at the
westem extremity of the Himalayan chain, and both, fed by streams of
melted snow from the northem side of this chain, flow westwards along the
extenaive valleys of Thibet. The two streams unite in the Punjab, and thence
to the ocean the Indus does not receive a aingle accessory, but pasaea through

248 PHYSICAL GEOGRAPHY.
a sterile desert. It empties itself into the ocean by a considerable delta, 60
mUes in length, and occupying 120 mUes of coast.
The Euphrates and Tigris form together the only important river system
in Western Asia. The former rises in the heart of Armenia, and after
running over a great extent of table-land, descends in rapids through the
Taurua Mountaina to the plaina of Meaopotamia. The Tigria riaea further to
the east, and after piercing the same chain of mountains at Mosul, descends
also to the plains of Meaopotamia. The two atreama unite near the city of
Bagdad, after which they run 150 mUes, in one stream, to the Persian Guff.
82 Bivers not communicating with the Ocean. — It now only remains to
consider those rivers which, terminating in great inland seaa of freah water,
and not proceeding thence to the ocean, form complete systems of drainage,
entfrely confined to the interior of extenaive fracts of land. Examples of thia
kind occur in Africa and America to a amall extent, but are nowhere so
remarkable as in Central Aaia, where nearly 1,2{K),000 aquare mUea of
country are drained by aix river systems, three ofwhich run into the Caspian,
two into the Sea of Aral, and the sixth into a comparatively small lake, north
of the great desert of Gobi. Another tract, nearly equal in extent to half
this area, and continuous vrith it, appears to have a multitude of sfreams,
which are either lost in smaU lakea after proceeding for a short diatance,
or disappear entirely in tho great sandy deserts which they fraverse.
Of these rivers, the Volga draina an area of nearly 4£)0,000 aquare mUes,
and, with tbe exception of the Danube, haa the largeat volume of water of
any river in Europe. The extent of ita development amounte to 2400 iniles,
and ita source (in latitude 57° N.) is nearly 1000 mUea from the Caspian
Sea, into which it discharges itself by no less than sixty -five moutha. The other
important river aystem terminating in the Caspian Sea (the Ural) rises in
the southern Ural chain, in latitude 55° N., at an elevation of 2132 feet above
the level of the sea. The whole courae of the river, including ite windings,
is probably not less than 900 mUes. It forms, for a considerable part of its
course, the boundary line of Europe, and, towards the south, ia enclosed by
steppes, and fiows in a bottoni varying from half-a-mUe to two and a half
mUea in width. It enters the Caspian by a smaU delta, the ialands of which
are covered with salt swamps.
The principal feeders of the Sea of Aral are rivera not inferi* to the
largeat in Europe ; one of them, the ancient laxartes, is, in the area which
it drains, of somewhat greater importance than the Danube, and ite develop
ment ia not less than 1200 mUes. It fiows from the east, through a country
tolerably fertUe, especiaUy near its mouth, but that fertiUty is confined to a
narrow band, and is bounded by deserts perfectly arid. The other river, the
Oxus of the ancients, now caUed the Amori, enters from the south. It drains
nearly 200,000 square mUes of country, has an extent of development of
1400 mUes, and the dfrect distance from its source to its mouth is more
than 800 miles. The only other important river in the continental system of
Central Asia ia that which empties itself into the small lake of Lob, proceeding
from the weat eaatwarda. Little is known of this disfrict, but the area
drained ia estimated at 177,120 square mUea, and the development of the
stream at 1080 mUes.
There are not wanting continental systems of drainage in the New World,
but they are comparatively smaU and unimportant. In North America, a
smaU area of this kind occurs between the Gulf of California and the Rio del
Norte; and the elevated lakes of the great plateau of the Andes, between
latitude 13° and 31° S., receive a number of sfreams which do not afterwards
proceed to the ocean. The Lake Titicaca, the largest in tbe South American
continent, occupying an area of about 4600 square mUes, and its surface
12,800 feet above the Pacific, ia the recipient of the sfreams of a considerable
district; these proceed by the River Desaguadero to a distence of about
180 miles into a small lake, and are there loat. The Cataleua Lake, the Tor
Lake, the Bianca Lake, and others in the same plateau, offer sunUar examples
on a much smaller scale.

241)

CHAPTER VI.

ATMOSPHERIC AND AQUEOUS ACTION.
$ 83. General nature of atmospheric and aqueous action. — 84. Changes produced by atmo
spheric action. — 85. Changes directly eflfected hy alterations of temperature and exposure
to cold. — 80. Glaciera and icebergs. — 87. Changes produced by the eroding action of
moving water. — 88. The transporting and distributing action of moving water. —
89. Changes produced by water acting by the aid of substances held in solution. — 90. Indi
rect efiects produced by water.
/~1ENEBAL Nature of Atmospheric and Aqueous Action. — The action of
\jr the afr loaded with a larger or amaUer quantity of water, and constantly
changing in temperature, and the incessant motion of water in its varioua
forms, whether as it pasaea under ground and emerges in springs, or moves
along the surface, conveying particles of solid matter and depositing them
in some new place, produce, on the whole, a very great amount of change
upon the Earth's aurface, greatly modifying the physical featurea of the globe,
and influencing thoae conditions essential to the well-being of animal and
vegetable life. A consideration, therefore, of what may thus be called atmo
spheric and aqueous action is an essential part of Physical Geography.
The mechanical action of water exhibits results in aeveral difterent waya;
for in one part of the world we find the aea with ita reatleas waves beating
againat the shore, constantly removing a portion of the coast, and depositing
it aa mud in the immediate vicinity; whUe in other places, rivera carry along
with them a quantity of earthy matter, manifested by their turbid appear
ance, and thia earthy matter cannot faU to be deposited where the progress
of the river is checked as it passes through nearly level plaina, or when ita
sfream meets the ocean, and its course onwards is thus completely termi
nated. The water carries mud along with it, however, only for a limited time,
and strictly in consequence of its being in motion. Whenever, therefore,
that motion becomes slower, a portion of the mud is deposited, and where it
is stopped, the remainder must necessarily fall. Thus a river sometimes
terminates in a friangular area of mud, caUed a delta; sometimes banka of
mud, greatly impeding narigation, extend fransversely across the mouth of
the river, and are thence denominated bara ; whUe aometimes there exist only
a multitude of narrow channels, none of them deep enough to be navigable
at the entrance. Where neither of these conditions occur, the mud is gene
raUy removed to a distance by powerful marine currents.
The action of water is not unfrequently dependent on meteorological
changes ; and amongst the most powerful agents of dCBay in cold climatea or
on mountain summits, must be ranked the expansion that takes place in
water shortly before and during the act of congelation. In this way it is
that although in temperate and cold climates the quantity of rain faUing may
not of itself be sufficiently great to produce, by simple mechanical abrasion,
any considerable removal of the soil, yet the severity of the frost and the
inequaUties of the temperature may more than compensate for this diminished
aource of degradation. Hence, among aqueoua changea we have to consider
also the phenomena oi glariers and icebergs, by whoae meana vaat quantities
of broken fragmenta of rock, often of large dimenaiona, are first removed
from the parent rock, and then conveyed by the aaaistance of marine currents
to very considerable distances. We have also to take into consideration the
action of running water, as weU directly and periodicaUy by rivers, as occa-

250 PHYSICAL GEOGRAPHY.
sionaUy by unusual floods. We have, too, to conaider the effect of the sea
upon coaat Unea, and of tidal and marine currents under various cfrcum
stances, whether these take place in the open ocean or in inland seas which
communicate vrith the ocean. Lastly, a certain amount of chemical change
is produced by water, either by acids contained in it, or by the affinity of
water and of the gaaes which it holds in solution for the various substances
it encounters. ... ™,
84 Changes produced by Atmospheric Action. — There is a conatant
tendency in all decompoaed or disintegrated substances to be removed by the
agency of rains and superficial waters to a lower level than they preriously
occupied, and finaUy to be transported into the sea. There is no rock, not
even the hardest, that does not bear some marks of what has been termed
weathering, or of the action of the atmosphere upon it. The amount of surface-
change so produced is exceedingly variable, depending much on local causes.
Thus, one rock may undergo complete disintegration in a certain situation,
though oompoaed of nearly the aame materiala aa another rock of the same
kind, of which the change has been comparatively trifling. When we contem
plate the present surface of our continenta and islands, we cannot but be struck
with the great effects that have been produced upon them by the agente com
monly known as existing causes; and among these effects, the weathering and
degradation of land are very remarkable, attesting a lapse of time far beyond
the uaual calculationa. The tora of Dartmoor, Devon, may be referred to as
excellent examples of the weathering of a hard rock. These are composed of
granite, which, as Dr. McCuUoch haa obaerved, are dirided into maases of a
cubical or prismatic shape. ' By degrees, surfaces which were in contact,
become separated to a certain distance, which goes on to augment indefinitely.
As the wearing continues to proceed more rapidly near the parte which are
most external and therefore most exposed, the masses which were originaUy
prismatic, acqufre an irregular curvilinear boundary, and the stone assumes
an appearance resembling the Cheese-wring (ComwaU). If the centre of
gravity of the maas chances to be high, and far removed from the perpen
dicular of its fulcrum, the stone faUa from its elevation, and becomes con
stantly rounder by the continuance of decomposition, tiU it assumes one of
the spheroidal figures, which the granite boulders so often exhibit. A
different disposition of that centre vml cause it to preserve its poaition for a
greater length of time, or, in favourable cfrcumstances, may produce a
logging stone.' The weathering of these tors is so exceedingly slow, that the
life of man wiU acarcely permit liiTn to observe a change ; therefore the period
requisite to produce their present appearance must have been very consider
able. The surface of the whole counfry round these disfricts atteste the same
great lapse of time. Whatever maybe the nature of the rock, it is dis
integrated to considerable depths ; porphyries, slates, compact sandstones,
frap rocks, — all have suffered; but the valleys appear to have preriously
existed, and the general form of the land to have been much the same as it
now is.
This destruction of the surface is common to most counfries ; and if the
rock so weathered be Umestone, there is, not unfrequentiy, a reconsoUdation
of the parta by meana of calcareous matter deposited by the water that
peroolatea through the fragments, and which dissolves a portion of them.
At Nice, the fractured surface thus reunited is so hard, that, if it occur on
a line of road, it must be blasted by gunpowder for removal. There are
some fine examples of this reconsoUdation upon tbe limestone hUls of
Jamaica ; aa, for example, near Bock Fort, and at the cUfla to the eastward of
the Milk lliver'a mouth.
The felapar contained in granite ia often easUy decomposed, and when
this is effected, the surface frequently presente a quartzose gravel. D'Aubuia-
son mentions that iu a hollow way, wbich had been only six years blasted
through granite, tho rock was entirely decomposed to the depth of three

ATMOSPHERIC AND AQUEOUS ACTION. 251
inches. He alao states that the granite country of Auvergne, the Vivarrais,
and the eastem Pyrenees, is frequently so much decomposed, that the
traveUer may imagine himself on large tracts of gravel.
Some frap-rocks, from the presence of the aame mineral, are so liable
to decompoaition, that there is frequently much difficulty in obtaining a
specimen. The depth to w-hich some rocks of this nature are disintegrated in
tfcnaica is often very conaiderable.
This decomposition ia attributed to the chemical, as weU as mechanical
action of the atmosphere. The oxygen of the atmosphere producea conaider
able alteration in rocks, more particularly observed m those containing iron,
which are thus often reduced from a hard to a soft substance. With the
slow and quiet changes effected by electricity on the surface, we are very
imperfectly acquainted, but most of us have heard of destructive effects
during a thunder-storm, of shivered rocks, and of fragments hurled from the
heights into the vaUeys beneath. In these electrical discharges, the Ughtning
often fuses the surface of rocks. Thus, De Saussure found a compound rock
on Mont Blanc fused on the surface, white bubbles being on the felspar, and
black bubbles on the hornblende. Similar observations have been made by
other geologists in other parts of the world.
At Peninis Point, St. Mary's, ScUly Ialanda, there is a curious example of
that decomposition of granite which antiquaries have termed rock-basins, and
considered the work of the Druida. The Kettle and Pans, as these depres-
aiona are there named, occur in the large blocks of granite on the top of this
promontory ; they are generaUy three feet in diameter, and about two feet
deep; they are mostly circular and concave, but there are others much
indented at the sides. ' Some have perpendicular sides and fiat bottoms,
aome are of an oval form, and othera of no regular figure. Many of the
blocks are six or seven yards high, eight or nine yards aquare, and several of
them have four, five, six, or more of these cavities in them. A large rock,
near the exfremity of this group, has two basins of an immense size, besides
several smaUer ones. The upper and larger one appeara to have been formed
by the junction of three or more large basina. It ia irregularly shaped, and
about eighteen feet in circumference, and six feet deep. \Vhen the water in
this basin has attained the height of three feet, it diachargea itself by a lip
into a lower baain, more regularly formed, the back of which ia about five
feet high, but which ia incapable of containing more than a depth of two feet
of water, owing to the decUvity of the aurface ofthe rock.' As a proof tbat
simUar decomposition aometimea takea place on the sides of a block, thc
author above cited mentions an oval cavity, six feet long, five wide, and nearly
four feet deep, thus situated.
There is scarcely a substance, which, having been exposed to the action
of the atmosphere for a considerable time, does not exhibit marks of
weathering. It wUl even be observed on cliffs of sandstone, in which the
cement variea in induration or otherwiae, producing the most grotesque forma,
which must be more or leas familiar to the leaat obaerving. Variationa in
temperature much assist the chemical decomposing power of the air.*
85 Changes directly effected by Alterations of Temperatu/re and Exposure
to Cold. — We have just seen how rapidly disintegration of solid rocks may
take place by atmospheric agency, and it may readily be imagined that when
during frost, and by a sudden and rapid decrease of temperature, the water
which had percolated into and fiUed narrow crevices, formed near thc surface
by ordinary exposure, was at firat diminished, and afterwards almost
instantaneoualy increased in volume, the rocks would split asunder with
irresiatible violence, and thus the effect be greatly increased. Various
mechanical results are derived both dfrectly and indfrectly in this way, aince

• Delabeche's Manual, pp. 45 — 47.

252 PHYSICAL GEOGRAPHY.
not only are fragments apUt off from large maases of hard rock, but whole
beds are altered in poaition, and way made for the subsequent removal of
others of softer material, to which the running water of warmer seasons is
now able to penetrate. On the shores of very cold seas, the cUffs are fre
quently formed more or leaa entfrely of frozen mud, and the heata of aummer
generally tend to modify them, and even greatly reduce thefr dimenaiona,
while on thefr reconstruction in the succeeding winter, way is made by the
increase of crevices, both in number and extent, for the stUl further deatruc-
tion of the whole maaa.
All the changea and modifications producedbyinequaUties of temperature
may, however, be regarded as destructive, effectmg, even when the change ia
least marked, periodical removals of very large quantities of gravel and
stones by the ordinary streams teaversing a country, and in other cases
tearing away enormous quantities of solid rock, and preparing them for
further tranaport by rivers or ocean currents. It is only where the climate
is more excessive than with us in England, that these modifications can be
seen on a sufficiently large scale to attract general attention. In Rusaia,
towards the mouth of the Dwina, there ia an annual diaturbance of the
banka of that river, which is sufficiently extensive to be worthy of notice,
for we find there long ridges or ledges of atones on the banka of the river
about 30 feet above its summer level ; the water, when at ite height, pene
trates into the chinks of thin beda of horizontal lime-stone, and in vrinter,
becoming frozen and expanding, great disruptions of the rock occur, and
stony fragments, often of large dimenaions, are entangled in the ice. In the
spring the fresh swoUen atream inundates its banks, and so expands the water
that the icy fragments are thrown up 18 or 20 feet above the level of the
stream. In the course of five or six hours, the water wUl rise suddenly
14 or 15 feet, with the ice one compact mass upon it, and when the preaaure
increases, the ice is actuaUy tom asunder, the oraah that reaulte resembling
the roaring of artiUery. What occura on ao considerable a scale in the river
Dwina, and in other Russian streams, has been observed to a yet greater
extent in Lapland, where granitic boulders, weighing several tons, have been
seen suspended like birds' nests in the branches of pine trees, 40 feet above
the summer level of the sfreams ; and in Canada, on me St. Lawrence, as weU
as in the great rivers of Siberia, where the volume of the water is greatly
more considerable, the changes of temperature more complete and more rapid,
and where everything in nature is on a far grander scale, the consequences
are stUl more marked. The packing of the ice in the St. Lawrence ia a phe
nomenon of this kind, and when the broken ioe is carried away by high tides
in the spring, blocks of stone weighing many tons are frequently removed to
a very conaiderable distance. The phenomenon of ground ice, however, or
ice which, in spite of the expansion of water in freezing, remains entangled
at the bottom of atreama, provea that thia action of water in the sohd form is
not confined to districts where the winter cold is excessive, but may extend
even to such latitudes and cUmates aa our own. Where, however, the cfr
cumstances are less unfavourable for the production ot such appearances as
in some of the Siberian rivers, large atones are occasionaUy lifted from the
river bed by the ice amongst them, and thus may be fioated along for a great
distance. Among the results of packed and ground ice may be mentioned
the removal of gigantic blocks of stone weighmg very many tons, sometimes
ahifted several met in a season by the American rivers.
86 Glaciers and Icebei-gs, — When in very cold climates, or in mountain
districts of great elevation, tho rocks are exposed to frequent change of tem
perature near the freezing point of water, there must of necessity De a very
considerable destruction produced, and this so much the more as the rocks
are lesa covered with vegetation, or a coating of soU or gravel. Thia wiU be
at once admitted, if we consider the constant abaorption of w^ater intocrerices,
the expansion of the water, and consequent widening of the crevices, and the

ATMOSPHERIC AND AQUEOUS ACTION. 253
ultimate splitting off by this mechanical degradation. No one who has not
himself had the opportunity of witnessing such phenomena, can do fuU justice
to thefr enormous extent and infiuence, and the more repeated observation of
the forms of the rock wUl not itaelf give an idea, since the forma originally
produced by the causea here referred to are perpetually repeated, although
the actual surface of rook itself observed, and perhaps sketched at one risit, is
closely imitated by that presented at another. Glaciers have been well described
by Professor James Forbes as ' icy streams moving do wnw^ards, and continually
supplying their own waste in the lower vaUeys, into which they intrude them
selves like unwelcome guests.' They act chiefiy aa mechanical agenta, trana-
Eorting to a diatance, and preparing for further travel, a vaat multitude of
locka of stone, fragments of rock, gravel, and mud, and are amongat the
moat powerful agenta employed by nature for this purpose. The quantity is
often so great aa almost entirely to conceal the mass of the ice under the pro
digious load which, during a long descent, ia accumulated upon it, whUe the
dimensions of the fransported masses are often gigantic, one having been
seen by Professor J. Forbes on the glacier of Viesch, 100 feet long, and 40 or
50 feet high, and another being described containing nearly a quarter of a
miUion of cubic feet of green slate, wbich has been conveyed by the glacier
of Schwarzberg, although this glacier^has since retreated at least half a mUe,
leaving the intervening space covered vrith smaller blocks.
The dimenaions of glaciers are, however, required to give some idea of
the amount of result they produce; thefr number also, if it were possible to
enumerate it, might assist us in this conception. In Switzerland, theae
remarkable bodies vary in length from a few hundred yards to as much as twenty
mUes, and in width extend sometimes to as much as three mUea. They may
be seen in almost aU the principal and a vast number of the secondary vaUeya,
and everywhere produce the same results and exhibit similar appearances.
But Switzerland, although it offers very interesting examples of glaciers and
glacier action, wbich may be visited with convenience and described at
ieiaure and in detaU by the observant traveUer, ia neither the only nor the
most remarkable. On the south-western exfremity of South America, we
find ' a range of hUls only from 8000 to 4000 feet in height, in the latitude
of Cumberland, with every vaUey filled with atreama of ice descending to the
sea-coast. Almoat every arm of the aea which penetrates to the interior
higher chain, not only in Tierra del Fuego, but on the coast for 650 mUea
northwards, is terminated by tremendous and astonishing glaciers; and in
Eyre's Sound, in the latitude of Paris, not only are there immense glaciers,
but about fifty icebergs have been seen at one time fioating outwards, one of
which was at least 160 feet in total height, and these were aU loaded with
.blocks of granite and other rocks of considerable aize, different from the clay
slate of the aurrounding mountains.'*
On the coast of Greenland, at Spitzbergen, and in other places in the
Arctic Ocean, where the temperature of the water is below the freezing point
of freah water, and also along the whole line of coast of the Antarctic Islanda,
there are conatantly broken off vaat fragmenta of ice which fioat away into
warmer cUmatea, conveyed by marine currenta. '
Three kinda of accumulation of ice are met with under these circumstances
—the vast expanse of frozen surface-water detached from the shore, forming
what are called ice-fields ; smaller fragments of these, denominated ice
floes ; and the lofty and massive portions, really broken off from glaciers,
being the icebergs of the cold seas. Each contributes to Ulustrate the power
of water as an agent of change on the Earth's crust, but the ice-fields and
fioea convey Uttle or no detritus to a distance. The icebergs, on the con
trary, whether numerous and of smaU extent, as they are sucoeaaively broken

• Darwin's Joumal ofthe Beagle.

254 PHYSICAL GEOGRAPHY.
off in a aea warmer than the temperature of frozen fresh water; or
aUowed to sweU into gigantic dimensions, as they creep along the sea-bottom,
till the amaUer specific gravity of this vaat accumulation of ice, which is a
little leaa denae than the aea water, causea a huge fragment to break off, and
riae into an ialand — in either case abound with rocks and gravel.
The appearance and magnitude of such icebergs, in the Arctic Ocean, has
been described aa very variable, some having been seen aground in water
three hundred fathoma deep, and othera floating one hundred and twenty
or one hundred and fifty feet above water, indicating a depth of nine hundred
to one thouaand feet, and a weight of not leas than forty to fifty miUiona of
tons. During the aummer, round the shorea of Cape FareweU, and throughout
the year down Davia's Straits, theae marveUoua engines for distributing broken
fragments of rock, course each other rapidly into the open ocean, and thence
they proceed along the coast of America to latitudes as far south as that of
Devonshire. By this time they have been most of them sufficiently broken
and melted to lose their characteristic features, and graduaUy fade away from
observation. From the Antarctic land similar drifts occur to stUl warmer
latitudes, and very large floating bergs have been seen off the Cape of Good
Hope, one ofwhich is mentioned as having been two mUes in cfrcumference, and
one hundred and fifty feet high, whUe%thers, if not of such great area, rose
from two hundred and fifty to three hundred feet above the sea, and were
therefore of great volume below.
The cUmate in high southem latitudes is, however, exteemely severe
compared with that of the northem hemiaphere, aince in Sandwich land, in
latitude 59° S., correaponding in paraUel to some parta of Scotland, the
country waa deacribed by Captain Cook as covered many fathoms thick with
everlasting anow, from the summits of the mountaina down to the very brink
of the aea-cliff, and this at the beginning of Febmary, the hottest season of
the year ; and even in the island of Georgia, five degrees nearer the equator,
or in the same paraUel as Yorkshfre, the line of perpetual snow descends to
the level of the ocean. StiU further towarda the Antarctic Pole, aa in the
sixtieth paraUel of south latitude, the temperature of the summer months
ranges between 11° Fahrenheit and the freezing point of water, so that
throughout the wide range extending from the two poles of the Earth half
way to the equator, there ia a constant deposition of gravel and rock,
removed and conveyed by the agency of ice. This although chiefly known
in its effects in the northern hemisphere, must be far more considerable in
reality towards the south, aince the moat southem glacier, which comes
down to the sea in Europe, is nearly twelve hundred and fifty mUes
nearer the pole than those which are found on the weat coast of South
America ; but evidence is not wanting of enormous reaulte in that part of the
world also, gigantic boulders ocourrmg in the islands of Tierra del Fuego,
on the high plains of Santa Cruz, and on the island of Chiloe, associated with
a great unstratified formation of mud and sand, conteining rounded and
angular fragmenta of aU sizes. In the vaat oeean along which theae bergs
and islanda of ice are conveyed, there must be disfributed an enormous
deposit of such materials, which are continuaUy added to and occasionaUy
reach the surface, as the undulations of the Earth's crust preaent new aurfacea
to the denuding and leveUing power of the wavea.
87 Changes produced by the eroding Action of moving Water. — Running
water, whether the occaaional result of rain recentiy fallen, and making its
way to some continuoua stream, or consisting of the "sfream of water itself in
its progress to tho ocean, exercises partiy by simple atteition, and partiy by the
abrasion of sand carried along by it, a very considerable mechanical action. Thia
action is twofold, either bemg of the nature of erosion, or the eating out a
channel for the progreaa of flie water, or else involving the deposit of mud
and atones, tending to fill up the bed of a river, a lake, or an estuary. The
waves of the aea beating upon a coast, whether produced by wind or oy tidal

ATMOSPHERIC AND AQUEOUS ACTION. 255
aoKon, also produce a considerable amount of destruction, and marine
currents eat out, from time to time, very large quantities of matter from the
sides and bottoms of the channels through which they run, especiaUy wheu
these are soft, or when the current is rapid or steady. The eroding power of
running water is aometimes seen in connexion with great fioods in different
parts of the world, as weU as in ordinary river sfreams and marine currents,
but the power ia chiefly manifest in the beds of streams. A few facts,
Uluafrating the nature of the reaulte, wUl be interesting and instructive.
The rapidity with wbich even the smallest streams hollow out deep
channels in soft and destructible soils, is well exemplified in volcanic counteies,
where the half-consoUdated ashes present but sUght resistance to the torrents
which fiow down the mountain aides. Sir C. LyeU mentiona some interesting
examples of this kind in his Principles of Geology, (seventh edition, page 200,
et seq.) Amongst them he states, that after the eruption of Vesuvius in 1824,
heavy rains produced sfreams of water, which, in three days, cut a new chasm
through sfrata of tuff and ejected volcanic matter, to the depth of twenty-five
feet. He also quotes the case of the Simeto, the largeat of the Sicilian
rivers, which, in the course of about two centuries, has eroded through lava
a passage from fifty to several hundred feet wide, and in aome placea from
forty to fifty feet deep. A remarkable inatance of the force of water eating
its way through a very considerable thickness of rock is mentioned also by
Sfr Thomas Dick Lauder, in hia account of the great fiooda of Morayshfre, in
Auguat, 1829. He atates, that in one spot, the river Dorback, which before
the floods swept round a conical-shaped hill, in a course of seven hundred and
thirty yards, leaving a narrow neck of clayey gravel not more than a hundred
feet in thickness, had nearly breached its way, but that, during the floods,
the whole of the neck of land was Ukely to be destroyed. In order to save
this, the river was assisted in its operations by human agency, and by one
blow of a pick-axe the barrier, reduced to a dam of a foot thick, and just of a
sufficient height to sustain the water, was burst at once. In the course of
fifteen or sixteen hours, the channel waa converted into a wide and complete
river course, and within four-and-twenty hours the river had worked its way
back to the depth of eight feet below the level of its old bed, now a dry
channel. By the next February, the new channel was twenty feet below the
level of the old river bed.
By far the most striking example, however, of thia action of water,
and of the progreasive excavation of a deep vaUey in soUd rock, ia aeen in the
river and FaUs of Niagara. The river flows over a fiat table-land, in a depreaaion
of which Lake Erie la aituated : where it issuea from the lake it is nearly
a mUe wide, and is three hundred and thirty feet above the level of Lake
Ontario, into which it empties itself at a distance of about thfrty mUes. For
the first fifteen mUes the surrounding country is almost on a level with its
banks, and the river glides along with a clear and tranquU current, falUng
only fifteen feet in aa many mUes. Approaching the Rapids, it ruahea over a
rocky and uneven limestone bottom, and is then thrown down perpendicu
larly one hundred and sixty-five feet into a ravine, varying from two hundred
to four hundred yarda in width, and from two hundred to three hundred feet
in depth. The river continuea through this gorge in the table-land, for a
diatance of about seven miles, and the table-land then terminates in a long
line of inland cUff facing towarda Lake Ontario. On emerging from the
gorge, the river proceeds, for the rest of its courae, into Lake Ontario, through
a flat country, nearly on a level with the waters of the lake. In this case,
the sfructure of the rocks which form the table-land is such as to render it
perfectly clear, that the faUa have graduaUy receded from the escarpment, or
cliff of the table-land, to thefr present position, and that they must, in the
courae of time, reach the upper lakea. When that ia done, the water wUl
have wom for itaelf a complete channel, not much unlike some of those water-
worn rarines met with in other countries, the reault of simUar mechanical
force acting at an earUer period of the Earth's history.

256 PHYSICAL GEOGRAPHY.
The mechanical action of water on exposed cUffs is sometimes very
sfrikingly Uhistrated, as weU directly on the rock exposed to the ceaseiess
dashing of the waves, as incUrectly when rocks are undermined, and then fall
by the action of graviiry. Of the former, innumerable examplea are to be
found along almoat every extended coast line fri the world, while the under
mining action, if not ao vridely traceable, is in many cases much more
efiectual. The prevalence of strong westerly gales coming in from the Atlantic, and
driving large waves upon the north-western coast of the Britiah lalands, has
broken the hard rocka of the Shetland lalands and those on the west coaat of
Scotland into deep caves and lofty pinnacles, so that almost every promontory
ends in a cluster of rocks, the fragments of the former land. A sublime scene
ofthis kind is described by Dr. Hibbert as occurring in the Shetland Islands,
in what is caUed the Grind of the Navfr, where a mural pUe of porphyry,
left as the last rampart againat the inroads of the ocean, has been
breached through in spite of its extreme hardness by the repeated assaults of
the waves, and the breach is widened every wiuter, large atonea being sepa
rated from its sides, and carried along to a distance of aa much as 180 feet.
The fantastic forma that are obaerved in the iaolated granitic rocka in the
whole of this diatrict are due to the devaatation thus produced, and the
ialanda at first separated from the main land, and afterwards tom to pieces in
this manner, must ultimately be carried away to form new beds at the bottom
ofthe deep ocean.
On the east coast of Scotland, although more sheltered, the wavea have
produced great devastation ; and in Yorkshfre and Norfolk, the wearing of
the coast has proceeded to a very considerable extent, even -within auch time
as the position of towns and viUagea on the coast is recorded by historical
documents. Almost the whole coast of Yorkslifre, from the month of the Tees to that
of the Humber, is in a atate of general dUapidation ; and it ia only at a few
pointa that the grasay covering of the sloping talus marks a temporary relaxa
tion of the erosive action of the sea. 'The chalk cUffa are wom into caves
and needles in the projecting headland of Flamborough, and between that
promontory and Spurn Point, the waste is extremely rapid, whUe Spurn
Point itaelf threatena aome day to become a mere island ; in which case, the
ocean entering the estuary of the Humber, must cause great mischief.
In old maps of Yorkshire, many spots are marked aa the aites of towna and
vUlages, whioh have long since disappeared. Several towns of note, upon the
Humber, are now only recorded in history ; and a port which was so con
siderable in 1332, that Edward Baliol and the confederate English Barons
saUed thence to invade Scotland, and which in 1339 was selected by Henry the
Fourth to land at, to effect the deposal of Richard the Second, is now
represented by an extenaive range of sands, dry at low water. In
Norfolk, also, the decay of the diffa is incessant and rapid. Between
Weybourne and Sherringham it was computed, in 1805, that although the sea
was gaining upon the cliffs, a period of seventy years would be requfred for
the sea to reach the spot where an inn was built. In the year 1829, nowever,
only a smaU garden was left between this buUding and the sea, seventeen
yards having been swept away within the prerious five years. At one point in
the harbour of Sherringham, there was a depth of twenty feet in 1829, where
forty-eight years previously there had been a cUff fifty feet lugh, with houses
upon it. On the same coast, also, and near the same spot, several vUlages
have disappeared, and large portions of parishes on the coast have been
swallowed up. A Uttle further to the south, a rillage has been partly swept
away during the present century ; and the town of Dunwich, which ia now a
amaU yUlage, vrithout the vestige of any better condition in former times, was
"J"-^ 1 ™°^* conaiderable port on tins coaat. Other parta ofthe east coast
of England, and the mouth ofthe Thames, exhibit aimUar phenomena; the
Goodwm Sanda being, doubtless, a remnant of land once projecting beyond

ATMOSPHERIC AND AQUEOUS ACTION. 257
the chalk chffs of the Kentish coast at Ramsgate, wliile the cliffs themselves,
a little further to the south, are continuaUy and rapidly being removed.
Without dweUing farther on these accounts, which, however, are not only
interesting but highly instructive as exempUfying important physical
changes, we may conclude, so far as the British islands are concerned, by
mentioning, and with some respect, the reports universal in the south
western extremity of our island, of a tract of land haring extended beyond the
present Land's End in CornwaU for a distance of nearly thirty mUes to the
SeUly Islands, though the intervening channel is now 300 feet deep.
Accounts of the fragments of ancient pottery, and even portions of houses
brought up by dredging, certainly lend some show of probabUity to this
fradition, even if they cannot be regarded as altogether conclusive.
It may weU be imagined, and is certainly the case, that our own coasts
are not the only ones subject to great alteration from the beating of the
waves, and the ceaseless inroads of the sea. The power of water to destroy a
coast line, is even more distinctly exemplified where the coast is low and flat,
as in the case of HoUand ; for there large tracts of land, and whole islands,
have been removed at a single inundation ; and in one case no less than seventy-
two villages were overflowed in one season, (in 1421,) thfrty-five of which
were frretrievably lost and disappeared for ever, thefr place having been
since permanently occupied by a sheet of water, caUed the Bies Bosch.
The bed of the Zuyder Zee, alao, waa in the time of Tacitus a portion of
tiie mainland, only partly covered with fresh water, but the sea has entfrely
obUterated the former isthmus, which is now changed into a water passage,
more than half the vridth of the sfraits of Dover, the breach being ffrst com
pleted about the year 1282, and afterwards widened. The important delta of
the Rhine, although rapidly increasing in some places by the continued accu
mulation of sohd matter, is thus greatly checked and interfered with by
the ocean, which removes, in many casea, in a very abort time, what has
perhaps taken very many years to be deposited. Of aU the United Provinces,
Friesland and Groningen have suffered and continue to suffer moat from
theae flooda. Expoaed to the fuU rage of tbe north, north-west, and west
winds, the watera of the angry Atlantic and Polar seas rush towards these
provinces, pour through the mlets of its barrier-reef — the Holder (Hels-deur
— ^heU's door), the VUe, and the more northem gates — heap themaelves upon
the inland Zuyder Zee, burst or overtop its dykes, and spread themselves over
the country, sometimes to the very borders of Hanover. On these occaaiona
thousands of men and cattle perish, the gates of the barriers become widened,
and the dominion of the inland aea enlarged.
Thus, in 1230, a hundred thousand men perished, chiefly in Friesland.
In 1277, the teact of land which now forms the DoUart, was swallowed up.
In 1287, the Zuyder Zee was enlarged, and eighty thouaand peraona
deafroyed, with cattle innumerable. In 1395, the passage between Vlieland
and the Texel and Wieringen became so widened, that large ships could sail to
Amaterdam. In 1470, twenty thousand men were swaUowed up, nearly aU in
Friesland; and in 1570, an equal number in that prorince alone. In the latter
year, the water rose six feet above the dykes, covered even higher parts of
the country with seven feet of water, and in Groningen desfroyed nine
thousand men and seventy thousand cattle. In 1686, it rose eight feet
above the dykes, destroyed six hundred houses, dug the dead out of thefr
traves, and converted Friesland into one wide sea. The seventh Christmas
ood, in 1717, caused stUl vrider damage in these northem provinces, burst
through most of the dykes, laid the town of Groningen several feet under
water, and destroyed twelve thousand men, six thousand horses, and eighty
thousand sheep and cattle. And the struggle has not even yet ceased ; for
when the vrinds and fioods conspfre to increase the volume of water over the
horizontal fract near the river's mouth, no human agency can prevent the
destmction that must ensue.
In other parts of Europe, history records invasions of the aea not less
S

258 PHYSICAL GEOGRAPHY.
extensive and scarcely less disasfrous than those from which the Netherlands
have so often sufi'ered. Thus, in the eighth century, a tract of land was
carried away on the north-west coast of France, near Mont St. Michel, and
connecting that high land vrith the main coaat ; and in the Bot of Biscay the
sea has in some places advanced so as to have desfroyed a breadth of two
mUes of coast vrithin a century.
At the head of the Adriatic there was a town anciently caUed Adria, and
said to have been buUt on the sea shore by a leader of the ancient Etrascan
race, about the time of the Trojan war. The present town, standing on the
rubbish of two others, is now nearly sixteen miles from the nearest mouth of
the river Tartarus, probably the oldest bed of the Po, and now terminating six
mUes within the farthest point of land projecting into the sea. Of late yeara,
in making excavations at the depth of several feet below the present surface
of the town, a former level waa found, with numeroua fragmente of Efruscan
and Roman pottery; and at a atUl greater depth, a second fioor, where aU
the earthenware fragments proved to be Etruscan alone, and there were
veatiges of a theatre. (?) In these facts, both the raising of the aoU and
progreas of aUurial deposits are demonsfrated, in waters but Uttle disturbed
by marine currents, and within a space of 3000 years.
Many other points on the coast of Europe would give abundant eridence .
of aimUar kind, but theae are aufficient to prove how extensively the eroding
power of water may assist to modify, not only a coast Une, but the coimtry to
some distance inland.
On the shorea ofthe two Americas, in varioua places, we have eridence of
change to an enormous extent. The tidal wavea and the marine currenta
have thus acted on the north-western coast, and the vast extent of sandy
aUuvial territory from the Gulf of Mexico to the summit of Long Island
appeara as if it were a late deposit, in part the debris ofthe Mexican and Carib
bean portions of the continent, carried north, and thrown off when the Gulf
Stream was formed. At the mouth of the Mississippi, the sea, of smaU depth
along the whole coast, continues to recede before the delta of the river; and
the Florida and Carolina shores, northward, form a aeries of lagoons on the
ocean side. The sfream rushes onwards in a north-east dfrecfron, and with
a graduaUy decreasing velocity and temperature, (though both are stUl very
perceptible off New York,) untU it is finaUy neuteaUzed at Nantucket, and
the last particles of deposit suspended in it are precipitated to form the banks
of Newfoundland. A continent torn asunder and washed away could alone
furnish the immenae aUuvial aurface and aubmarine banka here noticed. The
rivera of the United States and Canada are not of a nature to have added
more than feeble deltas, auch as that of the Hudson at Sandyhook.
The shores of the Arctic Ocean between Asia and America and the
intervening shaUow sea offer proof of recent incursions of the sea in thia part
of the globe, and under cfrcumatancea where the change from other causes
ia Ukely to be rapid. There can be Uttle doubt that the breach between the
two continenta, if not actuaUy made, has been, at least, greatiy vridened by
the action of currents setting southwards from the Polar Sea.
The mere action of the wavea at the mouths of the great rivers both of
Aaia and America is unquestionably very considerable, but it belongs rather
to the fransportiug and disfributing action than the mere desfructive force of
this agent, and this wUl come under consideration in the next section.
It ia sufficient now to remark, that aU over the world there is a perpetual
destruction of every exposed fragment of sohd matter, and that, in this way,
the modification of^ coast lines has been large, even vrithin the narrow hmits
of human and recorded obaervations.
88 The Transporting and Distributing Effects of Moving Water. — The
runnmg waters of a river convey along -with them the particles removed from
their immediate banks, and the country over or near which they pass ; and
tlie quantity of matter thus cai-ried along, and consequently the rapidity
with which it may form such deposite, varies with the length of its course,

ATMOSPHERIC AND AQUEOUS ACTION. 259
the volume of its waters, the nature of the country through which it flows,
the velocity of its own upper cm-rent, the quantity of rain which falls in a
given time in the regions from which its waters come, and the violence or
rapidity of descent wim which they faU from theheavena. Thus, a thousand
gallons of the waters of the Oxus, when in flood, are aaid to hold in aua
penaion two hundred and fifty pounds of mud (Burnes); of the YeUow Sea,
fifty pounds (Staunton); of the Ganges, twenty-two pounds (Everest); of
the river Wear, in flood, sixteen pounds (Johnston); of the Miaaiaaippi, six
pounds (Riddell), and of the Rhine, at Bonn, two-thirds of a pound, according
to Mr. Homer.
There is, no doubt, considerable uncertainty as to the absolute correctness
of these numbers. They show, however, that the teansporting power of
rivers varies very much, and is sometimes much greater than we snould have
supposed or could anticipate. Even the smaU proportion of matter brought
down by the Rhine is equal to 146,000 cubic feet of soUd matter in twenty-
four hours ; so that, in two thousandyears it would form a bed of rock three feet
thick and thirty-six mUes square. It is by thia sediment that the low banks
of the Rhine, where it is beyond the reach of the tide, have been graduaUy
raised and numerous channels fiiUed up, and by these means also the islands
at its mouth have been in great part formed.
Such is the origin of aUuvial soU, properly so caUed, and in this way are
produced those rich sea-bordering clays, whose fertiUty is such aa to induce
men to riak diaeaae in swampy climates, and expend unwearied toil in
snatching them from the watery dominion, and defending them by huge
dykea, which are too often deatroyed by the aubsequent incuraiona of the aea.
Thia transporting power of water is, of course, seen chiefiy in those rivers
which bear down to the sea a conaiderable volume of water from high
mountain districts. Many of the European rivers poaseas the required
conditions, and produce by their deposits very considerable additions to the
land or the adjacent bed of the ocean, and amongst them the river Po may
be mentioned as having vrithin the last few centuries frequently changed its
courae, cauaing great devaatation. This river has also produced great
accessions of land in that portion of the Gulf of Trieste in which it and the
Adige (to which its delta is now united) empty themselves. The rate of
increase of this delta is now, and has been for some time, much more con
siderable than in the middle ages, the mountain torrents having become more
turbid aince the clearing away ofthe forests of the Alps, and the waters being
so far confined by artificial embankments that they no longer spread over
the plains, and leave there the great accumulations which they have obtained
in thefr course, but convey everything at once to the sea. It is calculated
that the mean rate of advance of the delta of the Po, between the years 1200
and 1600 was about twenty-five yards per annum, but that the mean annual
gain from the latter period to the present tune has been as much as seventy
yards. The delta of the Rhone offers another interesting example of the
rapid increase of land at the mouth of a river vrithin the historic period, and
at the same time the partial filling up of a great lake. The Rhone, entering
the Lake of Geneva at its upper end, is turbid and discoloured, but at the
town of Geneva, where it passes out of it, ia beautifuUy clear and tranaparent.
Aa there is no perceptible current in the lower part of the lake, it is manifest
that the mud and sand brought in by the river must be deposited ; and as a
proof that this deposit chiefly takea place at the head of the lake, we find
there an ancient town, buUt by the Romans, which was once situated at the
water's edge, but now, after eight centuries, is more than a mUe and a half
inland. But the Rhone receives tributary sfreams, bearing with them a
large quantity of sediment, after it has passed Geneva ; and thus, besides
partial]^ fiUing up that lake, it carries with it into France, and at length
leaves m the Mediterranean, a very large quantity of mud and silt. There
are many documente which prove that the base of the delta has advanced
into the Mediterranean very considerably within the last eighteen centuries,
s2

260 PHYSICAL GEOGRAPHY.
Placea which are deacribed aa islanda a thousand yeara ago, and harbours
conatructed at that period, are now from three to six mUes from the sea, and
even a tower erected on the shore so lately as the year 1737, is afready a
mile remote from it.
The delta of the Rhine is, however, much more considerable than that of
either of the rivers hitherto mentioned, and exhibits abundant proof of change
by the increase of certain parta of it, and the constant shifting ofthe channels
through which the river fiows. The occasional encroachments of the sea, and
the stiU further removal of the mud brought down by the river also tend to
alter the delta. The present head of the delta of the Rhine is about eighty iniles
from the general coast line of that part of the continent, and forty mUes from
the Zuyder Zee. The whole of HoUand, without exception, is on the delta
of this river, and the thickness of the mud accumulated is very considerable,
although the nature of the deposit varies a Uttle at different depths. Many
islands have been destroyed, new sfraits and estuaries formed, and the coast
line greatly altered by the sea within a comparatively short period near this
important stream. The Danube and the NUe afford other examples of the
same kind and on even a larger scale. The delta of the former river occupies
an immenae area, ita two extreme channela being distant from each other
eighty mUes; but the case of the NUe is stUl more remarkable, ita delta occu
pying, with the lagoona, an area of 20,000 square mUes, within which are
contained aU the cmtivated lands of Egypt. The form ofthis delta, as described
by the ancients, is, however, exceedingly different in almost every respect from
that which is now to be observed, and the magnitude is also very different.
It has always consisted of a perfectly level plain, nowhere offering the
smaUest natural elevation, vrith the exception of a few sand dunes near the
sea. The eoU of the delta ia everywhere formed by the aUuvial matter
brought down by the river, and this each year is covered by a fresh coat
when the annual inundation spreads over the land.
But considerable as are the deltas of these European and African rivers,
those of Asia and America are stiU more remarkable. The Granges and the
Bramahpootra have been afready mentioned as entering the Bay of Bengal
through a considerable tract of country entfrely formed by the mud which
these rivera have brought down from the mountain country and the plains
which they drain. The delta ofthe former ofthe two rivers, which ia now
continuous with that of the latter, extenda for 200 mUea between the two
principal arma of the Ganges, which bound it on each side. When the river
is low, the tide extenda even to the head of the delta, a diatance of 220 nules,
in a dfrect Une from the coaat, but when awoUen by the tropical rains the
velocity of the afream ia sufficiently great to counteract the tidjd current, so
that the movements of the ocean are ^together subordinate to the force ofthe
river. We have thus during different periods of the year two distinct
operations produced by the action of water. During the flood season, the
delta increases greatly m height and area, whUe during the rest of the year
the ocean scours out the channels and removes very extensive aUurial plains.
The amount of deposits necessarUy depends on the quantity of mnd held in
suspension by the watera of the river, and aa in almost aU respects the Ganges
is favourably situated for receiving and conveying to the oeean very large
quantitiea of transported material, the rate of increase might be expected to
be, and is, more conaiderable than ui almoat any other river. In point of fact,
the average quantity of aoUd matter suspended in the water near the mouth
ofthe river during the rainy aeaaon haa been estimated by Mr. Everest to
amount to ,rLth part by weight of the water discharged. As the number of
cubic feet of water discharged per second in the four rainy months may be
estimated at half a mUlion, it ia easUy shown by calculation that during the
Hundred and twenty -two days of rahi, upwai-ds of six thousand miUions of
cubic teet of mud must proceed down the river and be deposited in or near
tne aelta. it is diffioiUt to form any notion of the true meaning of numbers
80 large; but in order to asaiat the imagination, Sfr C. Lyell has estimated that

ATMOSPHERIC AND AQUEOUS ACTION. 261
this quantity of sohd matter is equal in weight to fifty-six and a half times the
great pyramid of Eg-ypt if that were a solid mass of granite.* It wiU also assist
the reader to form an idea of this quantity to know that if a fieet of eighty
Indiamen, each freighted with fom-teen hundred tons weight of mud, were to
sail down the river every hour of every day and night for the four mouths
continuously, they would only fransport from the higher country to the sea
a mass of matter equivalent to that actually conveyed by the waters of the
nver. It is probable that tiie waters of the Bramahpoofra convey annuaUy aa
much sohd matter to the aea aa those of the Ganges, but the delta ia not ao
considerable. The river Missiaaippi also exhibits on a very large scale examples of the
power of running water, both in filling up lakes and forming an extenaive
Delta. The auperficial dimenaions of the true delta of thia gigantic river
amount to aa much aa about 14,000 square mUes, and the quantity of aoUd
matter annuaUy brought down by the river ia nearly four thousand miUiona of
cubic feet. As the mean depth of the deposit of mud and sand is upwards of
500 feet, it would thus appear that the whole area might have been formed
as we see it now in a period of about 67,000 years, but the delta is itaelf
only a portion of the great aUuvial plain in which it is placed, and this plain has
also been formed by the sediments of the river, and must have required at the
same rate more than 33,000 years for its accumulation. Sir C. LyeU has weU
obaerved, in reference to this subject, that the whole period during which the
Mississippi bas been teansporting its earthy burden to the ocean, though,
perhaps, far exceeding 100,000 years, must be insignificant in a geological
point of view, since the bluffs or cliffs bounding the great vaUey, andtherefore
older in date, and which are from 50 to 200 feet in perpendicular height,
consiat in great part of loam containing land, fiuriatUe and lacusteine sheUs,
of species stUl inhabiting the same countey.
The Mississippi is remarkable not only for its delta, but also because in
various parts of its long course, some considerable lakes are now in process
of formation, while others are being rapidly drained. The most considerable
exanmle of the former phenomenon occurs in Louisiana, in the basin of the
Red River, where Lake Bistineau, as well as several others, have been formed
by the gradual elevation of the bed of the river, in which the aUuvial
accumulations have been so great as to raise its channel, and cauae ita watera
during the flood aeason to flow up the moutha of many tributaries, and
convert parta of thefr courses into lakes. Sometimes these lakes are merely
reservofrs, alternately emptied and fiUed in the dry and fiood aeasons ; but in
other cases, some natural or artificial obstacle prevents the efflux of the
water, and produces a permanent lake. The Lake Bistineau, afready men
tioned, is of this kind : it is upwards of thirty mUes long, and has a medium
depth of fifteen to twenty feet. Numerous cjrpress frees are seen even in
the deepest parts, stUl standing erect under water, although they are now
dead, and the tops of most of them are broken by the vrind. It is indeed
possible that subterranean movements may have assisted in the production
of some of these lakea, but the causes mentioned ajpear to be the most
important. 89 Changes produced by Water acting by the Aid of Substances held in
Solution. — Springs of water charged vrith calcareous or sUiceoua matter may,
under aome cfrcumstancea, produce an effect by rio means inconsiderable,
especiaUy in volcanic districts. Although, therefore, the total amount of the
reaults thus produced ia not very great, thefr local extent renders them "
worthy of a paaaing notice.
Auvergne, in cenfral France, offera an example of calcareous incrustations
and deposits from springs, which have formed an elevated mound of white

* The base of this pyramid covers eleven acres of ground, and its perpendicular height
is ahout 500 feet.

262 PHYSICAL GEOGRAPHY.
limestone, two hundred and forty feet long, and at its termination sixteen feet
high, and twelve wide. Tuscany presents other examples of the same kind;
so that in some places of considerable extent the ground is completely coated
with deposited rock of this kmd, and sounds hollow beneath the feet. The
river Elsa, a tributary of the Amo, flows through a vaUey several hundred
feet deep, of which the whole containing district is of the same recently
formed rock.
At the baths of San Vignone and San FUippo, also in Tuscany, springs
iaaue of warm temperature, containing salts of Ume and magneaia; and
depoaita of calcareoua matter of very great thickness, occur in the immediate
vicinity: one stratum of many layers, used as buUding atone, having a
thickness of fifteen feet, and a portion of the main deposit descending in a
different dfrection to the rest, being more than two hundred and fifty feet long,
and aometimea two hundred feet deep. It is then cut off abruptly by a smaU
river, so that a much larger quantity of calcareous matter than that deposited
has evidently been removed to the sea.
Other ateeams, as in the Azores and the volcanic island of Iceland,
consisting of greatly heated water, contain, held in solution in the water, a
very large quantity of sUica, and, indeed, more or less of this mineral is
probably present wherever there is any quantity of the salte of soda in
solution. The silica in water is sometimes, but rarely, deposited, like the calcareoua
matter, in layers, producing chalcedonic masses, which often resemble stalac-
titie and stalagmitic incrustations, but more frequentiy it asaiats in cementing
various materiala aggregated together, and thus forming stone from loose
sand and the conglomerates and breccias of varioua districts.
90 Indirect Effects produced by Water. — In addition to theae examples
of the dfrect action of moving water, in conveying to a diatance fragments
broken off from cUffs, or displaced by the more gentle action of rivers, it is
worth whUe to notice, before concluding thia chapter, some less dfrect results of
aqueous action which assist greatly in producing change. Land-sUps in which
considerable fracts faU away from a coast by the undermining action of water
are phenomena of this kind, but they have reference rather to the structure
of the Earth than to the actual mechanical force of waves and currente. In
the year 1839, an extraordinary occurrence of the kind took place on the coaat
^i Doraetshire, between Lyme-Regia and Axmoutb. The cliffs here consiating
of chalk, repoaing first on sandstone, and then on loose sand, have for thefr
ultimate basis extensive beds of clay, shelving towards the sea. Numeroua
apringa of water, the drainage of the surrounding country for a considerable
diatance inland, came out along the shore, and in the course of an exceed
ingly wet season, so much of the sand had been removed, that a considerable
portion of the cUff was partly undermined, and on the morning of the 24th
of December, in the year mentioned, a crashing noise was heard, succeeded
by numerous fissures opening in the ground, untU a deep rarine was formed,
extending nearly three-quarters of a mUe in length, witii a depth of from a
himdred to one nundred and fifty feet, and a breadth exceeding two hundred
and forty feet; and, after a short time, an elevated ridge was formed more than
a mUe in length, and forty feet high, by the pressure of the descending rocks
producing an extended reef in front of the present range of cliffs.

PART II.
THE STRUCTURE OF THE EARTH.

CHAPTER VII.
THE CONDITION OF THE INTERIOR OF THE EARTH AND THE
REACTION OP THE INTERIOR ON THE EXTERNAL SURFACE.
5 91. Means of obtainmg a knowledge ofthe Earth's Interior. — 92. Intemal temperature ofthe
Earth as determined by deep sinkings. — 93. Thermal springs. — 94. Volcanoes. — 95. Vol
canic products. — 96. Distribution of volcanoes. — 97. Subterranean connexion of distant
volcanoes. — 98. Connexion of volcaJioes with earthquake action. — 99. Nature of earth
quake movements. — 100. Frequent repetition and wide range of earthquake action. —
101. Permanent change of level accompanying earthquake action. — 102. Origin of earth
quakes. — 103. Partial, but permanent, elevation at a distance from volcanoes. — 104. De
pression over large areas.
li^f^EANS of obtaining a Knowledge of the Interior of the Earth. — We
jyiL have now considered in aucceasion varioua phenomena connected with
the Earth'a surface, including the atmospheric and watery oceans reposing on
the land, and also some of the mechanical results of the mutual action of the
different forms of matter presented to us : we have next to deacribe the con
dition of the Earth'a cruat, or, in other words, to give an account of the actual
aolid aubatance of so much of the auperficial coating of our globe, aa it is
possible for us to become acquainted vrith, either by direct observation or fafr
induction. The observations requfred are of various kinds, but cannot, under
any cfrcumstances, have reference to such a depth from the mean level of the
surface, as wiU justify us in assuming with certainty the condition of the great
mass ofthe interior of the Earth. Since, however, we have in nature many
opportunities presented to us for determining the Earth's structure for a
depth of at least several mUes, owing to the fact that various portions have
been thrust up from beneath by subterranean force; and that by natural
crevicea and fissures in various rocks and by artificial sinkings to obtain
mineral produce, by regarding the structure of cUffs, both marine and inland,
and by marking the nature of aoUs and their relations with the underlying
rocks, we have many means of determining facts as to the materials of thia
crust and thefr mode of arrangement, it becomes a very essential part of
Physical Geography to consider the state of the interior bf the globe in various
parts of the Earth, whenever observation wUl aUow us to do so.
02 Internal Temperature of the Earth as determined by Deep Sinkings.
' — Whenever there haa been an opportunity by sinkings made to any con
siderable depth below the Earth's surface to determine the temperature, it
haa been found that whUe at the surface, the mean annual temperature is
more or lesa widely departed from in different parts of the year, according to
local circumstances, this variation becomes less and less considerable as we
descend ; so that after a time we arrive at a certain point, to which the heat of
summer, and the cold of winter, do not in any degree penetrate, but the
thermometer shows throughout the year the same point — namely, the mean
annual temperature at the surface. This point is at different depths in
various parta of the Earth. In the torrid zone, under the equator, it is often

264 PHYSICAL GEOGRAPHY.
not more than a foot from the surface, in our own climate it is from sisty to
sixty-five feet ; and thus connecting such points beneath the external surface
of the Earth, there is also an imaginary surface or stratum of mvariable
temperature, above which the seasonal changes are felt, but below which any
observations that can be made must be supposed to have reference to the
absolute temperature of the Earth.
It is not, however, necessarily the case that we can, from such observations,
judge of the tene condition of the Earth at great depths. The vast period of
time during which the sun has been shining upon our globe, and com
municating, in whatever way, heat as weU as Ught ; the amount of chemical
change unquestionably going on beneath the surface, excited by terrestrial
magnetism ; and other causes, of whose mode of action we know indeed but Uttle,
but which are not the leaa certain and important, and which certainly produce
great molecular change : — these may have been sufficient to produce a certain
amount of heat, which, however slowly it is propagated through so bad a con
ductor as the materiala of the Earth's crust, may in the lapse of time have
given to the mass, at least to some considerable distance in depth, an absolute
temperature much higher than even the mean annual temperature of the
tropics. Bearing in mind this possibUity, it may be mentioned, as the general
impression and belief amongat thoae who have inveatigated moat carefuUy the
facts of the case, that the internal heat below the atratum of invariable tem
perature, may really be considered aa a guide to the condition of the interior of
the Earth ; and when, therefore, we find, aa we do, that in descending below this
steatum, the temperature gradually rises, increasing pretty regularly for some
distance at the rate of 1° Fah. for every forty-five feet of depth, there
appears reason to suppose that at a comparatively smaU distance from the
surface of the Earth towards its centre, there must be heat sufficiently great
to reduce to a atate of fusion even the most refractory of those masaea which
preaent themaelves aa rocka at less considerable temperature. Assuming that
the increase continues regularly in the same ratio, we should reach the boiling
point of water at about two miles depth, and at a depth of twenty-four mUes we
ahould arrive at the melting point of fron. Now, when we conaider that the
Earth's diameter is nearly eight thouaand mUes, we shaU see how Uttie it is
poaaible to judge of the state of the interior, even with the assistance of the
conclusions drawn from such observationa as have been mentioned ; but it
should be observed that the experiments upon which these conduaiona depend
are very numerous, and have been very carefuUy made, and depend not
merely on such deep sinkings as are connected with mines, but also on
Artesian borings, in which the temperature of the water is found to be conatant,
and seems entirely derived from passing through the sfrata of the Earth.
The experiments aUuded to, do not exhibit a result absolutely uniform ;
the increase of temperature is by no means the same for the same depth,
even in mines in the same diateict ; and whUe the mean rate of increase in six
of the deepeat coal minea in Durham and Northumberland ia one degree Fah.
for a descent of forty-fom- EngUsh feet, it appears to be only one degree for
every aixty-five feet m some of the deep mines of Saxony ; whUe in others, in
the same district, it was necessary to descend thrice as far for the same
amount of increase. In CornwaU, careful observations, continued for eighteen
months m the Dolcoath mine, at the depth of 1380 feet, gave as the rate of
mcrease one degree for each seventy-five feet ; but in other mines, in the
same district, very different results ai'e obtained.* On the whole, there iano
doubt, from the irregularitiea manifested in every extensive series of observa
tions, both in the absolute and relative moreaae of the Uiternal heat of the

t A «," Ireland, observations made in the Knockmahou copper mines, in the county of Water-
lora, the mcrease, after making every allowance for tho vicinity of the sea, was found in 774
leet, to be only at the rate of one degree for nearly 82 feet. It was found that the tempera-
IZt """^ »'"^ly dimmishing, and remained more considerable iu the lode than in the containing
TO<ik.— Report of British Association for 1844, p 221

CONDITION OF THE EARTIl'S INTERIOR. 265
Earth at considerable depths, that up to the present time, no general law can
be considered as appUcable, and therefore no general conclusion can be safely
arrived at. Even the fact of the duninishing rate of increase for equal
inoremente of depth, although apparently true of depths not exceeding 150
fathoms, has been caUed in question by Mr. Henwood, whose obaervations,
extending over a considerable number of very deep mines, appear to have
estabUshed the fact, that after 150 fathoma the ratio alters, that depth appear
ing, in CornwaU, to present a limit to the continued increase of temperature
in the aame ratio. It also appears to be the caae in the mming district in
question, that this depth in the mines hitherto worked (and in which, there
fore, such observations were made,) is also the limit of the principal masses of
metalhferous deposits, and thus arises a possibiUty ofthis minimum of ratio
being, after aU, nothing more than a local pecuharity, ovring to the mode of
diafribution of metala and metaUiferous ores.
93 Thermal Springs. — Thetemperatureof water obtainedby artificialboring
haa nowhere amounted to more than 82° Fah., andin this caae, at (GreneUe,
near Paris,) the depth bemg about 1800 feet, the rate of increase below the
surface of invariable temperature showed 1° for 60 EngUsh feet ; but very
much higher temperatures than this occur in the water of springs in various
parts ofthe Earth. In England we find, at Bath, water rising through crerices
in afratified rock at the temperature of 66° Fah. In Germany, the springs
at TopUtz, Ems, Aix-la-ChapeUe, Wiesbaden, Carlsbad, and Borset, (Lower
Ehine prorince,) exhibit temperatures of 71°, 81°, 85i°, 108°, 117°, and 1211°
respectively; the mean annual temperature at the surface in theae diatricts
being not far from 50°. At Baden-Baden, where the mean temperature is
somewhat higher, the hottest spring shows a temperature of 96^°, and at
Buda, near Presburg, in Hungaiy, there are springs of 93|° .and 95f°
respectively. In the north of France, at Plombieres, there are springs whose
temperature ia 95f°, and others near Chaumont of 80°. Further south, near
Aurillac, there is a spring showing 118°; and at Neris, in the department of
the Allier, one of 89|° At Thuez, in the Pyrenees, water riaes at the tem
perature of 111|°, and at Ax, near Tarascon, 108°. In Italy, in Piedmont,
there ia a spring shovring 107°, and at Abano, near Padua, one of 121°. The
hatha of Nero have a temperature of 121°; at Coquinaa, in Sardinia, the water
attaina 98°; and in laohia there are springs whose higheat temperature ia 94^°.
At the base of Mount Olympus, there is a group of thermal springs, thewater
of one ofwhich raises the thermometer to 113°; whUe in Iceland, and in other
places more dfrectly adjacent volcanic disturbances, it is not unusual to find
permanent springs of nearly pure water within a few degrees ofthe boiling point,
and even in some cases above it. Theae apringa, for the most part, have been
flowing without change for a very long period, and occasionally afford good
eridence that during several centuries they have remained permanently at the
same temperature, the quantity of the water also proceeding from them with
undeviating regularity. This quantity varies of course exceedingly in different
springs, amounting sometimes to several hundred thousand cubic feet per day,
and in others being much more Umited. In many, the water is charged with a
sensible proportion of aaline ingredients, but in others it is perfectly pure.
The fact of there being so many locahties, in different and distant diatricts,
pouring water from the bowels ofthe Earth having a temperature higher than
the mean temperature of the atmosphere at the surface, is sufficient proof that
there are very vridely acting causes of a uniform nature far beneath the
surface, and that these causes may tend to elevate the temperature at those
more considerable depths to which man has not been able to penetrate.
It would be improper to omit in this account of the phenomena of thermal
springs some notice of these magnificent fountains of boUing water to which
the name of Geysers is appUed, and which burst from funnd-ahaped hoUows
inthe lava plains near Mount Hecla, in Iceland. The great eruptions ofthis
fountain seem to take place once in about twenty -four or thirty hours, but
not with any regularity, the discharge being greatly affected by the eruptions

266 PHYSICAL GEOGRAPHY.
of the neighbouring volcano, and the periods haring frequentiy undergone
great change. The emption is descnbed by Kmg -von Nidda as being
preceded by a hoUow rumbling sound, and a number of explosions, accom
panied by a violent quivering motion in the ground. The author then atates,
that ' having been driven from the spot by this movement, he tumed at a
Uttle distance, and beheld a thick pillar of vapour shooting like an arrow to
the clouds, and surrounding a body of water, which rose vrith a fiuctuating
motion to the height of eighty or ninety feet, some portions of the fluid
rising even above this, or streaming in arches from the cloud. Sometimea the
ateam divided, and exhibited the aqueoua column ahooting upwards in innu
merable raya, spreading out at the top Uke a lofty pine, and descending in
fine rain; at other times it closed in thicker darkness round the cenfre, veiling
it from the eyes ofthe spectator. The eruption continued about ten minutes,
when the water sank down into the pipe, and the whole was again in repose,
the basin being completely empty, and the water far dovm in the pipe, and
slowly aacending.' *
With regard to this subject of thermal springs, it ia right, however, to
make the same qualified remark aa that ofiered at the cloae of the last
section. In aome placea, the temperature of natural springs proceeding from
considerable depths beneath the aurface is not greater than the temperature of
the surface, and in some instances is even lower. H we take the case of aU those
springs which may properly be termed thermal, that is, of which the water
is somewhat warmer than the mean annual temperature of the afr at the
surface, we shaU find that whUst many of them occur in districte which now
preaent no indications of what are generaUy considered volcanic phenomena,
on the other hand, there are scarcely any, if any, volcanic districte in which
hot springs do not abound. Many of tliose districts, however, in which no
volcanoes now appear are reaUy and very distinctly marked by volcanic
phenomena of ancient date, wbUe the rest are almost all of them either at the
foot, or in the midst of some partiaUy elevated teacts or mountain chains.
Such mountains we shaU have to prove in a future chapter are connected very
directly with igneous action, often on a much larger scale than is manifested
in volcanoes themselves. Even where this is not ihe case, there are stiUaome
geological phenomena indicating, although more diatantly, such fractures and
dislocations as result from igneous action.
94 Volcanoes. — The connecting link between thermal springs and
eruptions of mixed gaseous fiuid and soUd aubatances, from conical elevations
caUed volcanoes, ia conaidered by Humboldt to be fr-aceable in the ao-caUed
Salses, or mud volcanoea, of which examplea occur in various districts, and
which combine a number of phenomena bearing upon the general question of
the condition of the Earth at some distance below its surface. One of these
mud volcanoes was first formed about twenty years ago on the shores of the
Caspian Sea, near Baku, and in thia instance fiames blazed up to an exfra
ordinary height for the apace of three hours, and during the foUowing twenty
hours rose about three feet above the crater, from which mud waa ejected, whUe
enormoua fragments of rock were hurled to a great distance around. But
such a condition of activity ia rarely aeen in mud volcanoea, which more uauaUy
conaiat of amaU mounds from eight or ten to thirtv feet high, having smafl
basins on thefr summits, fi-om which mud (generaUj- cold) and gaseous eruptions,
accompanied by noise, are more or less constantly issumg. For fifteen
centuries, a Sicilian Salse, near Girgenti, has been in this inferior stage of
activity; and many others of the same kuid are described in other parte ofthe
world; the temperature of the mud, and of the gases erupted, being often
higher than the mean annual temperature of the disfrict.
True volcanoes are phenomena very different in kind, as weU as enor-

* Krug von Nidda, Karsten's Archii-.. ix. 247. See tlic account of Iceland, Greenland, and
thc Faro Islands, in the Edinburgh Cabinet Li/irani. 1840, p. 69.

VOLCANOES. 267
mously greater in extent, and we may consider that they involve in every
case a more or leas continuous but permanent communication between the
interior of the Earth, or some large cavity, and the atmosphere, and although
such communication may be interrupted for months, years, or even centuries,
it may afterwards recur with aU ite original energy. When traces of the
first eruption exist, the volcano generally appears to have risen from the
middle of a more extended area of cfrcular or elongated form, elevated so as
to form a cup-shaped cavity or crater, and an isolated cone presents itself in
the cenfre of this, having at ite summit a simUar smaU hollow, also caUed by
the name of crater. As offering a tolerably complete exhibition of volcanic
agency, there are, perhaps, no more interesting and instructive examples
than those of Santorin in the Greek Archipelago, and KUauea in the Hawaiian
(Owyhee) or Sandwich group of islands. The former, thirty-six mUes in
cfrcumference, exhibits the form of a large and broken submarine crateriform
mountain, in parts of which volcanic activity may be constantly obaerved.
The latter preaenta the only weU-marked instance on our globe of a large
deep pit open to the sky, having clear bluff waUs for the greater part of its
cfrcuit, with an inner ledge or plain raised above the bottom, which consista
of sohd lavas, with aome cones of conaiderable aize, and some pools of lava
in a state of constant and active ebulUtion.
A more detaUed account of both theae indications of volcanic activity
would prove very useful, in enabUng the student to comprehend the sequence
of volcanic phenomena, but the Umits to which we are confined wUl not
aUow of this digression, and we can only quote the foUowing notice of the
Volcano (as it is caUed) of KUauea, on the southern declivity of the table
land of Hawaii, whose elevation is eight thousand feet above the sea, and
which occupies the centre of the island, measuring fifty mUes in length, from
aouth to north, and forty mUea in ita broadeat part. Near the edges of the
table-land are three volcanoes, the highest of wliich, Mouna Kea, is 13,587 feet
above the sea, and is now extinct. It is near the eastem decUrity, and is
opposed by Mouna Roa, which is near the aouth-weat corner, and is 13,175
feet high, and not in a atate of very recent activity, but exhibiting an ancient
crater not less than twenty-four mUes round. On the weatem edge of the
table-land is Mouna Huararai, whoae height is estimated at 10,000 feet,
and which is now active. On the southem slope is aituated KUauea, which
ia a depression below the general aurface of the slope of aomewhat irregular
shape, with almost perpendicular sides. The elevation of the slope, where
this vast pit occurs, is 3873 feet above the sea. The steep descent to the
crater is interrupted by two narrow plains or ledges, one of which is 715
feet below the upper surface, and the other about 100 feet. The surface of
the volcanic lakes is forty -three feet below the last-mentioned ledge. The
crater contains two lakes, the smaUer of which is ahnost cfrcular and nearly
1000 feet acroaa — the larger ia more than 3000 feet long, and in one place
2000 feet vride. These lakea are vaat caldrons of lava, in a state of furious
ebuUition, sometimes spouting up to the height of twenty and even seventy
feet. The fiery wavea run with a steady current at the rate of nearly three
mUes and a quarter per hour to the south, enter a wide abyss, and ultimately
pour into the sea. This remarkable volcano has, from time immemorial,
been prodigiously active, though it haa not, within the memory of living
men, been known to overflow except in 1787, when a dreadful eruption took
place, which lasted seven days.
There are few other instances of this kind on the globe, in an active
state. On the surface of the moon there are strictly analogous appearances,
repreaented on a much larger scale, some pit craters having been described,
which measure from 5 to 150 mUes in diameter, and 5000 to 24,000
feet in depth.
While this simmering and boUing of molten rock, and the formation of a
crater, is carried on in the large caldron-Uke pita juat described, other reaults
of volcanic action are illustrated by the foi-mation of conical hills, either in the

268 PHYSICAL GEOGRAPHY.
bUster-Uke sweUing of a considerable area, or the rapid accumulation or
emption of a single mountain. Thua, we find recorded by Humboldt, a very
striking instance of such subterranean movement, in the production of the
district and mountain of JoruUo, in the plains of Malpais, which form part
of the plateaux of Mexico. These plains are a hundred mUes distant
from the sea-coast, and 2500 feet high, and are bounded by basaltic moun
tains. No active volcano is near, and the whole occurrence presents a
view of one of the moat exfraordinary phyaical revolutions recorded in the
history of our planet ; for it ia rare, indeed, that man has an opportunity of
seeing so extenaive a change commenced and concluded within a period of
time so short as that of the ordinary duration of human existence.
What took place at JoruUo has occurred in former times on an infimtely
grander scale, not only in those disteicts where groups of volcanoes now pour
forth ffre and melted rock, but in a vast number of other places where this
fire haa long since spent itself. The phenomena of volcanoes muat be
conaidered, men, in reference to thoae which are extinct, as weU aa those
now active; and the disfribution of volcanoes becomes of interest, not only
with reference to the present land, but to the form of the Earth's surface at
aU antecedent periods. We have afready mentioned, that volcanoes are
grouped in two forms, the one consisting of cfrcular areas, in various parta of
which true volcanic cones arise ; the other, consisting of linear groupa, aome
timea continuous for very great diatancea. The former are exemplified in the
case afready given of JoruUo ; the latter, involving the loftieat and the most
remarkable phenomena of thia kind on the globe, wUl requfre aeparate notice,
the eruptiona that take place from them being on a grander acale, and
involving more complicated reaulta.
A volcanic eruption generaUy commences with subterranean noise, and
this ia succeeded by dense columns of smoke, impregnated with various
gaseous substances, often intermixed with a large quantify of aqueoua vapour.
Then foUow showers of aahea, aometimes accompanied by large maaaes of
rock, which are vomited forth vrith fearful noiae and with enormous force.
While these substances are thus being expeUed from the hoUow cup-hke cavity
at the summit of the cone, which terminates the volcano, melted rock (lava)
at the same time issues either from a breach in the side of the crater, or
from some fissure opened on the sides of the mountain. The order of the
phenomena is not indeed invariable, but this may be considered as a general
account of an ordinary eruption. In those casea in which the volcanic cone
riaea above the snow line, the beat of the mountain immediately before an
eruption is often so considerable, that the snow melte with exfreme rapidity,
so that the eruption is preceded by torrents of water, often deatroying
houaea, eatatea, and even whole towns, at a great distance from the
volcano. 95 Volcanic Products. — To Ulusteate the true nature and relative
importance of these different products of volcanic action, it may be worth
whUe to consider separately the three very distinct kinds which may be
designated as gaseous, including smoke and aqueous vapour ; sohd, consisting
cbiefly of ashes often in a minute state of dirision; and Uquid matter, con
sisting of that molten rock ao weU known under the name of lava. Virid
sheets of fiame have been frequentiy seen during volcanic actirity, rising to a
great height in the afr. Many such appearancea of flame are indeed con
sidered by Humboldt aa bemg due to reflectiona from burning matter
S rejected high in the afr during the eruption, and to aacending vapours
lumined by the ffre within the crater itself, rather than to frue flame arising
from the combustion of hydrogen. In aome cases, however, as at Baku,
there seems no doubt that columns of flame have risen to a sufficient height to
be visible to a distance of twenty-four mUes.
Under ordinary circumatancea, the quantity of steam given off in puffs
during an eruption is very conaiderable, and takea place at intervala of from
twenty to thirty aecrands. The greater part of the vapour consista of pure
water, but gaaes are also erupted at the same time, consisting partiy of

VOLCANOES. 269
carbonic acid gas, but including chlorine, nitrogen, aulphuretted hydrogen, and
sulphuroua acid. SiJphuric and muriatic acids, together with common salt
and muriate of ammonia, are mixed occasionally vrith the pure water. The
quantity of products of this kind tbat are thrown out in a single eruption are
certainly very large, but cannot possibly be estimated; for, in many instances,
such substances continue to be erupted for a very long period, especiaUy in
the case of volcanoes of moderate elevation, whioh thus seem to connect them
selves with those instances of almost perpetual activity already described.
The ashes ejected during eruptions differ greatly in every respect, not only
in quantity, but also in the mode of eruption, being sometimes reduced to
such exfremely fine dust, that when thrown into the afr, they rise through
several successive afrata of the atmosphere, in quantity sufficient to be
fransported by varioua atmospheric currents to almost equal distances, in
different and even oppoaite dfrectiona, whUe at other times they faU back at
once upon the volcano, assisting to raise its cone to a stUl greater height.
In the latter case, the ashes are generally of moderate dimensions, and one
thfrd of the height of Mount Vesuvius is composed entfrely of such material.
Examples are not wanting in varioua parts of the world of the conveyance
of fine dust from volcanoea to distances which would be incredible, U the
testimony upon which they are recorded were not beyond all question;
and, indeed, the cases are now so numerous, that although far from being
easily explained, the facts must be taken as bearing upon the most important
questions connected with volcanic actirity.
As one of the most recent examples of this transport of fine dust through
the afr, and one which, although sufficiently exfraordinary, is among the
leaat marveUoua on record, we may mention here, that on the 2nd of Sep
tember, 1845, at nine o'clock in the evening, a thick cloud was seen advancing
with a sfrong wind from N.W. by W. towards a ship sailing in latitude
61° N. and hmgitude 7° 58' W. This cloud, when it reached the ship,
covered everything vrith fine dust. On that same day had commenced an
eruption of Mount Hecla in Iceland, at the dfrect diatance of 500 mUes from
the ahip; so that the cloud of ashes muat have teaveUed at a mean rate of
fifty mUea per hour.
Far more exfraordinary accounta than these are recorded of the lofty
volcanoes in the Andes, and alao in aome of those in the ialands of the eastern
Archipelago. The volcano of Coseguina, on the weat coaat of Central
America, waa in emption in January, 1835, after twenty-aix yeara' repoae.
On the moming of the 20th of that month, a cloud rose in the dfrection of
the volcano, which, aeen at a distance of fifty mUea to the south, presented
the appearance of an immense plume of the whitest feathers rising with
considerable velocity, and expanding in every direction. From that time to
the moming of the 22nd, the cloud retained this appearance, but then a line
of intense darkness replaced it. Immediately afterwards, a fine white ash
was observed to fall, the black line rose rapidly, the Ught began to fail, and
darkness commenced, and soon increased so much, that in half-an-hour it was
blacker than in the thickest night. So intense was the obscurity, that men
could touch vrithout seeing each other, and the fowls 'went to roost as at
night. This state of perfect darkneaa prevaUed during the whole of that
day, and untU noon of the foUowing day, at which time objects became
visible at ten or twelve yards distance. In this state things continued for
two days longer, but for ten or twelve days the Ught waa partiaUy obscured.
During the whole time a fine white impalpable dust continued to faU. This
faU of ashes was not confined to San Antonio, which, as has been said, was
itself fifty mUes from the volcano. StiU nearer the central point, the dark
ness commenced earlier, but did not last so long; whUe in every place in
the immediate neighbourhood the ground was completely covered with
ashes, varying hi thickness from a few mches to upwards of ten feet. The
most extraordinary fact, however, with regard to thia emption remains to
be told ; for not only were the ashes conveyed in the dfrection of the wind to
a distance of as much as 700 mUes, at the rate of 170 mUes per day,

270 PHYSICAL GEOGRAPHY.
obscuring the sun in the island of Jamaica, and covering the earth with flne
dust, but they were carried to windward for 400 leagues, thus provmg that
they must have reached to an enormous height in the atmoaphere by the
violence of the eruption. It ia also recorded by the captain of a ahip in the
Engliah' navy, saUmg in latitude 7° 26' N., and 104° 45' W. longitude, at a
diatance of 900 mUes from the nearest land, and 1100 from the volcano, that
his ship sailed forty mUes through fioating pumice, some ofthe pieces being
of a considerable size. The actual amount of force vrith which such volcanic
products aa theae are ejected, is not very easy to estimate, and the calcula
tions that have been made on this subject are not so accurate as might be
wished. That it is enormously great, however, there can be no question ;
and it ia recorded by Sir WUliam HamUton, that atones were, on one occa
sion, thrown up so high above Vesuvius as to occupy eleven aeconda of time
in faUing to the level of the crater. AUowing for the difference of atmo
spheric pressure in a mountain above 3000 feet high, thia gives a force
equivalent to the pressure of between three and four hundred atmospheres.
Another example is recorded of the projection of a mass of rock, measuring
300 cubic feet, (and therefore whose weight was upwards of 200 tons,) from
the crater of Cotopaxi, to a distance of nine mUes.
The quantity of matter ejected from volcanoes in the form of lava is
more readUy measured than in either of the cases yet referred to. The
lava streams break out in irregular intermitting apringa of molten earthy
matter, and frequently continue slowly running for daya, and even weeka
together. Aa examplea of quantity, it may be mentioned, that m 1837,
Miount Vesuvius poured forth as much as thirty-four miUions of cubic feet,
and in 1794, during another eruption, upwards of forty-six millions. In
1669, Mount Etna poured forth nearly a hundred millions ; and in 1783, an
eruption took place in Iceland, more remarkable for the extent of its lava
current thau any other on record, the steeam having flowed along two
channels, one of them fifty milea in length and twelve to fifteen mUes broad,
the other forty miles long and seven miles in breadth. In the course of this
distance the fiery stream filled up a lake and obUterated a lofty cataract,
turning the watera of two ateeams into vapour, and entfrely occupjring their
beda. Although the thickness was very variable, being as much as five or
six hundred feet in the narrow channels, and not more than ten feet in the
plains, the lowest estimate ofthe measurement and weight ofthis mass is not
less than twenty thousand millions of cubic yards, or forty thousand mUUona
of tona of matter, poured out of the bowels of the Earth and spread over its
aurface within the abort apace often weeks.
g6 Distribution of Volcanoes. — Having considered thus the nature of
volcanic action, and of the substances which, imder various cfrcumstances are
erupted from volcanoes, it remaina that we should explain the mode of
distribution of these phenomena upon the Earth's surface. The best mode
of obtaining a general idea of this disfribution ia, by examining carefully a
globe or map of the world, in which the positions of the varioua volcanoea at
present or formerly active ia disfinctiy marked, and such a map wiU be
found in the atlas belonging to this volume.
The foUowing table wiU give a notion both of the position of various volcanic
groups, and the comparative number of distinct volcanic vente in different
regions. It includea about 400 described cases of volcanic cones, many of
which, indeed, have not been known to erupt within several centm-ies ; but
thia does not neceaaarUy remove them from such a Uat, as it ia very possible
for the internal ffre to slumber for a much longer period between two epocha
of outburat. By giving an idea of the aetuS diatancea vrithin which the
principal groupa are placed, as weU as the nuniber in each case, perhaps this
table wiU communicate a tolerably distinct idea of the importance of each
group. In many cases, however, the volcanoes are very closely congregated
m knots about the contee of the disfrict, whUe towai-ds its outekirts are only
a few cones and craters.

list ofthe Principal Volcanic Groups, with the Linear Extension
of each Group. Number Linear Exten-
of sion in British
Volcanoes. statute miles.

2 71 1
1 1
10 2! 1 '
2 1

2 ?
21 18
23

21 12 4
11 9
43 75

\\

!

450 ?

900 800
1700
1000 280
1000 700

Atlantio Ocean ;
Jan Meyen Island (Greenland) 
Iceland 
Azores 
Canary Islands 
Cape Verde Islands 
Ascension Island 
Trinidad Island 
Tristan da Cunha Island 
West India Islands 
Meditebkasean Gkodp :
Lower Italy 
Lipari Islands 
Greek Islands 
Red Sea 
Indian Ocean (west smE) :
Bourbon Island 
Mauritius Island 
Rodriguez Island 
Asiatic Continent :
Westem Asia 
Central Asia 
Eastem Asia 
Asiatic Coast :
Kamtchatka group 
Kurile Islands group 
Japan Islands group 
Bonin and Mariana Islands 
Formosa 
Luzon and the Philippine Islands 
Molucca Islands 
North-west coast of New Guinea 
Sunda Islands Gkoup:
Floris and adjacent islands to the west as far as
Serva 
Sumbawa and others 
Java 
Sumatra 
Andaman Islands 
EaSTEEN AEOmPELAGO :
Groups of islands between New Guinea and New
ilealand 
New Zealand 
Friendly Islands 
Pacific Ocean:
Hawaii (Owhyhee) group 
Society Islands 
Marquesas Islands 
Easter Islands 
Galapagos Islands 
Aueeica: Aleutian Islands 
North American series 
Mexico 
Guatemala 
Quito 
Peru and Bolivia 
Chile 
Tierra del Fuego 
Ahtabotic Land  3
Those groups to which no linear extension is marked, are for the most part detached, and
exhibit only imperfect communication with any other district. The groups connected by brackets
are probably related, but too imperfectly tojustify any statement as to their linear extension.

600 350 650 900 600

- 1
1
35 ....
10 ....
7 ....
38 ....

 1200
 2000
 700
 850

17 ....

. ... 450

12 ....

 600

22 ....
8 ....

 1200
 400

272 PHYSICAL GEOGRAPHY.
Looking, then, at theae volcanoes as offering means of communication
between the interior of the Earth and its surface, we find that whUe the
whole number of such vents is larger, by a great deal, than could be anti
cipated by observations made on the westem Continent, there are stiU very
extensive districts of land, and doubtless, also, large areas of the sea bottom
in which no such means are afforded for the eacape of gaseous or other
substances pent up within the Earth. And although it is certainly trae that
there are many parts, especiaUy in Europe, where abundant proof is afforded
of volcanic action during a period antecedent to the present, and thus the extinct
volcanoea add much to the surface which we know to have been provided with
vents within a comparatively short interval, there is yet daUy increasing
proof, that however powerful an agent volcanic force may be, it does not
directly or necessarUy affect the great mass of land upon the Earth. More
than half, however, of the coaat line of the existing land ia covered at
intervala sufficiently near to ensure subterranean communication at great
depths underground, but the great area of land within the coast, and the sea
bottom, so far as we know, is not sufficiently in relation with changes thus
induced, as to justify our regarding them as essential to existing conditions.
We shaU proceed to show in the next chapter, however, that there are
phenomena on record which connect this kind of igneous agency vrith
another more dfrectly influencing the general physical conditions of the
Earth's surface.
97 Subterranean Connexion of Distant Volcanoes. — Manyof the volcanic
regions referred to, exhibit very distinct relations vrith each other, although
far removed in point of distance, and separated or covered at the surface by
rocks of very various character ; but the volcanoes in the same system, or
vrithin moderate distances, are often ao dfrectly related aa to exhibit a
distinct reciprocation. Eemarkable inatances of thia have been obaerved in
aome of the volcanic cones of the Andes, and this relation has also been shown
in the case of the two most considerable European volcanoes.
98 Connexion of Volcanoes with Earthquake Action. — Earthquakes may
be regarded as convulsions of the Earth, of the nature of undulations propa
gated in various dfrectiona from a central point or Une beneath tbe surface of
the Earth, and consiat of a aeriea of perpendicular, horizontal, and even
rotatory motions, foUowing each other in rapid succession, aometimea being
so slight at the surface as only to be perceptible by those famihar to the
phenomenon, but occasionally producing the most complete and frightful
destruction over whole disfricts of the Earth. The origin of auch phenomena
must be regarded aa an upheaving force, more or less sudden in ite effects,
and greatly modified by the extent of area over which it has at first acted.
Earthquakes and volcanoes stand in intimate connexion with each other,
generaUy originating in or near the same parts of the Earth, often so dia
tinctly related in order of time and alternation of results, that they are
manifeatly aeen to belong to each other, so that when volcanic action is exhi
bited on a large scale, as in the Unear groups described in the Andes, the
Sunda Islands, and elsewhere, the activity of one volcano interferes vrith the
action of another, and the commencement of a great eruption is generaUy pre
ceded and often accompanied by earthquake undulations. As also we find, that
volcanoes are almost confined to the coast line bounding the Pacific, so
also, earthquakes are much less frequent in counteies forming the cenfral
parts of continents. It is, however, by no means the case that earth
quake action is reaUy thus limited, only that the undulationa are less
common and less considerable in amount in these districts than in others
nearer the coast.
If we begin by considering the nature of earthquake phenomena, aa
exhibited in the different kinda of undulationa that have been described, and
the local effecta recorded to have been produced, we ahaU find that the subject—
although one offering great interest to the general reader, and therefore well
adapted for works in which continuoua narrative is attempted — does not

EARTHQUAKES. 273
present that magnitude of interest which can entitle it to rank as a world-
phenomenon, unless we connect with these local efiects, those much more
wide, and indeed universal, changes of level of the general aurface of land,
and of the sea bottom, to the action ofwhich the form and phyaical features ofthe
whole surface of the Earth are due. We propose, therefore, to consider, fu-st,
and somewhat briefiy, the local phenomena that enable us to judge in some
measure of the nature and extent of the causes in action, and we may theu
proceed to investigate the efi'ects on a large scale, and the possible causes of
the undulation of the surface generally.
In Uluafration of the important fact of earthquakes and volcanoes being
connected phenomena, it is only necessary to refer to thoae volcanic dia-
tricta in different parts of the world afready described, and thefr history,
so far as that history has been handed down to us. The vicinities of Etna and
Vesuvius have been remarkable for many centuries for disturbances of this
nature. Most of the cities, not only of SicUy, but also of southern Italy, have
from time to time been the scene of destructive undulations, continued at short
intervals for a considerable period, sometimea exceedingly audden, and
fiightfuUy deatructive. These have been in moat caaes directly aucceeded by
eruptions from neighbouring volcanoea, the earthquakea preceding the
emption, and the shocks increasing in violence, untU the mountain reUeves
itself by discharging its contents ; so also when volcanoes in constant or nearly
constant action ceased to show aigna of activity, earthquakea have generaUy
been known to succeed. Thus, StromboU had an interval of repose for the
first time vrithin the memory of man, immediately preceding a series of earth
quakes which took place m the year 1783 ; and thus, also, the volcano of
Pasto, in Peru, ceasing to emit a dense, black column of smoke, which had
proceeded from ita crater for some time, the terrible earthquake of Eio
Bamba occurred, during which 40,000 persons perished. Perhaps, however,
the best example of this chain of connexion between earthquakea and
volcanoes is aeen in the series of events which took place in 1811 and 1812,
in the weatern world. The ffrat of theae events waa the audden elevation of
the ialand of Sabrina, in the Atlantic, near the Azores, from a depth of 120
feet, the phenomenon being accompanied by violent earthquakea, and a
diaengagement of amoke and fiame. Erom thia time, aevere ahocks were
felt in the laland of St. Vincent, near one of the most active volcanoea in the
Weat Indian Archipelago, and theae ahocka extended to the North American
continent, producing marked reaulta in the valley of the Misaiaaippi. In
December, 1811, an earthquake took place in the Caraccas, and another in
March, 1812, continuing several days, and entfrely desfroying the chief city
of the prorince. And lastly, on the 30th AprU, 1812, the volcano of St. Vincent,
which had been quiet for nearly a century, burst out with a tremendous explo
sion, which extended for 210 nules, into the plains of Calaboyo. Thia ended the
diaturbances, connected together at great depths, extending, aa we have seen,
from the Azores, and felt round the whole of the interior of the Gulf of Mexico.
It is needless to repeat examples of this kind, which aU tell the same tale.
Most of the great eruptions of modern times have beenjpreceded by earth
quakes, and most of the great earthquakes succeeded by volcanic emptions.
99 The Nature cf Earthquake Movements. — It has been mentioned that
the undulations coimected with an earthquake are of three kinds — namely,
undulatory, perpendicular, and horizontal; the latter sometimes producing
what appear to be rotatory or vorticose movements. Of these, the first kind
is the most common and the moat harmleas, the second is generaUy very
destructive, whUe the thfrd has rarely been felt, except in the most disastrous
and appalling catastrophes.
Earthquakes are occasionally, but not always, accompanied by detonations
and loud noise ; the kind of noise that occurs is also different in different
placea, being sometimea roUing, and occasionaUy like the cUnking of chains,
sometimes abrupt, like thunaer close at hand, and sometimes clear and
ringing, as if obsidian or other ritrified masses clashed, or were shattered in
T

274 PHYSICAL GEOGRAPHY.
subterranean cavities. In the Caraccas, there was heard over a district of
40,000 miles a loud noise resembUng thunder, unaccompanied by any shaking
of the ground, during the eruption of a volcano more than 600 mUes distant ;
and at the great eruption of Cotopaxi, in 1744, subterranean noises, as of
cannon, were propagated at great depth through the Earth for a distance of
more than 400 miles.
The undulationa of earthquakes are propagated in two very distinct ways,
sometimes extending and being exceedingly violent for very great distances
in linear direction, and sometimes extending from a focus almoat equaUy in
every direction. It ia an important fact that the linear dfrection of great
earthquakes generally corresponds with that of volcanic action in the ricinily.
It is probable, however, that even in what may be regarded as cenfral earth
quakes, the impeUing force is situated along a particular Une of country
mways the same in successive disturbances. Most earthquakes foUow the
dfrection of the mountain chains in the countries which they traverse, but
occasionaUy they cross this Une at right angles ; in the latter case, however,
the shocks have generally been weak.
As it is important to bear in mind the difference wbich reaUy exists between
central and Imear earthquakes, we may here give a short account of important
earthquakes in whioh each of these dfrections has been observed. Thus, the
great earthquake of Lisbon, which took place on the Ist November, 1755,
was felt in a cfrcular or oval area of enormous dimensions, commencing
apparently in the Atlantic, off the coast of Portugal, and reaching to the West
Indian islands, the lakes of Canada, the shores of the Baltic, and the hot
springs of Bohemia. This, therefore, may weU be considered as cenfral on avery
large scale, aince aportion of the Earth's surface, at least equal to four times
the whole area of Europe, was then simultaneously shaken. This earthquake
has been described at great length, and the phenomena were in the highest
degree interesting.
Another remarkable instance of a central earthquake, although of far less
extent, took place on the 5th February, 1783, in SicUy, on which occasion
Calabria, and about 200 other towns and viUages, were desfroyed within an
area of 600 aquare miles and 100,000 persons perished. This earthquake,
although so smaU in extent, exhibited all the pecuUar phenomena of vorticose
movement and vertical upheavals frequently repeated, which from thefr
nature must of necessity result in great injury to any buUdings on the
surface. The surface, also, itaelf ia in such cases rent asunder, and some
portions have been removed to a distance in a manner exceedingly difficult to
account for.
The earthquakes here described were more or lesa cenfral, the form
of the land disturbed being either cfrcular or oval, and in theae cases the
progress of the shocks may be compared to that of ring-like waves produced
on the surface of stUl water when a stone ia thrown m, or when a solid ia
lifted from the bottom. Such waves, both in the water and on land, are both
wider and fainter as thefr distance from the cenfre increases ; and thus in the
great Lisbon earthquake, while that city was so completely desteoyed, othera
both north and aouth of it at moderate diatancea were only partiaUy injured;
while in Ireland, although the shocks were distinctly felt, they ceased to be
mischievous, and at stiU greater distances the disturbing force was only risible
in ita effects on the waves ofthe sea or the water of deep springs. So also in
the Calabrian earthquake, whUe the country at one particular spot was rent
by deep chasms, and so violently shaken that the heads of the largest frees
are said to have almost touched the ground on either side, and whUe not only
was no kind of buUding able to resist the movement, but fracte of land were
actuaUy removed horizontaUy, so that fields planted vrith different kinds of com
had exchanged situations, yet, at a comparatively short distance, the towna
were not injured, and in the country the shock waa scarcely felt. It is alao
a remarkable and intereating fact with reference to cenfral volcanoes gene-

EARTHQUAKES. 275
raUy, that the disturbances are by no means equal at equal distances from
the cenfre, or universal at all intermediate places, proving both the true wave-
like nature of the movement generally, and its partial interruption by the
varying elasticity ofthe different rocks thi'ough which it passes.
Linear earthquakes are no less remarkable than central ones, and in
gome cases thefr phenomena are even more instructive. In 1837, a shock
occurred in Syria affecting a Une 500 mUes in length by only 90 in breadth;
whUe in South America there have been instances in which 1000 miles of
coaat have been afiected by disturbances whioh have not been transmitted in
an east or weat dfrection to any conaiderable diatance. On certain occasions
that have been recorded, earthquakea have been felt at various points along
Unes of stUl greater length, and a most remarkable example of this kind
occurred in the year 1835, when several towns were throwji down between
Copiapo and ChUoe. On this occasion, the whole volcanic chain of the ChiUan
Andes was in a state of unusual actirity, and almost at the same instant the
ialand of Juan Fernandez, 365 mUes from ChUe, was violently shaken. More
than 300 shocks were counted in this district between the 20th of Februai-y
and the 4th of March, in the year mentioned. Before this, however, in the
year 1822, the coast of ChUe had been risited by a most destructive earth
quake, felt simultaneously through a space of 1200 mUes from north to south.
It is unnecessary to miUtiply examples of this kind, the facts, although
very exfraordinary, differing but Uttle in different disturbances; and, in point
of fact, the multipUcation of accounts that have been given of particular
earthquakea would not aaaiat the reader in forming any conclusion as to the
original cauae of auch phenomena. It wUl be more useful to give the general
conclusions arrived at, by those who have studied this subject with a view to
determine the bearing of earthquake phenomena upon the structure of the
Earth'a cruat. The two most important points that have been determined
are these — Ffrst, the much wider extent and influence of subterranean move
ments commencing or connected with earthquakes than is ahown by the
accounts recorded of those places where the undulation is felt; and next,
the nature and amount of the upbearing force exerted, and the permanence
of upheavals and depressions ofthe surface.
IGO Frequent Bepetition and Wide Bange of Earthquake Action. —
Examplea are not wanting in various districts of repeated earthquake dis
turbances, at places far removed from recent or even recently extinct
volcanoea, and aome cases of this kind in the British ialands, where there is
a certain amount of regularity and periodicity in the phenomena, are well
worthy of notice. Thus it has been observed, that of a number of earth
quakes, occurring between 1842 and 1845, aU, or almost aU, took place within
a few houra of the moon'a first quarter, and have reference to great atmo
spheric chaMes, but the number of smaU shocks that have been felt and
recorded in Scotland, within the last few years, give a better notion of the
minuteness and frequency of such undulations, and render it probable, that
if other regions in which elastic igneous rocks are present at the surface
were the subjects of equally careful examination, there would be proof of an
almost perpetual vibration over tracts of vaat extent.
In the yeara 1841-42, between the 23rd July and Sth June, no lesa than
sixty ahocka have been recorded by Mr.MUne, aa felt at Comrie, in Perthahire,
twelve occurring on the 30th July, and the rest distributed at frregular
intervals, varying from some hours to two months. Between the 1st of July,
1842, and 1st of July, 1843, thirty shocks were felt in the same spot, but at
other places in the British Islands, within the same period (although not at the
same time), other earthquakes were observed, aome of them not inconsider
able in extent, the moat remarkable being on the 17th of March, 1843, when
Lancashfre, Cumberland, Dumfrieaahire, the Isle of Man, Belfaat, and even
the Channel lalands (Jersey and Guemsey), were all subjected to a consi
derable subterranean movement, variously described as resembling that of a
t2

276 PHYSICAL GEOGRAPHY.
ship in a heavy sweU, even inducing nausea, and aa like a loaded cart passing
along a atreet. This earthquake was not felt at Comrie, although certainly
much more extenaive than many of those recorded at that place.
The obaervations continuously made in Perthahfre, showed in the suc
ceeding year (between Auguat 1, 1843, and September 4, 1844) thirty-aeven
ahocks, the most severe of which were on the 25th August, 1843, and 14th
January, 1844. Of these, the earthquake of the 25th August was felt simulta
neously, and with about equal intensity, over an area of one hundred square
mUes, and onthe 12th June, 1844, when no shock took place at Comrie, a move
ment sufficient to excite general attention waa recogniaed in Huntingdonshire
and adjacent counties of England.
AVliat is remarkable iu theae caaes, is the very frequent repetition of
small and strictly local ribrations. Such phenomena are no doubt related to
the more widely known and frightful disturbances by which whole towns, with
their population, have been in a few seconds deafroyed, for theae have often
had scarcely vrider range, and the shocks are not more frequently repeated.
But if aome earthquakea have been thus limited, others again have pro
duced results over a vast area. The great earthquake of Lisbon has been
already referred to, and other simUar if not equaUy disasfrous occurrences
have had an equal extent. It appears, in fact, that the propagation of
the wave to which the vibration is due, is only limited by the nature of the
rocks through which it passes, and the original cfrcumstances under which
the shock waa produced.
Many caaes have been recorded in varioua parte of the world, tending to
show, that where once earthquake action exbibita itaelf, it ia likely to recur.
The sUghter and more frequent the vibrations, also, the less probabihty there
seema to be of any serious diaturbances, but neither thia nor any other
apparent law can be depended on. We are told by Humboldt, that ' on the
coaats of Peru, where rain^caroely ever faUa, and where haU, lightning, and
thunder are unknown, these atmospheric explosions are replaced by the
subterranean thunder, which accompanies the trembling of the earth. Prom
long habit and a prevalent opinion that dangerous shocks are only to be
apprehended two or three times in a oentury, shght oscUlations of the ground
scarcely excite so much attention in Lima as a haU-storm does in the tempe
rate zone.'*
The danger from earthquake action, and the relations borne to each other
by disturbances of this kind at distant spots, are not without important
reference to adjacent volcanoes. Among the most remarkable instances on
record of an important and destructive earthquake, at a great distance from a
known volcanic region, is that of Lisbon, but this city ia, after aU, not far
removed from certain portions of the bed of the Atlantic, where tme volcanic
eruptions unquestionably occur. Active volcanoea, therefore, though they
may perhaps be regarded as safety valves for the country in thefr immediate
vicinity, do not by any means prevent the occurrence of severe earthquake
shocks, which thence extend either in a cfrcular or oval area to vast distances,
interrupted and checked, it may be, by the condition and nature of the rocks
traversed, but not failing to produce some effect on the surface, and on the
various works of nature and art there expoaed.
Among the moat interesting of the permanent resulte thus produced, not
only near volcanoes, but over large contmental areaa, are thoae elevationa and
subsidencea which we proceed in the next section to consider.
loi Permanent Change of Level accompanying Eai-thquake Action. —
The earthquake of 1835, that destroyed the town of Concepcion, in South
America, and wluch had a north and south range, was felt over a fract of
country equal in extent to the distance between the North Sea and the
Mediterranean, and during this and other single earthquakea of the same

• Cosmos, Col. Sabine's translation, vol. i. p. 205.

CHANGES OF LEVEL IN EARTHQUAKE DISTRICTS. 277
kind, very extensive areas have been permanently affected by small elevations
or subsidences. Such movements, m horizontal position, have been also
repeated so frequently, that within a period geologicaUy recent, they have
upraised large portions of ChUe and Peru several hundred feet ; and however
it may appear by other observations, that permanent elevation by no means
invariably attends earthquakes, it must stUl be generaUy admitted that some
change in relative level is the usual result of continued earthquake action.
Examples of the permanence of the change produced during earthquakes may
be seen in the condition of some parts of Cutch, near the mouth of the Indus,
and other places on the delta of that river, and in a yet more striking instance
recorded by a recent traveUer in BrazU (Tschudi), to the effect that the bed
of a sfream, in one spot, is so altered in position, that the water, if it could
now be made to occupy its former bed, must rise up a steep incUne, having
formerly taken the course it did when the land was in a different position,
and at a lower level, and the water being now forced to find a new channel.
Although, however, there are few instances of repeated earthquakes
without permanent elevation or depression, to a greater or less extent, the
proofs of this change of level are often exceedingly difficult to obtain. Some
such casea are chiefiy valuable and intereating, not from thefr extent, but
becauae they have occurred in countriea often viaited, and are supported by
historic evidence of recent date. An examination of the present state of the
temple of Jupiter Serapis, in the bay of Baise, near PozzuoU, estabUshes the
fact of an elevation of more than twenty feet (and at one point more than
thirty feet) in the land on which the temple is buUt, and of several alterna
tions of level occurring between the thfrd century of the Christian era and
the present time. It is not necessary here to repeat the detaUs which have
been frequently given with regard to this subject,* but diatinct hiatorical
evidence is thus adduceable of considerable change of level of the land in
the vicinity ofthe volcanic mountains of Vesusius and Etna, and the evidence
reaches almost to certainty, that the elevation sometimea immediately accom
panied destructive earthquake action.
Among the striking examples on record, of permanent change of level in
earthquake disteicts, we may also mention the case of Concepcion Bay
afready referred to, where the ancient harbour, whioh once admitted large
merchant vessels, is now occupied by a reef of sandstone, and a tract of a
mUe and a half in length, where the water was formerly four to five fathoms
deep, is now a shoal, formed of hard sandstone rock. This is supposed to
have been caused by the earthquake of 1751.
In almost every earthquake a considerable amount of destruction is
caused by sUps of earth and partial subsidences, which we have not aUuded to,
as not offering phenomena of sufficient magnitude to serve our argument; yet

* Although it has not seemed advisable to encumber the text with those often repeated
accounts, the foUowing general conclusions, extracted from Mr. Babbage's account of the
Temple (.Quarterly Geological Jom-nal, vol. iii. p. 213,) may be found useful, and will perhaps
be deemed satisfactory, as illustrating the order of the various operations : —
1. The temple was probably constructed ahout the end of the second century after Christ.
2. A dark incrustation formed round the walls before the temple was ruined, and during a
slow and gradual subsidence to a small extent.
3. The temple became filled with volcanic ashes to the height of about seven feet from the floor.
4. A great calcareous deposit fonned in the fresh-water lake made by the hot spring.
5. Partial destruction of the temple.
6. Several of the columns corroded just above the calcareous deposit.
7. The area agam covered by volcanic ashes to the height of about lOj feet.
8. The temple again injured, and exposed to partial subsidence below the sea level. The
columns perforated by marine animals.
9. Third fllhng up with ashes to the height of 20 to 35 feet above the floor of the temple,
ID. Temple elevated to a height above its present position.
11. Temple laid bare in 1750 by excavations.
12. Gradual subsidence between 1328 aud 1845.

278 PHYSICAL GEOGRAPHY.
some of these have been remarkable, aa in the caae of an earthquake in Jamaica
in 1692, when the harboui- subsided so far, that large store houses were after
the diaturbance buried thirty-six feet under water, and the mastheads of
ahipa, that had been wrecked, were seen together with the chimney tops of
houses, projecting above the waves. A teact of land 1000 acres in extent,
alao sank down, so that the sea roUed in and remamed permanently over
thia spot.
102 Origin of Earthquakes. — That an earthquake is the result of riolent,
and generally convulsive, subterranean movement, of the nature of an
explosion, and is often accompanied by the sudden rending of sohd rocks, or
the sudden expansion of gaseous bodies, there can be Uttle doubt ; and thus,
although the ultimate cause may remain unknown, the proximate one may be
considered as established. Such a movement taking place in a subterranean
cavity, is neceaaarUy propagated as a central undulation if the disturbance
occur at a single point, but where a considerable distance is connected under
ground by continuous hoUows or vaults, the explosion may be felt as linear in
the manner afready described. When, alao, the wave or undulation com
mences at a great depth below the surface, and under the ocean, the bed of
the ocean vriU be upheaved, perhaps without fracture, owing to the super
incumbent pressure of a lofty column of water; but in this case, the whole
column of water must be lifted up, and a sea wave produced. When again
the shock passing through the Earth meets the afr, a wave of sound may be
generated, and thus three distinct waves are produced by a single and
instantaneous explosion. The wave produced in the sohd mass of the Earth
wiU itself be propagated with very different velocity, according to the nature
of the rock through which it pasaea, and the interruption it meeta vrith.
Whenever, therefore, an earthquake shock occurs, a true Earth-wave is
the ffrst and neceaaary result. This wave, in its rapid franait from the
centre or axis of disturbance to the apot where the undulationa are finaUy
lost, involves throughout its whole course a movement in space of every
particle of matter affected, and the elasticity of each mass or sfratum of rock
traversed, -wiU influence the mode in which the wave reaches the surface ; so
that, where a rock near the aurface ia brittle, there wUl be a fracture, where
it is aoft, there wUl be a manifest upheaval and depression, and these wUl
remain as permanent alterations of level where the actual movement, in one
or other direction, is prevented by the faUing in or displacement of other
rocks from recovering itself. The rate of propagation of the movement wfll
be exceedingly rapid, amounting always to several mUea per mmute, and
varying from twenty to twenty-eight, according to cfrcumstances.
Where the Earth-wave comea to the termination of the soUd portion of
the Earth's cruat under water, and Ufta the overlying sea, the elevation may
amount to a few feet, perhaps, and the water is necessarily lifted and let fall
to this extent. The Earth-wave, however, continuing to pass along and
moving more rapidly than this sea-wave, carries with it the smaU elevated
portion of the water, leaving also behind it the waves thus produced, which
foUow at a short interval. So long as this goes on in deep water, scarcely
any effeot can be observed at the surface, but no sooner does the wave reach
a shoal, or approach the shore, than the earthquake-wave becomes what is
technicaUy called a ' forced sea- wave,' which is a narrow ridge of water forced
forward by the great wave, and communicating a shock to ships, as if they
had struck upon a bank. This wave accompanying a shock upon a coast is
not considerable, and aa it reaches the coast whUe the beach ia itself elevated
by the earthquake, it scarcely appeara or is felt as an appai-ent recession of the
sea. It ia followed, however, at an interval dependent on the diatance of the
centre of disturbance, by the great aea-wave, which if the ahore be shaUow,
may roll in with irresistible forcc, and in its retreat carry with it the fragments
tolu up aud destroyed by the previous earth-wave. Lastly, a sound-wave
fornied in thc atmosphere, moving stUl more slowly than either of the others,
succeeds the earthqualic afler a eonsiderable interval of lime, and hke thunder,

PERMANENT ELEVATION OF LAND. 279
is only heard when the danger is past, although it often appeara to the
unphilosophical observer as a fearful addition, almost more to be dreaded
than the real undulation.
It occasionaUy happens that areas of disturbance, or districts exposed to
some repeated cause of earthquake, are sufficiently near to be within the
range of the same Earth-wave. The various disturbances in that case
produce thefr effects independently, but these may intersect, and either
desfroy or double each other. The magnitude of the wave propagated
in the crust of the Earth, wUl be increased at the surface according to a
general law in mechanics, by which vibrations fransmitted in elastic bodies
have a tendency to detach the superficial strata.*
103 Partial but Permanent Elevation at a Distance from Volcanoes. —
WhUe there is Uttie difficulty in comprehending the poaaibUity of various
movements of the Earth's surface, where that surface ia expoaed to the
undulations we have described, the case is different, if we find evidence of
pennauMit alteration of level in countries far removed, not only from exist
ing volcanoes, but even from those volcanic appearances which indicate the
former existence of igneous disturbance. Such, at ffrst sight may appear to
be the case with the Scandinavian peninsula and the west coast of the
British islands, which afford in various placea evidence of elevation, but
which have only very recently been recognised aa subject even to partial
earthquake action.
. In Northem Europe there appears to be an area of land whose length
is more than 1000 rnUes, reaching from Gothenberg, in Sweden, to the
North Cape, the northern extremity of European land, subject to slow
movement. In breadth, this teact reaches across the Gulf of Bothnia, and it
steetchea in aU probabUity far into the interior both of Sweden and Finland.
The elevation mcreases in amount as we proceed northwards, and it is
doubtful whether the amount of elevation is constant during equal periods of
time. The result is seen in various ways, but most strikmgly in what are
caUed raised beaches or elevated coast Unes, and the evidence on which the
fact of elevation is proved requfres now to be noticed.
So long ago as the commencement ofthe last century, a Swedish naturaUst,
Celsius, expressed hia opinion that the watera both of the Baltic and Northern
Ocean were graduaUy subsiding, and he inferred from numerous observations
that the rate of depression was about forty inches in a century. This view
waa supported by various facts observed, but controverted by others, such as
the absolute permanence of the water-level in some low islands for many
centuries without change; it was impossible also that a permanent depression
of the level of the sea could take place in. the Baltic and the Gulf of Bothnia,
without being general throughout those parts of the ocean in which the level
was the same. The riew of Celsius is not tenable according to the observa
tions that have been more recently made, but the fact of a change in the
relative level of land and water seems to be now distinctly proved, and in the
year 1807, Von Buch, on his return from a tour in Scandinavia, announced
hia conriction that the whole country from Frederickshall, in Norway, to
Abo, in Finland, and perhaps aa far aa St. Peterabutg, was slowly and
insensibly rising. He alao auggested 'that Sweden may rise more than
Norway, and the northern more than the southem parts.' He was led to
these conduaiona principaUy by information obtained from the inhabitants
and pUota, and in part by the occurrence of marine sheUs of recent species,
which he had found at several pointa on the coaat of Norway above the level
of the sea. He alao mentiona the marks set on the rocka. Von Buch,
therefore, has the merit of being the first geologist who, after a personal
examination of the evidence, declared in favour of the rise of land in
Scandinavia. The attention excited by thia subject in the early partof the pre-

* Humboldt's Cosmos, Sabine's translation, vol. i. p. 192.

280 PHYSICAL GEOGRAPHY.
sent century, induced many philosophers in Sweden to endeavour to determine,
by accurate obaervations, whether the standard level of the Baltic was reaUy
subject to periodical variations; and under thefr direction, linea and grooves,
indicating the ordinary level of the water on a calm day, together with the
date of the year, were chiseUed out upon the rocks. In 1820-21, all the
marks made before those years were examined by the officers of the pUotage
estabUahment of Sweden; and in thefr report to the Eoyal Academy of
Stockholm they declared, that on comparing the level of the sea at the time
of their observations with that indicated by the ancient marks, they found
that the Baltic was lower relatively to the land in certain places, but the
amount of changes during equal periods of time had not been everywhere the
same. During thefr survey, they cut new marks for the guidance of future
observers, several of which were examined by Sfr C. LyeU fourteen years
after (in the summer of 1834), and in that interval the land appeared to
have risen at certain places north of Stockholm four or five inches. Sir
Charles LyeU on this occasion convinced himself, after conversing with many
civU engineers, pilots, and fishermen, and after examining some ofthe ancient
marks, that the evidence formerly adduced in favour of the change of level,
both on the coasts of Sweden and Finland, was fnU and satisfactory. The
alteration of level evidently diminishes as we proceed from the northern
parts of the Gulf of Bothnia towards the soutn, being very slight around
Stockholm. These facts with regard to the shores of the Gulf of Bothnia are paralleled
and rendered more clear by what has been observed since in the northem
extremity of Scandinavia. It there appears that not only a narrow sfrip of
coaat, but the whole of Norway, from Cape Lindesnaes to Cape North, and
beyond that as far as the forteess of Vardhuus, has been in course of elevation
during a period immediately anterior to the historic period. On the south
east coast this elevation has amounted to about 200 yards, and the marks
which denote the ancient Une of coast, and which have been seen and
measured in many points, are so nearly horizontal, that the deriation from
horizontaUty cannot be appreciated, a cfrcumstance which renders it impos
sible to account for the change by assuming a number of smaU local or
independent disturbances.*
There are also on our own shores numerous instances known locaUy as
' raised beachea,' which prove the partial and very conaiderable upheaval of
the coaat in Walea, ComwaU, and elsewhere. At Plymouth and in ite
vicinity, there are remains of a beach sloping towards the sea, of which the
maximum height is thfrty feet above the present high-water mark, and fraees
of simUar beaches covered vrith pebbles and shingles and containing the shells
of the neighbouring sea are met with aU round the coast of ComwaU, some of
them rising to fifty feet above the sea, and others only just removed above it;
while simUar appearances on the Welsh coast show that the change of level
has reached there to as much as 1200 feet. The shores of the Irish Sea near
the mouth of the Mersey, and the whole coaat of Scotland, abound with
aimUar instances, many of which have been recorded in sufficient detaU to
prove distinctly the general fact.
It would, indeed, appear that no part of the western coast of Em-ope, from
France to the North Sea, is now at the same level as that it posseaaed some
agea ago. The change in most placea ia, however, gradual, and the amount
generaUy inconaiderable, the moat remarkable inatances being in the Mediter
ranean, where many cliffs covered with sheUs of recent species are not only
high above the level of the sea, but extend uniformly for very great diatancea.
WhUe, however, changes have been going on thus slowly, and for a
vast period of years, on the north-western coast of the Old World, the
southern extremity of America has been graduaUy assuming a form which

I.ycll's rriitciptt-s '>f Gcologi/, 7th edition, p. '105, r/ passim.

PERMANENT ELEVATION OF LAND. 281
is manifestly due to the action of causes strictly analogous. In South
America, indeed, everything is on a grand scale, and aU recent causes of
disturbance are there exceedingly active ; but the examination of the
surface vrith a view to discover, as far as may be, to what its pecuhar
appearance is ovring, has brought to Ught a series of movements of the
nature chiefly of permanent elevation, hardly traceable in other parts of
the world. Eecent shells — the sheUs of animals whose immediate descendants
of the same race are now hving in the Atiantic — are found on the shores
from Tierra del Fuego northwards for 1200 nules, and at the height of
about 100 feet in La Plata, and of 400 feet in Patagonia. The elevatory
movemente on this side of the continent have been slow, and the coast
of Patagonia, up to the height in one part of 950 feet, and in another
of 1200 feet, is modeUed into eight great step-like, gravel-capped plains,
extending for hundreds of mUes vrith the same heights; this fact shows that
the periods of denudation (which, judging from the amount of matter
removed, must have been long continued,) and of elevation were synchronous
over surprisingly great lengths of coasts. On the shores of the Pacific,
upraised aheUs of recent apecies, generaUy, though not always, in the same
proportionate numbers as in the adjoining sea, have actuaUy been found over
a north and south range of 2075 mUes, and there is reason to believe that
they occur over a space of 2480 mUes in length. The elevation on this weatern
side of the continent has not been equable; at Valparaiso, within the period
during which upraised sheUs have remained undecayed on the surface, it has
been 1300 feet, whUat at Coquimbo, 200 mUes northward, it has been, within
this same period, only 252 feet. At Lima, the land has been uplifted at least
80 feet aince the Indians inhabited that district; but the level, within his
torical times, has apparently subsided. At Coquimbo, in a height of 364 feet,
the elevation has been interrupted by five periods of comparative rest. At
several places, the land has been lately, or stiU is, rising, both insensibly and
by sudden starts of a few feet during earthquake shocks ; a fact which shows
that these two kinds of upward movement are intimately connected together.
For a space of 775 mUes, upraised recent sheUs are found on the two oppo
site sides ofthe continent; and in the southem half of this apace, it may be
safely inferred from the slope of the land up to the Cordillera, and from the
sheUs found in the central part of Tierra del Fuego, and high up the river
Santa Cruz, that the entire breadth of the continent has been upUfted.
From the general occurrence on both coasts of successive Unes of escarpments,
of sand-dunes, and marks of erosion, we must conclude that the elevatory
movement has been interrupted by periods when the land was either stationary,
or when it rose at so slow a rate as not to resist the average denuding power
ofthe waves, or lastly when it was in a atate of aubsidence.*
In estimating the value of the different hypotheses which have been
offered to account for this remarkable phenomenon of the gradual upheaval
of land, it must not be lost sight of, that the change, important as it is in
reference to the organic world, is exceedingly smaU compared with the whole
mass of the Earth. It is natural to conclude, however, that the upheaval
being so dfrectly coimected with volcanic disfricts, wher^ it is most manifest
and considerable, (as in South America,) and occurring elsewhere in spots
which are not without occasional earthquake movements, is connected in some
way with the heated condition of the Earth's interior. This heat, however,
may produce its effect in two ways, either by expanding gaaes and forcing
the crust to be upheaved by thefr agency, or by the actual expansion of
large and thick masses from the increase of heat which they very graduaUy
receive during subsidence owing to the increasing nearness of warmer portions
ofthe Earth.
It has been proved by experiment and calculation, that if a portion of the

* Darwin's South America, p. 2i6.

282 PHYSICAL GEOGRAPHY.
Earth's crust, 100 mUes thick, and of the expansibUity of sandstone rock,
were heated 600° or 800° Fahrenheit, this alone would produce an elevation
of between 2000 and 3000 feet. It is important to bear in mmd these facts,
and their bearing on Physical Geography.
104 Depression over Large Tracts. — The movement that goes on in the
way of elevation over such extensive areas as those we have been describing,
and which indeed appeara to have acted vrith regard to many other wide
tracta of flat land upon the Earth, is not unaccompanied by partial depreasion,
occurring even in aome diatricts where elevation is the prevailing movement.
Evidences of this are seen in submerged forests, or indications of the former
growth of trees where the sea now reaches; but other points of eridence, on
a much larger scale, are not wanting. If, however, there is difficulty in
meaauring accurately the relative level of land and water, ao as to discover a
smaU elevation, the difficulty of proving simUar moderate depresaion is stiU
greater. In spite of this difficulty, there is not wanting proof that whUe
elevation is going on on the eastem shores of the Atlantic, tiie westem coast
offers a converse phenomenon in the sinking down of part of the coast of
Greenland for a space of more than 600 mUes in a north and aouth direction.
Obaervations were made- on thia subject by Captain Graah, duringa survey
of Greenland in. 1823-24, and afterwarda in 1828-29, and othera by Dr.Pingel
in 1830-32. It appeara, from signs and traditions, that the coast has been
subsiding for the last four centuries from the firth caUed TugaUro, in latitade
60° 43' N., to Disco Bay, extending to nearly the 69th degree of north
latitude. Ancient buUdings on low rocky islands and on the shore of the
mainland have been graduaUy submerged ; and experience has taught the
aboriginal Greenlander never to buUd his hut too near the water's edge.
In one case, the Moravian settlers have been obUged more than once to
move inland the poles upon which thefr large boats were set, and the old
poles stiU remain beneath the water as sUent witnesses of the change.*
But far more striking, though not altogether dissimilar, memonals of this
gradual change are found in connexion vrith the work of Uving and dead
animals constructing a atony habitation in varioua parte of the fropical and
adjacent warm seas. Here the coral animals begin to buUd in moderate
depths off the coast, either of the mainland or the innumerable ialanda of
those seas, and appear to fiourish best where most exposed to the ceaseless
and violent dash ofthe waves. Increasing with enormous rapidity, the Uving
waU or reef aoon expands lateraUy, but is not continued downwards to a
f renter depth than ahout thirty fathoms, except in the case of smaU and
etached individuals of different species.
Now, it appears that in spite of thia limit ofthe depth of Uving coral reefs,
vast areas are interspersed with such reefs, so that in the space of ocean
extending from the southern end of the Low Archipelago to the northern end
of MarshaU Archipelago, (a lengtii of 4500 mUes,) every island, with one
exception, is atoU-formed, atoUs being cfrcular groups of coral, with a salt water
lake within them, the water within the lake being generaUy very shaUow, whUe
almost immediately outside the ialand, the depth is very considerable, and
sometimes unfathomable. To give some idea of the true extent of phenomena
of this kind, we may mention that some of these atoUs are oval-shaped,
measuring from fifty to eighty mUes in length, and nearly twenty mUea
in breadth, while one extenaive bank (the Chagos bank) presents all the
characteristics of an atoU, except that it does not reach the surface, but is
completely submerged. The longer axis of thia bank measures ninety miles,
and the shorter as much as seventy; ite cenfral part is a level, muddy fiat,
between forty nnd fifty fathoms deep, surrounded on all sides by steep
mounds, rising from twenty to thirty fathoms, with a breadth of from five to
twelve mUes, and the whole bank is bordered by a waU about a mUe wide.

I.yell, aiitv cit.. p. OOC.

PERMANENT DEPRESSION — CORAL REEFS. 283
rising to within five or ten fathoms from the surface. At a diatance of a mUe
outaide this waU, the depth of the sea is 200 fathoms.
In addition to these atoUs, coral reefs of a more continuous nature extend
as barriers at some distance from the coast line of Australia, and other large
islanda. Theae are caUed barrier reefs, and resemble atoUa in the depth of
the aea outside their outer waU, and also in having a lagoon channel. These
are also of enormous extent, extending on the west coast of New Caledonia
for 400 mUes, at a diatance of eight leaguea from the ahore, and on the north
eastern part of AuatraUa for 1000 mUes, averaging from twenty to fifty mUes
from the shore.
In addition to these two kinda, there is a third kind of coral reef, not
unuaally found fringing volcanic ialands in the Indian Ocean. These have no
lagoon channels, they are narrow, often not more than fifty to a hundred yards
wide, and they are lesa deep than those afready described.
The cause that has given to atoUs and barrier reefs their characteristic
forms is supposed by Mr. Darwin to have been the gradual subsidence of
portiona of the bed of the ocean over large areaa, and ia partly deduced from
the conaideration of these two cfrcumstances — namely, that reef-buUding
corals fiourish only at limited depths, and secondly, that vast areas are inter
spersed vrith coral reefs and coral islets, none of which rise to a greater
height above the level of the sea than that attained by matter thrown up by
the waves and winda. The foundation of each reef ia assumed to have been
rocky, but it cannot be thought probable that the broad summit of a mountain
Ues buried at the depth of a few fathoma beneath every atoU, with acarcely a
point of rock projecting above the surface over so wide an extent as that in
which these phenomena have been fraced. Much other eridence in favour of
the same view is adduced by Mr. Darwin, in his admfrable work On Coral
Beefs, which is accompanied also by a coloured chart of aU such reefs and
islanda, one colour marking those districts in which barrier reefa and atolls
occur, and another indicating the fringing reefs only.
It appears, then, aa the general concluaion with regard to this subject,
that when these two great types of structure — namely, barrier-reefs and atolls
on the one hand, and fringing reefs on the other, are thus laid down in colours
on map, a magnificent and harmonious picture of the movements which" the
crust of the Earth has vrithin a late period undergone, is presented to us.
We there see vaat areas rising, vrith volcanic matter every now and then
bursting forth through the vents or fissures with which they are traversed.
We see other wide spaces slowly sinking without any volcanic outbursts ; and
we may feel sure, that this sinkmg must have been immense in amount, as well
as in area, thus to have buried over the broad face of the ocean every one of
those mountains, above which atoUs now stand Uke monuments, marking the
place of thefr former existence. Eeflecting how powerful an agent, with
respect to denudation, and consequently to the nature and thickness of the
deposits in accumulation, the sea must ever be, when acting for prolonged
periods on the land, during either its slow emergence or subsidence ; refiecting,
also, on the final efi'ects of these movements in the interchange of land and
ocean- water, on the cUmate of the Earth, and on the distribution of organic
beings, it may be fairly assumed, that the conclusions derived from the study
of coral formations are amongst the moat important that can be presented to
the conaideration of the phyaical geographer.*

• Darwin On Coral Beefs, p. 148.

284

CHAPTER VIII.
STEUCTURAL PHENOMENA OF THE EAETH INDICATING
IGNEOUS ACTION.
5 105. Nature of igneous rocks in general. — 106. Extinct volcanic regions. — 107. Antient lava
currents and other products of extinct volcanoes. — 108. Other igneous rocks not volcamc.
— 109. Metamorphism. — IIO. Dykes and mineral veina.
^ATUBE of Igneous Bocks in General. — The igneous phenomena and
thefr results, so far as we have yet considered them, are hmited to
-the Earth's surface, and give little or no insight into the actual structure of
any portion of that auperficial crust which it is the object of geologists to
understand and deacribe. Thus, we have aeen that volcanoes, although of
great interest and importance in the general economy of nature, are too few
in number, and occupy too smaU an area, to affect the whole area of land to
any considerable extent, and though, no doubt, those elevations and depres
sions that we have discussed, and which are connected vrith volcanic action,
are of vast effect in their general result, when continued for a sufficient time,
yet even these, in the short space of human history, must have been totally
insignificant in modifying the general surface. But we muat now carry our
investigations somewhat farther, and we shaU soon discover that whUe
igneous action is not confined to one district or one period at present, but
affects various points of very vride tracts, and lasta often in the same fract for
an apparently mdefinite period, there are many other parte of the Earth
where, beneath the surface and in the rocka that are offered for inveatigation,
proof may be obtained of igneoua action, either dfrectly or indfrectly, andthe
usual reaulta may therefore be looked for in the way of former elevation and
depression, as weU as additional results derived from the disturbance of
material in a hardened state by violent mechanical force. In the present
chapter we may consider with advantage these pointe, and thus obtain
an insight into one very important department of geology, strictiy so caUed —
namely, that of mechanical rocks not left in thefr original condition of
mechanical apposition, but altered by the action of heat or chemical forcea ;
and of other rocks which offer no appearance whatever of mechanical origin,
but, on the confrary, seem to have formed part of the original skeleton and
framework of the globe, presenting themaelvea in the cenfral axes of moun
tain chains, or in the long-exposed and weathered surface of granitic bosses,
or roUed blocks broken from the parent rock and transported to a distance.
The various cfrcumstancea under which such rocks are presented — ^the
evidence of igneous activity at very early periods of the Earth's history, as
well as at more recent, but stiU distant times — the steuctural pecuUarities of
Tarious igneous rocks, and the structural changes produced by them — ^these,
together with the phenomena of segregation, and the coUecting of various
substances into veins and fissures, whence they may be extracted for the use
of man, wUl, when explained, enable the student to comprehend something
of the condition of a portion of the Earth, and form fit subject-matter for
careful study.
io6 Extinct Volcanic Begions. — As at present there are certain Unes and
smaU areas of volcanic activity, connected with which can be teaced a consi
derable amount of elevation on the Earth's siu-face, so may we find in many
places abundant proof of ancient volcanic agency in heaps of ashes, volcamc

EXTINCT VOLCANIC REGIONS. 285
cones and craters, and beds of lava, the burnt-out Ifres of former times, and
the result of eruptions and attendant elevations of which little or no other
record is preserved.
Appearances of this kind are not limited to such distinct marks of subter
ranean fires as we have mentioned, nor must we expect that eruptions that
have been succeeded by the frequent denuding action of marine currents can be
aa manifest and as easUy made out as where a ririd flame, a column of smoke,
or a current of molten rock, speak to the senses in a language that cannot be
questioned. But we need not feel leas certain of the former existence of
volcanic action in a spot becauae, at present, there are no eruptions, provided
we can discover true erupted products, auch aa ashes and lava ; and it ia well
known these are occasionaUy seen where there are abaolutely no indications
whatever of igneous disturbance at the surface, although, in other caaes, the
form of ancient volcanoes is partly preserved in the hUls of the district in
spite ofthe time that has elipsed smce the period of activity. There may,
however, be distinct conditions of igneous rocks where there is no evidence of
volcanic disturbance, and it is necessary to consider the extent and value of
the various phenomena in each case.
The principal and best knowm points at which volcanic eruptiona have
taken place on the continent of Europe, aince the commencement of the
tertiary period, from volcanoea which have now become totaUy extinct,
are in the vaUey of the Ehine, between Bonn and Mayence ; in the depart
ment of Puy de Dome, in Central France ; and on the north-east coast of
Spain, at Olot, in Catalonia. AU these have been perfectly quiet, and free
from the diaturbancea of volcanic action, during, and probably long before,
the exiatence of man upon the Earth, but aU of them exhibit, with the utmoat
diatinctness, series of volcanic phenomena exactly resembling those which are
described as characterizing Etaia and Vesurius in modem times. One vol
canic district of the Ehine extends for about twenty -four mUes from east to
weat, and from six to ten mUes from north to aouth. The volcanic cones have
here been forced up through schistose and micaceous beds of the middle and
older Palaeozoic periods, and the trachytic lava and basalt have been poured
out around the base of the hUls, often extending to considerable distances,
vrithout much reference to the present configuration of the country. A
number of ancient craters, some of which are now lakes, may be observed at
different points on each bank of the Bhine, but the waUs of these craters are
usuaUy made up of cinders and scoriae, and the deep indentions and fractures
ot the waUa often ahow the points whence a lava current must once have isaued.
On the whole, however, the lava aeems to have been chiefly erupted through
cracks and fissures in the subjacent rocks, and to have been spread evemy
over the surface, often in very thin bands.
By far the moat important feature of the volcanic diafrict of the Ehine,
though not that which presents itself most prominently to the paaaing risitor,
is the great extent of the basaltic platform, partly in the Duchy of Nassau,
and extending on the right bank of the ilbine, but reaching stiU further to
the east, and forming the hUls called the Vogels Gebfrge. In the former
district, indeed, the basalt is covered up in many places 'by a remarkable bed
of hgnite, or brown coal — but not less than 1000 aquare mUes of countey in
the neighbourhood of the Ehine have been in former ages overwhelmed by a
flood of lava, probably spread out beneath the watera of an inland lake long
since dried up. The thickness of the bed is not generaUy considerable.
A district in Central France — in former times the seat of subterraneous
disturbance — ^repoaea, or, rather, riaea out of a granitic platform : the Mont
d^Or, the moat conspicuous of the volcanic cones, rising suddenly to the
height of aeveral thousand feet, and being composed of layers of scoriae,
pumice-atones, and fine deteitus, with interposed beds of basalt. A consider
able number of minor volcanoea form an frregular ridge on the platform, and
extend for about eighteen mUes in length, and two in breadth. They are
usuaUy truncated at the summit, where the crater is often preserved entfre.

286 PHYSICAL GEOGRAPHY.
the lava having issued from the base of the hill ; and the lavas may often be
traced from the crater to the neareat vaUey, where they uaurp the channel of
the river, which in aome caaes haa aince excavated a deep ra-rine through the
baaalt. In Catalonia, tbe eruptions have burst entirely through secondary
rocks, and the distinct cones and craters are about fourteen in number, but
there are, besides, several points whence lava may have issued. The volcanoes
are most of them very entire, and the largeat has a crater 455 feet deep, and
about a mUe in cfrcumference. The currents of lava are, as usual, of consi
derable depth in the narrow defiles, but spread out into thin sheets over the
plains ; the upper part is sooriaceous, further down it is less porous, and at
the bottom it becomes prismatic basalt, about five feet thick, resting on the
subjacent secondary rooks. In addition to these, many other parts of Europe,
especiaUy in Bohemia, Moraria, and Hungary, exhibit remarkable and
exteemely interesting examples of extinct volcanoes. Some of these are weU
known for the hot springs which rise out of the ground in the vicinity, or the
hUla of volcanic OToducts which characterise the landscape, and of thia kind
are Carlsbad and TopUtz. Others are near existing volcanoes, but have stiU
aU the peculiarities of those which are extinct, and amongst this latter kind
are numerous instances in the Greek Archipelago.
It appears from the investigations of various fraveUers that the westem
part of Asia and the peninsula of India exhibit the phenomena of recently extinct
volcanic action on a scale far grander than is known in Europe, for in these
countries the lava has been poured out over an area of many thouaand square
mUes, and resta in flat tubular maases upon the country. The volcanoes of
Asia Minor are stUl in a state of disquiet, and the elevation of the chain of
the Caucasus has doubtless been continued to within a very recent period ;
while so closely does the past approach the present in this part of the world
and in America, that it is often difficult to decide to which period many of
the phenomena must be referred, and it has happened even in Europe, that
volcanoes, supposed to be extinct, have once more burst forth, and apparently
with tenfold violence, after a long period of repose.
The coast of Antrim, presenting the magnificent basaltic columns of
the Giant's Causeway, and an important adjacent district in Scotland
as weU aa Ireland, have long been celebrated as exhibiting very remark
able instances of the protrusion of large quantitiea of molten rock in
former times. In the part of Ireland aUuded to, there are many hundred
square mUes of countey, extending from the neighbourhood of BeUast to
Coleraine, in which a considerable series of rocka of the secondary period,
terminating vrith the chalk, have been covered in this way. On the coast,
especially towards the north, the basalt is seen capping the chalk, which
is usuaUy much altered and hardened into limestone, and the flints
are reddened as if burnt near the contact. In other places, clayey or
shaley beds are changed into hard siUceous rock, and sometimes in£cate
crystaUine structure ; whUe in others, again, as at BenEvenagh and elsewhere,
the basalt assumes a character of extreme grandeur, and successive stages of
ponderous and shapeless masses rise to the base of the steep basaltic summit,
and there break into pinnacles and precipitous cliffs. But in the interior of
the counfry, the protruded rock, although present, sinks to a low level, and
along the western shores of Lough Neagh and Lough Beg is so much con
cealed as to appear only in isolated lumps or smaU ridges, riaing here and
there above the surface. In many places, indeed, it is erident that the
softer parts of the rock have been carried away, and that the whole of the
detached portions were formerly continuoua ; and this ia not to be wondered
at, when we consider that the mineral composition and relative hardness is
very variable, and that the whole diatrict haa been exposed to dUurial action.
and to the denuding force of running water. It is not easy to account for
the occurrence of these large masaea of igneous rock in the north-east of
Ireland, or to connect them with any focua or cenfre of eruption. They have
probably been forced through wide cracks formed in the subjacent strata,
and thua belong to the claaa of phenomena sonietimes considered separately

ANCIENT LAVA CURRENTS. 287
from the tabular basalt, and denominated trap veins and dykea. But how
ever thia may be, aU the teue characters of lava are apparent in the rock
under consideration, and aU the strata discovered in contact with the basalt
have been altered by this foreign rock introduced among them. Phenomena
almost exactly simUar are seen in the Island of Staffa and in some others of
the western islands of Scotland, and the picturesque beauty of Fingal's Cave
and the Giant's Causeway has been too often described to render any account
of them necessary in this place.*
107 Ancient Lava-Currents. — It has been proved by the experiments of
Mr. Gregory Watta,t that the rock apoken of in the preceding page as
basalt, is in point of fact, nothing more than lava of ancient date, and
although in England baaalt and basaltic rocks are conflned to certain parts
ofthe countey, and to rocks of certain geological designation, they are found
elsewhere more generally diffused.
Basalt occurs in the older rocks in two conditiona, which may be
aeparately considered — namely, 1st, in the condition of an overlying maas, or
of beda alternating vrith the regular strata ; and 2nd, as dykes, traversing
stratified and other rocka, and filUng up cracks and fissures. In this latter
state it often forms the connecting link between the tabular masses and some
great subterranean reservoir, although in other cases it does not rise above
the surface of the rocks which it peneteates. Its mineral constituents are
essentiaUy the same as those of modern lava, but occasionally hornblende
predominates, when, from the pecuUar colour of that mineral, the name of
freenstone is appUed to the variety. The most usual characters of the
asaltic rocks of England are — (1) their iron-grey colour, approaching to
black ; (2) thefr frequent tenacity and hardness (whence their value in making
roads) ; and (3) a sharp and sometimes conchoidal fracture, and a granular
aspect, indicating the commencement of crystaUiae structure. They are very
liable to superficial decomposition, in which case the colour changes to a rusty
brown, owing to the oxidation of the contained fron, and the decomposition
sometimes peneteates a considerable depth into the mass of the rocks, exhi
biting spheroidal masses less decomposable than the reat of the rock. There
are aeveral beda and overlying maaaes of trap among the carboniferous rocka of
England, very many othera wiiich have only penetrated the Silurian rocka, and
which, therefore, must have been erupted anterior to the decompoaition of the
. Newer Palseozoic steata. It wiU be sufficient to aUude shortly to the principal
instances, in order to give a general idea of the nature of these rooks of
intrusion in our own country. Baaalt occura in overlying masses in many parts
of thenorthof England; eminencesof thiskindhaveoftenbeenchosenfortbesites
of feudal castles, and at Bamborough, where one of these castles was buOt, the
thickness of the mass has been ascertained, by boring for water, to be seventy-
five feet. A remarkable instance of overlying basalt may be observed forming
a group of hUls near the town of Dudley, m Staffordshfre. The rock here
has received the name of Eowleyrag,J from the vUlage of Eowley, situated
on one of the highest of the basaltic hUls. It is extremely hard and of coarse
texture, and has been used for paving the steeets of Birmingham; a similar
rock is found at a distance, forming the upper part ef the lofty hUls of
Titteratone Clee and Brown Clee, in Shropahfre. The trap in these places
distinctly repoaes on the coal measures, and where it comea in contact witb
the coal haa greatly injured ita quaUty, and reduced it to a aooty state. The
toadstone of IDerbyshire ia a well known rock, apparently interstratified with
the rocka of the Carboniferous period in that county, and it offera a very
striking example of bedded trap. This toadstone, wbich had generally been
described aa repeated in three distinct beds, has been supposed by Mr.
Hopkins to be the effect of only one, or, at the most, two eruptions of melted

* Ansted's Geology, vol. ii. pp. 208 — 213. t Trans. Boy. Soc. for 1804, p. 279.
t It was a mass of this rock which formed the subject of Mr. G. Watts' experiments, already
described.

288 PHYSICAL GEOGRAPHY.
rock, and he has endeavoured to show that the several beds, apparently
distinct, merely consist of the original one repeated in different parta of the
district by faults. The abundance and accuracy of the detaUed information
offered in support of this view render it difficult to doubt that the con
cluaion ia correct. The determination of this point is of much importance in
a country so valuable for its mineral resources, and the more so, becauae the
identification of the limeatonea and associated lead veins depends on the
position of the interstratified volcanic rock.*
Basaltic dykea of very conaiderable extent fraverse the carboniferous
limestone in many parts of the north of England, some of them being
as much as from thirty to forty feet in width. Theae dykes are either
vertical or very highly incUned, and the baaalt of which they are fonned
is of a greeniah-black colour and coarae texture. Sufficient evidence is sup
poaed to exist of their igneous origin, and ofthe rock having been injected m
a melted state, by the altered appearance of the wall of the dyke; for the
adjacent coal, in one example, at Walker, in the Newcastle coal-field, ia
actually converted into coke, which, on one side, was found to be in some
placea thfrteen feet thick, and on the oppoaite side upwarda of nine feet.t
But thia fact of the coal being completely charred and tumed into coke ia
common throughout the disfrict, whenever a basaltic vein fraveraea coal-
bearing strata.J The rocks of volcanic origin, which are most conmionly
aaaociated vrith baaalt, are those caUed trachytic, or trachyte, from then-
rough feel when rubbed between the fingers. Trachyte is sometimes con
sidered to bear the aame relation to granite that lava does to the ancient
basalts, and is compoaed chiefiy of felspar, combined frequently with a con
siderable proportion of ailex. It abounds in the volcanic diatrict of the
Ehine, and there forma a kind of imperfect buUding stone, and it is also
common in varioua forms in the Puy de Dome, where it appeara under very
simUar cfrcumstances. Besides the ordinary form of frachyte as a volcanic
rook, it appears yet more frequently in pulverulent masses of pumice,
forming what is called tuff or tufa, which has been found in rocks of aU ages,
interstratified vrith fossuiferous beda, but itaelf rarely containing organic
remaina. The preaence of this tufa invariably marks the vicinity of igneous
and erupted rocks, and in this way it is often useful to the geologist, more
especiaUy in the older formations.§ It has frequently been attempted, more

* At Teesdale, in Yorkshire, and elsewhere in the north of England, there are instances
of highly picturesque scenery owing to the presence of basaltic rocks in various crystalline cou
ditions. In these cases, the associated limestones are usually altered and converted into marble.
t Conybeare and Phillips' Geology of England and Wales, p. 447. It may be observed here
that this evidence, though very plausible, is by no means free firom otgection, and the change
observed may possibly be independent of the heat of the basalt.
X A still more remarkable instance than that in the text, of the alteration effected in the
neighbourhood of a trap-dyke, is related in the Transactions ofthe Northumberland Natural History
Society, vol. ii. p. 343. An account is there given of the greenstone dyke on Cockfield Fell,
and its eflfects on the coal strata in one of the collieries of the great north-eastern coal-field.
In working the coal towards this dyke, the change was observable at a distance of flfty yards,
the coal becoming dull, and losing its quality for producing flame. Nearer the dyke, it has the
appearance of half-burnt cinder, and still nearer, consisted of sooty matter, caked together,
while close to the dyke the bed was reduced in thickness from six feet to nine inches. Thia
dyke is nearly vertical ; it has been traced abont seventy miles from south-east to north-west,
and is in some places eighteen yards In width ; and it is calculated to have spoiled as much as
100 yards of coal along all that part of the seam traversed by the dyke throughout Cockfield
Fell. The observation made in the previous note will also apply here.
§ The pumice of commerce can hardly be regarded as a distinct mineral, as It is only a
cellular and filamentous state which several volcanic rocks (chiefly trachytes) are capable of
assuming. It is not met with in all volcanic districts, and seems to be erupted only under
peculiar circumstances. Vast quantities have heen quarried at the foot of Cotopaxi, one of the
celebrated volcanoes of the Andes, and it there occurs in beds distinctly stratified, and is often
associated with obsidian. The principal localities in Europe in which it abounds are the Wpari
Islands, and some of the islands in the Grecian Archipelago, Iceland, and the extinct volcaio
of the Rhine. It is also found iu Tenerifl'e, and in some of the volcanic islands of the
eastern Archipelago.

GRANITIC ROCKS. 289
especially by the continental geologists, to class the various rocks of igneous
origin with reference to thefr predominant minerals, but these arrangements
have never attained any very general acceptance in our own country. There
appear to be two series — those in which felspar or hornblende respectively
abound — in rocks of each geological period, and these in thefr most charac
teristic forms of granite or trachyte, and basalt or lava, are sufficiently distinct,
but they pass insensibly into one another by innumerable variations, which
demonstrate the simUarity of origin of aU the unsteatified rocks.
It may, therefore, be conaidered, on the whole, that the occurrence of
teappean rocks is a geological event belonging to all successive periods, and
affecting aU rocks whether stratified or not, but it is also evident, that while
no rocks bear more steictly the marks of igneous origin than those caUed
basaltic, even they are sometimes so distinctly stratified aa to have formed
thin layera alternating with fosaUiferoua ateata of aqueoua origin and probably
erupted from volcanic venta opening at the bottom of the ocean, as we
have reaaon to beUeve atiU happens occaaionaUy. There is, therefore, in
these phenomena — ^which, it muat be repeated, connect the rocks of known
igneoua origin, such as are stUl from time to time erupted, with the most
ancient of those rocks supposed to be plutonic — a still farther and more
intereating point rendered clear, the change being even indicated by which
the regularly stratified foaaUiferoua rocks pass first of aU into metamorphic,
and then into diatinctly igneoua formationa.
Theae facta vrith regard to ancient lava currents, erupted at various
times and under various cfrcumstances, afford ample proof that volcanic
agency, or some veiy nearly aUied force, has acted even during the formation
of the lower, and therefore older, of those mechanicaUy formed rocka met
vrith in almoat aU parts of the Earth's surface. We muat, however, now
consider other appearancea presented, in whioh igneous action appears clear,
though not in the form exhibited in either modern .or ancient volcanic vents.
io8 Other Igneous Bocks not Volcanic. — ^A very large portion of the
underlying rocks in many parts of the world, and almost aU the highest peaks
of the principal mountain ranges, are compoaed of rocka of which granite is
the type, and which aeem to have been upheaved from considerable depths,
bearing with them in most cases masses of sfrata originaUy deposited
horizontaUy upon them, but in the course of elevation cracked and broken, or
otherwise altered, according to the nature of the elevating force and the
mechanical condition of the beds themselves. These rocks are apparently
igneous, but whether they were ever in actual fuaion or not, thefr particlea
are now ao arranged as to exhibit clearly the action of crystalline forces, and
the rocks associated and lifted are not unfrequently penetrated by the granite
or crystaUine masses, or otherwise affected by them. The effects thus pro
duced are not attributed to ordinary volcanic action, for they are on too
large a scale, and too Uttle identical, to bear strict comparison with any
reaulte of auch action at preaent. They are, however, not unUke when fafrly
considered, and afford most useful material for such limited comparison as
the caae reaUy warranta.
The granitic rocks are very widely spread over the earth, and in moat cases
they form the underlying portion, with reference to any sedimentary rocks
that may appear. This might be proof either of thefr being the most ancient,
or the newest formed rocks, for if the former, they must occupy as they do
the lowest poaition, and if the latter, they may have existed in another form
for an indefinite period, although only recently placed in a state to affect or
upheave other rock's. It is, however, certain, that they reaUy are of various
periods, and although from thefr extensive range oflen regarded as the
foundation and soUd framework of the Earth, they are possibly in the very
act of formation far beneath the surface, even at the present day.
Granitic rocks, although by no means always of the same general
character, exhibit features which leave no doubt as to their nature, and may
U

290 PHYSICAL GEOGRAPHY.
be found in several locahties in each of the British Islands. Granite also
occurs abundantly in other parts of Europe, as in the Scandinarian moun
tains, the Hartz, the range of mountains separating North Germany from
Bavaria and Bohemia, the Alps both of Switzerland and the Tyrol, the
Pyrenees and the Carpathians. In Asia it forms the cenfre of the Caucasus ;
it occupies a large part of the Himalayan, Uralian, and Altai mountains, and
ia found alao in Siberia. In Africa it appeara in Upper Egypt, in the Atlas'
mountains, and at the Cape of Good Hope : it may also be traced along the
western part of the whole of the two Americas ; and appears again in the
islands of the South Pacific, and in AustraUa.
But granite is only one form of igneous rock, and many others, some
having the same general porphyritic character (crystals embedded in a base),
are found in various parts of the earth, either alone or in near association
vrith true granite (quartz, felspar, and mica). Such rocks, under various
names, have often been described in distinct groups as pecuUar crystaUine or
chemical products, but many of the pecuUaritiea they present, are probably
rather owing to a difference in the rate of cooUng of a large masa, than to
any original characteriatic. Thus, according to the rate of cooling, we inight
have a large or fine grained granite, or a nearly compact rock : or if the
quantity of felspar was very great, and the cooUng rightly proportioned, the
mica and quartz might be crystallized in a compact earthy or glaaayuncryatal-
Uzed baaia. In thia way a felspar porphyry might be produced from the
aame ingredients as ordinary granite, and the various greenstone, hypersthenic,
hornblendic, and other mixtures, do not requfre detaUed deacriptions in a
general account of igneous rocks.
Of the granite and simUar rocks presented in the British Islands, some
portions in Scotland (Isle of Skye), ComwaU, Cumberland, and elsewhere,
have not only forced up other rooks, but have also penefrated the fissures made
in them during elevation. This seema to prove two important points — ^namely,
that at least in these caaea, the granite waa more modern than the adjacent
and overlying masses, and also was ejected in a soft or nearly fiuid state.
Granite veins or dykes, fUling up crevices, are indeed by no means rare
phenomena, although they had not tUl a recent period attracted fnU and
complete attention.
The chief field for oliservation of igneous rocks vrithin the British Islands
is in Scotland, where almost every variety ia represented. The Grampian
and other mountain ranges are entirely composed of granite, and in the
adjacent islands it is repeated in aU its characteristic featurea. In Cumber
land and North Wales, felspar porphyries take the place of granite to a great
extent, and alternate vrith it. In CornwaU, granite re-appears in large
quantity and throws off numerous veina. In the Malvern bills, and those of
Charnwood Forest, in Leicestershfre, Syenite prevaUs, whUe hypersthene rock
frequently appeara, and sometimes, as at CuchuUin and Carrock FeU, forma
pinnacled mountains. The rock caUed clayatone, and clayatone porphyry,
and varioua amygdaloidal rocks, also present themselves, varying and com-
pUcating the phenomena.
Thus do theae igneoua rocka present themselves at or near the general
surface, in many important districts, and ofler for the inveatigation of the
naturalist many striking facts. The varioua rock«, abruptly riaing and exposed
at the surface, are often split by deep paraUel fissm-cs, sometimes formed into
largo fiattened globes, which put on also a columnar appearance — and some
times wom into mounds, scaling off in layers at the surface. The same rocks,
different only by the circumstances of their formation, are elsewhere spUt into
blocks, which might at first appear roUed or transported from a distance, but
which are really only the results of a pecuUar decomposition.
AU these and many other appearances have been described as, at some times
and in some places, characteristic of this group of rock masaea, which have
indeed little in common either in material or order of arrangement of the
material. It ia important also, to remark in conclusion, that the mineralogical

¦Jii .J J. ,

METAMORPHIC ROCKS. 291
and other peculiarities are whoUy independent of age or position, for we find
in oppoaite hemispheres in totaUy different climates, and under circumstances
perfectly distinct, the same general aspect and the repetition even in minute
detaU of many common igneous rocks.
109 Metamorphism. — The erupted rocks, whether granitic or basaltic,
not only act dynamicaUy, shaking, elevating, incUning, and lateraUy displacing
the superincumbent beds, but also modify the chemical combinations of thefr
elements, and the nature of their internal structure ; thus forming new rocks.
These under the names of gneiss, mica slate, clay slate, granular limestone
or marble, and quartz rock, are often very extensive, and are denominated
metamorphic. The theory of metamoi-phiam is now estabhshed with reference
to a great variety of rocks, and the nature and amount of change are fully
recognised. Observationa made vrith great care, and over conaiderable tracts of country,
show that erupted rocks have acted in a regular and ayatematic manner, ii
parta of the globe most distant from each other, granite, baaalt, and diorite
are seen to have exerted, even in the minutest; detaUs, a perfectly simUar
metamorphic action on the argillaceous schists, the compact limestone, and
the grains of quartz in sandstone. But whUst the same kind of erupted rock
exercises almost everywhere the same kind of action, the different rocks
belonging to this claas present in this respect very different characters.
The effecte of intense heat are indeed apparent in aU the phenomena ; but
the degree of fluidity has varied greatly in aU of them, from the granite to the
basalt ; and at different geological epochs, eruptions of granite, basalt, green
stone, porphyry, and serpentine, have been accompanied by the issue of
different substances in a state of vapour. According to the views of modern
geology, the metamorphism of rocks is not confined to actual change
effected at the contact of two kinds of rock ; but it comprehends all the
phenomena that have accompanied the issuing forth of a particular erupted
mass ; and even where there has been no immediate contact, the mere
proximity of such a mass has frequently sufficed to produce modifications in
the cohesion ofthe particlea, in the texture of the rook, in the proportions ofthe
sUicious ingredients, and in the forms of crystalUzation of the pre-existing
rocks. All eruptive rocks peneteate as veins into sedimentary steata, or into other
previously existing endogenous* masses ; but there is an essential difference in
this respect between plutonic rocks — granites, porphyries, and serpentines —
and those called volcanic in the most restricted sense — teachytes, basalts, and
lavas. The rocks produced by the stUl existing volcanic actirity present
themselves in narrow steeams, and do not form beds of any considerable
breadth, except where several meet together and unite in the aame baain.
Where it haa been possible to trace basaltic eruptiona to great deptha, they
have alwaya been found to terminate in slender threada, examples of which
may be seen in three placea in Germany, — near Markauhl, eight mUes from
Eiaenach, — near Eschwege, on the banks of the Werra, — and at the Druidical
stone on the HoUert road (Siegen). In these oases, the baaalt, injected
through narrow orifices, has traversed the bunter sandstone and greywacke
slate, and has spread itself out, in the form of a cup ; sometimes forming
groups of columns, and sometimes divided into thin laminae. This, however,
is not the case vrith granite, syenite, porphjo-itio quartz, serpentine, and the
whole series of unstratified rocks, to which, by a predUection for mythological
nomenclature, the term plutonic haa been applied. With the exception of
occasional veins, aU these rocks have been forced up in a semi-fluid or pasty
condition, through large fissures and wide gorges, instead of gushing in a

' This term has been used by Humboldt to designate all rocks formed or modified from
within, and therefore, not owing their essential characteristics to mere mechanical action. It
includes tbe igneous and metamorphic rocks of other authors.
u2

292 PHYSICAL GEOGRAPHY.
liquid stream from smaU orifices ; and they are never found in narrow streams
like lava, but in extensive masses. Some groups of dolerites and frachytes
show traces of a degree of fluidity reaembUng that of baaalt ; othera, forming
vaat craterless domes, appear to have been elevated in a simply aoftened state;
others again, Uke the trachytes of the Andes, in which Humboldt atates
that he haa often remarked a atriking analogy to the greenatone and syenitic
porphyries (argentiferous without quartz) are found in beds like granite and
quartzose porphyry.
Dfrect experiments on the alterations which the texture and chemical
constitution of rocks undergo, from the action of heat, have shotm that
volcanic masses (diorite, augitic porphyry, basalt, and the lava of Etna) give
different products according to the preasures under which they are melted,
and the rate at wbich they are cooled ; if the cooling has been rapid, they
form a black glaaa, homogeneous in the fracture; if slow, a stony mass of
granular and crystaUine structure, and in this latter case crystals are formed
in carities, and even in the body of the maas in which they are imbedded.
The same materials also yield products very dissimilar in appearance, a fact of
the highest importance in the study of eruptive rocks, and the teansformationa
whioh they occasion ; since, for example, carbonate of lime, melted under
high pressure, does not part vrith its carbonic acid, but becomea when cooler
granular limeatone or aaccharoidal marble when the operation is performed
by the dry method ; whUe in the humid process, calcareous apar ia produced
with a leaa, and arragonite with a greater degree of heat. The mode of aggre
gation of the particlea which unite in the act of crystallization, and conse
quently the form of the crystal itself, are also modified by differences of
temperature ; and even when the body has not been in a atete of fluidity, the
particles, under particular cfrcumstances, may undergo a new arrangement
manifested by different optical properties. The phenomena preaented by
deriteification, — by the production of steel by casting or cementetion, — ^by the
pasaage from the fibrous to the granular texture of fron, occasioned by increased
temperature and poaaibly by the influence of the long-continued repetition of
slight concussions, — may elucidate the geological study of metamorphism.
Heat sometimea eUcits opposite effects in crystaUine bodies ; for MitecherUch's
beautiful experiments have eatabliahed the fact, that without altering its
condition of aggregation, calcareous spar, under certain conditiona of tempe
rature, expands in one of ita axial dfrectiona whUe it confraete in the other.
Passing from these general considerationa to particular examplea, we may
mention the case of schist converted by the vicinity of plutonic rocks into
roofing slate of a dark blue colour and gUstening appearance ; the planes of
stratification are intersected by other dirisional planes, often almost at right
angles with those of stratification, indicating an action posterior to the
alteration of the schist, the latter sometimes containing carbon, and then
perhaps capable of producing galvanic phenomena.
Sometimes the contact and plutonic action of granite have rendered
argillaceous schists granular, and transformed the rock into a masa reaembUng
granite itself, consisting of a mixture of felspar and mica, in which laminae
of mica are found embedded. We are told by Leopold von Buch, that aU the
gneiss between the Icy Sea and the Gulf of Finland has been produced by
Tnetamorphic action of granite upon the sUurian strate. In the Alps, near
ihe St. Gothard, calcareoua marl haa been similarly changed by the influence
of granite, firat into mica slate, and subsequentiy into gneiss. Similar
phenomena of gneiss and mica slate, formed under the influence of granite,
present themselves in the ooUtic group ofthe Tarantaise, in which belemnitea
are formed in rocks which have afready in great measure assumed the
character of mica slate.*
Eemarkable inatances of metamorphism have been pointed out in the

» Humboldt's Cosmos, Sabine, p. 246—360.

MINERAL VEINS. 293
Tyrol, especiaUy on the Italian side, where limestone is altered by means of
fissures traversing it in every direction, the intervala and cavities being fllled
-with crystals of magnesia, and the original stratification completely obUterated.
Othera, not less remarkable, are found alao in the cliff on the coaat of
CornwaU, and in many of the western islanda of Scotland.
IIO Dykes and Mineral Veins. — One of the resulta of the intruaion of
igneoua rock, and the consequent change effected in the molecular condition
of the rock, ia the production of crevicea and fissures, which may either have
arisen from the absolute elevation and consequent disruption of the mass, or
from confraction, owing to the drying or heating of the mass. Generally
such crevices wUl be in two principal dfrections, the one identical with that
ofthe axis of disturbance, and the other at right angles to that axis — the
former wiU be the longer and more uniform series, but wUl often include
paraUel fissures at intervals — the other -wUl be shorter and more irregular,
and perhaps chiefly observable at intervals where there seem to have been
points of more abrupt violence. It may be considered also highly probable,
that since we find two kinds of fissures, one of considerable width at and near
the surface, but becoming narrower in descending, whUe the other continues
of nearly equal width to considerable depths, these two kinds are not
unfrequently due to different causes, the gaping cracks frequently identical
vrith faulte and dislocations of the steata resulting from upheaval, whUe the
more even and regular crericea are coimected with deeper-seated disturbances
or the gradual contraction of very large masses.
It is convenient to have two names to apply to phenomena which often
present themselves in such different manners. The broad cracks, aub-
sequently fiUed up with matter thrown up from below, or overfiowing and
so mnning in, we may call dykes ; whUe the narrower crerices, which,
though also fiUed with varioua minerala, present them in a different way,
are caUed veins. Examples ofthe former, fiUed with basalt or injected rock,
have been mentioned in a preceding section, (see p. 288,) and we have now to
conaider the latter, which are of great practical importance, aa containing not
only cryataUine earthy minerala, but a large proportion of the most valuable
of those ores from which the metals are obtained.
The mineral aubatances contained in these veins are of two kinds ; the one
being generaUy either sUex, fiuor-spar, or carbonate of Ume, aU earthy minerals,
and generaUy in a crystalline state, the other consisting of metaUic oxides and
salts, in greater or less abundance. The latter being the valuable produce of
veins, are eagerly sought for and worked : but the othera, not exhibiting any
trace of metallic ore, possess Uttle economic value. Two classes of veins there
fore exist, which are found to diff'er from each other in various respects, and
amongst the rest in compass-bearing and in thefr incUnation to the horizon.
It appears at first, that nothing can be more variable and unaccountable
than the relation of the metaUic ores in a mineral vein to the cfrcumstances
of position of the vein, but in spite of this, there reaUy exists a certain
amount of order, and an approach to regularity. In all districts traversed
by mineral veins, there are, for instance, what may be caUed systems of
veina, each syatem being characterized by some pecuUarities of position or
contents, and each, so far as we can judge, referrible to a diatinct period. In
CornwaU, there have been deacribed eight auch ayatems, and the same number
had been observed by Werner, at Freyberg. In the former district, three of
the systems run east and west, and one north and south, whUe another ranges
N.W\ and S.E., or N.E. and S.W. Of these, the eaat and west veins are
caUed right-rumning, becauae they include moat of thoae which are productive
for tin and copper, (the staple minerals of the district,) whUe the north and
south are caUed cross-courses, crossing the first at right angles, and being also
productive, but chiefiy for lead and fron. The others are caUed contra lodes,
and are few in number. The remaining three classes are also unimportant to
the miner, and are usuaUy fiUed with clay.
The systems of veins in the Freyberg districts are described by Werner,

294 PHYSICAL GEOGRAPHY.
and offer a series of facts somewhat analogous to those observed in Cornwall ;
but the metals are different, and so also are the prevaUing dfrections ofthe
lodes. The first and most ancient are chiefly north and south, and include
those veins from which the chief suppUes of lead and sUver have been obtained.
The second aystem (contra lodes) are more argentiferous, but much thinner.
Thefr dfrection is about north-east and south-west. The veins of the thfrd are
aU north and south, and those of the fourth are at right angles to them, being
what are called in CornwaU cross-courses. They both contain lead glance.
The others are less important.
In the EngUsh lead districts, the systems of veins are much more simple
than in CornwaU or Saxony ; the dfrection of the productive veins is, almoat
without exception, east and west, and they are traversed by cross-courses,
not productive, at right anglea to them. The underlie ia seldom considerable,
and it is tolerably uniform throughout the district.
On the whole, and viewed with reference to the whole disfrict, the dfrection
of the productive veins in ComwaU must be regarded as strikingly uniform,
and the mean of nearly three hundred observations, recorded by Mr.
Henwood, gives 4° S. of W., whUe the actual dfrection, in nearly two-thfrds
of the number, differs but Uttle from the average.*
Lastly, the fact of these veins being fiUed with various foreign substances,
often placed one upon another, in regular order, and repeating nearly the
aame appearances, under simUar cfrcumstancea, in the aame mining diatrict,
ia an important proof that they muat be referred to some vridely acting, if not
universal, cause, if we wish to account for them in any rational maimer.
Electricity, especiaUy in those two important forms, galvanism and magnetiam,
offers the best and the most satisfactory explanation ofthe greatest number of
the phenomena. The constant action of a force so influential in re-arranging
the ultimate elementary atoms of bodies, and causing them to enter into new
combinations, cannot faU to produce great changes when acting under favour
able cfrcumstances and for a long time. No doubt, however, tiiere have been
many causes, proximate, if not dfrect and primary, which have aU acted
separately as weU as jointly, and these may have operated at different periods,
each tending to bring about results for which it waa beat adapted, and aU
together assisting in comphcating the chain of phenomena now offered for
investigation. Mineral veins are very frequently faults or the result of the displacement
of rocks, as weU as simple crevices produced by confraction or separation in
consequence of upheaval. In both cases they are sometimes fiUed vrith aofl;
clay ; aometimes the waUa of the vein are lined vrith such clay, and sometimes
the interior or contents of the vein are diatinctly and at once separated from
the walla without the intervention of any clay or other substance.
Veins vary exceedingly in dimensions, from less than an inch in breadth
to many hundred yards, and from a length acarcely appreciable to many
mUes. They traverse aU kinds of rocks, but are greatiy affected by the kind
of material through which they pass. They often cross each other, and are
moved in position, the newer vein altering and heaving the older, and thefr
contents are greatly modified by aU the mechanical changes to which they
are exposed.
The metaUiferous ores contained in veins are very numerous, greatiy
varied, and highly important, as from them are derived the chief suppUes of
metals used m the arts. Many of the metals, as gold and platinum, are
found only in a native state, or aUoyed with other metals ; others, as sflver,

* See Ansted's G«o!(ig-2/, vol. il. p. 266. Tho actual numberof observations tabulated was 295;
ofthis number the direction in 182 instances was between west and south-west, and in 62 others
between west and north-west. Dividing Cornwall into ten districts, the mean direction of the
veins in seven of the districts is rauch more south of west than the general mean, as the other
three districts chiefly contain tho contra lodes.

METALLIFEROUS DISTRICTS. 295
copper, mercury, arsenic, bismuth, &c., are found occasionaUy pure or
alloyed, and m the metaUic state, but more frequently as metaUic oxides, or
mixed with other ingredients, and in an earthy state. Very common ores of
copper, tin, fron and manganese, are the oxides of those metals; other ores, also
very common, of copper, lead, sUver, zinc, antimony, arsenic, &c., are com
binations ofthe metals with sulphur (sulphurets), and others again with carbon
and oxygen (carbonates) ; wliUe some metals, such as cobalt, nickel, chromium,
&c., are almoat invariably found with other metals, such as arsenic and iron.
With the common ores are mingled generaUy smaUer quantities of other
metaUic salta and oxidea, from which the numerous varieties presented in tho
mineral kingdom are derived.
The metaUiferous districta of the Britiah islands are cbiefly confined to
the western and northern parts of England and Scotland, and the eastern
part of Ireland. CornwaU alone fumishes the whole of the tin and seven-
eighths of the copper obtained, the reat of the copper being from Walea ;
large quantitiea of lead are obtained from Durham and Northumberland,
Cumberland, Yorkshfre, and Derbyshfre, although CornwaU, Wales, and
Scotland also contribute no unimportant quantity. Large quantitiea of zinc
ore exiat alao in many of the lead diatricts of England, but are not now
worked to advantage. The iron ores of England are chiefly bedded, and do
not, therefore, admit of description in this place, but large quantities of rich
oxides (hcematite) are found in ComwaU, and in the northern part of
Lancashire. The tin of ComwaU, chiefly in the form of oxide, supplies not
only England, but a great part of Europe, a Uttle being obtained from
Saxony, and some small mines existing in Sweden and Austeia. The island
of Banca, in the Indian Archipelago, and the adjacent peninsula of Malacca,
also yield a considerable quantity.
Eussia is remarkable for numerous and rich suppUes of gold, besides
sUver and lead; these, however, being chiefly important in the more distant
easterly provinces of that vast empfre. France is comparatively poor in
metaUic produce. Austeia, chiefly in the Tjrrol, and Hungary, yield gold,
cobalt, fron, lead, sUver, and mercury. Scandinavia is rich in iron and
copper, whUe Spain yields mercury at Almaden, and lead and copper in other
places. Prussia, vrith the exception of some parts of SUesia, ia comparatively
poor, whUe Saxony ia remarkably rich in ores of sUver, lead, tin, and cobalt.
Various smaUer disteicts in Germany also offer interesting apota to the miner,
and amongst these the Hartz is perhaps the most remarkable.
WhUe Europe and Northern Asia thus offer a multitude of places whence
metaJUc riches may be obtained, other parts of Asia, especiaUy India and the
countey adjacent the Malayan peninama, together with Southern Auatralia,
are amply prorided with aimUar reaources. Nor is America less favourably
cfrcumstanced, since Mexico, Columbia, BrazU, and, aa has been lately shown,
California, are rich in the precious metala, copper, and quickaUver, whUat
elsewhere, aa in the United Statea and Canada, the metaUiferous minerals
already diacovered are numerous, extensively distributed, and of great value.
Africa again appears to contain several metals, among which gold is not the
least important, and many parts of AustraUa have afready yielded large
suppUes of mineral wealth.
AU these mineral districts offer the same general structure, and in most of
them simUar metaUiferous veins are found in the same kind of metamorphic
rock. Mountain-chains, or hiU-teacts, presenting distinct axes of elevation,
mark the line of greatest mineral riches in Great Britain and Scandinavia, the
Ural Mountains, the Altai Mountains, the mining countriea of the Hartz,
of Hungary and SUesia, the Eastem Archipelago and AustraUa ; while the
gigantic Cordilleras of the Andes, in South, and the Eocky Mountains in
North America, traceable throughout the whole length of the New World,
are also remarkable for thefr metalliferous produce.

296

CHAPTER IX.
STEUCTURAL PHENOMENA CONNECTED WITH
AQUEOUS ACTION.
J ill. stratification. — 112. Mechanical disturbance of beds. — 113. Order of superposition of
European strata. — 114. Lower Palaeozoic rocks. — 116. Middle Palaeozoic rocks. — lie. Car
boniferous system. — 117. Magnesian limestone, or Permian system. — 118. Upper New Bed
Sandstone, or Triassic system. — 119. Liassic group. — 120. Oolitic system. — 121. Wealden
group. — 122. Cretaceous System. — 123. Older Tertiary rocks of England, Prance, and
Belgium. — 124. Middle and Newer Tertiary formations of Europe. — 125. Tertiary deposits
of Asia and America. — 126. Newest deposits of gravel and diluvium.
QfTBATIFICATION.— There are two classes of stractural phenomena
A3 observable in aqueous rocks — ^the one including phenomena of deposition,
the other of disturbance ; the former presenting the result of many ages of
imiform action, simUar to that going on around us in every river and on
every coast, whUe the latter marks the intervals of such regular action, and
thefr interruption by upheaving and other forces from below, producing
mechanical displacement, and often attended with the incursion of such rocks
as we have been considering in the last chapter. As it is the object in the
present chapter to study those structural phenomena which are connected
with aqueoua action, it is manifest that we have to deal vrith the former of
the two classes of facts just referred to.
No one at aU acquainted with the coast of our own ialand, or with the
Earth's structure as exhibited in quarries, railway cuttings, coal mines, or
other places where that structure is laid bare, can have faUed to remark
frequent evidence of mechanical deposition and arrangement in the varioua
layers presented, and in the alternations of sand and clay, limestone and sand
stone. As little can it have escaped the notice of any careM observer, that
theae layera are not, for the most part, horizontal, but tilted more or less, and
sometimea very conaiderably, so that in teaveUing through a coimtry we may,
if our route Ues in a certain direction, croaa the edges of a number of beds in a
comparatively short distance, or, on the conteary, may continue on one bed
conatantly, though that bed ia manifeatly of no great thickneaa. In other
worda, the varioua beda possess a certain definite direction or length, and a
limited breadth, arising from and depending on thefr inclination to the
horizon, rather than thefr absolute thickness. This is expressed in geological
phraseology by the terms strike and dip, the former meaning the dfrection
m which the edge of the lifted up bed is to be traced along the Earth'a
surface, and the latter the amount of its inclination to the horizon, which
must necessarily be at right angles to the former dfrection, whatever that is.
The geologist, taking advantage of this sfructure and position of the beds, (the
result, no doubt, of the subterranean upheaving motion already described,)
learna to connect together appearances in different counteies, to extend his
knowledge of different beds and multiply very greatiy his obaervationa on
them, to diacover the cfrcumstances of their deposition, by looking at thefr
preaent aapect, and arrange them in auch order that he shaU be able to
recognise them when he desires to compare those found in distant places.
The materials, therefore, of the Earth's crust being to a great extent
rranged in layera, beda, or strata, and appearing to have been deposited
from suspension in water, the term ' stratification' includea a very large claas
of phenomena, and we may employ the expression ' stratified rock,'

STRATIFICATION. 297
as a descriptive and distinctive name. The rocks described in the last
chapter are, on the other hand, ' unsteatified,' for they exhibit neither the
appearance referred to, nor any marks of slow subsidence from water.
The general appearance of a stratified rock is that of numerous layers of
material of the same kind — ^whether simple limestone, sandstone or clay, or
any mixture of tiiese — forming together a group to which the name of bed
may be appUed, and which dififers from the separate leaf-like and irregular
layers in presenting characters somewhat more marked at its junction with
another such group or bed. Thus, a bed of clay may be of indefinite thickness,
and may even form an almost homogeneous mass ; but, provided it ia
separated from similar or dissimUar beds, it ia considered diatinct, even if
resting on, or overlaid by other clay of the same kind ; but minute differences
of colour or tenacity are generally manifest, and afford sufficient proof of
aqueous origin, by producing, in fact, these ordinary appearances of steatifi-
eation. The word stratum (plural, strata) is very commonly uaed as
aynonymoua with bed, as, on the other hand, bedding is synonymous with
stratification. When, as frequently happens, several beds or steata rest upon
one another, and are possessed of certain common characteristics, having
been apparently deposited continuoualy, the whole together are diatinguished
as a formation, and in this way we speak of the chalk or the London clay as
formations, meaning thus to express a higher step in generalization than
when we speak of them merely as strata.
But the further investigation of nature shows that there are not only a
great many of ihese formations, but that we may occasionally include several
of them tmder more comprehensive titles. In this way, a number of
formations together may be coUected into a system, so that, for instance, the
chalk and greensand formations, which have certain characters in common,
are spoken of together under the name of the ' Cretaceous System.' There is
a yet higher division also, which ia often adopted, and according to which the
whole aeries of ateata are collected into three great groups, and thia, aa its
moat striking feature, involvea a total diaaimilarity of fossU remains ; and the
lapse of a long period of time being supposed to have been the chief cause of
this change, the group is aometimes denoted by the term period. The
expreaaion series, ia alao conveniently appUed in aome casea, and ita uae may
occaaionaUy be the meana of avoiding difficulty or objection.
The whole number of strata thus grouped is exceedingly great, and thefr
total thickness, if added together, would amount to many mUea ; but
aa there are no minea ao deep, and no mountaina so lofty, as to exhibit
anything like the half of this thicknesa, it becomea necessary to inquire what
are the meana in the poaaeaaion of the geologist, by which he can attain a
knowledge which would thus seem necessarUy shut out from him. The
explanafron of these means introduces another and most important branch of
our science.
112 Mechanical Disturbance of Beds. — We have said that the beda are
generaUy tUted or removed by some elevatory process frcfm below into a more
mclined position, vrith reference to the horizon, than that in which they were
deposited. Now, since we find, on examination, that this elevatory process
has acted very frequently during the deposit of the beds that form the
series in such a countey as England, it appears that the formation of regular
steata has been accompanied from the very beginning by the action of forces,
sufficiently powerful to elevate, break asunder, or alter the poaition of the
whole mass of matter intervening between the point of appUcation of the
force and the surface of the soUd matter of the globe at the time, and that
these forces, although frequently shifting, were generaUy exerted in the
same or nearly the same dfrection. It is clear also, that since the
rocks have been very frequently consoUdated and greatly altered, (partly,
perhapa, by chemical and electrical cauaea, and partly by heat,) after they
were deposited but before they were disturbed, and. .then after this have
received the deposits of the next newer period — sufficient time must have

298 PHYSICAL GEOGRAPHY.
elapsed to aUow of aU this change, the greater part of which was, doubtless,
effected by a process not merely gradual, but even slow.
Of the magnitude and mode of action of these forces, the observations
which we are able to make on the rocka exhibited at and near the surface of
the Earth, and which we have already considered, enable us to form a very
real and useful notion, and although uniform in thefr nature, they have
E reduced two distinct series of phenomena. From the examination of the
rst it appears, that the disturbances have often been such as to produce
violent and sudden changes upon districts comparatively Umited in extent,
and that these changes have been accompanied by the eruption of heated or
melted matter from beneath the surface. From the other appearancea, we
leam that tracta of land or of sea bottom of great extent have been the
subject of slow and conatant alterations of level, apparently without riolent
changes or marks of disturbance observable at the surface. To the action of
the latter forces we must refer the general elevation of low and undulating,
and often of mountain, districts, both island and continent, and thefr occa
sional depression; whUe all local disturbances, and the first formation of
great mountain chains, belong to the other series, the forces acting at longer
intervals and vrith greater riolence over Umited tracts.
The geological result of these forces has been, as we have said, to alter
considerably the original horizontaUty of strata, to produce those phenomena
which are respectively known as dip and strike, to cause the exiatence of
dykes and faults, of anticlinal and synclinal eaces, oi domes of elevation or
saddles, and valleys of elevations, whUe the position of many beds originaUy
horizontal, but now seen lying on the upturned edgea of the underlying beda,
has introduced the neceaaity of employing auch terma aa conformable and
unconformable sfratification. These terma form a part of the technical
vocabulary of the geologiat, and their meaning requfres to be fiiUy under
stood before commencing any important geological investigations.
1 13 Order of Superposition of European Strata. — It ia highly neceaaary
to be acquainted generaUy with the whole series of mechanicad deposite, and
although it could hardly be expected that any one counfry could give a series
80 extenaive, yet it so happens that most of the beds found in any part of
Europe are met vrith also in the British islands.
The foUowing table, though chiefiy adapted for our own country, wiU
alao serve to give a general idea of the order of superposition of stratified
rocks, and of the groupa into which they have been coUected. It wiU there
be seen that we have a large nuniber of rocks and coUections of rocks to
consider and compare, and that they have been arranged, as haa been afready
intimated, into three principal diviaiona, caUed Pesiods, and in fourteen less
comprehensive groupa, caUed series, or systems. Of each of theae we ahaU
next proceed to give a brief outline, enumerating at leaat some of the more
remarkable facts that have been determined with regard to the materiala of
which these groupa have been made up, and the cfrcumstances under wbich
they are generaUy presented. It will be observed, however, that whUat in
the table we have thought it best to give the order of auccession in such a
way that the eye would not be deceived in referring to it, it has been preferred,
on the other hand, to commence the more detaUed description with the rooks
loweat in poaition, and therefore ffrst formed. The reason for ao doing wUl
be very manifest when it is considered, that to give a true idea of the order
of superposition in a table, the natm-al position must be observed, whUe to
speak of the rocks themselves, which are derived from each other, the history
is best given by commencing with the most ancient formations.

TABLE OF CLASSIFICATION OF ROCKS.

TERTIARY PERIOD.

British.
Modem Deposits.
Raised beachea.
Peat bogs.
¦ Submerged forests.
Deposits in caverns.
.Shell marls.
Newer Tertiary, or Pliocene Series.
r Upper gravel and sand.
TiU. Mammaliferous crag.
Fresh water sand, and gravel.

- Red crag.

Middle Tertiary, or Miocene series.
Coralline crag.

Lower Tertiary, or Eocene series.

^Fluvio-marine beds.
Barton clays.
Bagshot & Bracklesham sands.
London clay and Bognor beds.
Plastic and mottled clays, sands,
and shingles.

FoBBiGN Equivalents, or Synonyms,
AND Chief Fokeign Localities.
Similar appearances in Northern Europe,
Siberia, and America.

These beds, or their equivalents, are
known in various parts of Northern
Europe and America. Other, but very
different deposits, are the newer beds of
Sicily. Otliers, again, are found occupy
ing a large part of South America.
Loess of the Rhine.
Subappenine beds.
Brown coal (of Germany).
Belgian tertiaries (Crag).
The Sivalik beds (India) are supposed to
belong partly to this period.
Touraine and Bordeaux beds.
Part of the Molasse of Switzerland.
Vienna basin.
Certain European, Asiatic, North African,
and North American beds.
Paris basin.
Central France.
Molasse of Switzerland (lower beds).
Belgian tertiaries.
Various beds in Westem Asia and
India.
Various beds in North and South
America.
Nummulitio beds.

Cretaceous system.

SECONDARY PERIOD.

0

Upper chalk with flints.
Chalk without flints.
Lower chalk and chalk marl.

Upper green sand.
Gault. Lower green sand.
a. Kentish rag.
h. Atherfield clay.
,1 Speeton clay.

Wealden system.
"Weald clay.
¦ Hastings sand.
Purbeck beds.

Scaglia limestone of the Mediterranean.
Maestricht beds.
Senoniam division of D'Orbigny (Craie
blanche).
(Tm-oniam beds of D'Orbigny (Craie
< tufau).
[^Quadersandstein of Germany.
Albion beds of D'Orbigny.
Planerlcalle of Germany.
Neacomicm of Switzerland and France.
Hilsthon of Germany.
Pondicherry beds.
Bogota beds, South America.
? Aptian beds of D'Orbigny.
? Sils-conglomerat of Germany.
Near Boulogne.
North of Germany,

300

CLASSIFICATION OP ROCKS.

SECONDAET PEEIOD — Continued.
FoEEiGN Equivalents, oe Synonyms,
British. aud Chief Fobeign Looaukes.

Oolitic system.

&

1^

o
tA

Jura limestone is the usual continental
synonym of our oolitic series.
/Portland stone. Lithographic Umestone of Blangy.
Honfleur clays.
Solnhofen beds
Beds in South of Rusaia and in India.

a. Limestones -with clay and
cherty bands.
6. Siliceous sand.
VKimmeridge beds.
Coral and calcareoua grits.
Oxford clay.
a. Stiff clay.
6. Kelloway's rook.
^Cornbrash. Forest marble.
Bradford clay.
Great Oolite.
Stonesfield slate.
FuUers' earth.
^Inferior Oolite.

Nerimmn limestone.
Argile de Dives.

Etage Bathonien is the name given by
D'Orbigny to our lower Oolites.
Calcaire apoh/piers.
Cdkaire de Caen.

liassic system.
I Alum shale.
Marlstone.
Lower lias. Calcaire a gryphites.
White lias.
Upper new red sandstone, or Triassic system.
/Bone bed of Aust cliff.
Variegated marls, with salt and Kevper marls, or Mariies
gypsum. Mvschelkdtk.

>• Variegated sandstones.

Bimter Sandstein, or (}ris bigari-i.

PALEOZOIC PERIOD.
Magnesian limestone, or Permian system.
("Magnesian limestone. Zechstein.
< Dolomitic conglomerate. Kupfer-schie^er and other shales.
|_ Lower new red sandstone. Rothe-todte-liegende.

Carboniferous system.
' Coal measures.
a. Gritstones.
J. True coal-measures.
c. Freshwater limestone of
Burdie House, near Edin
burgh.

Millstone grit.
a. Coarse gritstones.
b. Laminated ehalea.
Carboniferous limestone.
ll. Banda of fossiliferous lime
stone.
b. Shales (Calp, Culm).

The coal-measures occupy an important
place in various parts of the Continent,
in Belgium, France, the Rhine, South
Russia, and also in North America, in
various parts of Asia, and in Australia.
The foreign synonyms are, Steiniolilen-
gebirge, Pet-rain houillier, Terrain carbo-
nifere, and Terrain anthraxifere.
The millstone grit is generally a bed of
subordinate importance out of the British
islands. The Kiesel-schiefer of Germany is an
equiv.alent of the carboniferous limestone.
The Belgian limestone beds, and others in
Northem -Bavaria, are in the same part
of the series.

CLASSIFICATION OP ROCKS.

301

PAL.a;ozoic period — continued.

British.
Devonian., or old red sandstone system.
' Quartzose conglomerates (Old
red sandstone) in South Wales
and Scotland ; represented by
coarse red flagstones and
slates in Devonshire and Corn
waU.
Cornstone and marl of the old red
sandstone. Calcareous slate,
Umestone, sandy beds, and con
glomerates of Devonshire and
Cornwall.
Upper Silurian series.
' Tilestone.Ludlow group.
a. Upper Ludlow shales.
b. Aymestry limestone.
c. Lower Ludlow shales.
Wenlock group.
a. Wenlock limestone.
b. Wenlock limestone.
Lower Silurian series.
f 50. Caradoc sandstone.
\ 51. Llandeilo flags.

FoEEiGN Equivalents, or Synonyms,
AHD Chief Foreign Localities.
Devonian beds are well known in Bel
gium, the Eifel, Westphalia, and North
Bavaria. In Russia, the old red sand
stone appears, and contains similar fossils
to those found both in the corresponding
beds in the British islands, and also in
Devonshire and Herefordshire. The Pa
leozoic beds of Australia are supposed to
be contemporaneous.

Silurian strata extend over much of
northernmost Europe, and corresponding
latitudes in America. They have been
found in Brittany, in WestphaUa, near
Constantinople, and in Asia Minor. In
South Africa, the southemmost parts of
South America, Australia, and China,
different contemporaneous rocks have
been determined. In mineral character
they are generally distinct from the Eng
lish beds, but offer no marked characters
uniformly present.

114 The Lower Palceozoic Bocks. — The rocks of the Palaeozoic or older
period are remarkable for possessing a certain atriking uniformity of mineral
character, in varioua very diatant parts of the globe in whioh they have been
examined. They either rest at once upon the granitic framework of the Earth,
or pass by a series of insensible gradations from crystaUine and altered rocks,
wbich appear to have been originaUy formed by the decompoaition of granite.
These latter rocks also were either deposited before any living creature
existed upon the Earth, or under cfrcumatancea whioh did not admit of their
preaence or preaervation. The Palaeozoic series consiat of (1) the group of
Lower SUurian rocks ; (2) the Upper SUurian rocka ; (3) the Devonian or Old
Eed aandatone ayatem ; (4) the Carboniferoua system ; and (5) the Magnesian
limestone or Permian system.
1. 2%e Lower Silurian Bocks. — These rocks are best known by the hard,
dark-coloured, gritty beds abundantly met with near the town of UandeUo,
in Caermarthenshire, and thence caUed Llandeilo flags, and the sandstones
vrith calcareous bands found on the fianks of Caer Caradpc in Shropahfre, and
denominated Caradoc sandstones. These, the original subdiriaions of the
Lower SUurian system, are, however, strictiy local, and cannot be traced
even throughout tbe northem part of Wales, although remarkably perfect
in South Wales and Shropshire. The older SUurian atrata thua determined,
are found to be repeated under varying mineral conditions, throughout North
Wales ; they occur also very distinctly, although not to any great extent, in
Cumberland and the Lake district ; they appear to e.rist in Ireland ; and they
are met with in the south of Scotland, and the west of CornwaU. In most
cases, the frue age ia somewhat doubtful, owing to the absence of any
satisfactory eridence of condition or superposition.
On the Continent of Europe theae rocks may be traced, though not with
out difiiculty, in various parts of Westphalia and from point to point into

302 PHYSICAL GEOGRAPHY.
Bohemia, and they havo been identified near Prague ; they appear also in
SUesia, and in tliis way seem connected with blue clays and other rocks,
probably of the same age, in Russia, lying horizontaUy and undisturbed on
the gneiss and other altered rocks of those disfricts. There is a much thicker
series of rocks of the same age in Norway.
In Aaia, the eastern flanka of the Ural chain aeem to exhibit some specimens
of the same ancient formations. In Southem Africa, simUar rocks have been
observed ; many parts of North America exhibit them expanded to an
enormous extent ; and in South America, the frowning precipices of Tierra
del Fuego and Cape Hoorn seem to be formed of contemporaneous deposits.
The thickneaa of the Lower SUurian beds, although exfremely variable,
ia so frequently considerable, that whatever may have been the cfrcumstances
of deposition, we are justified in supposing that a very long period of time
must have elapsed before the completion of the series. In our own country,
this thickness amounts to several thousand feet.
The proportion of argUlaceous matter and quartz, but chiefly the latter in
its various forms, is, on the whole, much greater than in any newer rocks,
and the mixture of calcareous matter less ; whUe the presence of mica is clear
proof of the preponderance of granite among those rocks to whoae degradation
the preaence of^these slates and sandatonea waa owing. In the Britiah Islanda
and very generaUy in other countriea, the group is represented by a greyish
coloured sandy stone, often slaty and flaggy. In North Wales the slates have
undergone an amount of mechanical pressure so considerable that they are
often folded and twisted into the most exfraordinary contortions. Sueh
reaults are, however, merely local.
2. The Upper Silurian Bocks. — The country of the ancient ' SUurea' in
Walea and Shropahfre, is the classic ground of these rocks in England, and
exhibits the most remarkable and beautiful series of them anywhere discover
able. They are here distinctly a separate group from the Caradoc sandstone,
and although thefr upper beds pass into the Old Red Sandstone of Hereford
shire and the neighbouring counties, there can be little difficulty in at once
perceiving that they form a great natural series, grouped into diatinct for
mationa. The neighbourhood of Wenlock and Wenlock Edge, and the hUlon which
Dudley Castle is built, ofier the best examplea of the lower of these forma
tions, and have given a name to them. They consist of Umestone overlying
shale, the latter — the Wenlock shale — generally of dirty, muddy appearance,
and of grey or blackish colour, containing impure argiUaceous and calcareous
nodules. This ia aucceeded by an impure limestone, (containing a good deal of
argiUaceous matter,) the difi'erent layera ofwhich are aeparated by clayey beds.
The uppermoat group of the Silurian rocks is best seen at Ludlow and its
vicinity, and comprises two beds of shale or mudatone (the Upper or Lower
Ludlow shales) with an intervening bed of limestone (the Aymestry limeatone)
somewhat less argUlaceous than that of Dudley. As might be expected, the
limestone is sometimes absent, and, in that case, two beds of shale united
represent the whole formation. The upper beds of the Ludlow shale pasa
upwards into sandy beds, and others which contain in incredible abundance
the fragments of several small fishes.
These subdivisions ofthe Upper SUurian rocks are strictly local, and should
not be looked for in other districts. In North Wales, the micaceous aand
stonea near LlangoUen, the Denbigh fiagstones, and a large series of rocks
probably belong to the newer part ofthis period. In Cumberland, a great
proportion of the mechanical rocks must also be referred to the same age ;
and in Ireland there are extensive simUar and contemporaneous groups of
strata. In the Border country and other parts of Scotland, there are rocks
of this age of umform eharacter, and much altered from thefr original
condition. On the Continent of Europe a considerable proportion of the so-caUed
grauxvacki of Belgium, Rhineland, and Northem Westphalia, similar beds in

CLASSIFICATION OF ROCKS. 303
Brittany, others in Spain, and others in the Thracian Bosphorus, near
Constantinople, have been shown to be of the Upper Silurian age. Other
rocks in Northem Europe, in Rusaia, and Scandinavia, ai-e yet more diatinctly
identifiable with our own SUurian afrata; and in North America, South
America, and the Polynesian lalands, there aeema good evidence that groups
of fossUs more or less characteristic and identical with English Silurian
species, mark a contemporaneous deposit of a very similar kind.
115 The Middle Palceozoic Bocks. — In the typical Silurian diatrict the
Upper Silurian rocka paas upwards into a sandy rock which is occasionaUy
micaceous and becomes a flagstone. This rook, under the name of tilestone, is
now ranked as part of the SUurian series. It appears most properly to belong
to the latter ; but the doubt that has been felt is a sufficient mark of the
perfect passage between these two formations which, in most parts of England,
difler completely in mineral structure. In fact, the so-caUed tilestones, which
are often nothing more than hard and coarse aandstones alternating with red
shales, pass into and are overlaid by a number of clayey and marly beds,
which afford an exceUent soU by decompoaition, and are locaUy caUed corn-
stones, and these again are covered up by thick and extenaive masses of eon-
glomerate and coarse sandstone, the conglomerate consisting, for the most
part, of quartzy pebbles imbedded in a red matrix, and known as the quartzose
conglomerate. The whole together make up the Old Red Sandstone Series of Here
fordshire and Monmouthahfre, and occupy a considerable district on the
borders of South Wales, being there developed to a very great thickness.
The Old Red Sandstone does not, however, always retainthe same character
as that described above : — as we advance northwards in England, the thick
ness of the bed diminishes, and it loses many of its peculiar features ; but it
appears again as a thick irregular conglomerate in Westmoreland ; and there,
as in Herefordshfre, the passage upwards from the SUurian rocks appears
complete. But it is chiefiy in Scotland that we find those huge masses of
enormous thicknesa, from which the common notions of geologiata concerning
the Old Red Sandatone are derived, and the beda there extend at intervals
for 120 mUes, fringing the old rocks and attaining a thickneaa of many
thouaand feet. They are also continued round the coaat, and are found in
many ofthe Weatem- lalands of Scotland. '
Of this aeriea there are aaid to be three aubdivisions, and it is not unlikely
that these are sufficiently weU exhibited in various districta to allow of their
being locaUy determinable. It is necessary, however, to look upon the whole
as the reault of cauaea acting during a long and unbroken period, probably
corresponding to the middle and upper portion of the Old Red Sandatone of
Herefordabire. In North Britain, the whole deposit rests on the gneiss; the
lowest bed is a conglomerate of enormous but variable thickness, evidently
made up ofthe broken fragments of the old granitic and porphyritic rocks, rolled
and tossed about for ages in a tooubled sea, the hardest stones being often
rounded into buUet-shaped pebbles, by their long and incessant attrition
againat each other. Tbese conglomerates, however, are not universal, being
sometimes succeeded and sometimes replaced by a series of remarkable bitu
minous schists, which, in Orkney and Caithness, abound with the remains of
fishes, and exhibit also some fragments of vegetables, the whole being over
laid by rocks of marly character, sometimes becoming a mere friable clay.
The uppermost beda consist chiefiy of quartzose sandstone.
The Old Red Sandstone was formerly supposed to be a local formation
entfrely confined to the British Islands, and its true importance, as representing
a very weU marked G-eological epoch, has only lately been fully recognised.
Although, however, it might well be supposed accidental that so large a series
of coarse sandstones should be deposited as we find in Scotland and Here
fordshfre, a nearly aimilar series is found in Russia, covering a vast fract of
counfry ; and in the Westem States of North America, a group has been
described strikingly similar to the lower part ofthe Old Eed of Scotland,

304 PHYSICAL GEOGRAPHY.
The beds, now caUed the Devonian Series, which take the place of the
Old Red Sandstone in the south-west of England, are for the most part
calcareous slates, often sandy, and sometimea alternating with extensive sandy
beda, and with imperfect limestones.
In Ireland, the Old Red Sandstone is represented by coarse conglomerates,
and occasionaUy by arenaceous clayey beds.
On the Continent of Europe, although true Devonian sfrata exiat and are
abundant, they are so compUcated, and the order of superposition is so
difficult to make out, that they could hardly have been determined, had
not thia obacurity been firat cleared away by investigations in onr own
counfry. In Belgium, the Devonian limestones pass out of those belonging to the
SUurian period without any break of continuity, and appear to include a
perfect series, paaaing, also without any break, into the carboniferoua
rocks. On the right bank of the Rhine, near Cologne, where SUurian and
Devonian beds appear, the whole series is inverted, the Devonian actually
overlying the SUurian sfrata ; and, farther to the south, in the north of
Nassau, there are extreme contortions, marks of which may be aeen at the
fortress of Ehrenbreitstein on the banks of the Rhine, near Coblentz, and still
more on the banks of the Lahn, going up towards Ems and Naaaau. The
Ruasian atrata exhibit no auch extreme conftision ; but they include many rocks
totaUy difierent in mineral composition from any that are known to be
contemporaneous, although they also represent almost every form that the
Devonian strata or Old Red Sandatonea assume in other parts ofthe world.
ii6 The Carboniferous System. — The uppermost beds of the Old Red
Sandstone and the Devonian series are often found to paaa by a succession
of shaly beds, or by an alteration of fine conglomerates and shales, into a
black imperfect Umestone, succeeded by other limestones, less argiUaceous,
and very soon covered up by extensive and thick Umestones. The bottom
beds of the aeriea are commonly aeen in Ireland, and they are found alao in
the lale of Man, where they Become fiaggy limestones, and they are also
- probably represented in the carbonaceous rocks of Devonshfre. Generally
speaking, however, the overlying limestones do not pass into the Old Red
Sandstone or Devonian shales by any passage of this kind, but cover them
irregularly and often unconformably.
The distinguishing feature of the carboniferous rocks, wherever they have
hitherto been found, consists in the very profiise disfribution of carbon in
various shapes through almost every member of the series. This is ahown
in the lower beda by the prevalence of carbonate of lime, in the middle ones
by the occasional remains of vegetables, and in the upper by fhe existence of
entfre beds of carbonaceous matter, commonly used as fuel in this counfry,
and well known as coal. None either of the older rocks or those of newer
date, can be at aU compared with these Palaeozoic sfrate in respect to the
abundance of carbon they contain.
Owing in many cases to subsequent movemente of dislocation in the
districts where these rocks appear, they are oflen broken up into fragmente,
and distributed into areas whicli have the character of baains or hoUow
depressiona. In thia way especiaUy, the rocka which contain the largeat
quantity of vegetable carbon or the ' coal sfrata' are limited in range, but
this ia not the only reaaon for thia Umitetion, since they muat have been alao
greatly confined in the actual area over which auch large contributiona of
orgamc matter could be accumulated.
The general order of superposition of the carboniferous series seems to
have been (1) a vridely-spread formation of limestone, for the moat part the
work of the coral animal ; (2) a aeries of gritstones or coarse aandstonea,
called the millstone grit, alternating with, ana sometimes replaced by ahalea ;
and (3) a great series of sandatonea and shales, containing amongst them the
various beda of coal, nnd also containing thin seama of fron ore, and generaUy
spoken of as the coal measures.

CLASSIFICATION OF ROCKS. 305
The first of these beds is generaUy caUed the Carboniferous or Mowntairt
Limestone. It occupies a prominent place in the Geology of England, and
contributes much to the picturesque beauty of Yorkshire, Derbyshfre, &o.
In the north of Yorkshfre, several thin beds of coal are met with in its lower
part, although in other districte of England the vegetable remains are chiefly
conflned to the coal measures. It often abounds in caverns, some of which
are of great extent ; and, in Derbyshire and elsewhere, numerous mineral
veins traverse it and yield a considerable quantity of lead and zinc ore.
The Millstone Grit is an important deposit in the north of England, where
it occupies an extenaive tract of country, and is extremely thick. In the
middle and south of England, however, it fades away, and is almost lost,
being feebly repreaented by a thin pebbly gritatone intervening between the
true carboniferous Umestone and the coal measures. In Ireland, it re-appears
in great force in the mountains about EnniskUlen.
The Coal Measures must be considered with reference to the various
diatricts in which thefr vaat value and importance are chiefly felt. The great
Nortii of England or Newcastie coal field is partly covered up by the Mag
nesian Umestone in Durham, and is occasionaUy worked through this bed.
It contains about eighteen workable seams of coal (whose total thickness
is about eighty feet) alternating with shale and sandstone, and greatly
disturbed by faulte and dykes. The coal is the most bituminous and one of
the beat adapted for economical purposes of any yet known.
The Lancashfre coal field occupies a considerable area, and is connected
vrith that of Yorkshfre. It includes perhaps the most perfect series of the
rocks of the period anywhere existing, and consists as uaual of aandy beds
and shales, alternating with a large number of coal seams, seventy-five of
which (whose total thickneaa ia 150 feet; are deacribed. In its upper part
occurs a pale blue limestone of fresh-water origin, which is again met vrith in
other coal fields nearly a hundred mUes distant, and appears also at various
intermediate pointe.
The South Staffordshfre coal field is remarkable as the only representative
of the Carboniferous rocks in that part of England, the MUlatone grit and
Carboniferous limestone being both absent, tt exhibits a great prepon
derance of shale, and the number of its coal seams is only eleven, but the
thickness of one of these is unusuaUy great, amounting to upwards of thfrty
feet in some places.
The South Welsh coal field contains about ninety-five feet of coal distri
buted in about thfrty workable seams, the most powerful of whieh is about
nine feet thick. The associated shales and sandstones are of very unusual
thickness, and they contain besides coal an abundant supply of fronstone
ore. A considerable part of the coal in this district is non-bituminous, and
diatinguiahed by the name of Anthracite.
Beaidea theae, there are numerous smaUer deposits of coal in the middle
and weat of England, and in Walea, aU of which poaaess local importance,
but which we cannot now atop to deacribe.
The basin of the Clyde in Scotland, is no lesa interesting for ita carboni
ferous depoaita than important from thefr extent and value. In this district,
the Old Red Sandstone is the general base of the coal afrata, thick sandstones,
occasionally containing coal, teking the place of the lower carboniferous Ume
stone. Thin beds of Umestone then succeed, and on these rest the great
maaa of the coal-bearing strata, wbich greatly reaemble the similarly situated
beds in England, but wuch include seams of fronstone ore yet more valuable.
There appears, however, to be a freshwater limestone in this part of Scot
land underlying the coal meaaurea, and possibly contemporaneous with a
bituminous shate in the North Stafibrdahfre coal field.
The coal aeams in the Clyde vaUey amount in number to eighty -four, but
they are mostly thin ; the coal, however, is good. The total thickness of the
deposit is estimated at about 5000 feet.
The coal fields of Ireland are not unimportant, though they have hitherto

306 PHYSICAL GEOGRAPHY.
been Uttle worked. The principal one worked is that of Leinster, and as
much as twenty or thfrty feet of bituminous coal have been found in another
smaU field near Tyrone. In Connaught there ia also a supply of fronstone
ore. France and Belgium both contain a considerable number of coal fielda, but
they are mostly of small dimensions, and in the latter country are greatiy
disturbed, inclming at a considerable angle to the horizon, and worked hke
mineral veins. The French coal fields are aU of very smaU size.
Rusaia is not vrithout an extensive series of sfrata of the date of the Carbo
niferous rocks ; and in the nortbem part of the empfre there seema to be a
proapect of workable coal, the lowest beds of the syatem containing (as in
Yorkshfre) a few seams of variable thickness, but of great value. In the
south of Russia, very good bituminous and anthracitic coal is found in
conaiderable abundance, but the beda are much disturbed by faulte.
North America contains coal-bearing sfrata of great value, and of enormous
extent, gigantic coal fields existing in the Weatern States and the British
provinces. The coal meaaures here, as in Europe, form tbe uppermost part
of the carboniferous series, and the number of seams hitherto known ia
about ten, having an aggregate thickneaa of fifty feet. There ia one bed
of thirty feet, worked like a quarry from the aurface.
Tn V an Diemen's Land, and probably in several parts of Asia, there are
sfrata of the Carboniferous period, greatly resembling those of our own
island, and consiating of limeatonea overlaid by coal-bearing afrata. Much
yet remains to be done in making out satisfactorUy the true poaition of theae
strata with reference to the weU-known Carboniferoua series of Europe.
117 The Magnesian Limestone, or Permian System. — The coal meaaurea
in the north of England usuaUy terminate with, or rather paas iuto, a
sandstone, diff'ering from the ordinary coal grits in being discoloured with
oxide pf fron, giving it a red colour. This sandstone, which is frequently of
coarae texture, and ia very irregular in thicknesa, compoaition, and extent, ia
the Lower new red sandstone oi EngUsh Geologiata, and corresponds with a
aomewhat aimUar maaa of contemporaneoua origin in Germany, there called
Bothe-todte-liegende, a name not unusuaUy appUed also in England. There ia
often an apparent break of continuity between tbe Lower new red and the
next superior bed of Magnesian Limestone, but this is not universaUy the
case ; and marly beds, with thin bauds of sheUy limestone, unite and
amalgamate the two formationa. The Magnesian limestone is extensively
developed in the north of England, and is there sometimes aa much as five
hundred feet thick. It receivea ita name from ita mineral composition, which
ia a mixture of carbonate of magneaia with carbonate of Ume. It is a very
variable rock, sometimes hard and perfectly crystalline, forming an admirable
buUding-stone, (in this atate called Dolomite^ and sometimea in thin beds of
loose texture — occasionaUy laminated — here and there oohtic, like the free
stones of a later period — and on the coast of Durham possessing a singular
concretionary structure, the cliffs appearing as if made up of pUes of cannon
baUs. In tbia latter caae the carbonate of lime would appear to have formed
into nodulea, and the magneaia ia left in a powdery atate, filling up the
interaticea. The Magnesian limestone in the north of England appears to be
capped by gypseous marls of no great thicknesa, and these are often entirely
absent ; but further aouth, not omy thia capping, but the bed itself in ite most
characteristic form, is absent, and is replaced by a conglomerate, made up of
fragments of carboniferous limestone, cemented, together by a red or yellow
magnesian paste. The Lower new red sandstone, without magnesian lime
stone, overlies the coal fielda of Staflfordahfre and Shropahfre, but ia repreaented
in a aomewhat difi'erent form from that whieh it usumly takes.
The beds intervening between the coal meaaures and the Upper new red
sandstone are not extremely important in England, but are much more widely
extended and more manifestly diatinguiahed aa a group in various parta of
the Continent. In Germany and some parts of France these rocks are of

CLASSIFICATION OF ROCKS. 307
considerable interest ; one of the beds associated with the magnesian lime
stone containing a copper ore that has bdfti much worked. The mag
nesian Umestone series there forms two groups, the lower one argiUaceous,
and the upper calcareous, the latter being in all cases mixed with a certain
proportion of magnesian earth. In Russia this system is developed yet more
perfectly than m Germany ; it occupies an enormous frough in the
carboniferous limestone in the ancient kingdom of Permia, and conaists of a
freat number of sfrata of very variable mineralogical character. It has
een proposed by Sfr R. Murcbiaon to denominate me whole series, from its
Russian tjrpe, the Permian system.
ii8 The Upper New Bed Sandstone, or Triassic System. — This system of
deposits ia the lowest or oldest of the middle period, and is diatin
guiahed from the earlier formed beda partly by mechanical position, and
Sso very strikingly in the nature of the organic contents. Like those of the
Permian system just described, the rocks now under consideration are less
perfectiy developed in England than in some districts on the continent of
Europe. They consist for the most part of an extenaive series of yeUow or
red sandy beds, alternating with red, green, or blue marls, and containing
large masses of rock-salt and gypsum, (sulphate of Ume,) and although the
beda thus characterized hardly admit of distinct aubdiviaion in England,
owing to thefr great aimUarity in mineral compoaition, they are elsewhere
divided by a band of limestone, (the Muschelkalk,) and in that case the lower
sfrata {bunter sandstein or gris bigarrd,) are usuaUy more sandy, and the
upper (keuper) more marly. A similar difference in the character of the beds
obtains also in some parts of England.
The Upper new red sandstone is generaUy seen spread evenly over the
upturned edges of the underlying Palaeozoic rocks, which have undergone
much displacement before the deposit of this newer bed. The sandstones,
generally of moderately fine texture — ^less coarse at any rate than the Lower
new red sandstones — occupy in this way a large superficial area, and are seen
in the extenaive plains of the middle and west of England, and filling up all
the vaUeya in the carboniferous limestone of the North. Their thickness is
considerable, but not very easUy calculated.
The continental beds of this period differ in some important pointa from
thoae of England, but preaerve a general analogical resemblance. The lower
part, caUed Bunter sandstein by the Germans, and Gres higarrS by the
French, ia a fine grained, soUd sandstone, passing upwards into an earthy
clay. To this succeeds the Muschelkalk, a Umestone of rather peculiar
appearance, often argUlaceous, and not unlike some of the SUurian limestones
in mineral character, but sometimea very diff'erent, and even becoming
exfremely bituminous. The keuper or mames irisees — coloured marls, often
containing vegetable remains — cover up the muschelkalk, and terminate the
series. The upper beds of the Upper new red aeriea in England have been
identified with the keuper, and are aometimes spoken of aa ' variegated marla.'
119 The Liassic Group. — The beds of this formation, so caUed, it is
supposed, from thefr frequent appearance in striped bands or layers,
may be traced through England, from Lyme Regis m Dorsetshfre, by
way of Somersetshfre, Gloucestershfre, Worcestershfre, Northamptonshfre,
Leicestershfre, Rutland, and Lincolnshfre, to the Humber, and then through
the East and North Ridings of Yorkshfre to the coast at Whitby. In aU
this fract the general features of the formation are the same, and from
Gloucester northwards, there is an average and nearly uniform breadth
of about six mUea, the total thickness of the deposit being generaUy
above 600 feet. The rock is Uttle disturbed, and has a regular dip,
being conformable to the underlying and overlying strata, except where
it comea in contact vrith the mountain limeatone in Glamorganshfre and
Somersetshfre. The Uas is generaUy subdivided into three parts, the lower
portion reposing on a thin bed full of fishes' bones, and consiating of a
lower Umeatone containing a large proportion of clayey matter alternating
x2

308 PHYSICAL GEOGRAPHY.
with shales, often calcareoua. Theae are overlaid by a bed caUed the marl-
stone, (a marly Umestone of a very pale colour,) and above this there is
another and a final bed of tough blue calcareous clay and shale, which passes
into sandy beds, and so graduates into the ooUtes which next succeed. The
uppermost bed is sometimes caUed the Alum shale, and is greatly developed
at Whitby, where it ia burnt for alum. The lower beds are exhibited best in
Dorsetshfre, and the marlstone in Gloucestershfre.
On the Continent the Lias poaaessea nearly the aame Uthological character
aa in England, but the lower beds are more aandy, and the middle onea more
calcareoua. The upper marla are the most uniform of the continental liassic
beda, and they moat nearly resemble the contemporaneous EngUah strata.
I20 Tlw Oolitic System. — This interesting group of formations is so
admirably exhibited in England, and occupies so large a proportion of the
surface of our counfry, that it has received even more than its due share of
attention, and wais aomewhat too prominently put forward in aU ite numeroua
and intereating aubdivisions, in the first determination of Geological series.
The beds caUed Oolitic (from the Greek worda aav (Son), an egg, and
Xidos (lithos), a stone,) are usuaUy subdivided into three weU-marked groups,
aU of them characterized more or less by the presence of limestones ; tee
pecuUar structure of which (the rock being made up of innumerable smaU egg-
shaped particles) has given its name to the formation. The general character
of the OoUtic syatem in England may be described as consisting of three
ridges running N.N.E. and S.S.W., with broad vaUeya or plaina intervening.
The ridges in this caae represent the escarpments of the hard Umestone beds
of the Lower, Middle, and Upper group of Oolitic sfrata, and the plains, the
less coherent or softer beds, interposed between them. In this way the
series may be fraced through England to the east of the Lias, and parallel to
that formation ; but in many places, more eapeciaUy in the north of England,
the upper series is wanting, and in the south the lower part is indifi'erently
repreaented. Thus the order of the relative preponderance of difi'erent
members of the series observable in the Lias is here reversed, the lower
Oolitic beds being chiefiy developed in the north, and the upper ones in the
south. The principal limestones of the lower series are ihelrferior and the <3reat
Oolites, and these are separated from one another by marly beds, used as
fuUer'a earth, and by a thin fiagatone remarkable for ita fossUs, and caUed the
Stonesfield Slate. Under the Inferior OoUte there are sandy beda, which
greatly preponderate in Yorkshfre, and contain numeroua vegeteble fossils.
The Inferior OoUte itself contains about forty or fifty feet of freestone ; and
the Great, or Bath OoUte, which is more important in economic value,
presents a large series of exceUent buUding stones, alternating with coarse
sheUy beds, but sometimes replaced by a thick clay, called ' Bradford Clay,'
At the top of the Lower Oolitic group is a bed called locaUy the Combrash,
which decomposes into an exceUent vegetable soU, and is chiefly made up of
clays and sandstones with calcareoua nodules.
The central portion of the Oolitic seriea consists, for the most part, of a
thick bed of tough blue clay, caUed the ' Oxford Clay,' -very widely extended,
not only in England, but on the Continent, and overlaid by beds of a more
calcareous nature, sometimes taking the form of a, frue coralline limestone,
and aometimes only containing a mixture of calcareous matter in sandy beds.
In ita moat characteriatic form, tbia upper bed (the Coral rag) ia chiefly seen
near Calne and Steeple Ashton, in Wiltshfre, and at Malton, in Yorkalure.
The upper Oolitea, Uke the middle ones, consist chiefly of a thick bed of
tenacious clay, locaUy overlaid by Umestone. In this case, tiie clay is called
Kimmeridge Clay, from a vUlage near Weymouth of that name, where it is
weU exhibited ; and the bed may thence be fraced northwards as far as Lin
colnshfre, and even into Yorkshfre, resting on the Oxford Clay, sometimes
without the intervention of the Coral rag, and forming the great fen district
of Cambridgeshire. Over the Eimmeridge Clay there is in the south of

CLASSIFICATION OF ROCKS. 309
England a very extensive development of limestone in Portland Island, the
quarries of which have been worked for manycenturies ; but this does not
reach farther north than Buckinghamshfre. Where best seen, the Portland
rock includes aeveral banda of coarse, eai-thy limestone, alternating with a con
siderable thickness of freestone, and covered up vrith a bed containing a
substance Uke vegetable mould, in which the stumps and roots of trees are
found. This singular sfratum, the Dirt-bed, is met vrith over a somewhat
extensive area.
North of Yorkshfre, the secondary rooks are very rarely exhibited in the
Britiah islands, but in two or three vaUeys in Scotland, and eapeciaUy at
Brora, there has been described a series Ibelonging to the OoUtic period.
The beds are not ooUtic in structure, and contain hut Uttle calcareous matter.
On the continent of Europe, there are many spots in which rocks contem
poraneous with the EngUsh Oolites resemble them also in mineral character
and general appearance. Near Caen the Great oolite and a considerable
overlying series have been described by French geologists. Among the Jura
Mountains, and even in the Alps, the three subdivisions are preserved aa in
England, and thia is the caae also in the north of Europe, whUe in Russia,
the whole series is divided into two portions, the lower being very locaUy
distributed, but the upper part calcareoua and ooUtic, and vridely spread over
the country. In the Caucaisus the beds of this period are greatly altered,
and have been described as primary.
In Asia, the north weatem paxt of the peninsula of India haa afforded
eridence of an intereating group, probably contemporaneoua with the OoUtes.
The beda containing coal in vfrginia, formerly deacribed aa carbonU'erous,
belong alao to the aecondary period, and are of the aame age as the lower
OoUtes of Yorkshfre, which they resemble.
121 The Wealden Group. — Lying immediately on the top of the OoUtes
and paasing out of them so graduaUy that the actual junction can hardly be
determined, there is found in the south-east of England, a remarkable group
of fresh-water beda, classed together under the name of 'Wealden,' and
consisting of a very thick and vairied seriea of arenaceous beds baaed on lime
stones of amaU extent and pecuUar character, and covered by a bed of clay.
This whole series may be described as a series of clays and aands vrith aubor-
dinate beda of limestone grit and shale, containing the remains of organic
bodies whose condition manifestly ahows that they have been subject to the
action of river currents, but not to attrition from the waves of the ocean.
The subdivisions are found only in some of the southern counties of
England, and are not vrithout some interest, the Purbeck, or lower beds,
being remarkable for the presence of a sheUy limestone taldng a good
EoUsn, and known as Purbeck Marble, whUe the Hastings Sand, though of
ir greater thickness, hardly presents greater complexity. The Purbeck
beds, including a fissile limestone, and as many as fifty -five beds of workable
limestone, attain in aU to the thickness of about 125 feet, and are much
disturbed from thefr original position. The Hastings Sand consista at its
base of friable sands suaa. as those seen at the chffs near Hastings, and
upon them are found first an extensive series of arenaoeous beds containing
buUding atone, and then aome bluiah grey aandatones, or calcareous grits, of
no great thickness, known aa the TUgate beds. The Purbeck atrata are
chiefly found in the westem part of the Wealden diatrict, and where the
fractured chalk expoaea the lower beda in the vale of Wardour and the other
vaUeys of elevation in Dorsetshire and WUtahire, whUe the Hastings sand is
found not only in the vicinity of Haatings, where it is exposed on the sea
chff, but also throughout the whole Wealden district.
An upper band of clay, called the ' Weald clay,' intervenes between
the Hastangs sand and the Cretaceous group, and is found along the Une of
the North and South Downs, near the base of the escarpment of the chalk,
and again in the Isle of Wight in the same position. It occupies a fract,
about six mUes wide in the broadest part, between the Hastings sand and

310 PHYSICAL GEOGRAPHY.
newer rocka, and consiats of a tenacious argillaceous bed reposing on beds of
sandstone and sheUy limestone vrith layers of argUlaceous fronstone.
There are in the Isle of Skye, and in one or two places on the coast of
France, opposite the Weald of Kent, smaU patches of afrata, nearly of
the aame age ; and in the north weat of Germany a considerable thickness of
contemporaneous fresh-water beds haa been alao determined. With these
exceptions, the transition from the Upper ooUtes to the Cretaceous rooks is
abrupt, and there is reason to beUeve that a long interval must have elapsed
between the deposit of the two series.
No marine beds are yet determined which can with safety and certainty
be referred to the Wealden period. In other worda, the period during which
these beds were being deposited in England was either occupied by com
pleting some of the Upper ooUtes in other seas, or else during that time there
was a cessation of depoaita over wide fracta, owing either to thefr being above
the aea or the bottom of a deep ocean.
122 The Cretaceous System. — This group of sfrata has received ite name
from tbe almost universal presence in it of the white chalk (creta) which
forms its upper dirision in most parts of Europe. The whole formation haa
feneraUy been divided into three parts, (1) the Lower greensand, represented
oth in some parts of England and on the continent of Europe by very
extensive and thick beds; (2) the Gault and Upper greensand; and (3) the
Chalk ; but the two latter groupa aeem to poaaeaa more analogies with one
another than they do with the lower division.
The Lower Greensand of England is exhibited in a varied but characteristic
form, in the cliffs between Folkstone and Hythe, and alao near Maidstone, in
the county of Kent, and at the back of the lale of Wight, where it expanda
so as to occupy a very prominent place in the Geology of the district. Under
the name of Neacomian, beds of nearly the same age have also been deacribed
from the -ricinity of Neuchatel in Switzerland, aind from the aouth of France.
There are aome placea in the south-east of England where the passage
upwards from the Wealden to the Lower Greensand is very difficult to frace,
owing to the aimUarity of the clay beds in the two depoaite. Near Hythe
this is especialh' the case, and here also there ia an adinfrable aection of the
whole Lower Greensand aeries. A simUar,* and equaUy interesting section
may be seen in the Isle of Wight, between Atherfield and Black-gang Chine,
but there is no passage there from the Weald clay into the Atherfield day.
In the more central counties of England, in Bedfordshire, Cambridgeahfre,
&c., where the Lower Greensand is stUl an extensive bed, it is remarkable
for Uttle more than its deep red colour, a phenomenon apparently due to the
preaence of a considerable quantity of the peroxide of fron.
The Lower Greensand of the aouth of Prance and of Switzerland consiste
of calcareoua beda of considerable thickness, and in Germany the beds of the
same age are repreaented sometimea by extensive beds of aand, and aometimes
by clays. It is not eaay to determine very distinctly the identity of date of
the different beda of the cretaceous formation in the Pyrenees, the Carpathians,
the Caucasus, and the south of Italy ; but there can be Uttie doubt that a
very large proportion of the whole must be referred to the lower dirision.
The Gault and Upper Greensand are chiefiy exhibited in the eastern and
southem districts of England, and there form a weU marked group, presenting
distinct features.
The Gault, the lower member, is best seen near Folkstone, (to the east of
the town,) where it appears from the cliff section to be about one hundred and
twenty feet thick, and to rest on the Lower Greensand. It is a stiff blue clay,
and ia mixed with a small portion of iron pyrites. From Folkstone the aame
clay may be traced, retainmg ita appearance and pecuUar mineral character
throughout the east of England, everywhere coming iu between the Lower
and Upper beds of Greensand. A little to the north of Cambridge it begins
to thin out, and on the coast of Norfolk, where it comes out again to the aea,
it is not more than fifteen feet thick.

CLASSIFICATION OF ROCKS. 311
The Upper Greensand is somewhat variable both in thickness and in
feneral appearance. It often forms a kind of step at the foot of the chalk,
aving a smaU, but well marked, escarpment towards the Gault ; but this is
by no means always the case, and as it goes northward it loses the cherty
character for which it is remarkable in Surrey and the Isle of Wight, and
merely serves to separate the GaiUt from the Chalk. Both the Lower and
Upper beds of Greensand have received thefr name from the prevalence
throughout both of them of smaU green particles of sUicate of fron.
The Chalk is a very weU-marked and mteresting formation, both on account
ofthe pecuharity of ite mineral composition, and its great uniformity in all
respects throughout a very extensive area. It is also remarkable for the
layers of fiint distributed through it, Above the white chalk vrith fiints there
ia found at Maeatricht a yet newer bed, alao of the Cretaceoua period.
The lower part of the chalk is somewhat impure, owing to the presence of
argiUaceous matter and iron vrith grains of sUex, but these disappear in the
upper beda ; and the sUex, inatead of being disfributed in grains, is coUected
into distinct layers, each of which appears to have generaUy coUected round
some spongeoua body as a cenfre. In this state the chalk is an almost pure
carbonate of Ume, vrith a very smaU per centage of fron.
In some districts on the Continent of Europe, the upper part of the
cretaceous system bears a afrong reaemblance to the contemporaneous beds in
England ; and true white chalk has been fraced not only in France, but in
Denmark, Poland, Cenfral Russia, and the Caucasus. Under another form,
the beds of this period are found in the South of France and in Italy, there
forming hard crystaUine limestones and Umestones made up of the fossU
remains of foramiuifera, and other beds ; whUe, in the central plains of Aaia
Minor, aemicrystalUne rocks of the cretaceous epoch occupy a prominent place
in the Geology of the disfrict. Remarkable beds of the same age have also
been deacribed by Sfr C. LyeU, and bv American Geologiata, aa occurring in
New Jersey and other parts of the United Statea ; but these seem to reat
immediately on the oldest Secondary rocks, without the intervention of the
OoUtes. R does not appear that any true chalk exists in America, but the
formation is exfremely calcareoua, although perhapa chiefiy arenaceous.
123 The Older Tertiary Bocks of England, France, and Belgium. — It is
only of late yeara that the department of Geology profeaaing to treat of atrata
newer than the chalk has assumed its due importance, and the reason of this
it is not difficult to comprehend, for the Tertiary sfrata form a far lesa pro
minent group in northern Europe than the rocka of older date, and have for
thia reason been long considered as of inferior importance, and even as mere
superficial deposits not worthy of being deacribed aa a distinct ayatem. But
thia relative predominance of older over newer depoaita is reversed in the
south of Europe, in aome parta of Aaia, and in South America, where even
the newest group of afrata haa undergone great change of poaition, and
where thousands of square mUea of comparatively modern depoaita atteat the
vaatneas of recent operations.
It is worthy of remark with regard to these sfrata, that a large proportion
of them bear marks of having been formed in the vicinity of extensive tracts
of land, and that in this respect theyare contrasted with the older rocks,
which were for the most part formed at the bottom of deep seaa studded here
and there with islands, such as these we now find in the Eastern Archipelago.
It is also clear that after the termination of the deposits of the secondary
period, and probably during a long interval concerning which we have no
records, land had arisen from the deep waters ; and the bottom of the sea,
preriously the receptacle of chalky mud, assumed by degreed the outline of
the continents now marked out by the mountain chains of Europe, Aaia, and
America. But, however this may be, the rocks of the Tertiary period in
northem Europe are for the most part local depoaita, and have been formed
either in lakes, rivers, or estuaries, by matter conveyed along by freah water,
or elae in narrow conflned seas not far from land. Hence it arises that a

312 PHYSICAL GEOGRAPHY.
variety of causes have come into operation, such as irregular depth, sudden
and considerable alterations of depth, and others, sufficient to modify greatiy
the conditions of animal life.
The Tertiary sfrata of Europe having been thus formed in small areas, do
not usuaUy admit of general descriptions, but requfre the groups to be each
separately described with reference to other contemporaneous deposits, but
stUl more with regard to local cfrcumatancea.
The Tertiariea of Europe and Westem Asia form a very variable series,
consisting, in England and Belgium, of stiff clays, alternating with sand and
resting on a coarse sand and gravel ; and in Paris, of a number of Umestones
and marla alternating vrith gypaum and sUiceous sfrata. They are deposited
in vaUeys or depressiona in the older rooks, and in England (in the Isle of
Wight) some portion of them has been so greatly disturbed, that the beds are
actuaUy vertical. This, however, is an exception to their uaual position,
which is that of beds not much changed from thefr original horizontaUty. • •
The older Tertiaries of England are chiefiy confined to three patches,
which were originaUy, no doubt, connected and continuous, but are now
detached and contained in frough-shaped hoUows in the chalk. These are
called, respectively, the London, the Hampshire, and the lale of Wight
baaina, and the stiff clay which predominates in them, and which is very
abundant near London, is known as the ' London Clay.' The London clay
often, but not always, rests on a series of samdy and graveUy beds, inclosing
bands of potters' clay, and to these the name ' Plastic Clay has been
fiven ; but, in the Isle of Wight, a distinct group of sanda forma the base.
t ia now certain that no mere mineralogical attempt at subdiriding thia group
of sfrata will succeed ; and Mr. Prestwich has shown that the great mass of
clay in the lower part of the London series is strictly contemporaneous with
the hard aandy beda at Bognor, from which the clays at Barton chff are
aeparated by no leaa than 700 feet of sands.
The strata which occupy the Paris basin differ exceedingly in point of
mineral character from the beds just described. Over the chalk is uauaUy
found a freah-water depoait of clay and lignite, and thia is succeeded either
by a coarse sandy limestone containing many fossU shells, or by a siliceous
limestone of fresh-water origin, almoat without foaaila. Next, above these
limestones, separated only by a bed of sandstone, is usuaUy found a aeries
of marla, containing amongat them a considerable quantity of gypaum, and
in the quarriea from which the gypaum has been exfracted, (to make Plaster
of Pans,) an immenae number of the remains of land animals were found
during the early part of the present century. Last of aU, in the Paris
series, there are two groups of marls and sands, one freah-water and the
other marine, developed to some extent, and separated from the gypsum by
a thin bed of oyater shells.
The tertiary sfrata of Belgium are cbiefly seen in the prorinces of South
Brabant and Limburg, and thefr general character is that of sandy beds
containing oxide of iron, alternating with and overlying a series of badly
developed marls and Umestones. The whole sequence is rarely exhibited in
the aame locality, but the total thickness of the deposite is not great. At the
base of the depoaita in many locaUtiea, are argUlaceoua marls, found chiefly in
the northern and weatern parta of the basin. Theae are of blue or black
colour, tenacioua, impervioua to water, and containing beds of septaria.
In central France, and especiaUy near Auvergne, is a group of sandstones,
marls, and Umestones, extending for a considerable distance from north to
aouth, and having an average- breadth of about twenty mUea. SimUar
depoaits, belofting to the older part of the tertiary period, are found near
Le Puy, in Velay, and near AurUlac, in Cantal, the latter being, however,
remarkable for containing a large proportion of sUex, probably derived from
hot springs. Many other small beds are met with in tiie same district.
On the aouth flimka of the Alps, near Vicenza, in Lombardy, a band of
limeatone occiu-s, and another at Monte Bolca, both ofthe older Tertiary period,
and both remarkable for containing remains of organized beings, chiefly

CLASSIFICATION OF ROCKS. 313
fishes. The beds here are marly Umestones, interstratified with thick beds of
compact limestone, and the whole series is overlaid by tabular basalt.
There is evidence showing that many parts of Greece and Asia Minor
were the recipiente of important deposits, apparently from some great fresh
water l^e, not long after the termination of the chalk.
124 Middle and Newer Tertiary Deposits of England and Europe. —
Overlying the older Tertiaries in England there is little more than a heap of
gravelly strata, almost exclusively confined to the neighbourhood of the Eastern
Coast. These accumulations are caUed ' the Crag formation,' and they appear
to belong to a somewhat extended period, and to be dirisible into three parts,
the lower being the Coralline Crag, so caUed from the numerous remains
of corals found throughout the bed ; the next the Bed Crag, diatinguished by
ita deep ferrugineoua atain; and the uppermost, the Mammcdiferous or
Norwich Crag, whioh is of more recent origin than the Red Crag, and con
tains bones of large mammaUa, and occasionaUy freah-water shells. All these
beds are of Umited extent, the CoraUine Crag ranging over an area of about
twenty mUea long, and three or four broad, ita total thickness averaging not
more than twenty feet, whUe the Red Crag, although extending to double
that thickness, is stUl smaU in every respect. The MammaUferous Crag
appeara to be an estuary deposit.
At varioua placea in the vaUey of the Thamea, and on the banks of the Stour
and Medway, fresh-water deposits have been found, some of wbich appear to
correspond m age with the newer portions of the crag, whUe others are stiU
more modem. Pn the vaUey of the Clyde, near Glasgow, extenaive beda, of
comparatively modem date, have been deacribed under the name of ' Kil,'
chiefly conaiating of unstratified clay mixed frregularly with gravel ; simUar
or contemporaneous beds have been found at Bridlington, on the Yorkshfre
coast, and at various other locahties, where eridence of recent change of
level has been sometimes also seen in the raised beaches and sub-marine
forests. The middle tertiaries form a much more decided group in various river
baaina on the Continent than they do in our own country. They occupy a
conaiderable portion of the weat of France, filling up the baains of the Lofre
and the Garonne ; they fifll up alao a great part of the vaUey of the middle
Rhine ; they alone are to be met vrith in the whole of the great vaUey of
Switzerland, between the Alps and the Jura chain ; and they proceed towards
the north-eaat from Svritzerland, foUowing the courae and partly occupying
the valley of the Danube. Frompoint to point they may be fraced spreading
out into extensive series near Vienna and in Styria, and occurring again in
the plains of Hungary; they are also found in Poland and Rusaia ; they
appear both in normem and aouthern Italy, and on the shores and islands of
the Mediterranean; and they are probably represented in the neighbourhood
of Lisbon, and in the south of Spain. They thua form a most extensive
OToup indicating, vrith much distinctness, that many portions of what is now
Europe were submerged during the middle tertiary period.
The newer tertiary period is not lesa amply repreaented in Europe than
the middle one; but it is chiefiy in South Italy, in the Morea, and in the
ialanda of the Eaatern Archipelago, tbat the more ext&aive beda must be
sought for, although the vaUey of the Lower Ehine, near Bonn, and a portion
of cenfral France, beaidea a large diafrict in southern Rusaia, also present
important contemporaneous beds.
The newer tertiaries are not aU of the same age, and the beds so caUed
must have been in the course of formation for a very long period. Those in
Italy admit of being subdivided into two groups, the older of which is caUed
Sub-Apennine, and attaina a great thickness near Parma. These beds consist
for the most part of greyish, brown, or blue marls, containing calcareous
matter, and overlaid by thick sandy beds. The Sicilian beds are distinctly
newer than these, and are equaUy extensive, aince in the aouth of SicUy hUla,
2000 feet high, are formed entfrely of the uppermost of them. Marls, with
occasional limestone, form the great maas of the materials of these strata.

314 PHYSICAI. GEOGRAPHY.
Fresh-water beds of the newer period are found at CEningen, on the Laie
of Constance, consisting chiefly of fetid marlatonea and Umeatones, and
occupying depressions m the molasse. These beda are of great thickness,
but smallextent.
The newer Tertiary deposits of the Rhine and Naaaau are remarkable for
the preaence of very extensive beds of Ugnite, so thick as to be worth
working, although the coal is too earthy and imperfectly bitumenized to be a
valuable fuel.
Other deposits of the same age are found occupying an extensive region
in southern Russia, and weU exhibited in the cliffs on the Sea of Azof. They
consist of beds of white and yeUow limestone, covered by sanda and sUiceoug
grits. Similar beds occur in the Crimea, and the neighbourhood of Odessa.
125 The Tertiary Deposits of Asia and America. — TiU within a ve^ few
years nothing was known of the great extent of these formations, and they
are not even yet described in such detaU that we can speak with certainty as
to their geological age. The westem part of Asia, generaUy, seems to exhibit
a great variety of volcanic phenomena of recent date, accompanied by a
conaiderable extent of modem Tertiary deposits, chiefly lacustrine, and con
sisting of calcareous marls, and white limestone containing chalk. Some of
these have been afready aUuded to, from thefr vicinity and resemblance to
European tertiaries, as for example, the beds at Smyrna, and othera on the
shores of the Caspian. There are, however, others fiirther east, which now
require consideration.
In the westem part of India, near Bombay, thick beda of Tertiaiy lime
stone have been found, chiefly near Cutch, which are covered by argUfaceoug
grits, and belong probably to the older part of the Tertiary period. Similar
beds have been described as occurring in the more cenfral province of
Mewar, and also at Delhi. Beyond this the Tertiary beds of tiie Sewalik
range commence.
The formations composing the SewaUk or Sub-Himalayan hUls, conaiat of
beda of boulders or shingle, of aanda hardened to every degree of conaiateney,
of marly conglomerate, and of an infinite variety of clays. The sfrate dip
towarda the north, at anglea varying from 15° to 35°, and the breadth of the
inclined beds is from six to eight miles.
In a part of the Sewalik district, west of the Jumna, there ia an
interminable aeriea of clays and sandstones, the former being most abundant,
and in the upper part of the aeries, there occurs a sandstone rock, generaUy
soft, but often in hardened masses, owing apparentiy to the presence of
organic bodies, chiefly bones. A very large and remarkable group of
organic remaiins has been obtained from fragmente embedded in this way
in sandstone. The Tertiary afrata of the SewaUk hUls appear to have extended along the
whole of northern India, north of the Ganges, and they occur also near
Bombay, on the one aide, and in the Bfrman empfre, in the upper part of the
drainage of the great Irawaddi river.
There is a deposit, in various parts of India, caUed Kunkur, which is very
generaUy distributed, and appears not to be confined to one period, although
certainly not very ancient. This deposit is especiaUy abundant in the counfry
running up from Gujerat to the north-east, towards Delhi, and appears
covering bUls two or three thousand feet above the sea.
Little is known of the exiatence of Tertiary beds in the great plains of
Siberia and northern Aaia, and we are equaUy without information concerning
China, Chineae Tartary, and Japan. There are not known to be any weU
marked tertiaries of older date in the ialanda of the Eastern Archipelago.
North America presents considerable tertiary beds in Vfrginia, the two
CaroUnas, Georgia, and Alabama, chiefiy belonging to the older part of the
period, and others of nower date in other diatricte. In Vfrginia there are
greenish aands, replaced to the south by white limestones, of no great
miokness, nearly contemporaneous with our London clay, and these, after

CLASSIFICATION OF ROCKS. 315
being traceable for several mUes, are lost under newer deposits, of consi
derable thickness, consisting of clay and loam, alternating vrith quartzose sand
and beds of pure siUcious rock, fuU of interstices.
Over the series of older sfrata thus described there is found, occupying
a vride horizontal range, a deposit of clay of the middle Tertiary perio(f
spread over immense plains, but Uttle above the level of the Atlantic. These
are replaced, in Massachusetts, by white and green sands and conglomerate,
resting on Ugnite. Upwards of ten thousana aquare milea of country are
occupied by these deposits, whUe othera of somewhat newer date occur at
the mouth of the Potomac river in Maryland, and consist chiefiy of clay
and sand.
In South America, the rocks of the Tertiary period are more extensive atnd
important than in any other part of the world, extending in an unbroken line
from the great plain of the Amazons to the Sfraits of Magelhan, a distance
in aU amounting to 2,500 mUes, whUe in some placea they are not leaa than
800 mUes broad. Throughout this vast fract three prmcipal groups have
been determined — ^the loweat conaiating of aandatones and marly Umeatones
covered vrith gypseous clay, which retains water on its surface and produces
marshes; the middle, or ' Patagonlan series,' as it haa been caUed, larger in
extent and nearly the same in mineral character, and the highest or newest
depoait, the 'Pampas clay,' is a single bed, probably one of the largest ever
yet formed on the earth, covering a space of 180,000 square miles, and
throughout chiefly argUlaceous. It is partly covered up by alluvial aands.
126 The Newest Deposits of Gravel and Diluvium,. — The regularly
sfratified depoaita are often aeen to be more or leaa covered up and hidden by
a maaa of neterogeneoua material, generaUy unatratified and depoaited in
irregular heaps, but almost alwaya bearing marka of having been fransported
from a distance. The fragmenta of tranaported rock wmch make up this
mass are caUed 'boulders,' or 'erratic blocks,' when of large size and
angular, and are in this case rarely far removed from the parent rock ; but
they are more commonly smaUer and rounded, as if they had been long roUed
against one another at the bottom of water, and in this state, and especiaUy
when mingled with fine sand, they are called ' gravel.' Such material has
often been conveyed from great distances, amounting sometimes to many
hundred mUes from the place whence the rocka which compoae it were
derived. The whole deposit when of this nature is not unfrequently caUed
diluvium, or dUuvial drift, whUe alluvium, on the other hand, is a term used
in confradistinction to dUuvium, and signifies the ordinary effects of fluviatUe
action. The origin of gravel and dUuvial drift is a subject which has long
atfracted the attentaon of geologists, and which ia not yet clearly made out.
The dfrection of the drift, which can be fraced by foUowing up the gravel to
ita source, varies very considerably in different districts, but it generaUy
seema to have traveUed from some mountain chain, vrith the elevation of
which the existence of theae aingular heapa aeems to have been connected.
Among the more remarkable and instructive Ulusfrations of the phenomena
of gravel, must be ranked the gravel hUls in the south of Seandinaria, and the
isolated patches in the plains of Northem Europe — the escars, or gravel hUls
of Ireland — the detritus of England, as fraced from the Cumberland hUls to
the north, south, and east — the dUuvial phenomena of Svritzerland and Italy
—the gravel of North America, and that of some part of the southem
exfremity of the New World.
Coimected with gravel phenomena, there must also be considered the
rubbed, grooved, and poUshed condition of the rocks on which this material
has been heaped, as these appearances have been the groundwork of theories
suggested, and requfre to be accountefl for in the explanation of the
phenomena. The tertiary deposits in many parts of South America near the banks of
the great rivers are not, however, of this nature, as in most cases they appear

316 PHYSICAL GEOGRAPHY,
to consist of nothing more than the mud depoaited at various pomte and
over wide areas, which some mouths of the gigantic rivers of that country
once traversed. The shifting ofthe actual river course, and its replacement
by thick mud, is, in the case of aU rivers possessed of deltas or depoaitmg
much mud, an event so much a matter of necessity, that we need not here
aUude further to it. „ ^ , —
With regard to the gravel beds and erratic blocks of North Europe, they
are chiefiy grouped in eUiptical areas, vrith the longer axis pointing to some
part of the Scandinarian mountains. The larger blocks are generally near
the surface. The blocks consiat principaUy of granite. Syenite, porphyry,
and hard Umestone, and have been found in Poland and Russia as well aa
North Germany, reaching from the Ems and Weser to the Dwina, and
even the Neva. In Scania they are however much more abundant, and
the quantity of material greater, tliough the blocks are not larger.
The diaperaion of blocks from the Cumberland hUls is also remarkable,
as the rocks themselves of which these mountaina are compoaed are very'
distinct and pecuUar, and very easUy recognised. The granite of Eavenglass,
on the westem border of the region, haa been drifted to the south acroaa the
sea, along the fiat or hollow of Lancaahfre, west of the Penine chain, and
over the plains of Cheshfre and Shropshfre towards the vaUey of the Severn.
In this long course the quantity of pebbles and bouldera is very consider
able, and it is evident that the currents, whatever they were, wluch carried
the bouldera, reapected the preaent levela of the country, for they have not
once crossed the Penine cham to the eastward, nor penefrated far into the
principality or the border districta, where the graveUy deposite have been
derived from the neighbouring hUls. From the eaatern side ofthe Cumbrian
mountains, the granites of Shap FeU and Carrock FeU have been fransported
northwards to Carlisle, southwards by Kendal andKfrkby Lonsdale to beyond
Lancaster, eastwards over the vale of Eden, and up the Penine escarpment
at Stain Moor above Brough. Having here mounted the summit, the
boulders diverge to the eaat-by-north, eaat and south-east, cross many lower
ridges, and sweep over the oolitic moors and the chalk wolds to the sea-side at
Scarborough and Flamborough Head, a distance of 110 mUea. In thia course
three ridges amd two vales were crossed, but the present configuration of
the ground has manifestly undergone no change, aa the paaaage of the Penine
chain ia at only one point, and that the lowest, opening dfrectiy to the west.*
The phenomena of rubbed surfaces of rock beneath accumulations of
gravel, and in the track of large blocka and conaiderable masses of dUurial
material, are important as pointing to the probable origin of the accumulations
themselves. The appearance ia sometimes exactly that producid now by the
action of a glacier moving along slowly, loaded vrith a heavy weight of trans
ported matter, or elae appears due in a simUar way to the action of ice,
which must in that caae have drifted on the spot where we now find the
gravel, when the level of the surrounding land was much below its present
poaition. There can be Uttle doubt that the toanaporting power of floating
and drifted ice, aa affording a ready means of removmg large heaps of rock —
as accounting for the deposit of these in one spot, far removed from the
mountains whence they were derived, and aa explaining the marks of
mechanical preaaure and rubbing met with in the vicinity of iaolated large
blocka, or considerable quantitiea of amaUer ones— is a probable and aatia-
faotory explanation of the phenomena of gravel.
Many of the Umestones of various geological periods are remarkable for
containing caverns, originaUy, perhaps, mere cracks in the sfrata, but since
then worked into holes by the passage of water, or by other mechanical
means. Theae have often served as the dens of wUd animals; and,
when afterwards sUted up, and thefr floor covered with stalagmitic incrusta-

• Phillips's Treatise on Geology, (Edinburgh, 1838,) p. 209.

CLASSIFICATION OF ROCKS. 317
tion, whatever remaina these animals left have been accurately preserved,
and may often be obtained for investigation. We learn in this way, that
large hyaenas and bears once roamed over the waste expanae of our own
ialand and of Europe, and that theae fierce carnivora were accompanied by a
singular race of ruminants and pachyderms ; among the former being large
animals of the deer fribe and a gigantic ox, whUe the latter included the
elephant, and a nearly aUied genus, whose habita appear to have requfred the
ricinity of extensive marshes.
It IS, however, almost exclusively the remains of carnivora that are found
in the caverns, which must in many cases have been the resort of successive
generations of wUd animals for a long series of years. The species of bear
and hyaena, whose remains are chiefly abundant, were much larger and more
powerful than any of those now Uvmg, and there are indications also of a
verylarge feUne animal (a tiger) existing contemporaneously with them.
The gravel in various parts both of England and elsewhere contains nume
rous fragments of the bones of the larger quadrupeds, once the inhabitants of
this region. Among them may be enumerated the elephant, the rhinoceros, a
hippopotamus, several large cervine animals, one of them remarkable for the
enormous spread of its horns, and some large species of the Bos. AU these
were contemporaries, and Uving also at the same time were the wolf, the fox,
the badger, the otter, and a number of apecies stUl remaining. Conceming
the nature of the revolution which, extending over the whole of Northem
Europe, deafroyed entfrely aU veatiges of the larger mammaUa aa indigenous
species, aUowing the amaUer onea to remain, it is not easy to decide in the
present state of our knowledge.
In other countries, as in Asia, America, New Holland, and New Zealand,
there are similar proofs of the former exiatence of gigantic animala of
analogoua apeciea to those which compose the existing faunas, and we every
where find marks of extensive changes produced on the surface indicated
by the presence of numerous fragmenta of rock, fransported from a great
distance, and more or less evenly spread over the face of the country.
The only ultimate cause that can be assumed, with any degree of proba
bUity, as accounting for these phenomena, is the alow and successive eleva
tion of large fracts of land at certain intervals. It is not unlikely that such
elevation, even if in some places permanent, might be accompanied by a partial
sinking, and there is evidence of recent elevation and also of depression to a
very great extent over most parts of the whole world. Such evidence is seen
in ancient sea beaches, and in deposits once formed quietly at the bottom of
the sea near coast lines, but now raised many feet, and sometimes many
hundred feet above the existing sea level ; while not far off the preaence of
decayed foreats running out towards the sea at levels below that of high
water, affords not leas satisfactory proof of partial depression.
Thus we have seen that the structure of tbe Earth's crust, considered
simply in a mechanical sense, offers a vast variety of facts, which it is
not easy at once to explain ; that, however, aU these facts point to some
regular plan and system in the elaboration of the existing surface ; and that
the successive depoaits which may be traced have been altered and disturbed
by frequent upheavals. These general results of the inveatigationa of
geologists requfre, however, to be considered and compared vrith reference
to the organized beings which also greatly modify the Earth's surface, and
whoae conditions of existence we next proceed to discuss.

PART IIL
ORGANIZATION.

CHAPTER X.
THE DISTRIBUTION OF VEGETABLES IN SPACE.
{ 127, The meaning and nature of organization, and especially of vegetable life. — 128. Natural
arrangement and classijication of plants. — 129. Influence of climate on vegetation. —
130. Influence of soil on vegetation. — 131. G-eneral range of plants in various countries at
moderate elevations. — 132. The hotanical regiona. — 133. Distribution of plants in vertical
space. — 134. Eange of cultivated plants. — 135. General considerations of the distribution
of plants Jn distant botanical centres.
rilHE Meaning and Nature of Organization, and especially of Vegetable
JL Life. — The vegetable world preaenta ua with aome of the moat readily
understood of thoae forma of matter which are endowed with vitaUty, being
prorided vrith organa enabling them to form new and pecuUar combinationa
of various elementary aubatances. In other words, we have in this depart
ment of natural science a new force infroduced, modifying the action and
altering the results of other forces — a body not only capable of selecting and
separating the various material elements, and bringing them into new combi
nations, but also of reproducing another body, which, though at first
different in many respects, wiU, after passing through certain transformations
and metamorphosea, repeat the individual and continue the race.
The basia of atmcture of aU the various and dissimUar vegetables ia,
however, the aame — it is a little closed vesicle composed of a membrane,
usuaUy transparent and colourless. The ceU-waU consists of carbon, hydrogen,
and oxygen, while a semi-fluid investing substance contains also nifrogen.
Tbese elementary aubatancea, in varioua proportiona, make up the maaa of aU
vegetation ; and the ceUs in the course of their development becoming crowded
closely together, form into three principal tissues, according to the shapes of
the ceUs, and thefr importance to the hfe of the plant. We may indeed
regard the ceU aa a Uttle independent organized body living for itseli alone.
It imbibes fiuid nutriment from the surrounding parte, out of which, by
chemical processes, which are constantly in action in the interior of the cell,
it forms new substances, which are partly applied to the nufrition and growth
of its waUa, partly laid up in store for future acqufremente, partly again
expeUed as useless, and to make room for the enfranee of new matters. In
this constant play of absorption and excretion, of chemical formation, frans-
formation, and decomposition of substances, especiaUy consiste the Ufe of the
cell, and — since the plant is nothing but a sum of many oeUs united into a
definite shape — alao the Ufe of the whole plant.*
Since, then, every plant in ita course of formation, and every undeveloped
part ofa plant, consists of theae celia, which in thefr growth, and by preaaure
againat each other, become six-sided, radiated, cyUn(frical, spindle-shaped, or

• Sohleiden's Plant, translated by Henfrey, p. 45.

DISTRIBUTION OF VEGETABLES IN SPACE. 319
even filamentary, and which aometimes multiply so rapidly, that in ono
fungus, (Bovista gigantea,) 20,000 new ceUs are formed every minute, we
may weU understand the necessity of making out something of thefr
stmcture, mode of growth, and natural relations. By one modification ofthe
ceUs is formed the external layer of the plant or epidermis, a membrane
which appears continuous, and which, as bark, is known to every one.
Another modification produces tubular channels, which appear to the naked
eye aa fibrea, but which aUow of the paaaage of the fluid contents or sap
cfrculating through the plant, or else serve as afr vessels ; whUe a third
continuea the development of these vascular bundles, and at length produces
what is caUed wood. Those plants, and parts of plants, which consiat neither
of bark nor wood, exhibit the ceUa either in their aimple atate or as vascular
bundles, ao that these three conditions may be considered as the fundamental
ones, and as involving aU that need be at first regarded.
The contents of the ceUs of plants are, however, also very important, and
may be divided into two groups — those soluble and insoluble in water. The
former include albumen, gum, sugar, and the agreeable acids of fruits, such
as maUc and citric acids. The lati;er are chiefly the fat oils, such as are
found in the kernel of the almond and the fruit of the oUve, and the aromatic
oils which characterise many plants. Of aU these various contents, however,
the starch found in the ceUs, under certain cfrcumstances, and composing a
large portion of the nutrient matter of plants, is the most important. It
occurs in every part of every plant, but only the roots, tubers, seeds, fruits,
and more rarely (as in the sago palm) the pith, aifford sufficient to serve as
food, or repay the trouble of separating it.
Such being the general condition of the matter of which plants are made
up, it is stiU only when endowed with ritality that they exhibit the properties
peculiar to organization. The ceU-formation, the first reault of Ufe, changes
that which was merely a mineral into an organized body, and then all the dif
ferent planta are distinguished from one another by the shape or plan according
to which the ceUa are united together. The form, therefore, and modifications
of form, as they develop the system in plants, are matters without a strict
knowledge of which the idea of the vegetable kingdom cannot be conceived,
and in order to assist in this conception, it ia well to deacribe the language of
naturaUata in thia department of science with reference to a single plant.
A plant, then, may be said to consist of the foUowing parts, although it
must be remembered that aome of them are absent, and othera greatly
modified in particular natural groupa. There ia a continuous principal trunk
or stem, vrith various lateral appendages, of which three kinds may be traced,
namely, the root, the leaves, and the buds; but the latter being, in fact,
repetitions of the whole plant, except that they are not free at the lower
exfremity, and the roots agreeing perfectly, in aU thefr characters, vrith the
free exfremity of the plant, we have the plant really made up of a stem or
aria, terminating downwarda in roota and rootlets, which attach it to some
sohd support, and upwards in a seed-bud, whence the original plant ia
repeated, and leavea, which vary greatly in thefr form and nature, since
amongat them, and belonging to them, muat be ranked all the beautiful fiowers
and deUcious fruits preaented by the vegetable kingclom. Different in
external appearance ajs these are, thefr true character no longer admits of a
doubt, and the change that takes place belongs to development, according to
weU marked and invariable laws. According to the kind and degree of
development that is natural to plants is thefr ultimate and characteristic form,
and specific definition.
128 Natural Arrangement or Classification of Plants. — The first begin
nings of vegetation are seen when a green film covers old damp walls, or is
depoaited on the aidea of a glaaa, in which soft water has stood for several
daya in aummer. Theae consist of the simple ceU, vegetating as an inde
pendent plant, and are succeeded in organization by the confervae or mould,
where the cells are arranged in Unes and filaments. Then come those long.

320 PHYSICAL GEOGBAPHY.
thin, and lettuce-Uke leavea, sometimes green, sometimes red, often found
on the coaat, and afterwards the vaat tribe of Lichens and Fungi, which with
the aea weeda (Algce), form the three groups composing one large class of
plants. In the ffrat mentioned tribes there are no deflnite o^ana, but in
theae latter there are ceUa aeparated from the rest, and destined to the pro
duction of reproductive ceUa ; but it is important to remember that, in aU
plants, the same organ may serve the most different vital offices in different
plants, and the same vital process may belong to the leaf in one plant, to the
stem in the other — except, indeed, the organs of reproduction, which are not
appUed to any other use.
In the higher sea-weeds and lichens, the forma which in the Fungi (and
alao in thoae lichens covering waUs, stones, and palings, vrith a whitish-grey
or yeUow scurf) are very indeterminate, put on a more definite and regular
character, exhibiting constant shapes, which resemble stems and leaves,
though they have not the same uses, nor the same relation to thefr detailed
structure. AJI these plants, however, present this one great peculiarity, that
in none of them is there, properly speaking, either stem or leaf, and they are
consequently fiowerless, and have no visible organs of fructification, in the
usual mei niig of the term. They thus form a separate natural group, which
is associated by very close natural resemblances with another group, of
which the Mosses, Ferns, and Club Mosses, are weU known examples. In
aU these, there can be distinguished a distinct stem, vrith leaves, but a
pecuUar series of gradations ia presented in the formation of the repro
ductive ceUs, which first come into more intimate connexion vrith the
leaf, and at last aaaert so afrongly thefr claim to definite foUaceoua organs,
that they lose all resemblance to the other leaves. Thus, in the Masses
and Ferns, there ia a pecuUar approximation in form to the atmcture of the
reproductive organa of more highly organized plante, whUe in the Club
Mxjaaea, the resemblance is even greater, and the analogies are more
real. AU the various natural groupa above referred to are described by
botanists under the general name of Cetptogamia, and the second group
are also caUed Acotyledons, owing to the plant not growing from a seed,
which contains nourishment for the young indiridual during the earUeat stage
of ita exiatence, although in some respects resembling plante of higher and
more compUcated organization. In all other plante the stem and leaf are
the elementary organs, but definite leaves are franaformed ao as to form
reproductive celia, and these are therefore sometimes caUed sexual plants, to
distinguish them from the Cryptogamous fribe.
The sexual plants are again subdirided, one group exhibiting a very simple
inflorescence — mdeed, no flower in the ordinary sense — and presenting the seed
naked and undefended. The whole fir tribe, the misletoe, and a fanuly of
tropical plants (the Cycadaceee) are of this kind, and offer a sfriking confrast
to the other plants where the inflorescence is remarkable and characteristic.
The phanerogamous planta are therefore either Gymnosperms (naked-seeded)
or Angiosperms (covered-seeded) ; and the latter are eitiier developed from a
bulb or aingle-lobfid seed, aa the palms and grasses, and are called Mono
cotyledons (smgle aeed-lobed), or from a double seed, like the beam, thence
called Dicotyledons (double seed-lobed). The plants of the two series not
only differ eaaentiaUy in thefr apparently unimportant characters, but in all
the rest of their organization ; and are ao stiikingly distinct in their external
appearance, that a little practice enables the eye to recognise them at a
glance. Thua the first or monocotyledons generaUy have the fibre-like wood-
bundles scattered throughout the stem, as in the maize, whUe the second has
a closed firm cfrcle of wood, Uke the wUlow ; in the leaves of the first the
veins are usuaUy paraUel, as in the graaaes, but in the others they ramify
like the branches of a tree, and form an elegant net work on the aurface of
the leaf, aa in the Ume ; tind finally the number three prevaila in the floral
arrangements of the firat, as in the tulip, whUe the number five is that found
characterizing the other, as in the primrose. The two series proceed paraUel

BJ <
5 o

DISTRIBUTION OF VEGETABLES IN SPACE. 321
vrith each other in respeot of inflorescence, from the simple to the more com
plicated forma, so that in the highest stage, where a number of separate
flowers are united into one definite whole, arranged according to a marked
type and defined with cfrclets of leaves, we find on the one side the grasses
and on the other the so caUed Composite, of which the daisy, dandelion,
thiatie, &o., are well known examplea, holding side by side the highest station
in existing vegetation.
Thus, then, we find aU the plants brought within range of description, by
referring to these important, because natural, characteristics, and it may be
worth whUe here to recal the principal points, and express in a tabular form
the outline of the classification aa a matter to which we shaU frequently have
occasion to refer.
1. Thallophttes. (Confervw, Fungi, Lichenes, Algce.) Stemless, and often
without leaves or roots, growing in a centrifugal manner, and capable of
undergoing modifications in the individual cells.
2. Acotyledons. (Liver-worts, Mosses, Ferns, Equisetacece, Club-mosses, and Bhizo-
carps.) Having stems, vascular bundles, all developed at the same time,
embryo a simple cell or congeries of oeUs, growth simultaneously upwards
and do-wnwards from the central axis or stem, no visible floral develop
ment.
3. AufGiosPEEMS. (Coniferce, Cycadeacece, Loranthacece.) Inflorescence very
simple, not presenting a true flower, seed-bud and seed naked.
'4. Monocotyledons, also called Endogens. Having one seed-lobe, whioh forms
one small leaf in the embryo atate, the fresh leaves springing from the
centre, and the footstalks of the old leaves forming the outside of the
stem ; the vascular bundles defimte, and converging towards the interior ;
not having true wood ; illustrated by the palms and grasses — all the arrange
ments haring reference to the number three and its multiples.
^ 5. Dicotyledons, also called Exogens. Increasing by successive coats from
without, the grovrth of each year forming a concentric circle of wood
round the central pith ; having two lobes in the seed, symmetrically
arranged, and appearing as two small leaves above the ground when the
plant first grows ; vascular bundles indefinite ; the floral and other arrange
ments govemed by the number five. Most of the common forest-trees of
temperate climates, as the oak, beech, &c., are examples of this group.
129 Influence of Climate on Vegetation.— ^Plants being thus very variously
constituted, and offering so many varieties of structure, are greatly infiuenced
by various causes, ofwhich cUmate and soU are the most direct and important.
Tims in tropical climates monocotyledonoua planta abound, and in temperate
regions dicotyledonous, whUe in polar or extremely cold countries, the vege
tation is chiefiy cryptogamic. On the other hand, certain tribes of plants are
strictly confined to particular local conditions, which, at least to some extent,
are connected with the soU, directly aa weU as indfrectly.
We have already, in speaking of the distribution of temperature on the
globe, explained those causes on which cUmate depends, and the vast difference
m climate that may exiat in placea having the same latitude, but different
longitude ; in others, having the same mean annual temperature, but different
summer and winter heats ; and in others, having the same exfreme Umits of
temperature, but not on the same isothermal. Vegetation is greatly infiuenced
by almost every diatinct change of climate, although individual plants wUl
adapt themaelvea permanently to considerable ranges of heat and cold.
With regard to the extreme Umits of temperature at which vegetable
organization can exist, we may aay, that although aeeda will not germinate
at a temperature below the freezing point of water, (according to Goppert's
recent obaervations, 39° Fah. is the limit,) stUl even the extreme cold requfred
to freeze quickaUver doea not destroy their vitaUty. So also, on the other
hand, no aeed wUl germinate in water whose temperature is 122° P., and
at the heat of 144° in vapour, and 167° in dry air the vitaUty of com is
desfroyed. It is indeed probable that a long continuance at much leaa
extreme- temperature would be absolutely destmctive, since in the caae of
Y

822 PHYSICAL GEOGRAPHY.
gram an exposure to 95° F. for three days has been effectual in preventing
subsequent growth.
It has been observed generaUy that the mean temperatures of different
seasons and single months form the best guides for purpoaes of botanical
geography, since, if the isothermal lines only are attended to, the most
extreme diasimUarity may exist in real climate. In those placea whioh have
the aame iaotheral linea, (equal mean aummer temperature,) and in which
the maxima of heat for certain Umited periods are nearly the aame, there is a
sufficient reaemblance to aUow of the growth of simUar planta, although in
the one place the vrinter may be mUd, and in the other very aevere.
It is weU known that the leaves and flowers of the aame plant are
unfolded at different perioda of the year ; earUer in the warmer regions,
later in the colder. M. G. de. St. Hilafre once observed the peach frees at
Brest without leaves or blosaoma on 1st of April; on the Sth he found
them in fuU bloom at Lisbon ; on the 25th, at Madefra, the fruit had set; and
on the 29th he got ripe peaches at Teneriffe. Numeroua other examples
might be quoted, the general result being that for each degree that the
station of a plant is nearer the pole, the time of flowering ia delayed almost
four days, but there are many cauaes which greatly modify this law, and it
may be otherwise and more accurately expressed by aaying, that vegetation
is retarded, on an average, three days if the temperature be diminiahed one
degree of Fahrenheit, Sthough, after aU, such calculations have no very
sound basis. It requfres Ught and the action of the chemical raya ofthe sun
to stimulate plants to activity, and perhaps heat may be a much leaa important
element than haa often been auppoaed.
Climate altera and is combined vrith a change in the condition and
pressure of the atmosphere aa we ascend from plaina towards table-land and
the higher portions of mountain-chains. This is seen equaUy weU in what
ever part of the world the investigation is made, and modifies very greatiy
both the present and past diatribution of vegetebles on the Earth. Thus, at
the foot of a mountain, the plants of the plain appear, but they graduaUy
disappear aa we aacend, and a traveller familiar with the vegetation, oxJUrra,
of an arctic or temperate cUmate, wiU find, in aacending high mountaina
vrithin the fropics, that he sees first one and then another group of famUiar
forms prevaUing over the fropical forms of vegetation that he has left in the
plains. After a time, even the trees cease to grow to thefr fuU height,
Duahea being the largest plants, and, at length, as he approaches the Umit of
perpetual snow, the bushes give place to herbs, these to Uchens, and but a
few of the forms of plants of the arctic zone are missing, whUe even the
same species re-appear after having been lost throughout the whole space
between the arctic regions and the summite of these mountains.
There ia, therefore, a certain paraUeliam between the disfr-ibution of
vegetation from the level of the aea to the limit of perpetual anow, and that
from the equator to the polea, although the gradual change of vegetation
takea place much more alowly towards tiie poles than with increasing Stitude.
With our present knowledge it ia now no longer difficult to perceive that this
paraUeUam exactly agreea with that which we find between the gradual
decrease of heat from the equator to the poles, and that from the plain to
the limit of perpetual anow.*
It is extremely difficult even to imagine any hypothesis which shaU
explain the true influence of cUmate on vegetation, for we often flnd plants
capable of undergoing great changes in temperature and even in aU other
constituents of cUmate without injury, and yet naturaUy limited in extent
within very narrow bounds. On the other hand, however, we find foreat
freea and natural tribea of weU known plants altering thefr external character
and form to a very great extent when exposed to a change of oUmate, either

Meyen's Botanical Geography. Translation published by tlie Ray Society, p. 26.

DISTRIBUTION OF VEGETABLES IN SPACE. 323
by removal to a different latitude, or by being transplanted to more or leas
considerable elevations above the sea level.
As an example of another kind we may take the case of barley, which is
cultivated from the exfreme limits of culture in Lapland to the heights
immediately beneath the equator, although it ia only within a very narrow
zone that it apparently flourishes under natural conditions. It has been
found by some curious experiments that in several places under latitudea
varying as much as forty degrees, the actual number of days between planting
and reaping multipUed by the mean temperature is nearly the same, so that
to define accurately the conditions of temperature requfred to maintain any
plant in a flourishing condition we must state within what Umits its period
of vegetation may vary, and what quantity of heat it requfres.
The great importance of considering the exfremes of temperature in
speaking of cUmate is, however, best Ulusfrated in the case of the vine, which
wUl indeed grow, and, in some seasons, produce eatable fruit in many districte
beyond certain weU defined limits vrithin which drinkable vrinea are grown to
profit. For this latter purpoae a mean annual temperature of more than
49° Fah. is sufficient, provided the mean winter temperature ia above
32°.8 Fah., and the mean summer temperature at leaat 64°.4. Thua, at
Bordeaux, (latitude 44° 50',) the mean temperature of the year ia 56°.8, of
vrinter 43°.2, and of aummer 71°- On the Baltic, (latitude 52^°) at a apot
somewhat beyond the exfreme verge of the wine-drinking countriea, the
corresponding figures are 47°.5, 30°.8, and 63°.7 respectively, and here wine is
produced, but can hardly be called drinkable. On the east coast of Ireland, in
latitude 55°, the myrtle nourishes as luxuriantly as in Portugal, but the summer
temperature being low, the vine wiU very rarely ripen its fruit in the open
air, for the mean temperature for the month of August being only 60°.8 Fah.,
the proper aummer average ia not approached, and the mildneaa of winter,
which raises the isothermal, cannot make the required difference. Thus, the
culture of the vine and the profitable Umits of other plants useful to man,
depend more on the isotheral than the isothermal line, and are Uttle affected
by great cold occurring in winter.
130 Influence of Soil on Vegetation. — Plants are generaUy attached to
the earth mechanicaUy, and derive very important inorganic substances from
the soU in which they grow. Many, however, can exiat permanently in
water, whUe aome few seem to requfre nothing more than they can obtain
directly from the air, and othera derive aupport only indirectly from the aoU,
being attached as parasites to other plants.
Almost all soUs, even fine quartzose sands, the most barren of aU, contain
some soluble matter which plants can avail themselves of, and if we remove
any plant to matter perfectly insoluble and water it with distUled water, it
ean never attain to perfect development, although wdth carbonic acid gas and
water it wiU continue to Uve. Water is thua abaolutely essential, and
carbonic acid not less so, to the exiatence and reproduction of aU vegetable
matter, but much more than this is generaUy requfred, and it becomea
important to know how far the presence or absence c^ particular minerals,
the nature of the materials of which a soU is principaUy made up, or the
mechanical condition of such materials affect the capacity of the soU for
receiving and nourishing certain plants or natural groups of plants.
From the different habits afready alluded to it vriU readily be seen that
a division into aquatic, land, and parasitic plants, includes almost aU the
various kinds we are likely to meet with.
The first class includea many groups, and with them may be properly
assoriated shore plants, amphibious and inundated planta, and some others ;
whUe the third or last class includes thoae only which are Umited, ao far as
thefr habitat ia concerned, to other treea and vegetables. But it is with the
aecond class that we have now to deal, and theae also are much subdivided, aa
wehave aand plants, limestone plants, clay plants, gypsum plants, turf plants,
bog plants, and marsh plants. We may also consider in reference to thia
v2

324 PHYSICAL GEOGRAPHY.
subject the mechanical condition of the soU and aubaoU, some plants growing
on hard rock ; others on fragmentary or broken rock, boulders, or gravel ;
others on material in finer subdivision or sand ; and others again on tough
argUlaceous rock ; while, again, there are whole tribes of plants which seem to
have especial reference to cultivation, becoming so far modified by artificial
culture that their true habits are rarely now to be recognised. It wiU be
convenient to foUow the arrangement of Dr. Meyen (see Geography of Plants
before quoted) in this part of our subject.*
Sand plants, or fiint plants, are of pecuUar character in aU parts of the
Earth, and the greatest number of them are probably grasaea. Amongst
them are aCarex (C. arenaria), an Arundo (A. arenaria), aeveral species of
TussUago and PotentUla, and several other plants usuaUy found in sandy
plains, whUe one (Elymus arenarius) grows naturaUy and freely iu shifting
sand hUla on the sea coaat, and ia often uaed with great advantage to bind
loose sand, and prevent ita being drifted by the wind when no mechanical
contrivance -wiU aerve and no other plant wUl grow upon it. Beaidea these
there are aome planta confined to river aand.
There are plants which are found almost exclusively in rocks, and others
again, are more common on loose stones, amongst the former of which a great
number of Cacti and other succulent plants in the fropics may be mentioned,
together with the greater number of^ ferns, lichens, and mosses. These are
found indifferently on quartz and calcareoua rock, but particular species are
limited more closely in geological poaition.
Gravel planta have been conaidered aa chiefiy growing on the detritna of
mountaina, auch as Saxifraga rivularis, Banuncula alpestris, and B. gla-
rialis, and some apeciea of Sida have been described, of^ remarkable beauty,
growing on a white frachytie sand on extensive fracts in the plateaux of
Peru, at an elevation of from fourteen to sixteen thousand feet.
Plants growing on calcareous rocks, whether chalk or limeatone, form
another group, of which the famUy Orchidece preaenfa many species. Calca
reous mountains exhibit many pecuUaritiea in thefr vegetation, having for the
most part few woods, but generally rather a shrubby and bushy vegetetion,
and, therefore, they possesa a number of smaU planta whieh grow in the ahade
of these bushes. The chalk of our own ialand is weU known aa growing a
short but sweet herbage, and on the ridges of the hUls the yew and some few
©ther coniferous frees grow to large size. In addition to the plante grovring
on the calcareous rocks, some are found also where gypsum forma the
subaoU, but this is by no means a common condition in nature. The pre
sence of magnesia in rocks is generaUy unfavourable to the growth of plants,
and the rocks that are very hard and not readUy decompoaed or disin
tegrated by atmospheric influence are also usuaUy barren.
Mixtures of sous are often found to be most favourable for the growth of
tiiose classes of plants that naturally abound on the mineral that prepon
derates, but it must not be forgotten that even those plants which pecuharly
belong to a soU, appear also very frequently elsewhere ; and it haa even been
observed, that some which have undoubted preference for a soil of a particular
nature have a much wider cfrcle of diafribution than othera which grow in
common mould.
Other mixtures, such as those which result in the formation of bog-earth
and turf, have a peculiar vegetation, seen in those counfries where turf-
moors, bogs, and marahes are frequent and extensive. The apeciea which
grow on turf are diatinguished by growing aociaUy and by an exceaaive
development of root. The Sphagna is an example of this, and is a plant
which rarely aUows any othera to appear where it has taken up ite abode.
Bog plants grow on very wet soil, and as bogs are very frequent m northern

Moyou's Botanical Geography, ante cii., p. 46 et passim.

DISTRIBUTION OF VEGETABLES IN SPACE. 325
counfries and in the higher parts of mountains, such plants are found on the
Alps, the Harz mountains, the mountains of SUesia, the plateaux of the Andes,
and in Ireland. These, however, and turf plants are often mixed, as, in fact,
a smaU addition of moisture turns a turf moor into a bog, and a stUl further
addition to a marsh, but aa marahea often contain sheets of water besides being
permanently softer than bogs, they include also some aquatic plants and
some peculiar to themselves. It is evident in aU these cases that the
quahties of the soU have in many important respects a decided influence on
tiie presence of certain plants and on their abundant increase.
It is a singular fact, that a large number of plants seem to have attached
themselves to civUized man, since they foUow his footsteps as he advances,
and thus appear to exhibit a kind of domestication. The higher and more
stimulating quaUty of the soUs used for the cultivation of the food plants is
no doubt often the reason of this, but there are also others, and a number
of species have been grouped by Schouw, one of the most eminent botanists
in reference to the geography of plants, into waU-plants, ruin-plants, roof-
plants, fiank-plants, and rubbish-plants. These possess habits which are at
once understood by their names, and in most cases show a decided preference
for artiflcial over natural conditions of existence.
Certain species also appear in fixed and singularly remarkable situations,
as for instance, there is an exfremely pretty fungus, which is found on and
appeara abaolutely limited to wine caaks. There is also one (a Conferva)
which grows on window panes, and another on paper. These habitats are
remarkable as being purely artificial, and not presenting any very analogous
substance in nature.
131 General Bange of Plants in various Countries at moderate Elevations.
— However clear it may appear that plants are greatly affected by soU,
situation, and culture, so that whUe some have naturaUy a wide range, others
are limited in this respect, from causes easUy understood, it is yet equally
clear, that there are other natural limits of distribution which it now becomes
necessary to treat of. There are in this matter two very different clasaea of
facta to be conaidered. The Heath planta, for example, occur on dry, sunny,
sandy plains ; they extend from the Cape of Good Hope through Africa,
Europe, and Northern Aaia, to the extreme limits of vegetation in Seandi
naria and Siberia ; these plants are distributed in this great region in such a
manner that South Afiica has a vast number of distinct species, of which,
however, never more than a few individuals grow side by aide, whUCj.towards
the north, the number of species suddenly diminishes in an important degree,
the number of indiriduals increasing, tUl at last in the north of Europe
a single species (the common Heather) overspreads whole countriea m
millions of single indiriduals. The range of disfribution, or the area of a
plant, includes aU those locahties in which planta freely grow, the expression
' natural habitat' denoting the particular station or stations to. which it has
been appointed by nature.
There are three ways in which we may speak of this, area — namely, in
latitude or diatance from the equator towards the poles — in longitude or
distance on a line paraUel to the equator — and in vertical distance from the
sea level. The two former may be caUed ' distribution in horizontal space' —
and the latter ' distribution in vertical space.' There is also another distri
bution determined by the examination of the fossU remains of vegetables in
various rocks, which as it appears to present something Uke analogous con
ditions, is now known as ' aistribution in time.' In the present section we
have to freat of distribution in horizontal space.
The distribution of plants is chiefly regulated by that of heat on various
parte of the Earth's surface ; and as this, again, has a certain relation to the
paraUels of latitude, it foUows that the diatribution ia according to latitude
principaUy, the longitudinal extent of the area being much leas important.
The area of a plant, vrith reference to its extent in latitude, is called its
' zone of latitude,' or more simply ' zone,' and it is caUed the ' region,' when

326 PHYSICAL GEOGRAPHY.
vertical range is referred to. The term zone of longitude is applied, though
more rarely, to the horizontal range of plants in districts within simUar limita
of longitude. The zone of every plant has a polar and equatorial Umit beyond which
the plant does not appear, but those plants whose polar limits extend to
extreme latitudes are exceptions to this, as weU as those whioh cross the
equator, and enter the opposite hemisphere. The former are generaUy caUed
polar or arctic plants, and the latter tropical plants, but tms is not quite
accurate, aa an arctic plant may appear ¦witmn the arctic zone without
aacending to the highest latitudes. SimUar examples might be given of
tropical planta which do not reach the equator.
There are many conditions, some of which we have afready adverted to,
which modify and interrupt the range of particular species of plants. Thus,
for example, if a plant requfre a certain degree of heat, and ite presence
chiefly depends on this, it may appear in aU thoae placea which have the aame
mean annual temperature, and thus exhibit a greatly interrupted range,
especially when we combine vertical with horizontal distribution. The prim
roses, the anemones, and the gentians, of the plains of northem Europe,
re-appear in this way at a certain elevation in the Swiaa Alpa, whUe Salsola
kali, having an exfraordinary and pecuUar relation to the aea coast, haa an
almost uninterrupted range on the shores of most parta of the world.
It is clear, also, that there is an artificial, as well as a natural, range of
plants, for man is enabled to transplant many, as, for instance, the cereals
and the vine, so as to have com in almost every country, whUe the grape,
indigenous only within narrow Umits, is now infroduced and is cultivated to
advantage in South Africa, AusfraUa, the islands of the Eastem Achipelago,
and many parts of America, on the Pacific as weU as the Atlantic side.
Many planta seem to grow with much more than natural luxuriance when
introduced into new counfries.
GeneraUy it is found that plants vrith a naturaUy wide range may be
extended much farther artifieiaUy, whUe plante of limited area are generaUy
spread vrith difficulty, and we may lay it down aa a role, that the range of
plants is wider the lower the degree of thefr development. Thus, the
Cryptogamise — especiaUy the Uchens and mosses, — and probably the Algae,
are distributed uninterruptedly from one end of the Earth to the other, and
of one hundred and sixty-seven plants, common to Europe and AuatraUa, as
many as one hundred and twenty-two are Acotyledons, thfrty only being
Monocotyledons, and fifteen Dicotyledons. On the other hand, some
plants have a range aa remarkably Umited, being confined to an island or
a mountain. Plants vary ao much in the extent of thefr range, that general rules can
scarcely be laid down conceming them, but it has been supposed by Schouw,
that in the temperate zone of the northern hemisphere, a distance of 10° — 15°
is the most common breadth of the area of a plant, while the extremes do not
extend more than five degrees aa a minimum and thirty as a maximum.
The longitudinal extent of a zone is often much greater, since there are
some planta which range as a belt round the globe. There are, however,
caaea of very Umited range in thia dfrection, generaUy caused by the
existence of aome natural obatacle, as a broad expanse of water, or a lofty
mountain ridge.
The aubject of the diatribution of planta may be dirided into two perfectiy
distinct branches, one of which treate of the distribution of the forma
which point out the groupa of plants, whUe the other does not inqufre
conoernmg the abaolute predominance of any particular group or type, but
considers the relative proportions founded on actual numbers, which any
fiven group, by its number of species, bears either to the whole masa of
nown plants, or to the number of^species of other groups. The former givea
what may be called the Physiognomy of plants, since in it the general aspect
is regarded, while the other presents the true Statistics of plants. As an

DISTRIBUTION OF VEGETABLES IN SPACE. 327
example, it is weU known that a particular group of plants, such as the ferns,
may determine the natural character or floral physiognomy of a countey
without therefore being predominant by the number of its species, because,
although in the aame country, aome other plants, such as the Composites,
may exceed the ferns in the actual proportion they bear to the sum of aU
the phoenogamous plants, yet a single species of fern may cover ten times
more ground than all the Cfompositae together. The ferns here preponderate
by the mass of individuals, not by the number of species.
It is at any rate a fact, and a very important one, that plants are
distributed over the Earth's surface according to certain laws, but of the
tme nature of these we are not perfectly acquainted, for although we know
some of the external causes which place the more developed and nobler
forms of vegetation in the hot zones, we know of no cause why the same
species of plants are not always produced under simUar conditions of climate.
Ijius, the aingular group ofthe Cactaeece is properly pecuUar to the torrid and
aubfropical zonea of America, two apeciea only having been met vrith in Asia,
and none in Africa. But the form of Cactua has its representative in the
Old World, for we have on both sides Euphorbice, which we should certainly
consider Cacti, if we were ignorant of thefr organs of fructification. It ia equaUy
inexpUcable why the Old World should possess abundance of heaths (Ericce),
whUe only a representative form " (not a frue heath) comes in thefr place in
America ; but these and other remarkable facts agree in showing that the
greater number of famUies of plants are disfributed over the whole globe,
mdiridual representatives of the groups appearing wherever a fertUe soU is
exposed to Ught and afr.
In the disfribution of planta, it has alao been obaerved, that the apecies
of genera, as weU aa the genera of famiUea, proceed aometimea from a point,
and range themaelves round it in concentric cfrcles, or spread from it like rays
in various dfrections, while in other and more common cases, they are arranged
in belts. OccasionaUy these methods are modified by the sooial or isolated
habit of the plant, wlucb is a very important cfrcumstance in its distribution.
Genera, as weU as families, attain their maximum in some one place on
the Earth, and when in addition to this the number of individuals in which
the genus or famUy grow is sufficient to influence the physiognomy of
the flora, it has been found convenient to give a special name, generaUy
formed from that of the counfry or zone. The Pahns and others are thus
almost exclusively confined to the torrid zone, and are regarded there as
characteristic, although species extend far to the north and south of the
two fropics.
When a famUy of plants predominates in any zone, either by a number
of indiriduals or species, and in another zone there are only a few or aingle
forma of it, the famUy ia aaid to be represented by the few species, and these
are then caUed the representatives of^ the famUy. Thus, the Heaths of the
Old World have thefr maximum in South Africa, but the beautiful shrubby
forms abundant at the Cape of Good Hope are represented in the south of
Europe by one species (E. arborea.) So the Acaciae characterise New
HoUand, but one species (A. heterophylla) is the represfentative of the famUy
in the Sandwich Islands, and in the form and growth of its leaves seems
even to connect in the northem hemisphere two forms of prevalent vegetation
in AusfraUa. If we consider the general features of the vegetation spread over the
globe, or the different impressions which, at different places, it makes upon
us, we shaU soon remark certain principal groups, which are more or leas
clearly separated from the surrounding planta. These groups, which are
distinguished by thefr peculiar physiognomy, sometimes agree also in artificial
characters, and form certain genera and famUiea, but sometimes it ia the
whole vegetation of the diatrict which has received a pecuUar character from
the arrangement or grouping of the different forms of its plants. If we
were to classify the whole maaa of vegetation according to the peculiarities in

328 PHYSICAL GEOGRAPHY.
physiognomy which it presents, the classification must be twofold, both
geographi(^al and botanical. When the geographical principle ia taken, we
may divide the vegetation according to the countriea, or larger fracts, in
which it is found, and caU such diviaiona ' Floras,' which are further
designated by the names of the countriea, but such diviaiona may also be
called ' regions,' or phyto-geographical kingdoms. The whole surface of
the globe has been mapped out into such divisions, which we now proceed
to enumerate. 132 The Botanical Begions. — Two eminent authora have suggested
divisions of thia kind. The first is that of M. de CandoUe, with reference to
natural stationa, and the other by Profeaaor Schouw, who haa taken tho most
remarkable features of the vegetation of geographicaUy marked districts.
We quote the tables as given by Professor Balfour, in his ManuM of Botany,
not long since pubUshed : —
PLANTS AS GROUPED ACCORDING TO THEIR NATURAL STATIONS.
A. Plants growing in Water, whether Salt or Fresh.
1. Marine plants, such as Sea- weeds, Lavers, &c., which are either buried in the
ocean, or float on its surface ; alao such plants as Euppia and Zostera. In the
Sargasso Sea there are floating meadows of Sargassum bacciferum, gulf weed. This
sea extends from 22° to 36° north latitude, and from 25° to 45° west longitude from
Greenwich, an area of 40,000 square miles.
2. Maritime or saline plants. These are plants which grow on the border of the
sea or of salt lakes, and require salt for nourishment, as Salicomia, glasswort, Saisola,
salt wort. Anabasis. Such plants are often caUed Halophytes (sea plants). Under
this head may be included littoral aud shore plants, such as Armeria, sea pink, Glomx,
and Samolus.
3. Aquatic plants, growing in fresh water, either stagnant or running ; as Sagittaria,
arrow head, Nymphcea, water lily, Potamogeton, pondweed, Subularia, awlwort,
Uiricula/ria, bladderwort, Stratiotes, water-soldier, Lemna, duck weed, Pistia, Confence,
Oscillatorice, and Ranwnculus fiuviatilis. Some of these root in the soil, and appear
above the surface of the water ; others root in the soil and remain submerged ; while a
few swim freely on the surface vrithout rooting below.
4. Amphibious plants, living in ground which is generally submerged, but occasion
ally dry, as Banunculus aquatUis and sceleratus, Polygonum amphUnv/m, Nasturtium
amphiiium. The form of the plants varies according to the degree of moisture. Some
ot these, as limosella aquatica grow in places which are inundated at certain periods
of the year ; others, such as Rhizophoras (mangroves) and Avicen/nias, form forests at
the mouths of muddy rivers in tropical countries.
B. Land Plants which root in the Earth and grow in the Atmosphere.
5. Sand plants ; as Carex arenai-ia, Ammophila arenaria, Elymus arenari-as, and
Calamagrostis armaria, which tend to fix the loose sand, Plarttago arenaria, Bemiaria
glabra, Sedum acre.
6. Challi plants ; plants growing in calcareous soils, aa some species of Ophrys,
Orchis, and Cypripedium.
7. Meadow and pasture plants ; as some species of Lotus, bird's-foot trefoil, a great
number of grasses and trefoils, the daisy, dandelion, and butter-cups.
8. Plants found in cultivated ground. In this division are included many plants
which ha-ve been introduced by man along with grain, as Centaurea cyan-us, com blue
bottle, Sinapis arvensls, common wild mustard, Agnstemma, com-oockle, several
species ot Veronica n-ai. Euphorbia, Lolium temulentum, Convolvulus anensis, Oichorium
intyhus, also plants grovring in fiUow ground, as Bumex acetosella, Cardwus nutans,
Ecliiwm vulgai-e, Artemisia campestris, and Androsace septentrionalis. In this division,
garden weeds are included, such as groundsel, chickweed, Lamium amplexieaule,
Clienopodium vwlgare, and viride.
9. Rock or wall plants ; Saxifi-ages, Wall flower, Linaria cymbalaria, J>raba muralis,
species o{ Sisymbrium and Sedum, Asplenium, Buta nmraria, and some lichens and
mosses. 10. Plants found on rubbish heaps, especially connected with old buUdings, Some

DISTRIBUTION OF VEGETABLES IN SPACE. 329
of these seem to select the habitations of man and animals on account of certain
nitrogenous and inorganic matters, which enter into their composition. Among them
may be noticed. Nettles, Pellitory, Docks, Borage, Henbane, Xa/nthium. Here, also,
have been placed some plants immediately connected vrith the habitation of man, s,.ch
as Racodium ceUare, a fungus found on wine casks, Conferva fenestralis, an alga
produced on window panes, and Conferva dendrita, one developed on paper. Some
plants, as Semperviimm tectorum, select the roofs of houses.
11. Plants growing in vegetable mould ; such as bog-plants, or those growing on
wet soil, so soft that it yields to the foot but rises again, and marsh planta growing in
wet soil, which sinks under the foot and doea not rise. To tbe former class belong
such plants as Pinguicula alpina, and Prirrmla fa/rinosa; to the latter, such as
Menyanthes, C&marum, Bidens cei-nua.
12. Forest plants, including trees which live in society, as the Oak, the Beech,
Firs, &c., and the plants which grow under their shelter, as the greater part of the
European Orchises, some species of Carex and Orobanche. Some plants especially grow
in pine and fir-woods, as Linmcea borealis, and some Pyrolas.
13. Plants of sterile places, found in barren tracts by road sides. Thia is a hetero
geneous class, and contains many plants of uncertain characters. Under it are included
the plants of uncultivated grounds, as those found on moors, where Calluna vulgaris,
common heather, and various Heaths, Jumper, Andromeda, and some species of Poly-
trichum occur.
14. Plants of the thickets or hedges, comprehending the small shrubs which
constitute the hedge or thicket, as the Hawthorn and Sweet-briar ; and the herbaceous
plants which grow at the foot of these shrubs, as Adoxa, Wood sorrel, Violets ; and
those which climb among their numerous branches, as Bryony, Black Bryony, Honey
suckle, TraveUers' joy, and some species of Lathyrus.
15. Plants of the mountains, which De Candolle proposes to divide iuto two
sections : — 1. Those which grow on alpine mountains, the summits of which are
covered with perpetual snow, and where, during the heat of summer, there is a
continued and abundant flow of moisture, as numerous Saxifrages, Gentians, Primroses,
and Rhododendrons. 2. Those inhabiting mountains, on which the snow disappears
during summer, as several species of snap-dragon, among others the Alpine snap
dragon. Umbelliferous plants, chiefiy belonging to the genus Seseli, meadow Saxifrage,
Labiate plants, &o. C. Plants growing in Special Localities.
16. Parasitic plants, which derive their nourishment from other vegetables, and
which consequently may be found in aU tbe preceding situations, as the Mistletoe, species
of Oroba/nche, Cuscuta, (Dodder,) Loranthus, Baffiesia, and numerous fungi.
17. Pseudo-parasitic plants or Epiphytes, which live upon dead vegetables, as
Lichens, Mosses, &c., or upon the bark of living vegetables, but do not derive much
nourishinent from them ; as Epidendrum, Aerides, and other Orchids, as well as
Tillandsia, Bromelia, Pothos, and other air plants.
18. Subterranean plants, or those which live under ground, or in mines and caves,
almost entfrely excluded from the light ; as Byssus, Truffles, and some other cryptogamic
plants. 19. Plants which vegetate in hot springs, the temperature of which ranges from
80° to 150° of Fahrenheit's thermometer, as Yitex agnus-castus, and several crypto
gamous plants, as Ulva thermalis, the hot-spring laver.
20. Plants which are developed in artificial infusions, or liquors, as various kinds
of Mucor, causing mouldiness. i
21. Plants growing on living animals ; as species of Sphceria and Sa/rcirmla and
various other Fungi and Algae.
22. Plants growing on certain kinds of decaying animal matter, such aa species of
Onygena, found on the hoofs of horaes, feathers of birds, &c., some species of Fungi,
whioh grow ouly on tbe dung of animals, and certain species of Splachn/mn,
Of these groups of plants a large number were recognised by De
CandoUe, the others being added by Bory St. Vincent. We next give the
more generaUy recognised and more geographical divisions of Schouw, which
are based on varioua observations made in many parts of the world, and agree
with the conclusions arrived at by Humboldt and others, who have carefuUy
studied thia important department of Phyaical Geography : —

330 PHYSICAL GEOGRAPHY.
PLANTS GROUPED IN GEOGRAPHICAL REGIONS.
I. The region of Saxifrages amd Mosses, or theAlpime Arctic Flora. — This region ig
characterised by the abundance of mosses and Uchens, the presence of the saxifrages,
gentians, the chickweed-tribe, sedges and vriUows ; the total absence of fropical fami
lies ; a notable decrease of the forms peculiar to tbe temperate zone ; by forests of firs
and birches, and an absence of other forest trees ; the smaU number of annual plants,
and tbe prevalence of perennial species ; and finally a greater liveliness in their simple
colours. This region is divided into two provinces. 1. The province of the Canoes,
or the Arctic Flora, wbich comprehends aU the countries within the polar circle, with
some parta of America, Kamtschatka, New Britain, Canada, Labrador, Greenland, and
the mountains of Scotland and Scandinavia. 2. The province of primroses and
Tampions, or the Alpine Flora ofthe South of Europe, which embraces the flora of the
Pyrenees, Svritzerland, the Tyrol, Savoy, &c., the mountains of Greece, the Apennines,
and probably the mountains of Spain.
II. The region of the UmbeUifercus amd Cruciferous Plamts, (to which the hemlock,
parsley, waUflower, cresses, &c., belong.)^These tribes are here in much greater
number than in any other region ; roses, crowfoots, mushrooms, amentaceous and
coniferous plants are also very numerous ; the abundance of Carices and the fell of the
leaves of almost all the trees during winter form also the chief features ofthis division.
It may be separated into two distinct provinces. 1. The province of the CSchoracese
(including the sow-thistle, dandeUon, lettuce, &c.), which embraces aH Hie north of
Europe, not comprehended in the preceding region — namely, Britain, the north of
France, the Netherlands, Germany, Denmark, Poland, Hungary, and the greater
part of European Russia. 1. The prorince of the Astragali and CynM-ocephxila! (to
which the milkveteh, burdock, thistle, &c., belong), which includes a part of Asiatic
Russia and the countries about Mount Caucasus. 'The cultivated plants include those
most useful and important in the temperate zones.
III. The region of the Labiates cmd CaryophyUce, (to which the pink, catchfly, sand
worts, &c., belong), or the Mediterranean Flora. — It is distinguished by the abundance
of the plants belonging to these two orders. Some tropical femilies are also met with,
such as palms, laurels, arums, plants yielding balsam and turpentine, grasses belong
ing to the genus PanicTim, or millet, and the true Cryperacece, or sedges. The forests are
composed chiefly of the amentaceous and coniferous tribes, as birches, oaks, &c., the
copses of Ericacece, or heath tribe, and Terebinthacece, as the mastach, &c. We meet here
with a great number of evergreen trees. Vegetation never ceases entirely, but verdant
meadows are more rare. Schouw dirides this region into five provinces. 1. The
province of the ciatuses, including Spain and Portugal. 2. The province ofthe sage
and scabious, the south of France, Italy and SicUy. 3. The province of the shrubby
Labiatw, the Levant, Greece, Asia Minor, and the southem part of the Caucasian
countries. 4. The Atlantic province, the north of Africa, of which he does not yet
know any distinctive character. 5. "the province of the honseleeks, the Canary Isles,
and probably also the Azores, Madeira, and the north-west coast of Africa. Many
houseleeks and some spurges with naked and spring stems particularly characterise
this province.
IV. The region of the Bhamni and Caprifoliacecs, (to which the buckthorn and
honeysuckle belong,) or the Japanese region. — This region is as yet too little known to
enable us to determine accurately ita characteristic features. It embraces the eastem
temperate part of the old continent, namely, Japan, the north of China, and Chinese
Tartary. Its vegetation appears to occupy a middle place between that of Europe and
that of North America, approaching more to the tropical than to the European.
V. 77ie region of Asters and Solidagos, (Michaelmas daisies and golden-rods.) — This
is marked by the great number of species belonging to these two genera, by the great
variety of oaks and firs, the sraall number of ci-uc^erous and mnbelliferoM plants, ths
total absence of the heath, and the presence of more numerous species of whortleberry
than are to be met with in Europe. It comprehends the whole of the eastern part of
North America, with the exception of what belongs to the first region. It has been
divided into two prorinces. 1. That of the south, which embraces the Floridas,
Alabama, Mississippi, Louisiania, Georgia, and the Carolinas. 2. That of the north,
whioh includes the other states of North America, such as Virginia, Pennsylvania, New
York, &o.
VI. Tlie region qf Magnolias, comprising the raost southem parts of North America.
— The tropical forms whioh ahow themselves more frequently than on a similar parallel
ofthe old continent, are the chief feature in the vegetation.

DISTRIBUTION OF VEGETABLES IN SPACE. 331
VII. The region of Cactuses, Peppei-s, and Mdastomas. — These families .ire here
predominant, both as regards the nuniber of the speoiea and of the individual plants.
It is divided into three provinces. 1. The prorince of the ferns and orchises, com
prehending the West Indian Islands. 2 The province of the palms, the lower parts of
Mexico, New Granada, Guiana, and Peru. 3. Brazil also seems to form a province,
and may perhaps constitute a region of itself.
VHI. The region of Cinchonw, or Medicinal Barks, which comprises a part of the
elevated regions of South America included in the torrid zone. The Cinchonce belongs
exclusively to this region and forms its principal feature.
IX. The region of EscaUonias, Whortlebeiries, and Winter's Barks. — It embraces
the highest parts of South America. We also meet with Alpine plants, as saxifrages,
whitlow-grass, sandworts, sedges, and gentians. Perhaps also the mountains of Mexico
belong to this region, although they may form a separate prorince, that ofthe oaks and firs.
X. The Chilian region. — The Flora of ChiU differs essentiaUy from those of New
HoUand, the Cape of Good Hope, and New Zealand, although an approach to them ia
observable in the genera Goodenia, Araucaria, (Chilian pine,) Protea, Qwn/nera, and
Anci^rvjm. XI. Tke region of Arboi-escent Compositce, (or arborescent plants, with flowers like
the dandelion, daisy, &c.) — The great number of ayngeneaious plants, more particularly
of the femily of Boopideae, forms the chief feature of this flora, which approaches in a
remarkable manner to that of Europe, whilst it differs entirely from those of Chili, the
Cape, and New Holland. This region comprehends the lower part of the basin of La
Plata, and the plains which extend to the west of Buenos Ayres.
XII. The Antarctic region, formed by the countries near the Straits of Magellan. —
There is a considerable ajBBnity between the vegetation here and what is aeen in the
north temperate zone. Polar forms, however, diaplay themselves in the apeciea of
saxifrage, gentian, arbutus, and primrose. There is also a resemblance between tho
flora of this region and those of the moimtaine of South America, of Chili, the Cape,
and New Holland.
XIII. The region of New Zeala/nd. — This flora, besides the plants peculiar to New
Zealand, comprehends several others whioh belong to the extremities of America,
Africa, and Australia, or New Holland.
XIV. The region of Epacrides and Eucalypti. — It coraprehends the temperate
parts of New Holland and Van Diemen's Land, Besides the two families whence it
receives its name, it is characterised by the presence of a great number of Proteaceoe,
myrtles, Stylideos, Bestiacece, Diosmeoe, Acacias, &c.
XV. The region of Mesembryamthema, or Fig Marigolds and Siapelias. — These two
genera, as well as the heaths, are very abundant here. The latter is found in greater
quantity here than anywhere else. The region embraces the southem extremity of
Africa. XVI. The region of Western Africa. — We are only acquainted with Guinea and
Congo, the vegetation of which is a mixture of the Floras of Aaia aud America, though
most resembling the former. Thia region is characterized by a conaiderable number of
graases and sedges, and the peculiar genus Adansonia, the baobab, (the largest kno-wn
tree in the world.)
XVII. The region of Eastem Africa. — In regard to the eastem coast of Africa, our
knowledge is very imperfect. The region ia chiefly distinguished by the genera Dcmais,
Atribora, L>ombeya, and Senacia.
XVIII. The region of the Sdtaminece (of the turmeric, cardamom, Indian shot, &c.),
or the Indian Flora. The Scitaminece here are much more numerous than in America,
as weU as the leguminosce, such as pease, broom, &o., cucwrbitdcew or the cucumber
tribe, and tUiacece, or the lime-tree tribe, although in a leas degree. In consequence
of the imperfect state of the science, we cannot subdiride this region into provinces.
It comprehends India, east and west of the Ganges, the islands of Madagascar, Bourbon,
and Mauritius, thoae between India and New Holland, and perhaps the fropical part of
this last continent.
XIX. The mountains of India ought to form one or two regions, the vegetation of
whioh differs from that of the plains. These countries, perhaps, constitute one region
with the whole of central Asia.
XX. ITie Floras of Cochin China, Tonquin, and the north of China, notwithstanding
their resemblance to that of India, present a sufficient number of peculiar indigenous
plants to constitute a distinct region.
XXI. The Flora of Arabia and Persia, differing from that of India and the Medi
terranean, forms a particular botanical region, characterised by the numerous species

332 PHYSICAL GEOGRAPHY.
of cassia and mimosa, (to which senna, the sensitive plant, &c., belong,) which are
found in it. It appears probable that Nubia and a part of central Asia belong to it.
Abyssinia, the elevated parts of which possess such a different climate, may perhaps
form one of the great subdivisions, or even a totally distinct region.
XXII. The Islands of the South Sea which lie vrithin the tropics form undoubtedly
a separate region, though vrith but a slender degree of pecuUarity. Among 214
genera, 1 73 are found in India, and most of the remainder are in common vrith America.
T'he bread-fruit tree is among the characteristics of these islands, although it is not
confined to this region.
Marine plants are also confined to particular regions, from causes analogous to
those whioh limit or favour the extension of terrestrial plants. Thus, the Northem
Ocean from the pole to the fortieth degree, the Sea of the Antilles, the eastem coasts
of South America, those of New HoUand, the Indian Archipelago, the Mediterranean,
the Red Sea, &c., present so many large marine regions, each of which possesses a
peculiar marine vegetation and often characteristic plants.
133 Distribution of Plants in Vertical Space. — Juat aa the mean annnal
temperature of any part of the Earth ia found to diminish as we advance from
the equator towards the poles, although greatly modified in different districts
from local cfrcumstances, so does it decrease regularly and rapidly as
we aacend from the plaina into the higher regions of the atmosphere, so
that starting from the burning heat of cenfral America, at or near the sea
level, we pass quickly through all changes of temperature, tUl in a few hours'
fraveUing we reach the icy region where perpetual snow and ice prevent aU
vegetation. The most striking exempUfication of the mere change of tem
perature is recognised in rising rapidly in a baUoon ; bnt when one ascends a
nigh mountain, a simUar but more gradual decrease of temperature is observed
to correspond with striking differences in the vegetation. At the foot of
the mountain the plants of the plain appear ; these graduaUy vanish as we
continue to mount — trees are found up to a certain height, but no further —
then bushes prevaU ; after which, towards the exfreme elevations, the bushes
giveplace first to herba, and at length to only a few Uchens.
The traveUer who has visited the counfries to the north wUl, when ascend
ing high mountains in aouthern latitudes, very soon enter regiona amongat
whoae vegetation he wiU recognise northem plants. At the hmit of per
manent anow on these mountaina he vriU mias but a few forma of the planta of
the arctic zone, and even -wUl find identical species which do not once appesu-
in the plaina in the whole apace between the arctic regiona and the aummit
of those mountaina.
There is therefore a certain paraUeUam between the diatribution of vege
tation from the level ofthe aea to the Umita of perpetual snow, and that from
the equator to the poles, although the gradual change ia far more rapid in the
former than in the latter case. This pai-aUeUsm also exactiy agrees with
that which we find between the gradual deoreaae of heat from the equator to
the polea, and that from the plain to the limit of perpetual snow.
In ascending from the level of the ocean in the temperate and frigid zonea,
we find aa we riae upon the alopea ofthe mountaina that plants decrease both
in the size ofthe individuals and also in thefr numerical development, whUe
in the tropica the mass of vegetation is more limited in the plaina than in the
lower mountain regiona. Thia ia also the caae with the greater variety of
species which in common with these decrease in an upward dfrection, and
the remark is applicable especiaUy to the temperate zones, since in the cold
zonea the plants of higher regions" cannot differ much from thoae of the plains,
becauae the snow limits have but httle absolute elevation. The distance of
the Umits of trees and shrubs from the snow Une is also greater in the torrid
than iu the temperate and frigid zones.
In central and southern Europe the foUowing difference is observed
between the flora of the plains and that of mountains of 4000 feet eleva
tion. The proportion of monocotyledona to dicotyledona, which in the plains
ia aa one to four, decreases with the elevation (but only on dry moimtain
slopes), tUl ut the height of 8526 feet it is as one to seven, and in particular

DISTRIBUTION OF VEGETABLES IN SPACE. 333
cases even aa one to nine. Moist mountain slopes, on the confrary, favour the
growth of monocotyledons, as here the proportion becomea one to three.
The fropical famiUes which have representatives in the plains disappear
altogether in the mountain flora, and this is also the case with those famUies
which have their maximum number of apeciea in the torrid zone. Examples
of the first are found in the palms, and of the second in the laurels. Other
famiUea which have thefr maximum in the torrid and diminiah in the tem
perate zone, exhibit thia decreaae stiU more on the slopes of mountains, as
exemplified in the Leguminosce and Euphorbiacece.
Among the famUies which have thefr maximum in the temperate zone,
there are many that undergo but little change with increased elevation, aa
the weU known famiUea Composite, Crucifera, Umbelliferce, Bosacete, and
othera ; whUe some famUies decrease both towards the poles and the snow
line in vertical space (e.g. Liliacece, Ldbiatce, Sfc); and others, again, appear
as subordinate groups, vvhich have thefr maximum in the higher regions.
In some caaes the proportion becomea greater with increased elevation, as
seen especiaUy with the saxifrages, mosses, and Uchens.
In the European Alps the Composites, from the number of species, are the
prevailing family ; after these foUow, in nearly equal number, the Cyperacece,
Alsinea, Graminece, Cruciferce, Leguminosce, Bosacete, Saxifragece, and Umbel
liferce; but the maaa of vegetation is formed bythe Catkin-bearing plants
(Amentacece), fhe grasses, and the genus Bhododendron. As characteristic
marks of the Alpine fiora may be noticed, first, that the number of annuals is
very smaU ; second, that the fiowers are of great size in proportion to the
whole plant ; and thfrd, that the colour of the fiowers, and mdeed of the
entfre plants, is brighter and purer than in the plains.
Alpine plants afford more nourishment to cattle than thoae grown on
plaina, and planta with thorns or very hairy plants are seldom found in the
Alpine regions.
On ascending a mountain in the torrid zone, aa in the Cordillera ofthe
Andea, the tropical fanuUea diaappear altogether at the height of about 7000
feet, or at leaat become repreaented by aingle apeciea ; the number of species
graduaUy decreasing, and those of famUiea which attain thefr maximum in
temperate zones replacing them and increasing with the height. Thus of 327
genera, to whioh the plants on the declirity of the Andea at a height of 7800
feet and upwarda belong, aa many as ISO, or more than one-half, are common
to the temperate zone.
As, therefore, the physiognomy of the vegetable kingdom is characterised
by certain plants in the different latitudinal zones from the equator to the
poles, so is it also in the vertical dfrection in the mountain regions which
correspond with the zones; and proceeding from the vegetation of the
equatorial zone, we foUow the series of vegetable regions in ascending Unea
one after the other, and may compare them with the different zonea as
foUows : — 1. Region of palms and bananas . . Equatorial zone.
2. Tree fema and figs  Tropical zone.
8. Myrtles and laurels ... . Sub-tropical zone.
4. Evergreen trees  Warm temperate zone.
5. European trees  Cold temperate zone.
6. Pines  Sub-arctic zone.
7. Rhododendrons ...... Arctic zone.
8. Alpine plants  Polar zone.
This table ahows that each of the zones of higher latitudes possesses a
region less than that which precedes it, but it must also be understood that
many modifications occur in nature in particular locahties. Thua the limit of
frees in the equatorial zone, in the Andes of Quito, is marked by an Escal-
lonia (not a Conifer), whUe in the temperate zone, in the Himalayana, the oak
is the last tree at 11,500 feet above the sea on the south side, and the birch

334 PHYSICAL GEOGRAPHY.
the last on the north side at 14,000 feet. SunUar exceptions occur with regard
to the limit of shrubs.*
134 Bange of Cultivated Plants. — Several natural famiUes and many
genera and species of plants bear so dfrectly on the habits and even existence
of man in the counfry where they abound, that the subject of cultivated plants
becomes of great interest in a treatise on Physical Geography. The plants of
this kind resolve themaelvea into about five groups, which we wUl now con
sider separately. They are (1) the cereals, (2) the tuberous roots, (3) the
treea bearing food, (4) the planta used in the preparation of luxuries, and
(5) the plants used in the manufacture of various articles of clothing.
The CbeeaIs include a number of cultivated grasses bearing grain, of
which wheat, barley, rye, oats, rice, maize, mUlet, buckwheat, &c., are in
various countries the chief food of man. Of these the firat four are generaUy
used in Europe, rice in Asia, maize in America, and mUlet in Africa.
The culture of Wlieat ia carried on in every quarter of the globe, from
latitude 60° to 64° in Europe to the torrid zone, and even at tbe equator at
an altitude of about 3000 feet. Its vertical limits in South America are
between 3600 and 10,000 feet, the grain being exteemely productive at
moderate altitudes in hot counfries.
In the middle of the temperate zone, as in Erance, its cultivation is not
successful above 5400 feet. The productiveness in cold countries with
indifferent cultivation is not more than five or six fold; but in Hungary,
Croatia, and Sclavonia, it is from eight to ten fold ; in La Plata twelve fold ;
in the north of Mexico seventeen fold, and in the equatorial parts of the
same counfry twenty-four, and even in favourable seaaona thirty-five fold.
Aa instances of extraordinary productiveness, Humboldt mentiona an inatance
in Mexico of wheat planta sending up forty, sixty, and even seventy stalks,
the ears of which were ahnost equaUy weU fiUed, and contained from 100 to
120 grains each.
The other grains of Europe, barley, rye, and oate, are only cultivated as
bread corns in the northern and colder countriea. In Seandinaria, harlev
extends to 70° north, rye to 67°, oata to 65°, wheat not being cultivated with
profit above 62°. So alao these other cereals are grown at higher elevations
than wheat, barley being cultivated in Peru for fodder, at the very exfreme
elevation of 13,800 feet above the sea.
There is much doubt as to the native counfry of the cereals. It haa been
suppoaed that wheat growa wUd in Aaia Minor and Persia, and barley in the
north of Africa — perhapa Egypt. Oats do not appear to have been used by
the ancients, but though they have been recently introduced aa cultivated
grain, thefr native habitat ia exfremely doubtful.
Bice probably supports a larger number of persons onthe Earth than any
other single article of human food, as its use is universal in eastem and
southern Aaia, and it is common in the north of Africa and the aouth of
Europe, besides being now extensively cultivated in North America. There
are two varieties of this vegetable, one growing on mountain alopes, and the
other in swamps ; and of these, the latter, the most common, and also the moat
productive, yielding one hundred or one hundred and twenty fold, and in aome
places even four hundi-od fold ; whUe the mountain rice does not produce
more than forty fold when grown continuaUy on the same ground, or eighty
fold on newly prepared spota. This kind, however, though leaa rapidly
increased, is more esteemed and more valuable, inasmuch aa it may be Kept
longer without apoiUng.
Maize is indigenous only in Ameriea. aud thrives best in the hottest
and dampest fropical cUmates, yielding in some cases aa much as eight
hundred fold, and in leas fertUe lands three hundred or four hundred fold;
while one hundred fold is regarded as a poor crop in fropical countries.

• Johnston's Physical Atlas, • The Geoginphical Distribution of Plants."

DISTRIBUTION OF VEGETABLES IN SPACE. 335
though in the temperate zone, as in CaUfornia, it does not produce more than
seventy fold, and m stUl colder counfries the yield ia stUl smaUer.
Maize haa been introduced into Asia, and its growth had spread over
India, China, and Japan very many centuries ago. _ It is not, however, so
favourite a food as rice. In America, the vertical Umits of its growth arc very
high, as it has been actually cultivated artifieiaUy at an elevation of 12,800
feet, and Humboldt describes vast maize fields on the plateau of Mexico 8680
feet above the sea.
Turkey millet or Negro-corn is also a grain of hot countries, much grown
in the East Indies, and ranging to very conaiderable heights. Its hmits in "
other reapecta are not accurately determined.
Thb Tubesous Boots. — Of these, tho potato is beyond doubt the best
known, and most vridely spread in temperate cUmates. It was infroduced
about 260 years ago from America, (where it appears to be indigenous in the
cold regions, at considerable heights on the Andes,) and vrithin a very short
space of time ite cultivation haa extended over the whole of Europe, up to
latitude seventy-one degrees north, and has reached the lower plains of India,
China, and Japan, the South Sea Islands, AustraUa, and New Zealand. The
frue native country and natural Umits of thia uaeful food plant are not
accurately known ; but it is supposed not to be indigenoua in North America,
whence it waa firat brought to Europe. It is to this day chiefly and most
carefuUy cultivated in South America.
The Arum or Taro, as it is caUed in the Sandvrich Islands, is an exfremely
important tuberous root, cultivated -with extraordinary care in the hottestpart
of the torrid zone, and ranging now in the East Indies and China, in the W eat
Indies, in Africa, and at aeveral points in the continent of America. The
tube of this plant, which requires almost more than any other the intense
heat of a vertical sun to ripen it properly, attaina the aize of a chUd's head,
and is very delicate in flavour. It requfres much moisture, and is Umited in
vertical disfribution to about 1000 feet above the sea.
The Manioc, from which ia made Casaava bread, ia another important
fropical food plant, cultivated in America, where it ia probably indigenoua,
and alao in Guinea. Tapioca is made from this plant.
The Batata, the Tam, and some otber tuberous roots, are very exten
sively used for food in aU parts ofthe torrid zone. Yams have been recorded
to weigh as much as 474 pounds, being nine and a half feet in cfrcumference,
but the usual dimenaiona and weight are very much amaUer.
The Food-beaeing Eeuit Tebes. — Of these, the Bread-fruit is one of
the most important, but ia confined to the torrid zone, and chiefiy abounda in
the islands of the Indian Archipelago and the South Sea. It has never been
observed in the vrild state.
It is the fruit of this tree that fumiahes food, and the fruits are very
abundant during eight or nine months of the year, the dried and prepared
bread made from them lasting during the rest of the year. Each fruit is
round, and often of considerable size ; it is generaUy plucked when unripe,
and ia peeled, wrapped in leaves, and baked.
The Plantain or Banana yields another exceedingly common and most
nutritioua food to the inhabitants of fropical countriea. Several species ofthe
genua Musa produce, however, fruita that receive this name, and aU of them
are occaaionally cultivated, the process of culture being exceedingly simple,
and merely consisting of the removal of the old trunks Mter they have borne
fruit. The plantain ranges very vride, and it is doubtful whether its native
country is in the Old or New "World, or whether some species are not
indigenous in both. In the plains it can be cultivated as far as thfrty degrees,
or even thirty -five degrees of latitude, and on the mountaina some species
reach nearly 3000 feet above the sea. According to Humboldt, the banana
yields in a given extent of ground forty-four times as much nutritive matter
aa the potato, and 133 timea as much aa wheat.

336 PHYSICAL GEOGRAPHY.
The Cocoa palm is an mhabitant ofthe coast, and is incredibly abundant
in the South Sea Islands, and those of the Indian Archipelago, nearly three
miUions ofthe nuts having been exported in one year from Ceylon alone, where,
indeed, there is a forest of cocoa palms several leagues broad, sfretching along
thecoast for twenty-six mUes, and containing eleven milUons of fuU-grown frees.
Each tree wUl bear from 200 to 300 nuts in the year, and wUl Uve for nearly
a century. The limits of growth of this palm are about twenty-eight degrees of
latitude, and a height of about 2000 feet.
The Date palm is another free belonging to the same famUy, and its fruit
*is also extensively used as food. It ia indigenoua in the north of Africa, in
Aaia Minor, and Arabia, and haa been transported as far east aa Batavia. It
will grow in Italy, in latitude forty-four degrees, and in SicUy te the height
of 1700 feet, but is not there fruitful. In Arabia and Egypt, it affords the
chief food of the inhabitants.
The Sago palms, of which there are several, are confined to the Eastern
Archipelago, and the palm which auppliea the large quantity of palm oil used
in commerce to the coaat of Guinea. Other pahns are useful for various
purposes of luxury, but not aa principal articlea of food.
The Olive is a most valuable plant, growing in South Europe, between the
Umita of forty -four and a half degreea, and thirty-six degreea north latitade;
but it cannot endure severe winters, and thua cannot be generaUy grown at
conaiderable elevationa. In warmer cUmatea than thoae of Europe, it appears
to grow more luxuriantly, and haa been introduced with succeaa into America.
It la alao grown in many parta of Mexico.
The Chestnut spreads over the whole south of Europe, but finds its true
home in the warmer part of the temperate zone. It reaches eastwards to
China, and thua eroases the Old World from Spain to the Pacific. By art the
chestnut has been induced alao to grow north of the Alpa, and ia now found in
northern Germany and England. Many other freea aupply fruite occaaion
ally used as the food of man, but they do not form a supply on which he can
safely and constantly depend.
Food-Plants used as Luxtteies. — Of these the Sugar cane ia, perhaps,
the most important. Indigenous in the Old World and cultivated in China
and the eastern islands before the historical era, this valuable plant was
introduced into America by the Spaniards about the year 1520, and since
then has been greatly cultivated in the fropical islands of the West Indies,
and also on the mainland.
The tract vrithin which it can be cultivated sfretches far beyond the
tropics, reaching even to the latitude of South Europe, and in Mexico and
Columbia it may be grown at the height of 6000 feet on the warm mountain
slopes. It is understood to succeed best with a mean temperature of 76° or
77 , but wUl grow with advantage when the temperature is not below 67° or
68°. The total amount of sugar produced was calculated in 1833 to exceed
600,000 tons. There are several varieties of the sugar-cane, and the raw
cane when ripe is much used as food.
The Tea plant is another of those shrubs which have become highly
important, but this is owing to the presence of a stimulant rather than any
nutritive quality. China la the native counfry of thia plant, and it there
extends as far north as 40°, growing also in the mountain diafricta to the
south, particularly on those mountains whioh separate China from the
Bfrman empfre. The British territory in North Ijidia, eapeciaUy Aaaam,
has alao been found favourable to the growth of tea, and indeed it seema to
flouriah throughout the sub-fropical zone in the eaatern part of the Old
World. Coffee, a very important substitute for tea in various countriea, is
more tropical in ita habita than tea, but admits of great range artificially,
whUe mate, or Paraguay tea, serves as the substitute in BrazU and many pai-ts
of South America.
The F«»e ia a plant which has been employed by man in the manufacture
of a spirituous liquor frora the very earliest period, and has been so long

DISTRIBUTION OP VEGETABLES IN SPACE. 337
cultivated and so widely fransported artificially, that its native station ia not
certainly known, nor can it be distinctly made out, whether all the varieties
now used (aa many as 200 mi^t be enumerated) have been derived origmally
from one or aeveral distinct apecies.
We have already had occasion to speak of the limits of culture of the
rine, which is regulated much less by mean temperature than by summer
heat, but it is chiefiy the duration of the summer that infiuences the ripening
of the friiit. ExceUent wine is made with a mean temperature 60 Fah.
and it is probable, that if damp and too much moisture are avoided, every
greater heat wUl also succeed. Although the Old World is the natural habitat
of thia plant, it haa been introduced into America, and flourishes on both
aides of that Continent, and in both the northern and southern hemisphere,
wherever the Umits of temperature and dryness are obtained. Ita polar
limits may be considered to be between 49 and 55° in the northern, and
about 40° in the southem hemisphere.
Tobacco, the Betel nut, and Opium are aU very important and very
widely spread vegeteble productions, used in various parts of the world for
thefr stimulating and soothing properties. The former seems to have been
known in China long before its introduction into Europe from America, and
several species are determined rangmg even as far as 55° N. lat. and grown
very extensively in various parts of cenfral Europe, while a large quantity is
also cultivated in New Zealand. The largest quantity and best kinds of this
plant aregrown in hot countries, especially in the tropical parts of America
and the West Indian Ialanda. The betel nut, obtained from the Areca palm,
and uaed with what is caUed the betel pepper, is employed in the same
manner on the shores of eastern Asia, and in the varioua islands of the Indian
Archipelago. Opium, again, is very largely used for simUar purpoaea by the
Turka, Malays, and Chineae. Some idea may be formed of the extent to
which it ia grown, from the fact that in fourteen years, from 1818 to 1831,
above fourteen milUona of pounds weight were conveyed into China through
Canton alone, besides an enormous quantity consumed by the Malays, the
inhabitante of Cochin China and Siam, as well as India and Persia.
Plants used in Clothing. — ^Besides the food plants there are others
alao greatly modified by civilization, and conveyed by man to distant parta of
the Earth, but only becauae from them he is enabled to derive a portion of
the clothing which he requirea to shelter him from cold, and enable him to
withstand the rigoura of winter in most parts of the Earth. The Cotton
plant and Hemp are the plants moat important in this respect — the former,
however, being the moat widely apread, and perhaps the most useful, is that
which deserves chief attention. Not only is the cotton plant cultivated in
the fropical parts of every land ofthe Old and New World, but it extends far
beyondTthe fropica even to countriea whoae mean temperature ia not more
than 62°, reaching thua the most southerly parte of Europe. The number
of species of the free is, however, large, and no doubt various species are
indigenous in different locahties. As to the quantity suppUed, some idea may
be formed from the statement that England is estimated to consume annuaUy
three hundred millions of pounds.
The hemp is also a plant of vast importance, and although its growth is
greatly extended by culture, there can be Uttle doubt that it is capable of
much farther increase, if it were not that other plants in different countries
supply the aame material. Thua, in New Zealand a large and handsome reed
(Phormium tenax) yields fibres capable of being spun into fine thread, and
also made into the stoutest cables.
135 General Considerations of the Bepresentation of Plants in distant
Botanical Centres. — The general laws of nature as derived from the observa
tion of a vast multitude of facts connected with the distribution of vegetables
seem to he— first, that certain districts originate distinct groups of plants
which are capable of a wide range, although the actual extent of the range,
both in apace and time, is dependent on various external circumstances,
Z

338 PHYSICAL GEOGRAPHY.
Such places are technically caUed ' specific centres.' Secondly, that in similar
cUmates, whether in the same hemisphere at the same level or otherwise,
there are either individuals of the same species, if circumstances have been
favourable for their transport, or else that the species resemble each other
so manifestly, as to be m a proper and simple sense ' representatives.'
Thirdly, that in placea not aeparated in latitude by any distinct natural
barrier, such as a lofty mountain chain or a broad tract of sea, and
situated in very different climates, and in different latitudes, there ia
a graduated transition from the flora of one district to that of another,
generic forms lingering much longer than specific, and whole famUies being
rarely obliterated till after a long series of changes. For placea situated at
very difi'erent levels the same observation is true, and the aame law holds
good, as is iUustrated in the existence of palms and other fropical forms of
vegetation far north and south of the fropics, on the one hand, and far above
the ordinary Umits we might have anticipated (judging only by temperature),
on the other. Fourthly, tbat in spite of the usual absence of identical
species in diatricts removed by a lofty chain of mountains, a broad fract of
ocean, or a complete zone of temperature, there are some apeciea which
cannot at aU be diatinguiahed from each other in the fioraa of the arctic and
antarctic zone — ^in those of New South Wales and north Europe, and in
those of tropical Africa, Asia, and America. The rarity of such instances
is not to be taken as any explanation or solution of the difficulty, for, if pos
sible, it adds to it, nor has anything yet been suggested which reaUy and
importantly bears on the true question at issue. The cases of exception to
the general rule alao are of a nature which rather increaae the puzzle,
since in large intermediate areaa certainly capable of supporting a particular
kind of vegetation, the expected planta are not found, notwithstanding that
at the two exfremities some common species appear. It is perhaps only
when we study carefuUy the disfribution in time, that these apparent
anomalies cease, and resolve themaelvea into the working out of one far more
general and important law, according to which the succession of races as weU
as any single race ia arranged, and the peopUng of the world with an infimte
but harmonious variety, which shaU exhibit mutual relations throughout aU
time, is fuUy provided for.
We have chiefly dfrected attention in these observations to the physio
gnomy of plants, but the study of thefr statistics would lead to the same or
nearly the same conclusion, though perhaps by a different path. In what
ever way vegetation is considered, it is found to be distributed according to
these or similar laws, and tending to bring out analogous results.*

" Of somewhat more than 20,000 species of plants catalogued in De Candolle's Prodromus,
It appears that 3210 are European; 6004, Asiatic; 3731, African; 2111, North American;
6742, South American ; and 922, Australian, The island vegetation in each case is included in
the list for the adjoining ma<-land.

OOi)

CHAPTEE XI.
THE DISTRIBUTION OP ANIMALS IN SPACE.
{136. Organization of animals. — 137. Classification of animals. — 138. Statistics of animals. —
139. Nature and degrees of resemblance amongst animals, and comparison of their struc
ture. — 140. Natural grouping of animals in a Fauna. — 141. Distribution of the Faunas. —
142. Arctic Fauna. — 143. Temperate Faunas. — 144. Tropical Faunas. — 145. Special dis
tribution of Quadrumana. — 14G. Distribution of Carnivora. — 147. Distribution of Bodentia.
— 14S. Distribution ot Ruminantia. — 149. Distribution of Pachydermuta. — 150. Distribution
ot the Edentata a.nd Marsupialia. — 151. Distribution ot Jiirds. — 152. Distribution ot Rep
tiles. — 153. Distribution of the Jlfarme Vertebrata. — 154. Distrihation ot the Articulata. —
155. Distribution ofthe Mollusca and Radiata.
OBGANIZATION of Animals. — Animal Ufe presents many points alto
gether pecuUar, and exhibits forms of organization not leaa different
from those afforded by plants than are seen in the latter when they are com
pared with inorganic subatancea. It wUl, therefore, be advisable briefiy to
conaider the more essential of theae before proceeding to the subject of the
diatribution of animals in space, and it is desirable to determine, as far aa
possible, the aimpleat forma of animal Ufe, and their relationa with organic
matter of greater complexity, and with inorganic bodies.
The greater part of the atmcture of animala consists of tissues, of which
fibre ia the elementary form. There are two kinds of fibre, muscular and
nervous, the one forming the flesh, and the other the brain, the spinal chord,
and the nerves ; and in the more highly organized forma aeveral others occur,
serring for varioua important purposea. In animala of lesa complicated
structure, as in some of thoae caUed ' polypi,' and in infusorial animalcules,
there are, however, myriads of individuals made up of nothing but ceUs in
contact vrith each other.
The structure of animala ia, in all the higher groups, so manifestly different
from that of vegetables, that it would seem superfluous to allude to the points
of distinction. The old definition, that minerals increase only by mechanical
additions, whUe vegetables live, and animals Uve and move, is not, indeed,
aufficientiy accurate, since plants are sometimes endowed with a kind of
instinct, and an appearance at least of voluntary motion, and animals, on the
confrary, are sometimes almoat without either instinct or the power of moring
at wiU. In proportion aa- we deacend to the lower forms of each, and compare
them together, we find the differences leaa marked, ao that it becomea at
length difficult to pronounce whether an object before us iia animal or plant.
Thus, the sponges have ao great a resemblance to some of the polypi, that
they have generaUy been classed with animals.
Animals and planta differ in the relative predominance of the elements,
oxygen, carbon, hydrogen, and nitrogen, of which they are composed. In
vegetables hardly a trace of nitrogen is found, except in seeds and aome
special producta, but it enters largely into the composition of animal tissues.
Another peculiarity of animals is the presence of limited cavities for the
reception of certain important organs, such as the skull and cheat in higher
animals, and the abdomen in ahnost all. The possession of a digestive
carity involves marked differences between the two grand divisions of organic
nature, for in plants the fluids absorbed by the roots are conveyed to the
whole plant, by means of the trunk and branches, before they oan reach the
leaves, where they are to undergo a process analogous to digestion; while,
z 2

340 PHYSICAL GEOGRAPHY.
on the contrary, the food of aU animals passes at once into the digestive
cavity, and ia there elaborated into fluids, which being afterwards cfrculated
through the body, are in a condition to be at once separated by the proper
organs, and appUed to the requfred purposes of renovation or increase.
Plants commence thefr existence uauaUy from a aeed, but admit alao of
increase by varioua meana of mechanical division, having reference in all caaes
to the original nature of leaves as individuals of compound bodies.
Animds are developed from an egs, the animal germ being the result of
successive transformations of the yolk, whUe nothing simUar takes place in
plants. The subsequent development of indiriduals is also different in the
two kingdoms, as to method, form, and dimensions; the two latter varying
during the whole Ufe of the plant, but attaining a limit in the caae of each
speoiea of animal, eapeciaUy m those of complicated organization.
In the effects they produce on the afr there is also an important difference,
since animals consume oxygen and give off carbonic acid gas, whUe plants
reverse the process, absorbing carbonic acid gas and giving off oxygen. If
an animal, therefore, be confined in a small portion of afr, or if of aquatic
habits, in water containing afr, this soon becomes so vitiated by respira
tion as to be unfit to sustain life; but if Uving planta are confined with
the animal at the same time, the afr is kept pure, and no difficulty ia expe
rienced. This, at least, is the case by day, and the practical effect of flie
compensation is very important, vegetation restoring to the atmosphere what
is consumed by animal respfration.
Lastly, aU animals have, more or less distinctly, voluntary motion and
sensation, whUe planta, although endowed with a certain aensibUity, appear
to have neither true aensation nor actual voUtion. Life in anuMls ia
manifested by two functions instead of only one, as in vegetables, and the
organs of animal Ufe which involve the posaession of a certain amount of
intelUgence, relation, and aelection, which enable us to approach at wiU our
feUow-creatures, to perceive their existence and act accordingly, are quite
distinct from those which merely affect the functions of vegetable hfe, such
as nutrition and reproduction.
To underatand the development of animala and the facte of chief unpor-
tance in thefr stracture and mutual relations, we must conaider a Uttie their
different organa and functions, and as the possession of a nervous syatem is
at once the characteristic of aU animals, and the function whioh, when preaent
m its highest form, ia the mam cauae ofthe vast difference of mteUectoal and
reasoning power traceable between species and famiUea, this must first be
discussed. ¦ I'^^j'^j® appear to be ui nature four prmcipal types -withm which may be
included aU the varieties presented of this most important and essential
characteristic of animal organization. Theae aie— first, that in which the
nervoua ayatem la grouped into two principal masses, the brain and the spmal
marrow; secondly, where it is coUected into a series of smaU gangUa. knots,
or smaU brains of nervous matter, placed at mtervals beneath tiie aUmentary
canal and connected by threads, and a somewhat larger ganglion placed
above the oesophagus; thirdly, where the nervous matter is collected in a
single gangUonic circle, the prmcipal sweUings of whieh are placed symmeta-i-
cally above and below the oesophagus, and whence the filaments which
supply the organs in different dfrections take thefr origin: and fourthly,
¦where the nervous matter is distributed in a single ring encfrchug the mouth,
disposed in a horizontal position and in a stariike form. The first tvpe
includes aU animals called vertebrated, or having a back-bone; the second,
the insects, cruataceans, and other animala, whose body is made up of rmgs or
portions nearly detached; the thfrd, all animals such aa those mhabiting
univalve and bivalve shells, (the moUusks, or soft animals, as they are
called ;) and the fourth, the star fishes and other radiated anUnals.
Ihe nerves, thus important in communicating to the animal all impres-
siona from without, are usually so arranged as to render particular organa

DISTRIBUTION OF ANIMALS IN SPACE. 341
acutely perceptive to what are caUed the senses, which are recognised as five
in number, under the names, sight, hearing, smell, taste, and touch. The
impressions communicated in this way produce voluntary or involuntary
results, chiefiy acting on the other functions of the body, of which the organs
of locomotion, or prehension, and of mastication and digestion, are the most
prominent. Nutrition is a function absolutely essential to the continuance of Ufe, and
involves a continual interchange of substances between the animal body and
the external world. ' In early Ufe, during the period of growth, the amount
of substances received is greater than that which is lost. At a later period,
when the growth is completed, an equilibrium is estabhshed between the
matters received and those rejected; while at a stUl later period, the equi
hbrium is again disturbed; more is rejected than retained; decrepitude
begins, and at last the organism becomes exhausted, the functions cease, and
death ensues.'*
The reproduction of animals is not less necessary for the continuance of
the race than nutrition is for that of the individual. It is effected in plants,
as we have aeen, by the modifications of what appears to be part ofa sim^e
body, but is really an individual member of a highly complicated one. In
animals it is almost universaUy accomplished by the asaociation of individuals
of two kinds, males ani females, each characterised by pecuUaritiea of structure
and external appearance, and both necessary for the production and proper
fertilization ofthe germ ofthe future individual.
All animals are produced fi-om eggs, and when enveloped in this way are
called embryos — the period passed in this condition being caUed the embryonic
period. Eggs are usuaUy oval or spherical in shape, and are contained in the
body of the female in sacs called ovaries, being at that time of very minute
size, and merely consisting of Uttle ceUa containing what is caUed yolk or
yolk-substance, with other simUar ceUs, namely, the germinative vesicle and
the germinating dot.
The number of eggs is large in proportion as the animal is of lower organi
zation ; thus the ovary of a herring contains more than 25,000 eggs, whUe
that of birds does not- contain more than one or two hundred, and the higher
mammaUa produce only one at a birth.
At a certain period the eggs leave the ovary, and being fertUized are either
discharged by the animal (laid), or else remain vrithin the body tUl the young
is fuUy developed. Animals in which the former habit ia usual are called
oviparous, while those which produce living young are said to be viviparous,
or in some cases ovo-viviparous.
The formation and development of the young animal within the egg is a
moat mysterious phenomenon, and the changes undergone differ materially
in the various natural groups of animals. In some animals, there are inter
mediate conditiona between the embryonic and perfect atate, but generaUy,
and indeed invariably in the more highly organized groups, the young as it
emerges from the egg, or is bom, possesaea the external form and habits of the
species. The metamorphoses in the exceptional cases are sometimes extremely
curious, and thefr cause very difficult to comprehend.
137 Classification of Animals. — In considering the arrangements of the
nervous system we have seen that four important distinctions can be drawn
amongst animala, and theae point to a natural diviaion into four departmenta,
which are generaUy caUed, reapectively, I. Veetbbeata ; II. Aeticulata ;
III. Mollusca; IV. Eadiata.
Of these the vertebrata are conveniently grouped into four classes, which
aU have an intemal skeleton wdth a back-bone for its axis. The classes are
1. Mammals (animals which suckle thefr young); 2. Birds; 3. Beptiles ;
and 4. Fishes. These divisions are aU so well known and so natural that they

• Principles of Zoology, by Agassiz and Gould, (Boston, 1848,) p. 72.

342 PHYSICAL GEOGRAPHY.
requfre no special description, but thefr subdivisions are alao important. The
most convenient arrangement is perhaps the foUowmg -.
CLASS MAMMALIA, (QUADRUPEDS AND BIPEDS.)
Oedbb. Example.

I. BiMANA (two-hamded) . .
II. QuAnKCMANA (fowr-handed)
III. Chikoptera (finger-winged)
IV. Insectivoba (insect-eating) .
V. Plantiqeadb Cabnivoea
VI. Dioitigeaub Cabntvoba .
VII. AMPmsiA (aquaMc mammals)
VIII. RODENTIA (gnawing) . . .
IX. Rdminantia (ruminating) .
X. Paohydeemata {thiclc-skimned)
XI. Edentata (toolhless) . . .
XII. Mabsdpiata (pouched) . .

Man.Monkeys.

Hedgehog. Bear, Badger.
Cat, Lion.
Whale, Porpoise, Seal.
Rat, Hare, Squirrel.
Ox, Sheep, Deer.
Elephant, Rhinoceros, Pig, Horae.
Sloth, Ant-eater, ArmadiUo.
Opossum, Kangaroo.

CLASS AVES, (BIRDS.)
I. Raptoees (birds of prey) . ¦ ¦ Vultures, Hawks, Owls.
II. SOANSOEES (climbers)  Cuckoos, Woodpeckers, Goatsuckers.
III. OsoiNES (songsters)  Sparrows, Linnets, Crows.
IV. Gallinace^: (gallinaceous birds) . Pheasants, Fowls, Pigeons.
V. Geallatobes (waders) .... Herons, Bitterns, Plovers.
VI. Natatoees (swimmers) . . . Geese, Divers, Gulls.
CLASS REPTILLi, (BEPTILES.)
I. DiNOSAVRiA*  Megalosamrus, Iguamodem.
II. Enaliosavria*  Ichthyosaurus, Plesiosam-us.
III. Ceooodllia  Crocodiles.
IV. Laoebtilia  Lizards.
V. Pterosauria*  Pterodactyl.
VI. Cheloota  Tortoises, Turtles.
VII. OPHmiA  Serpents.
VIII. Batbaohia  Frogs.
CLASS PISCES, (FISHES.)
I. GANOin (scales splendent) . . Sturgeon.
II. PLACom (scales plated) .... Sharks and Rays.
III. CTENoro (scales comb-shaped) . . Perch.
IV. Cycloid (scales cii-cular) . . . Cod, Herring.
The Aeticulata are divided conveniently into three classes — 1. Insects;
2. Crustaceans ; and 3. Worms. The Mollusca also into three — 1. Cephalo
poda (having locomotive and prehensile organs ranged round the mouth) ;
2. Gasteropoda (creeping on a flattened disc or foot); 3. Acepliala (having
no distinct head, and enclosed in a bivalve sheU). The Eadiata again
are divided into three classes — 1. Echinoderms (bearing spines on the
external surface, like the sea-urchins) ; 2. Acaleplie (jeUy-fish, often stinging
Uke nettles, aa the medusae) ; 3. Polyps (fixed like plante, and vrith a series
of fiexible arms round the mouth — often compound) . The fiirther subdivisions
it is not necessary here to discuss.
The technical or natural history names of animala, aa of plante, are
composed of two terms, one generic, including a considerable variety of
structure united by some marked and important characteristics, and the
other specific or trivial, forming an adjective or qualifying addition to the
generic designation. Several genera combined together (possessing aome
characters in common) are caUed a family — famiUes are combined to form

• Those orders and genera of which the names are printed in italics, ai-e uotuow represented
on the Earth by any existing species.

DISTRIBUTION OF ANIMALS IN SPACE. 343
orders, and ordera form classes; the various divisions corresponding to
which names we have afready enumerated in the preceding page.
Since the specific name is the ultimate point to which we arrive in classi
fying, it is important that every one should have a clear idea on this subject.
A Genus is generaUy founded! on some diatinct pecuUarities of anatomical
stmcture ; such as (in the case of a Vertebrate) the number, disposition, and
proportiona ofthe teeth, clawa, fina, &c.; whUe a Species dependa on characters
which are aometimes external, aometimes apparently tririal, but whioh are
always supposed to be sufficiently real to prevent accidental admixture of race.
There is also recognised another and a lower distinction, that of Variety, which,
unhke Species, includes apparent and possible mixtures of race. It has been
usual to consider that nature has set a broad and marked barrier between
speoiea, not aUowing of any infraction, but this appears to be in reaUty a some
what arbifrary assumption, although there ia no doubt that the production of
varieties from what are generaUy regarded as distinct species is rarely effected,
except under the influence of exfraordinary external circumstances.*
The real difficulty in the caae of animala, aa in planta, arises from an
occasional interference with what appeara at firat to be an universal law, that
of the production of aimilar types in parts of the Earth widely removed, but
of similar climate. We shaU have occasion to revert to this part of the subject.
We quote the foUowing from the introduction to a work afready referred
to (Agassiz and Gould's Principles of Zoology) as fitly concluding tms section,
by stating what is most requfred of the elements of Zoology for the purposes
of Physical Geography : —
' Eor each of these groups, whether larger or smaUer, we involuntarily
picture in our minds an image made up of the fraits which characterise the
group. This ideal image is caUed a Type, a term which there is frequent
occasion to employ in speaking of the Animal Kingdom. Thia image may
correspond to some one member of the group, but it is rare that any one
roecies embodies aU our ideas of the class, f'amUy, or genus to which it belongs.
Thus we have a general idea of a bird, but thia idea does not correspond to
any particular bfrd, or any particular character of a bfrd. It is not precisely
an oafrich, an owl, a hen, or a sparrow ; it is not because it has wings, or
feathers, or two legs ; or becauae it has the power of fiight, or buUds nests.
Any or aU theae charactera would not fully represent our idea of a bird, and yet
every one has a diatinct ideal notion of a bird, a fish, a quadruped, &c. It is
common, however, to speak of the animal which embodies most fuUy the
characters of a group aa the type of that group. Thua we might, perhaps,
regard an eagle as the type of a bird, the duck as the type of a swimming-
bfrd, and the maUard as the type of a duck.'
138 Statistics of Animals. — It ia not poaaible to appreciate the importance
ofthe subject we are now considering, either with reference to the grand
featares of general Zoology, or the detaUs concerning the diafribution of
animala, vrithout some reference to actual statistics. It is not enough to
regard nature generaUy with admfration, or even to study carefuUy som.e
detached points — we must also become acquainted vrith tiie extent of material
for observation and learn the tme spirit that animates the whole. ' We must
acqufre a proper conception of the varied affinities which combine beings
together, so as to make of them that vast picture in which each animal, each
group, each class has its place, and from which nothing could be removed
without desfroying the proper meaning ofthe whole.'
It is only withm a short time that Zoology has so far extended itself as to
become fafrly beyond the grasp of any single individual. A century ago, the
number of known animals did not exceed 8000, and thus fewer species
were kno-(vn in the whole Animal Kingdom than are now contained in many
private collections of certain famUies of insects merely.

• This subject will be found considered in further detail in paragraph 166 in the chapter on
Ethnology.

344

PHYSICAL GEOGRAPHY.

The number of vertebrate animals may now be estimated at 20,000. Of
these there are about 1500 species of mammals pretty preciaely known, and
the number may probably extend to 2000.
There are about 4000 or 5000 species of birds well known, and the probable
number ia 6000.
Tho number of reptUea is about the same as that of mammals — ^namely
about 1500 described species, and 2000 in all.
The fishes are more numerous. The number in the museums of Europe
are about 5000 to 6000 species, but the total number may extend to 10,000.
The invertebrata are much more numerous. Of MoUusca there are pro
bably from 8000 to 10,000 species in coUections. There are coUections of
marine ahella, bivalve and univalve, which amount to 5000 or 6000, and
coUections of land and freshwater shells extending to 2000 spedea. The
total number of moUusks may probably exceed 15,000 species.
Among the Articulata it is difficult to estimate the number of apecies.
There are coUections of coleopterous insects which number from 20,000 to
25,000 apecies, and it is quite probable that by uniting the principal coUections
60,000 or 80,000 apeciea might now be counted. For the whofe department
of Articulata, comprising the cruatacea, cirrhipeda insects, red-blooded worms,
intestinal worma, and infusoria, so far as they belong to the department, the
number would already amount to 100,000, and may be aafely eatimated as
reaching^double that aum.
The Eadiata, including the echini, starfishes, medusae, and polyps, cannot
be estimated at less than 10,000 species. We may thus present the foUowing
tabular view.

Mammals
BirdsReptiles ...
Fishes

Known. 1,5006,000
1,500 6,000

Estimated.

Known
number of

Estimated nmnber of

2,000 6,000
2,000
10,000

species.

species.



14,000
10,000
100,000 10,000

20,00015,000
200,000 10,000

134,000

250,000

Total Vertebrata . . .
Mollusca 
Articulata 
Radiata 
Grand total 
This large number of species of animals must be stUl further increased,
and perhapa even doubled, if we include also those no longer represented,
but whose remains are preserved to us in the afrata of the Earth'a crust.
These wUl, however, require separate consideration.
139 Nature and Degrees of Besemblance amongst Animals, and Com
parison of their Structure. — There is no subject more important to the general
student of natural history, and there is none which has more worthily occupied
the attention of the best and most phUosophic naturaUsts, than the true
nature of those resemblances which are presented everywhere in nature,
which evidently have important meaning, but which, when made use of, are
so likely to lead their pursuer into error, tiiat they are the very points on
which the greatest and most miachievoua miatakea have been made. We
muat endeavour here to make the reader acquainted with aome of the simpler
meanings of homology, analogy, and afiinity, as they are requfred to be
understood in considermg the aistribution of animals.
Analogy and homology are relations of simple resemblance in portions ofthe
living framework without reference to identity of race, whUe affinity is a relation
obtaining between the correaponding parts of animala of the aame race — and
-thua, at the outset, there are important and real distinctions to be recogniaed.
But there ia more than this, and there are alao important diatmctiona to be drawn
between the former ( erms. An analogvchas been defined to be ' a part or organ

DISTRIBUTION OP ANIMALS IN SPACE. 345
in one animal which has the same function, or does the same work aa another
part or organ in a different animal;' while a homologue is ' the same organ in
different animala under every variety of form and function.' It wUl not be
difficult to underatand, from these definitions, something of the true meaning
of the words on which so much afress haa been laid, but a few examplea wiU
render thefr use still more clear.
In a very general way we may ahow this, by conaidering the nature of the
wings by which various animals fly, the legs or arma which others use for
walking and running, and the fins by means of which fiahea awim — in a word,
of the organs of locomotion. There is analogy between the wing of a
butterfly and that of a bfrd, for both of them serve for fiight, but they are
not homologous, since a different organ is employed. On the other hand,
the fore leg of a quadruped is homologous to the vring of a bfrd, but not
sfrictiy analogous, for the aame organ is employed, but the aame purpose is
not attained. Thus, also, the fin of a porpoise is homologous to the fin of a
fish, being at the same time analogous, since both are employed in swimming,
and both are modifications of the same organ.
Affinities are different, and indicate closer relations. Thus, there is affinity
between the leg and foot of a man and the paddle of a seal, for both are
constructed on the same plan, and the affimty in this case is far more
important than the analogy and homology that exist between seals and fishes,
in thefr stmcture and habits. Affinities, rather than analogies and homologies,
are therefore most useful in guiding us in the arrangement of animala.
Eesemblancea are fraced not only in the parts of the individual or
apecies, but in general external character, with regard to genera and larger
groups. UsuaUy we may consider, that in any natural arrangement, such as
we have endeavoured to give, there wUl be resemblances of affinity between
aU species coUected together in any group, whether large or smaU — that, in
otber words, aU animals in the first place — aU vertebrata in the next — aU
mammals in the thfrd — aU monkeys in the fourth — and aU baboons in the
fifth place, have different degrees of affinity, graduaUy becoming closer as the
number of species included is amaUer. On the other hand, there wiU be
analogy between aome vertebrata and aome moUuaca or articulata, between
carnivorous quadrupeds and birds of prey, between different fribes of car
nivora and so on ; and thus each natural group of organic beings wUl present
reaemblancea of different kinda, which must be estimated, each according to
ita true value, in any general view of the whole Animal Kingdom.
It ia important also to remember, that investigations conceming the true
nature and relationa of animala ahould not be limited to the adult, but extend
over the whole courae of development. If thia ia not done, aome pecuUarities
of structure which are predominant at one period of Ufe, wUl be exaggerated
in importance, and othera neglected. Thus, the organs of respfration, which
appear to be most essential characters for classification, if we regard only the
fuU-grown animal, are found, on examining and comparing thefr various states
in the same indiridual, to be quite subserrient to the nervous system. The
comparative study of development is also not lesa valuable, aa a means of
estimating the relative poaition of animala. Thus, the caterpillar, in becoming a
butterfiy, passes from a lower to a higher development, and therefore, those
animals, such aa worms, which resemble the caterpillar, must occupy a lower
rank than thoae approaching the butterfly.
All animals undergo changes, or metamorphoses, during the earUer period
of thefr existence, although in many cases, especiaUy in those of higheat grade,
theae take place before bfrth, and during the embryonic period. It ia only
by connecting the two kinda of transformation — namely, those that take place
before and those after birth, that we are ftimiahed with means of ascertaining
the relative perfection of animals ; so that, in fact, auch franaformations
become a natm-al key to the gradation of types. No one can properly
appreciate the structure of animals and the difference of races, or com
prehend, even in a very inferior degree, the law that governs the placing of

346 PHYSICAL GEOGRAPHY.
groups in certain districts, adapts them a certain climate and certain food,
and enables them to resist certain changes, without knowmg something of the
nature of analogy and afflmty, and the changes of structure that take place in
the individual and the species, in paaaing through aU the varioua forms of its
existence, as an organized being.
140 Natural Grouping of Animals in a ' Fauua.' — The coUection of
animals inhabiting any particular region, including aU the speoiea, both
aquatic and terrestrial, is caUed its Fauma, just as the plants of a country
combine to form its Flora. It is not necessary that every species ahould be
pecuUar, only there must be some special disfribution of femUies, genera, and
species, and a preponderance of certain types, sufficientiy important and
prominent to impress upon the group weU-marked features. Thus, the fauna
of New HoUand la characteriaed by the exiatence there of tribea of quadrupeds
of the Marsupial order, that of South America by Edentata. The polar
bear and reindeer are characteriatic of the arctic regions of the Earth, and
certain peculiarities of structure m monkeys at once distinguish the faunas
of Asia and America, in those parts where monkeys appear.
As animals feed either on other animals, or on vegetables, it ia erident
that, ultimately, the diatribution of animals wiU depend on vegetable life.
Thua, there arises a relation between the fauna of a locahty, its climate, and
its flora; but although this is certainly very important, it must not be
forgotten that whUe plants chiefly inhabit land, animals range far more
widely, and exist to such an extent in water, that it has been even aaid, that
the ocean is the frue home of the Animal Kingdom, and this is certainly the
case in those extreme latitudes where vegetable life entirely ceases, and
where the aea teema with animala of aU classes and aU dimensions. The chief
influence of exfreme cold seema to be to render more uniform the distribution
of apecies, ao that many of the large quadmpeda, for example, are common to
Europe, Aaia, and America, within certain high latitudes, whUe the faunas of
tropical Aaia are totally diatmct from those either of fropical Africa, or fropical
America. A wide fract of deep sea, and the existence of broad desert fracts,
lofty mountaina, and distinct zones of climate on land, Umit Faunas very
strikingly, as we find on comparing the productions of the Cape of Good
Hope vrith those of Cape Horn, and this is even the case when latitade and
climate are very nearly simUar. The depths of the ocean are, indeed, quite
as impassable for marine species as high mountains are for terrestrial
animals, and it would be as difficult for a fish or a moUusk to cross from the
coast of Europe to that of America, as it would be for a reindeer to pass
from the arctic to the antarctic regions across tbe torrid zone. It is pro
bable that the deepest parts of the ocean are absolutely untenanted, for there
seem there no means of subsistence, and few animals are organized so as to
reaiat the preaaure of a column of water many thousand fathoma in height.
The animal inhabitanta of the sea are, therefore, aa atrictiy limited to
districts as those of the land ; and as by far the larger proportion depend on
the adjacent ahores more or less for thefr means of existence and thefr shelter
from natural enemies, no doubt the limits of the marine are less easily
defined than those of terrestrial Faunas, but stUl marked differences are
discernible, whUe freshwater species vary, not only in different zones, but
even in the rivers and lakes of the same disfrict.
The range of species does not depend on powers of locomotion, but on the
contrary, animals which move slowly and vrith difficulty, generaUy ha,ve a
vride range, whUe thoae which are active are often very narrowly hmited.
Thus, the common oyater extenda on the American coaat from Cape Cod
to the Carolinas, aud is, as we know, alao common over a long Une of coaat on
thia side of the Atlantic, ao that ita range is absolutely very great ; and when
compared to that of some fleet animal, as the moose, appears enormous. It is
indeed poaaible that Iho very want of power to travel really confributea to
tho difiusion of this and somo other species, since when once removed they
cannot retum, and thoir eggs beuig left to the mercy of marine currenta, may

DISTRIBUTION OP ANIMALS IN SPACE. 347
be drifted very far, whUe fishes depositing thefr spawn in sheltered bays and
inlete, are secured from wide dispersion.
The nature of their food has an important bearing upon the grouping of
animals, and upon the extent of their distribution. Carnivorous animals are
generaUy less confined in thefr range than herbivorous ones, becauae their
food is almost everywhere to be found. The herbivora, on the other hand,
are restricted to the more limited regions corresponding to the different zones
of vegetation. The same remark may be made with respeot to bfrds. Birds
of prey, hke the eagle and vulture, have a much vrider range than the
granivorous and gaUinaoeous bfrds. StUl, notwithstanding the facUities they
nave for change of place, even the bfrds that wander widest recognise limits
which they do not overpass. The condor of the CordUleraa doea not deacend
into the temperate regions of the United Statea ; and yet it ia not that he
fears the cold, since he is frequently known to ascend even above the highest
summita of the Andes, and disappears from view where the cold is most
intense. Nor can it be from lack of prey.
PinaUy, to obtain a frue picture of the zoological disfribution of _ ammals,
not the terrestrial types alone, but the marine apeciea, muat alao be included.
Notwithatanding the uniform nature of the watery element, the animala which
dweU in it are not dispersed at random, and though the limits of the marine
may be leas easUy defined than those of the terrestrial fauna, stiU marked
differences ofthe animals in the great basins are not less observable. Pro
perly to apprehend how marine animals may be disfributed into local faunas,
it must be remembered that thefr residence ia not in the high sea, but along
the coaste of continents and on soundings. It is on the banks of Newfouni
land, and not in the deep sea, that the great cod fishery is carried on ; and it
is weU known that when fishes migrate, they take oare to run along the
ahores. The range of marine apecies being therefore confined to the vicinity
ofthe ahorea, thefr diafribution muat be subjected to laws simUar to those
which regulate the terrestrial faunas. Aa to the fresh-water fishes, not only
do the apecies vary in the different zones, but even the different rivers of the
same region have species pecuUar to them, and not found in neighbouring
sfreams. A vei^ influential cause in the distribution of aquatic animala is the depth
of the water. The moUuaka, and even the fishes found near the surface
between high and low water, differ, in general, from those Uving at the depth
of twenty or thfrty feet, and these again are found to be different from those
which are met -with at a greater depth. Thefr colouring in particular varies
according to the quantity of Ught they receive, as haa also been ahown to be
the case with the marine plants.
It is sometimes the case that one or more animals are found upon a
cert,ain chain of mountains and not elsewhere ; as for instance, the mountain
sheep upon the Eocky Mountains, or the chamois and the ibex upon the
Alps. The aame is also the case on aome of the vride plains or prairies. This,
however, does not entitle such regions to be considered as having an
independent fauna, any more than a lake is to be regarded as having a
pecuhar faima exclusive of the animals of the surrounding country, merely
becauae some of the apeciea found in the lake may not ascend the rivers
emptying into it. It is only when the whole group of animals inhabiting
a region has such jpecuUarities as to give it a distinct character, when
confrasted with animals found in surrounding regions, that it is to be
regarded as a separate fauna. Such, for example, is the fauna of the great
steppe or plain of Gobi, in Asia, and such also that of the chain of the
Eocky Mouutains may prove to be when the animals inhabiting them are
better known.
The migration of animals might at first seem to present a serious difficulty
in detei-mining the character or the limits of a fauna; but this difficulty
ceases, if we regard the country of an animal to be the place where it makes
ita habitual abode. As to bfrds, which of aU animals wander the farthest, it

348 PHYSICAL GEOGRAPHY.
may be laid down as a rule that they belong to tbe zone in which they breed.
Thus the guUs, many of the ducks, mergansers, and divers, belonging to the
boreal regions, though they pass a portion of the year with us. On the other
hand, the swaUows and martins, and many of the gaUinaceous bfrds, belong
to the temperate faunas, notwithstanding that they migrate during vrinter
to the confines of the torrid zone. This rule does not apply to the fiahea who
annually leave thefr proper home and migrate to a distant region, merely for
the purpose of spawning. The salmon, for example, comea down from the
north to spawn on the coasts of Maine and Nova Sootia.
Few of the mammals, and these mostly of the tribe of Eodents, make
extensive migrations. Among the most remarkable of these are the Kamts
chatka rats. In spring they dfrect thefr course westward in immenae froops,
and after a very long joumey, retum again in autumn to thefr quarters, when
thefr approach is anxiously awaited by the hunters, on account of the fine
furs to be obtained from the numerous. carnivora wbich always follow in their
train. The migrations ofthe lemmings are marked by the devastations they
commit along thefr courae, as they come down from the borders ofthe Frozen
Ocean to the vaUeys of Lapland and Norway ; bnt thefr migrations are not
periodical. 141 Distribution ofthe Faunas. — ^We have stated that aU the faunas of
the globe may be divided into three departments, corresponding to as many
great cUmatal divisions — namely, the glacial or arctic, the temperate, and the
fropical faunas. These three (Urisions appertain to both hemispheres, as we
recede from the equator towarda the north or south poles. It vriU hereafter
be shown that the fropical and temperate faunas may be again dirided into
several zoological provinces, depending on longitude or on the pecnhar
configuration of the continents.
No continent is better calculated to give a correct idea of diatribution into
faunaa aa determined by climate than ihe continent of America, extending
as it does across both hemispheres, and embracing aU latitudes, so that all
cUmates are represented upon it.
Let a fraveUer embark at Iceland, which is situated on the borders of the
polar circle, with a view to observe, in a zoological aapect, tne prmcipal
pointa along the eastem shore of America. The result of his observation
wUl be very much as foUows. Along the coast of Greenland and Iceland,
and also along Baffin's Bay, he vnU meet vrith an unvaried fauna com
posed of animals which are, for the most part, identical with those of the
arctic shores of Europe. It vriU be nearly the same along the Labrador
coast. As he approaches Newfoundland, he wiU see the landscape, and with it
the fauna, assuming a somewhat more varied aspect. To the vride and naked,
or turfy plains of the boreal regions succeed foreste in which he wiU find
various animals which dweU omy in foreste. Here the temperate fauna
commences ; stiU the number of species is not yet very considerable ; but as
he advances southwards along the coasts of Nova Scotia and New England,
he finds these species graduaUy increasing, whUe those of the cold regions
diminish, and at length entirely disappear, some few accidental or periodical
visitors excepted, who wander during vrinter as far south as the Carolinas.
But it is after having passed the boundaries of the United Stetes, among
the AntUles, and more especially on the southem continent along the shores
of the Orinoco and the Amazon, that our traveller wiU be forcibly stmck
with the astonishing variety of the animals which people the foreste, the
prairies, the rivers and the sea shores, most of which he wUl also find to be
different from those of the northem continent. By this exfraordinary rich
ness of new forma he wiU become aensible that he is now in the domain of
the tropical fauna.
Let him stiU fravel on beyond the equator towards the tropic of Capricorn,
and he will again flnd the scone change aa he enters the regions where the

DISTRIBUTION OF ANIMALS IN SPACE. 349
Bun casts his rays more oblic[ue]y, and where the contrast of the seasons ia
more marked. The vegetation wUl be leas luxuriant, the palms wiU have
disappeared to make place for other trees, the animals wUl be less varied, and
the whole picture wUl recal to him, in aome meaaure, what he witneased in
the United States. He wUl again find himself in the temperate regions, and
this he wiU trace on, tUl he arrives at the extremity of the continent, tbe
fauna and the flora becoming more and more impoverished as he approaches
Cape Hom.
FinaUy, we know that there is a continent around the South Pole.
Although we have as yet but very imperfect notions reapecting the animals
of this inhospitable cUme, still the few which have afready been observed
there, aU present a close analogy to those of the arctic region. It is another
glacial fauna — namely, the antarctic. Having thus sketched the general
distribution of the fauna, it remains to point out the principal features of each
of them. 142 Arctic Fauma. — The predominant feature of the arctic fauna is its
uniforndty. The species are few in number, but, on the other hand, the
number of indiriduals is immenae; we need only refer to the clouds of birds
which hover upon the islands and shores of the north : — ^the shoals of fishes —
the salmon among others, which throng the coasts of Greenland, Iceland, and
Hudson's Bay. The same uniformity appears in the form and colour of the
animals. There is not a single bfrd of brUUant plumage, and not a fiah with
varied hues. Thefr forms are regular, and thefr tints as dusky as the
northern heavens. The most conspicuous animals are the white bear, the
moose, the rein-deer, the musk ox, the white fox, the polar hare, the lemming,
and various seals, but the most important are the whales, whioh it is to be
remarked rank lowest among the mammals. Aniong the bfrds may be
enumerated some sea-eagles and a few waders, with an immense number of
other aquatic species, such as guUs, cormorants, divers, petrels, ducks, geese,
&c., aU belonging to the lowest order of bfrds. Eeptiles are altogether
wanting. The Articulata are represented by numerous marine worms, and by
minute cruataceana of the orders Isopoda and Amphipoda. Insects are rare
and of inferior types. Of the type of MoUusks, there are Acephala, particu
larly Tunicata, fewer Gasteropods, and very few Cephalopods. Among the
Eadiata are a great number of jeUy-fishes, particularly the Beroe ; and to
conclude with the Echinoderms, there are several star-fishea and Echini, but
few Holothurise. The clasa of Polypi ia very scantUy represented, and those
producing stony corals are entfrely wanting.
This aaaemblage of animals is e-ridently inferior to the other faunas,
especiaUy to those of the fropics. Not that there ia a deficiency of animal
Ufe ; for if the species are less numerous, there is a compensation in the
multitude of individuals, and also in this other very significant fact, that the
largest of all animals, the whales, belong to this fauna.
It has afready been said that the arctic fauna of the three continents is
the same ; its southern limit, however, is not a regular Une. It does not
correspond preciaely with the polar circle, but rather to the isothermal zero,
that is, the line where the average temperature of the year is at 32° of
Fahrenheit. The course of this Ime presents numerous undulationa. In
general, it may be said to coincide with the appearance of frees, so that it
passes where forest vegetation succeeds the vast arid plains, the barrens of
North America, or the tundras of the Samoyedea. The uniformity of these
plains involves a corresponding uniformity of planta and animals. On the
North American continent, it extends much farther southward on the
e.iatern shore than on the western. From the peninsula of Alashka it bends
northwards towards the Mackenzie, then descends again towards the Bear
Lake, and comes down to near the northern shore of Newfoundland.
143 Temperate Faunas. — The faunas of the temperate regions of the
northem hemisphere are much more varied than that of the arctic zone. At
its northern margin, the leaves, excepting those of the pines and spruces, fall

350 PHYSICAL GEOGRAPHY.
on the approach of the cold season, and vegetation is arrested for a longer or
shorter period. Inaecta retire, and the animals which live upon them no
longer find nourishment, and are obliged to migrate to warmer regions, cn
the borders of the tropics, where on the ever verdant vegetation they find
the means of subsistence.
Some of the herbivorous Mammals, the bats, and the reptUes which feed
on insects, paas the winter in a state of torpor, from which they awake in
spring. Omers retire into dens, and live on the provisions they have stored
up during the warm season. The Carnivora, the Euminanta, and the most
active portion of the Eodents, are the only animals that do not change either
tbeir abode or thefr habits. The fauna of the temperate zone thus presents
an ever-changing picture, which may be considered as one of its most
important featurea, since these changes recur with equal constancy in the
Old and the New World.
Taking the confrast of the vegetation as a basis, and the consequent
changes of habit imposed upon the denizens of the foreste, the temperate
fauna has been dirided into two regiona, a northem one, where the trees,
except the pines, drop thefr leavea in winter, and a southem one, where they
are evergreen. Now aa the Umit ofthe former, that of the deciduoua frees,
coincides, in general, vrith the limit ofthe pines, it may be said that the cold
region of the temperate fauna extends as far as the pines. In the United
States this coincidence is not so marked as in other regions, inasmuch as the
pines extend into Florida, whUe they do not prevaU m the westem stetes ;
but we may reckon as belonging to the southem portion of the temperate
region, that part of the country south of the latitude where the Palmetto or
Cabbage free (Chamcerops) commences, nearly aU the statea to the aouth of
North Carolina ; while the states to the north of this limit belong to the
northern portion of the temperate region.
This diviaion into two zones ia supported by observations made on the
maritime faunas of the Atlantic coast. The line of separation between them,
however, being influenced by the Gulf Sfream, is conaiderably farther to the
north ; — namely, at Cape Cod. It has been ascertained, that of one hundred
and ninety-seven MoUusks inhabiting the coast of New England, fifty do not
pasa to the north of Cape Cod, and eighty-three do not paas to the south of
it; only sixty-four being common to both sides of the Cape. A simUar
limitation of the range of fishes has been noticed by Dr. Storer, and Dr. Hol-
brook has found the fishes of South CaroUna to be different from thoae of
Florida and the West Indies. In Europe, the northern part of the temperate
region extends to the Pyrenees and the Alps ; and ite southem portion con
sists of the basin of the Mediterranean, together with the northem part of
Africa, as far as the desert of Sahara.
A pecuUar characteristic of the faunas of the temperate regions in the
northem hemisphere, when contrasted with those of the southem, is the great
simUarity of tbe prevaiUng types on both continents. Notwithstanding the
immense extent of country embraced, the aame stamp ia everywhere exhibited.
Generally l^e same famUies, frequently the same genera represented by
different species, are found. There are even a few species of terresfrial
animals regarded as identical onthe continenta of Europe and America, but
their auppoaed number is conatantly diminished, as more accurate observations
.are made. The predominant types among the Mammals are the bison, deer,
ox, horse, hog, numerous Eodents, especially squirrels and hares, nearly aU
the Inaectivora, weasels, martins, wolves, foxes, wUd cats, &c. On the other
hand, there are no Edenteta, and no Quadrumana, with the exception of some
monkeys on the two slopes of the Atlas. Among bfrds there is a multitade of
climbers, passerine, gallinaceous, and rapacious birds. Of reptUea there are
lizards and tortoises, of small or medium size, serpents, and many bafrachians,
but no crocodiles. Of fishes there is the trout famUy, the cyprinoids (carps),
the sturgeona, the pikes, the cod family, and especiaUy the great famUy
of herrings and scomberiods, to which latter belong tho mackerel and the

DISTRIBUTION OP ANIMALS IN SPACE. 351
tanny. AU classes of the MoUusks are represented ; though the Cephalopods
are less numerous than in the torrid zone. There is an infinite number of
Articulata of every type aa well as numerous Polyps, though the true corals do
not appear abundantly.
On each of the two continents of Europe and America, there is a certain
number of apecies which extend from one exfreme of the temperate zone to
the other. Such, for example, are the deer, the bison, the cougar, the flying
squirrel, numerous bfrds of prey, several tortoiaea, and the rattlesnake in
America; and in Europe the brown bear, wolf, swaUow, and many birds of prey.
Some species have a stUl vrider range, Uke the ermine, which is found from
Bhering's Straits to the Himalayan Mountaina, that is to say, from the coldest
regions of the arctic zone, to the southern confines of the temperate zone. It
is the same with the musk-rat, which is found from the mouth of Mackenzie's
Eiver to Florida. The field mouse has an equal range in Europe. Other
apeciea, on the confrary, are limited to one region. The Canadian elk is
confined to the northern portion ; and, on the other hand, the prafrie wolf,
the fox-squirrel, the bassana, and numeroua bfrds, never leave tne southem
portion.* In America, as in the Old World, the temperate fauna is fiirther subdi
rided into several districts, which may be regarded as so many zoological
provinces, in each of which there is a certain number of animala differing from
those in the othera, though very closely aUied. Temperate America presents
us with a striking example in this respect. We have, on the one hand —
I. The 6.una of the United Stetes, properly so called, on thia side of the Rooky
Mountains. II. The feuna of Oregon and California, beyond those mountains.
Though there are some animals whioh traverse the chain of the Rocky Mountains,
and are found in the prairies of the Missouri, as well as on the banks of the Columbia,
as tor example, the Rocky Mountain deer (Antilope furcifer,) yet if we regard the
whole assemblage of animals, they are found to differ entirely. Thus, the rodents,
part of the ruminants, the insects, and all the moUusks, belong to distinct species.
The faunas or zoological provinces of the Old World whioh correspond to these are —
I. The fauna of Europe, which is very closely related to that of the United States
proper. II. The fauna of Siberia, separated from the fauna of Europe by the Ural
Mountains. III. The fauna of the great Asiatic table-land, whioh, from what is as yet known
of it, appears to be quite distinct.
IV. The &mia of China and Japan, which is analogous to that of Europe in the
birds, and to that of the United States in the reptiles, as it Is also in the flora.
Lastly, it is in the temperate zone of the northem hemisphere that we meet with
the most striking examples of those local faunas which have been mentioned above.
Such, for example, are the faunas ofthe Caspian Sea, of the Steppes of Tartary, and of
the Westem Prairies.
The faunas of the southem temperate regions differ from those of the
fropics as much as the northem temperate ftiunas do ; and like them, also,
may be distinguished into two provinces, the colder* of which embraces
Patagonia. But, besides differing from the tropical faunas, they are also
quite dissimUar to each other on the different continents. Instead of that

* The types which are peculiar to temperate America, and are not found in Europe, are,
the opossam, several genera of insectivora, among them the shrew-mole, (Scalops aquations,)
and the star-nose mole, (Condylura cristata,) which replace the mygale of the Old World ;
several genera of rodents, especially the musk-rat. Among the types characteristic of Araerica
must also be reckoned the snapping-turtle among the tortoises; the menobranchus and
menopoma among the salamanders ; the garpike and amia among the fishes ; and, flnally,
among the Crustacea, the limulus. Among the types which are wanting in temperate America,
and which are found in Europe, may be cited the horse, the wild boar, and the true mousi;.
All the species of domestic mice which live in America have been brought from the Old World.

352 PHYSICAL GEOGRAPHY.
general resemblance which we have noticed between aU the faunas of tho
temperate zone of the northern hemisphere, we find here the most com
plete contrasts. Each of the three continental peninaulas whieh jut out
southerly into the ocean represents, in some sense, a separate world.
The animals of South America, beyond the tropic of Capricorn, are iu aU
respects different from those at the southem extremity of Africa. The
hyenas, wild boars, and rhinoceroses of the Cape of Good Hope have no
analogues on the American continent ; and the difference is equally great
between the bfrds, reptUea, and fishes, insects and moUusks. Among the most
characteristic animals of the southem extremity of America are peculiar
speoiea of seala, and eapeciaUy, among aquatic birds, the penguins.
New Holland, with its marsupial mammals, with which are associated
insects and moUusks no leas singular, fumiahes a faxma stiU more peculiar,
and which doea not approach thoae of any of the adjacent countriea. In the
seas of that continent where everything ia ao strange, we find the curious
shark, with paved teeth and apinea on the back (Ceafracion Phihppi), the only
living repreaentative of a fanuly so numerous in formffl: zoological ages. But
a most remarkable feature of this fauna is, that the same types prevaU over
the whole continent, in its temperate as weU as its fropical portions, the
species only being different at different locaUtiea.
144 Tropical Faunas. — The fropical faunaa are distinguiahed on aU the
continenta by the immense variety of animals which they comprise, not lesa
than by the brilliancy of thefr coverings. AU the principal types of animals
are represented, and aU contain numerous genera and species. We need only
refer to the tribe of humming-bfrds, which numbers not less than 300 species.
But what is very important is, that here are concentoated the most perfect
and also the oddest types of aU the classes ofthe Animal Kingdom. The
tropical region ia the only one occupied by the quadrumana, the herbi-
voroua bata, the great pachydermata, such as the eleMant, tbe hippopotamua,
and the tapir, and the whole famUy of edentata. Here, alao, are found the
largest of the cat tribe, the Uon and tiger. Among the bfrds we may mention
the parrots and toucans, as essentiaUy tropical; among the reptUes, the largest
crocodUea and gigantic tortoises ; and finaUy, among the articulated animala,
an immenae variety of the most beautiful insecte. The marine animals as a
whole are equally auperior to thoae of other regions; the seas teem with
cruataceans and numerous cephalopoda, together with an infinite variety of
gasteropods and acephela. The echinoderms there attain a magnitade and
variety elaewhere unkno-ivn ; and laatly, the polyps there display an actirity
of which the other zones present no example ; whole groups of islanda are
covered with coral reefs formed by those Uttle ammals.
The variety of the tropical fauna is farther enriched by the cfrcumstance
that each continent furnishes new and peculiar forms. Sometimes whole
types are limited to one continent, as the sloth, the toucans, and the hum
ming-birds to America ; the gfraffe and hippopotamus to Africa ; and again,
animals of the same group have different characteristics, according as they
are found on different continenta. Thus the monkeys of America have fiat
and widely separated nosfrila, thfrty-aix teeth, and generally a long pre-
hensUe tail. The monkeys of the Old World, on the confrary, have noafrUs
close together, only thfrty-two teeth, and not one of them has a prebenaUe
tail. But theae differences, however important they may appear at fii-at glance,
are subordinate to more iraportant characters, which establish a certain general
affinity between aU the faunaa of the tropica. Such, for example, ia the fact,
that the quadrumana are limited on all the continents to the warmest regions;
and never, or but rarely, penetrate iuto the temperate zone. This disfribution
is a natural consequence of the distribution of the palms ; for aa theae trees,
which constitute the ruling feature of the fiora of the tropics, furniah to a
great extent the food of tho monkeys on the two continents, we have only to

DISTRIBUTION OF ANIMALS IN SPACE. 353
frace the limits of the extent of the pahns, to have a pretty accurate indica
tion ofthe fropical faunaa on all three continenta.
The tropical fauna of Asia, comprising the two peninsulas of India and
the isles of Sunda, is weU marked. It is the country of the gibbons,
the red ourang, the royal tiger, the gavial, and a multitude of peculiar
birds. Among the fiahea the family of Ohetodona is most numerously
represented. Here also are found those curious spiny fishes, whose intri
cate gUls suggested the name (Labyrinthici) by which they are known.
Fishes with tufted gUls are more numerous here than in other seaa. Tho
insects and moUuaka are no less strongly characterized. Among others is
the nautilus, the only living representative of the great famUy of large
chambered aheUa, which prevaUed so extensively over other types in former
geological ages.
The fropical zone of Africa is distinguished by a striking uniformity in
the disfribution of the animala, which corresponds to the uniformity of the
atmcture and contour of that continent. Ita most characteristic apecies are
spread over the whole extent of the tropics; thus the giraffe is met with
from Upper Egypt to the Cape of Good Hope. The hippopotamus is found
at the same fiine in the Nile, the Niger, and Orange Eiver. This wide
range is the more significant aa it alao relates to herbivorous animala, and
thus supposes conditions of vegetation very simUar over wide countries.
Some forms are nevertheless circumscribed within narrow districta, and
there are marked differencea between the ammals of the eastem and westem
shores. Among the remarkable species of the African torrid region are
the baboons, the African elephant, the crocodUe of the NUe, a vast number
of antelopes, and especiaUy two species of ourang-outang, the chimpanzee
and another large and remarkable animal of the same kind, recently described
by Drs. Savage and Wyman. The fiahea ofthe Nile have a tropical character
aa weU aa the animala of Arabia, which are more aUied to thoae of Africa than
to those of Asia.
The large island of Madagascar has its pecuUar fauna, characterized by
its makis and its curious rodents. It is also the habitat of the" aya-aya.
Polynesia, exclusive of New Holland, furnishes a number of very curious
animals, which are not found on the Asiatic continent. Such are the herbi
vorous bats and the galeopithecus, or fiying maki.*
Several weU marked faunaa may be diatinguiahed in the fropical part of
the American continent — namely,
I. The fauna of BrazU, characterized by ita gigantic reptilea, ita monkeys,
its Edentata, its tapfr, its humming-bfrd.s, and its astonishing variety of
insects. II. The fauna of the westem slope of the Andes, coinprising ChUi and
Pem ; and distinguished by ita Uamaa, vicunaa, and bfrds, which differ from
thoae ofthe baain ofthe Amazon, aa alao do the insects and moUuska.
III. The fauna of the AntiUes and the Gulf of Mexico. This ia eapeciaUy
characterized by its marine animals, among which the manatee is particularly
remarkable ; an infimte variety of singular fishes, embr^jing a large number
of Plectognaths ; also MoUusks, and Eadiata of peculiar species. It is in this
zone that the Peniacrinus caput-medusee is found, the only representative in
the existing creation of a famUy so numerous in ancient epochs, the Crinoidea
with a jointed stem.
The limits of the fauna of Cenfral America cannot yet be weU defined,
from want of sufficiMit knowledge of the animals which inhabit those regiona.
145 Special Distribution of Quadeumana. — In addition to the facts
already given vrith regard to the various faunas in different parts of the

* For the whole of this account of the distribution of the faunas, the author is indebted to
an excellent abstract given by Prof. Agassiz, in his Principles of Zoology, recently published in
America. The above five sections are adopted with little change from that work, chapter xiii.
AA

354 PHYSICAL GEOGRAPHY.
world, it is desfrable that we should consider also the special distribution of
various races and natural tribes of animals. Of those which are calculated
to give useful information of this kind, the great division of Vertebrata
includes by far the larger number, and we now proceed to explain in what
manner the class of Quadrumana is constituted with reference to chmate
and position.
Of the Quadrumana there are two subdivisions, the Simice, or monkeys,
and the Prosimite, or makis. Of the former there are two famihes, the
one having obUque and vride set nostrils and a human-like system of teeth,
and characteristic of the Old World; and the other having nostrils placed
at the side and vride asunder, with three false grinders on each side of both
jaws, found only in America. There are in all one hundred and seventy
described species, of which seventy -nine belong to the former and ninety-one
to the latter country. There are thirty-two species of makis, making m aU
two hundred and two described Quadrumana.
With regard to the distribution of these two hundred and two apeciea,
we find that the apea are concenfrated in counfries under the equator, and
there have their maximum. Of the three equatorial regions of Aaia, Africa,
and America, that of America (BrazU) has by far the greatest number of
species, the amount being nearly double that of the continente of the Old
World. Probably the greatest number of species of apea occur in the SUvas,
on the banka of the Amazon, whence they extend to the eastem decUriiy of
the Andes; they do not, however, croas the chain, aince, on the whole weatem
side of the CordUleraa, from Panama to ChUi, only one or two aperies of
the spider-monkey (Ateles) occur, and these are confined to Pem. Not only
is the maximum of aU the apes of the New World found in BrazU, but the
maximum of each single genus also occura there.
Of nine genera of monkeys found in the Old World, five are common to
Asia and Africa. Four of these (the baboons, magote, macacos, and long-
taUed monkeys, Cercopithecus) belong to the group of taUed monkeys,
and the other (the Oranga) to the taUlesa monkeys. Of the other four genera
the taUed gibbons are found only in Sumafra, and the solemn apes
(Semnopithecus) occur pretty -widely distributed in the islands of the Indian
Archipelago, and are met with also in India and China, but nowhere in
Western Asia or Africa. The whole group of the gibbons correaponda pretty
nearly in diatribution with that of the solemn apes, and the two groups are
simUarly limited, whUe thumbless apea (Colobus) are atrictiy Umited to Africa,
and chiefiy confined to about sixteen degrees on each aide of the equator.
The Baboons (Cynocephalus) are large, ferocious, and dangeroua apea,
attaining the aize of a wolf, and remarkable for thefr canine physiognomy,
whence their name haa been derived, (kvvti, cyni, dog, Ke<f>dKT], cephaU, head.)
There are two groupa of them — viz., the baboona proper and the mandriUa.
One apeciea of the former is nearly confined to the Cape of Giood Hope,
another to the vicinity of the Eed Sea, another to Northem and Cenfral
Africa, and another to Asia (East Indian lalands). The mandrills are exclu
sively met with in Cenfral Africa.
The Magote are represented in North Africa and Europe by the Barbary
ape, and in Sumatra by another species. The Barbary ape is not indigenous
in Europe, but has migrated from Ceuta to Gibraltar, the only European
locality in which it occurs.
There are two divisions of macacos — the long-tailed and short-teUed.
They are both widely spread, but the second di-vision occurs only in Asia,
inhabiting Hindustan, Ceylon, Java, and Sumafra. The apecies of the
former abound in the East Indian Islands and occur alao in Africa.
The Tbumbleaa apes ( Colobus) form a peculiar African group of the Asiatic
genua Semnopitliecus, (Solemn apea). The latter are long-taUed and have a
slender body; they are mUd, intelligent, and slow. They abound in India,
Ceylon, and the South-eastern Arcmpelago, and one apeciea extenda into
China, Cochin China, and the Malay peninsula, where its flesh ia highly

DISTRIBUTION OF ANIMALS IN SPACE. 355
Erized as an article of food. The African thumbless apes have a singular
ead of hafr, and there are several (eight) species of them.
The Long-tailed monkeys (Cercopithecus) are chiefly African, where they
are described as being singularly abundant. The proper habitat ofthe genus
ia Weatern Africa, but aix apecies occur in Asia, one of which is common to
the two continents. One species reaches far aouth in Africa, and another
inhabits the ialand of Mauritius.
The TaUless monkeys are of two groups, the long-armed apes (gibbons)
and the orangs. The former inhabit only the most secluded parts of India
and the Eaatern Archipelago ; the latter are found both in Aaia and Africa,
but are limited to about thirteen degreea latitude on each aide of the equator,
and occur chiefly in tho interior of the country.
The Monkeys of the New World differ remarkably from those of the
Old, especially in their smaUer aize and lesa ferocioua mannere, in the
possession of naked caUositiea, and in the want of cheek pouchea. They
form two groupa, and include, as we have afready said, a very large number
of species. The monkeys ofthe first group aU possess prehensUe taUs; they
include the howlers, (nine species,) the spider monkeys, (two,) the gluttonous
monlceys, (two,) and the weepers, (twenty -three.) The species of the first
genua are of large size and have the widest cfrcle of distribution, being found
as far north as Panama, and extending also to the south polar Umit of the
whole race. The spider monkeys inhabit chiefly BrazU and Guiana ; they
are generaUy mild, timid, melancholy, and inactive. The gluttonous monkeys
are strictiy confined to the fropical counfries in the interior of South America,
and the weepers, although found in greatest numbers in Guiana, extend
southwards to the fropic of Capricorn ; they are mUd, quick and Uvely in
thefr movements, and exceUent cUmbers. The aecond group of American
monkeya are chiefly BrazUian, and they generaUy have large tails and bushy
hafr. The Makis include thirty4wo species, of which fourteen are Lemurs, and
aix Boris. The Lemurs are exclusively confined to Madagascar and the
adjacent islands, and ao are also another group (lichanotu^, the largeat of
the tribe, attaining the aize of a baboon. The Lorises are distributed
through Asia, and are remarkable for thefr nocturnal habita, and large
aparkUng eyes.
Among the Monkeys of the Old World, one of the solemn apes (Semno
pithecus entellus) ascends to the greatest height attained by the Quadrumana,
and where there is wood, indiriduals are found on the slopes of the Himalayan
Mountains, 1 3,000 feet above the sea. In Africa the Macacus montanus is
found in Abyssinia, to the height of 8000 feet, and one of the howling monkeys
of America occurs on the eastem side of the Andea, at more than 11,000 feet
elevation. 146 Distribution of Cabnivoea. — The Carnivora are so important, as
weU by thefr number as in thefr disfribution, that they requfre to be con
sidered in some detaU. The famUies of Carnivora are five — four of them
terrestrial, and the fifth marine. They are divided into sixty-six genera,
and about five hundred and twenty-aix apeciea ; of these the first family, or
bats (Chieopteea), includes two hundred and twenty-four species ; the inaect-
eatera (Inseotivoea), sixty-one; the Plantigeada, thfrty-four; and the
DiGiTiGEADA, one hundred and ninety -five ; the remainder are Amphibia.
The distribution of the Bats is moat considerable within the tropics, where
there are seventy -two apeciea in Aaia, forty-one in Africa, and fifty-five in
America, vrithout including the apeciea in New Guinea and the ialandla of the
Pacific, which number twenty-five species. The most extensive genus (that
including the common bats of Europe) is also the most widely distributed,
ranging from the Arctic cfrcle to the extremity of AuatraUa, and alao into
South America.
The Insectivora are pretty generaUy distributed throughout the great
continents, but are entirely absent in the islands of the Pacific Ocean,
aa2

356 PHYSICAL GEOGRAPHY.
including AustraUa, and in South America, below the tropics. The greatest
number of species (twenty-five) occur in fropical Africa, but there are fifteen
in tropical Aaia, and four in tropical America. The shrews are found
throughout, and the hedge-hogs almost so ; the moles are pretty general in
north, temperate, and arctic climatea, but are almost entfrely absent in the
fropics. Generally, the Insectivora are remarkable in not foUovring the
general law with regard to Carnivora, that of increasing and attaining all
their marima in tropical climates.
The Plantigrades, Uke the Inaectivores, are abaent in the ialands of the
Pacific, in Auatralia, and temperate South America, but differ remarkably in
thefr tropical distribution, only two species occurring in Cenfral Africa, while
twelve fropical species are American, and eleven Asiatic. The bears are the
more generaUy diatributed, and are found throughout ; the gluttons present
the same number of species within the fropica and in the Arctic cfrcle, but
are, with one North American exception, entfrely abaent in the temperate
climatea. The Digitigrades are met with everywhere, the dogs being the most widely
distributed ; the cats are next in importance in this respect (being absent
in AusfraUa and the Pacific Islands), and then the martins and otters must
be mentioned. This famUy, although not so numeroua as that of the bats, is
the most important, since it contains the fiercest and strongest of aU the
Carnivora. The moat interesting groupa among them are — Canis (dog), and
Felis (cat) — the former ofwhich, in aome form or other, haa representativea in
every country from the Arctic Sea to the aouthemmost islanda in the Paciflc,
and m the Old as weU as in the New World. Some particular species are
also very vridely apread, the wolf occupying both continents, from the Arctic
Cfrcle to the north coast of Africa and the Isthmus of Panama, extending
eastwards into India, and westwards to the westem shorea of Ameriea.
The fox ranges over the greater part of Em-ope, and almost the whole of
northem Asia; the jackal, the representative species in Africa, extends
from the Senegal to India, and from Abyssinia to southern Euaaia- The
whole fribe is, however, remarkably poor in species in India beyond the
Ganges, and also in the Indian Archipelago, which, in other respects is rich
in Carnivora. The genua EeUs is found in aU parts of the world, except in the islanda
of the Paciflc, Jiipan, and the PhUippines, and the vast expanse of AusfraUa.
The apecies inhaoiting America differ greatiy in appearance from those of
the Old World, and are generaUy smaUer in size. They are also confined to
the eaatern aide of the Andes. The Uon is spread over almost the whole of
Africa, from the Cape of Good Hope to Barbary, but is confined in Asia to
a much smaUer region, not extending beyond lat. 32° north, and chiefly met
with in the jungle counfries of Infia, and the borders of the Euphrates.
The puma, the Uon of America, has a far vrider range, extending from
Patagonia, in lat. 54° South, to CaUfornia on the one side, and the Canadian
lakes on the other, in lat. 50° north, a distance of 7000 mUes. The tiger,
more active than the lion, and nearly equal in sfrength, is very differently
distributed, ranging through almoat the whole of India, Siam, and China,
extending northwarda far into Central Aaia, and southwarda into Sumafra
and Java. The jaguar, or American tiger, haa its prmcipal habitat in BrazU
and Paraguay, but reachea aouthwarda only to the latitade of ChUoe, and doea
not extend northwarda beyond the bordera of Mexico.
The vertical disfribution of the Carnivora is, of course, very different in
different zonea of latitude. In Europe, in the Alps, the bata range to about
8250 feet, several species occurring at that elevation. The hedge-hog,
amongat Insectivora, is met with at the same height, but the shrewa a httie
lower. The black and brown bear are found in the Alps, between 5000 and
8000 feet, and the Pyrenean bear at neai-ly 9000 feet. The stoat (ermine),
amongst Digitigrades, has been mot with at the height of 9600 feet. The
martin, the wolf, the otter, the wild cat, and the lynx ascend in the Alps to

DISTRIBUTION OP ANIMALS IN SPACE. 357
about 8000 feet, and in the Pyrenees a Uttle higher. In Northern Europe,
the glutton and the wolf ascend the higheat of the Scandinavian Alpa, from
whidi the latter animal frequently deacends to the plaina, when the mountains
are covered with snow.
In fropical Asia, one species of bat ascends to the height of 9600 feet ;
a apeciea of weaael occupies a heightof 8000 feet; the tiger rangea, in Java and
Sumatra, from the sea-shore to nearly 4000 feet above it, and on the continent
of India pursues its prey to an elevation of 9600 feet, where vegetation loses
ite fropical character. This animal, as well as the leopard and panther,
frequent the naked, woodless, table-lands of Thibet, at a height equivalent
to that of Mont Blanc. In fropical Africa, the Uon of the Cape dweUs on
table-lands, at an average height of nearly 5000 feet above the sea ; and, at
the same elevation, one of the hyenas (H venatica) pursues not only the
antelopes, but even the lion and panther, attacking them in herds, and over-
powermg them by numbers. In fropical America, the bear lives at 16,000
feet above the sea, on the confines of the snow-line ; the puma rangea in
the CordUleras of ChiU, to the height of 11,000 feet (also cloae to the anow),
whUst, in Peru, the jaguar scarcely attains the height of 3000 feet, although
the ocelot is met with at double that elevation.
The Amphibia, being marine animals, obey laws of distribution very
distinct from those to which the land quadrupeds are subject, and may be
more conveniently considered afterwards.
147 Distribution of Eodeniia. — There are in aU six hundred and four
species of Eodents recognised and described, which are grouped into ninety-
five genera, and these again into four principal famiUes — namely, the squirrel
family (including also the beaver), the rat family, the porcupine famUy, and
the hare famUy. In aU these, the species of the same group generally have
a wide range in the same zones of climate, except when they are inhabitanta
of high ridges of mountains, in which case they foUow the course of the
mountaina, even when, aa in tbe Andes, these run from north to south. There
are also examples of groups, for the most part confined to high latitudes, but
re-appearing in low latitudes at considerable elevations. It is also worthy of
remark, that the great mass of the South American Eodents belong to a
group, naturaUy distinct from and of lower organization than the mass of the
species in the Old World, and the northern parts of the New.
Ofthe squirrel famUy, (153 Species,) as many as ninety apecies are tme
squfrrels, ofwhich thfrty-two are East Indian, twenty-four North American,
twelve from Aaia, (excluding the East Indies,) eleven Central and South
American, and only two European. Of the genus Pteromys, (flying squirrels,)
almoat aU the apeciea are confined to Eastern Asia and the Indian Islands,
and the rest are North American. Africa is remarkably poor in aU kinds of
squirrela, having only eighteen apeciea, aixteen of which are true squirrels,
and two referred to a genus which has no other representativea. The Beaver,
the only other well-known and intereating rodent of this famUy, except the
marmot, preaenta two apeciea, the European and the North American beaver.
The former is found in the rivera of temperate and Northern Europe and
Aaia, between latitude thirty-aix degreea and aixty-aeven degrees ; the latter
ranges on both sides of the continent of North America, but chiefiy on the
eastem side, between the northem limits of tree vegetation, and the con
fluence ofthe Ohio with the Missiaaippi river. The Marmots are conflned to
high mountain localities, or nearly so, and are found in the Alps, in Poland,
and Euaaia, in Europe ; in the hiUy region of Nopaul and Thibet, and also in
the valley of Cashmere, in Aaia ; and in America, from the aixtietii paraUel of
latitade, on the Eocky Mountains aa far as Texas.
The Eat famUy contains 306 acknowledged species, 195 occurring in the Old
World, and 114 in the New. Of aU the genera, the common rat is at once
the moat numeroua and the moat widely diafributed ; its seventy-five species
being distributed in pretty equal proportions through every zoological region
on the globe ; one of them, the common brown rat, occurring in aU parts of

358 PHYSICAL GEOGRAPHY.
the world ; others, auch as the black rat, the field mouse, and the harvest
mouse, extend through Europe ; the Barbary mouse, and another species,
through North Africa ; several others occur in South Africa, and otners in
various parts of Aaia. The apeciea peculiar to Central and South America
are, however, very few, even these being doubtfully ascribed to the genua.
Of the other genera of this famUy, the common dormouse (Myoxus) occur
throughout the southem and westem parta of temperate Europe, and other
species in Africa and Asia Minor. The Jerboa has a range extending from
North Africa into Eastem Europe, and Weatem Asia. The Hamster is
another animal limited in pretty much the same way, but not extending to
Africa. Beaidea the recogniaed animala of thia group, there are a number of
species found in South America, which have been doubtfully ascribed to it,
and requfre further examination. The group of Voles (Arvicola) axe also
interesting, and widely spread. The water vole, or water rat of England, is
found throughout Europe and Northern Asia, extending eastwards as far aa
the river Lena, in Siberia, and northwards to the Ajctic Ocean. Other
species are found in most of the countries of Europe and Northem and
Western Asia, and there is also a considerable number peculiar to North
America. The Lemming is a curious genus, confined to the polar regiona of
both hemispheres, and the countries immediately adjacent.
The third famUy of Eodents includes the common Porcupine of Europe,
and some other genera spoken of under the same name, such as the Canada
porcupine, and the prehensUe porcupine. The ffrst named ia indigenoua in
Southern Europe, Asia Minor, and Northem India, but it occura also in
Barbary, and re-appears at the Cape of Good Hope. The Canada porcupine
ia a widely apread North American repreaentative, and the prehensUe porcu
pine extends from the north coast of South America, as far south as Bohria.
Belonging to tbe same famUy, we have also the Agouti, a weU known
BrazUian genus, and the spotted cavy, found throughout the whole of South
America, as far down as Paraguay. The Chinchilla, the Biscacha, the
Guinea pig, the Capybara, and many other animals are also referred to it ;
and, indeed, in the New World, we have as ma^ as seventy-seven species,
instead of the six found in the Old World. This important fact in the
distribution of the Eodents is weU worthy of observation.
The fourth and laat famUy of Eodenta preaenta only two genera, the Hare
and the Lagomys. The varietiea of tbe common hare and rabbit, and the
speoiea of the same genus moat nearly alUed, may be said to inhabit the north
temperate portiona of the eastem hemisphere generaUy, some being confined
to the warmer parts, but others ranging quite up to the Arctic Cfrcle. Some
species occur also in India, others in North Africa and E^pt, others in Asia
Minor, Sjrria, and Arabia, and others again at the Cape of Good Hope. There
are in aU twenty -two species distributed in this way, and fourteen in various
parts of North America, from the Arctic Cfrcle to Texas. One species only is
met with in South America, and this ranges throughout BrazU, and extends
to Peru, Bolivia, and Paraguay. The genus Lagomys, is, with one exception,
confined to the Old World, and chiefly to the northern exfremity of it,
although an 7\merican species is found on the Eocky Mountains, between the
forty-second and sixtieth paraUels.
148 Distribution q/'EiTMiNANTiA. — The animals of this order, which is
one of the most natural and best deflned of all the primary groups of quad
rupeds, are distinguished from aU others by the existence of four stomachs,
arranged for the act of ruminating or ' chewmg the cud.' They are aU essen
tiaUy herbivorous; they have cloven feet ; and it is only amongst them that
apeciea are met with whose foreheads are armed with true horns.* There are
in aU nine genera, repreaented by the Camel, the Llama, the Musk-deer,

* The horn of the rliinooeros consists of parallel horny fibres, scarcely indicated on the
ekuU, and belonging only to thc skin.

DISTRIBUTION OP ANIMALS IN SPACE. 359
the Deer, the Giraffe, the Goat, the Sheep, and the Ox, respectively : they
are most numerous near the equator, but are disfributed over all latitudes in
the northern hemisphere, as far as the Arctic Cfrcle. They are, however,
totaUy absent in AustraUa, New Guinea, the South Sea Islands, and
Madagascar. The greatest number of species of Euminants occur in Asia and Africa,
each of these counfries possessing more than one-thfrd of all the species, so
that, on the whole, the Old World possesaea as many as 128 apeciea, whUe in
the two Americaa tiiere are only twenty-three species.
Of the particular genera, the Camel is a native of Asia, and now extends
over Arabia, Syria, and Asia Minor, to the foot of the Caucasus, the south of
Tartary, and India. It extends alao in Africa, from the Mediterranean to
the Senegal, and from Egypt and Abyssinia to Algiers and Morocco, and it
abounds in the Canary Islands. The Bactrian camel, distmguished by its two
humps, its rougher and shaggier hafr, and sfronger and more muscular frame,
is almost unknown in South-western Asia, but abounds in the countries
north of the Taurus and the Himalayan Mountains, extending, it is said, to
the borders of China. The Llamas, the camels of the New World, present
three species, differing from the true camels, by being much smaUer, and
having no hump on the back. They are cbiefly "distributed on the westem
side of the Andes, extending from Venezuela and New Granada, through
Pem, BoUria, and ChUe, into Patagonia, and even to the wooded islands of
Tierra del Fuego.
The Musk-deers, of which there are seven species, are distributed in
various parts of Asia, chiefly south of the Himalayans, but two species are
found in Africa. The whole group ia distinguished by the absence of true
homs. The tme deers have sohd horns or antlers ; they include on the
whole thirty-eight species, twenty-eight of them being found in the Old
World, and of these, twenty-one in the East Indiea. The largest of the
genua, the elk or mooae deer of America, inhabita the colder regions both of
the Old and New World ; the European elk, a distinct species, is found iu the
forest regions of Scandinavia, Eastern Prussia, Poland, Lithuania, and Eussia,
extending eastwards into Asiatic Tartary, and southwards to the Caucaaua ; the
reindeer haa ita southemmoat limit in America, in latitude fifty degrees north.
but ia most abundant between 63° and 66° north latitude. In Asia it traverses
Siberia and Kamschatka, and in Europe is found in Iceland, Spitzbergen,
Scandinavia, and Northem Eussia, but chiefly in Finmark and Lapland.
The FaUow-deer inhabits central Europe, aafar aa flfty-three degrees north
latitade, but extends alao to the north of Peraia and China, and ia found in
the northem part of Africa, aa far south as Abyssinia. The common stag or
red-deer is also a native of the temperate countries of Europe, but ranges ten
degrees farther north than the faUow-deer, and has not been found south of
the Caucaaua. It occura in Siberia, from the Altai Mountaina to the Lena
Eiver. The roebuck ia also vridely diafributed in Europe, as far as fitfty-eight
degrees north latitade, and in Asia, eastwards to the Eiver Lena, and south
wards to Peru ; it is common in the north of England, and in the north of
Scotland, but is uiiknown in Ireland. In North America there are six apecies,
and in Central and South Anierica eight, one species being common to the
two Americaa. The moat remarkable is the Vfrginian deer, which ranges
from Canada, as far south as Lomsiana.
The Gfraffe is an isolated genus exclusively confined to Africa. There
are two species, one inhabiting Nubia, Abyssinia, and the countries near
Lake Tchad, the other a southem species, found in south lat. 29°, near the
Orange and Lion Eivers. Africa is alao the head-quartera of the Antelopea,
containing thirty-four apecies, whUe Asia has only ten, Europe two, and
America one. 'The European antelope, the Cha/mois, inhabits the alpine dis
tricts of Europe and Westem Asia, being found in the Alps, Pyrenees, the
Tafra, the mountains of Greece, the Caucasus, and the Tauras. The Goats,

360 PHYSICAL GEOGRAPHY.
like the European antelopes, inhabit alpine countries, and of these the Ibex
is well known, and ranges even to a greater height than the chamois, being
found occasionally even above the snow line. The greatest numberof species
of the goat famUy are Asiatic, and only two are met vrith in the New
World. The Sheep are considered to have inhabited origmally Westem Asia.
There are in all twenty-one species, thirteen of them Asiatic (excluding the
East Indies), and five East Indian, there are also two in the Eocky Moun
tains of North America. In a domesticated state they have been introduced
into most parts of the civilized world. The Bovine tribe (oxen), of whieh
there are thfrteen species, comprise the largest of ruminating animals, and
are widely distributed over most countries of the globe. The Buffalo, long
known as a domesticated animal in India, has spread westwards to the westem
extremity of Europe, and eastwards to the islands in the Pacific Ocean. The
Cape Buffalo is a much more ferocious animal, wandering in large herds over
extensive disfricts in South Africa. The two American species, the bison
and the musk ox, are both confined to North America, the former extending
from New Mexico and California to about 64° north latitade, while the latter
is peculiar to the frozen regions of the continent, its southem range com
mencing where the bison terminates, and extending thence over the barren
regions of the Polar disfricts to MelvUle Island, thus attaining vrith the
rein-deer the highest latitude of any known species of ruminant.
The vertical diatribution of ruminants is not uninteresting, the Chamois
and Ibex reaching in the Alps to the snow Une (8900 feet), while oxen graze
and sheep pasture within a thousand feet of this elevation. The common
stag in the same parts of the counfry reaches only to 7000 feet, and the
fallow-deer to 6000. In the table-lands of Central Asia, the goate and sheep not
only reach the height of from 10,000 to 16,000 feet, but one species is described
as bounding Ughtly over the encrusted snows of tbe higher ridges of the
Himalayan Mountains, where its human pursuers find it difficult to breathe.
Another species, the Yak, seems actuaUy limited to districte where the
temperatare is below that of the freezing point of water, and even the Bactrian
camel attains in the table-landa of Cenfral Aaia a height at from 3000 to 5000
feet above the sea. In South America, the Llama inhabite the bleak and
rocky precipices ofthe Andes and regions bordering on the limit -of perpetaal
snow. In the cold cUmate of Patagonia these animala approach the vicinity
of the sea, but further north large herds attain (as on Cmmborazo) a height
of 15,800 feet, and on the BoUrian Andes an elevation of 18,000 feet.
149 Distribution of the Pachtdbemata. — Of this famUy there are nine
genera containing thirty-nine species. Only one species (Sus — ^the swine) ia
indigenous in Europe, whUe nineteen are Asiatic, tweniy African, and seven
American. Besides the S?rine, the Asiatic genera includea the Elephant,
Ehinoceros, Tapfr, and Horae, and to these in Africa are added the Hippo
potamus, Hyrax, and Phascochoerus, whUe in America we have only the -
Peccaries and Tapirs. The animala of this order are not only few in number,
but much smaUer in size in the New World than in the Old. In North
America they are totaUy abaent, and so also are they in AusfraUa. On the
other hand, m Africa they are singularly abundant, and highly characteristic.
If we refer to the particular genera, we find the Elephant inhabiting the
whole of the peninsula of India, the Birman Empire, and Siam, extending
alao to Cochin China. It aacenda the Himalayan Mountains to the height 01
6000 feet, and reaches southwards to the exfremity of Sumafra, although it
has never yet been proved indigenous in Java or Borneo. The African
species reachea from tlie Mountaina of the Moon nearly to the Cape of Good
Hope, thua ranging in the weatern part of the Old World from 31° aouth
latitudo to 13° north, nnd in the eastern part from 6° south latitade to about
30° north. The Hippopotamus at present extends from the Orange Eiver,
near the Cape of Good Hope, to the upper Nile in Dongola, and occaaionaUy
still farther north. The Ehinoceros is more subdivided into species than the

DISTRIBUTION OF ANIMALS IN SPACE. 361
elephant or hippopotamus, there being four African and three Asiatic ; it is
conflned to nearly the same Umits aa the elephant, but extenda a little
farther north into China, and also into Java. The common or one-horned
African species, and the corresponding one-horned species in India, are the
most widely distributed, the others are smaller and chiefly found in the
interior of the country. The genus Sus (or svrine) is disfributed into three
groups, the European-Asiatic, the Indian, and the South African. The first
contains only the common swine, which ranges from the shores of the
Atlantio to the Pacific, extending westwards from the borders of the Sahara
to the Baltic prorinces of Eussia, and eastwards from the Gulf of Tonquin to
Lake Baikal in Siberia. The other species are far more narrowly distributed,
one of them forming a passage to the Tapfrs, and another nearly confined to
South Africa, and extending into Madagascar, where it is the sole repre
sentative of the whole fribe.
The Hyrax (daman) is a singular and interesting genus of pachyderms,
approaching the rodente in some respects, and at present only known in
South Africa, in the counfries bordering the Nile, and in Syria. The
Phascochcerus (warthog) is also exclusively African, inhabiting the coimtry
between Abyssinia and the northem exfremity of the Cape Colony, and rare
even vrithin these Umits. The other Pachydermatous group of the Old
World ia that which includes the Horse, the Ass, and tiie Zebra. It ia not
possible now to determine the original Umita of the teue horse, though it
appears to be a distinctly Asiatic species. The ass seems characteristic of
Cenfral Asia, and the zebra is pecuUar to Africa, where there are several
species ranging southwarda aa far as the Cape of Good Hope.
The only remaining Pachyderms are the Peccaries and Tapirs, the former
abaolutely confined to South America, the latter chiefly characteristic of that
continent, but not uncommon in the islands of the Asiatic Archipelago. The
Peccaries inhabit denae forests, and extend from the peninaula of Yucatan
in Cenfral America to Paraguay, cUmbing the eastem alopes of the Andes to
the height of six thousand feet. The common American tapfr is met vrith
from Nicaragua (latitade 14° north) to the Pampas of La Plata, in latitude
40° south, and aacenda the Andea to as great a height as the peccaries.
Another species inhabits chiefly the most elevated parts of tiie Andes of New
Granada. igo Distribution of the Edentata and Marsupialia. — Of tiie former
of these remarkable groupa there are six recognised genera, four of them
confined to the New World, one occurring only in Africa, and one (Mamis)
reaching into Asia. South America contains three times as many species as
aU the remaining countries of the World, and ia in every respect the metro
poUs of the order. We ahaU see also in a future chapter that this distribu
tion has long obtained.
The prindpal genera ofthe Edentates are the Sloths, the Armadillos, and
the Ant-eaters. The former rangea from the southem Umite of Mexico as far
south as Eio Janefro ; and from the eastern coast to the slope of the Andes
there are four species, aU inhabiting the frees of the gigantic and primeval
forests of those countries. The armadiUos, ofwhich there are eleven species,
range in Uke manner through Central and Southern America, they vary in
their habits, Uving in the plams as weU as on the table-lands, and extending
into the lower regions of the Andes to the height of about 3000 feet. There
is one remarkable and closely alUed genus (Chlamyphorus) inhabiting ChUi
and La Plata, and intereating from the enormous atrength exhibited in ao
smaU a frame. The American ant-eaters, the largeat of the Edentata, are leas
widely distributed than the sloths and armadillos, both in vertical and hori
zontal space.
The Edentates of the Old World number only five apeciea in aU. The
African genua includes one ant-eater (Orycteropus) very different from the
American species, and extending from the Cape Colony to Congo. The
Pangolin, or scaly ant-eater (Manis), has fom' species, and ranges from the

362 PHYSICAL GEOGRAPHY.
Senegal in Africa, in a narrow band southwards to the equator, occurring
also in North-eaatem India, and thence eastward to Formosa, and in the
islands of Sumafra, Java, Borneo, and the Celebes.
As South America is the country of the Edentates, so on the continent of
AustraUa and its adjacent islands we find the great majority of the Marsupial
tribe, although of these also a few representative forma have been found in
America. The whole order has been divided into eight famUies, which present
a remarkable diversity of structure, and consequently of habit, some species
amongat them being herbivorous, aome carnivorous, and others insectivorous.
AU, however, present the striking pecuUarity of the order — ^namely, the pre
mature bfrth of the young, and the existence of a kind of bag or pouch,
situated beneath the beUy of the female to receive them at thia period, and
retain them for a considerable time even after they have grown to a large size.
The Ornithorhynchus and Echidna, two of the most remarkable animals
known, form one group of the marsupials, and are almoat confined to South-
eaatern AuafraUa and Van Diemen'a land. The Kangaroo family, whichnmnbers
not fewer than forty apeciea, are very vridely diatributed in Ausfraha and New
Guinea, and have been said to occur in Java. The Wombats, ofwhich there
are two species, are found chiefly in the southem and eastem part of Ausfrsilia
and Van Diemen's land. The Phalangers are vridely distributed not only in
AustraUa but in New Guinea, and many of the Asiatic islands, extending even
to the Celebes. The Dcmjuridie (including the Thylarinus, or Ausfraiian
dog) are limited to New South Wales and Van Diemen'a land, while the
Opossums are an excluaively American famUy, extending from the southem
Umita of Canada to the thfrty-aixth paraUel of aouth latitade. They are
nearly conflned to the eaatern side of the continent, and one, a Brazilian
species, Uves in the water. The whole number of species of marsupials may
be estimated at not leaa than 126 ; and the group found in Ausfraha is the
more important from the absence in that country of other mammals, and the
number of representative forms of various tribes which it includea.
151 Distribution of BiEDS. — ^Bfrds, Uke other Vertebratea, exhibit the
greateat number of species in the fropical cUmates, with the partial exception,
nowever, of the continent of Europe, which contains 490 apecies, whUe,
although fropical America haa 624, fropical Aaia preaents only 450, and
Africa only 211. North temperate America affords in aU 178 species, and
the north frigid zone in America as many as 103. There are, also, other
apparent anomaUes when we examine the different orders in detaU ; as, for
example, there are 186 European species of Oscines (singing-bfrds) and 112 of
Natatores (swimmers), whUe in fropical America there are 319 of the former
and only 26 of the latter group. Europe and tropical America possess the
greatest number of bfrds of prey, and the cUmbers and songsters are most
abundant in the latter country. Tropical Asia presente the greateat number
of Gallinacece, and Europe the greatest number of waders and swimmers.
If we take the particular genera, we flnd amongst the bfrds of prey the
Vulture tribe the most remaMable, and the largest of aU flying bfrds. The
habitat of the Condor, of which individuals have been found in the Andea
of Quito measuring fifteen feet from tip to tip of the vrings, is exclusively
confined to the vicinity of the Andes, and breeds at an elevation of from
10,000 to 15,000 feet above the sea. Humboldt, on one occasion, saw this
enormoua bfrd fioating over the aummit of Chimborazo at an elevation of
upwards of 22,000 feet. The species ranges from the Sfrait of Magalhaens
to 7° north latitude. Of the other vultures several are American, and there
are also species dispersed through Africa and India. The bfrds of prey of
Europe include five vultures, thirty-four hawka, and fifteen owls, many of
them extending into North Africa and Asia. The greater number of speoiea
occur in the south of Europe, and as many as twelve range through various
parts of tho Alps. These include one vulture, two eagles, five hawks, and
four owls.
The order of eUmbiiig birds, including the parrots, cuckoos, king-fishers,

DISTRIBUTION OP ANIMALS XN SPACE. 363
and others, are chiefly confined to the fropical zone ; but they also occur
abimdantly in the southern hemisphere, vmere they extend to very high
latitadea, reaching even beyond New Zealand as far as Macquarie in latitade
56° south. In f£e northern hemisphere they attain in the United States
the latitade of 42° north. Forty apecies are found in the fropical regions of
South America, while only three inhabit the opposite coast of Africa. The
Bfrds of Paradise, a small but very remarkable group, are Umited to a few
islands in the neighbourhood of New Gumea, migrating according to the
monsoons. The Toucans, and some other groups, are also confined within
very narrow Umits. Of European cUmbers there are twenty-three species,
some of them, as the Woodpecker and Hoopoe, ranging throughout the whole
continent, but others more local. Eight of them inhabit or fraverse the
higher parts of the Alps.
Of tiie order of songsters (Oscines), ihe Humming-bfrds, the smaUest and
most brUliant of the whole tribe, are aU natives of America, and chiefiy of
the fropical portions of that country, but they range to the height of 10,000
feet on the Andes, and have been met with breedmg in the Island of Juan
Femandez (33^° S. latitade), and as far north as latitude 61° on the shores of
Behring's Sfraits. Of the 186 «peoies of this order found in Europe, as
many as 100 belong to the typical genus from which the order has received
ite name, and which are aU of them song-bfrds. Forty -three of these extend
into Africa, and ten reach to fropical Asia; there are also ten European
species of Larks; forty- three of Finches, ofwhich one, the common Sparrow,
extends over moat parts of the known world ; twenty-eight Nut-hatchers,
including amongst them aix apecies of Corvus (crow), and five species of
SwaUow. These are aU of them pretty generaUy disfributed throughout
the coimtry, and range alao into the adjoining continents.
The gallinaceous bfrds are far more numerous in the Old World than the
New, the greatest number of species (72) being found in tropical Asia,
and some of these being now domesticated in almost every country. The
Pheasant thus extends, in its natural diatribution, from the Caucaaua through
Cenfral Aaia to China, and southwards as far aa Java; the Peacock is a
native of India ; the Pigeons (of which six species are European) extend into
the two-great continents ; and the Turkey is pecuhar to the New World, its
proper limite appearing to be from the lathmus of Panama to the north
western exfremily of the United States. It does not appear to be indigenoua
on the weatem aide of the Eocky Mountains, or in South America. Only
twenty-eight species of the order are found in Europe, and many of these are
not natives ; but the grouse, the pheasant, the common fowl, the pea-fowl, the
partridge, and many others are ofthis kind, and are too weU known to require
further aUuaion. Two species of pigeon, four of grouse, and two of partridge,
have been found amongst the higher passes of the Alps.
The order Grallatores, or waders, is most abundant in the north tem
perate zone, but by far the moat remarkable species occur in fropical and
southern countriea — thua, the African and South- American Ostrich, and the
Auafralian Emu, aa weU as the Cassowary, are amongst, the most exfraor
dinary, as they are the most gigantic of birds. The former (the ostrich) has
a tolerably wide range, and haa been met vrith to the height of 7000 feet, on
the high plateau of the UspaUata Mountains, in South America. One
South American species extends to 54° south latitade, and the African species
ranges from the Cape of Good Hope to Barbary, and has extended as far as
the southern declivity of the Caucasus, and the shorea of the Black Sea.
The most numerous European genus is that which includes the Snipes, of
which there are thirty-eight species, sixteen of them extending into North
Afiica, and twenty-five into Siberia. The Ibis andthe Flamingo are recognised
species in Europe, but belong to Africa and Asia.
Tbe Natatores, or swimming birds, including the ducks, peUcans,
penguins, guUs, and many others, are, Uke the waders, more abundant in
European than tropical latitudes. There are one hundred and twelve

364 PHYSICAL GEOGRAPHY.
European species, of which forty-four belong to the duck genus, and thirty.
three to the guUs, of each of these more than half extendu^ into Asia. The
Eider-duck is an intereating and important species, chieffy inhabiting the
shores of the Arctic Ocean, and the land immediately adjacent, extending
in Europe to the Orkney Ialanda, and even into Germany, and in America to
the latitude of New York.
The migration of birda is a fact in thefr natural history^ which fbUy
accounts for the vride extent of country over which many species are found.
Some proceed to very distant spota in aearch of food, or at, the breeding
aeaaon, and many of the sea-fowl are found oyer many thousand mUes of
ocean, and are rarely seen to rest, whUe other birda, althongh not naturally
migratory, proceed from one spot to another on the occasional faUure of food
in their natural district. The habits of bfrds in migrating are very different,
some going singly, some in smaU groups, others in flocks of many thouaanda.
When in great multitades, they generaUy have a lea,ier, as in the caae of the
swaUows and martins ; but when the groups are smaUer, the bfrds often fly
in very regular order — wUd geese, for example, in the form of a wedge. The
swift, a remarkable bfrd in its power of suataining rapid and long-continued
flight, ia said to proceed at the rate of one hundred mUes per hour, and the
wUd duck and wUd pigeon four or flve hundred mUes in a day. Migrating
bfrds generaUy retum to the aame apot, within a few days of the same time
of the year, and often occupy the same nest for successive years.
152 Distribution qf Eeptiles. — Of the existing ordera of reptiles, the
Saur-ia, including crocodUes and lizards, number two hundred and three
species; the Chelonia, or tortoises, sixty-nine species; the Serpents two
hundred and aixty-flve species, and the Batrachians (froga), one hundred and
twenty species — making in aU six hundred and fifty-seven. Of this number
more than twice as many are fouud in the countries of the torrid zone than
appear in temperate cUmates. Tbe Chelonia are most numeroua in the United
Statea, where there are nineteen, in Brazil (fifteen), and in the Indian islands
(thirty-three). In Afr-ica (Barhary) there are aix species, and in Europe,
except in Italy and Turkey, only three in aU. Tbe Sauna include thirteen
species of CrocodUea, nine of them American, and four Aaiatic and African.
Tie remaimng Sauria are far more vridely diatributed in Africa and South
America than m the reat of the world, BrazU being the richest in species, and
containing in aU as many as forty-two. Serpents are far the moat abundant
in the East Indies and in Cenfral and South America, and most of aU in the
Island of Java, where no lesa than fifty -aix species have been determined,
whUe in the adjacent Island of Borneo there is not at present a single one
known. The Batrachians are most numeroua in Cenfral and South America,
but thfrty-nine species are North-American, and twenty-three European.
Asia, Africa, and AustraUa show a remarkable absence of the animals of this
order. GeneraUy, reptiles may be regarded as more Umited to warm climates
than any other animals, and better able from thefr sfructare, and the slowness
of thefr cfrculation, to bear the extreme rigour of an excessive climate than
the absence of hot summers that characterizes island countries.
Of the Chelonians, the common marsh tortoise of Europe attains the highest
latitade, extending in Prassia to lat. 52° north, whUe a corresponding species
in North America reaches to 50° north. Some of the sea-turties have been
met with in the northem hemiaphere, even so far north aa the Shetiand
ialanda (lat. 60° 30"), but the uidividual in queation may probably have been
drifted thither by atorms, ita uaual range being only to the shores of France,
to about the fiftieth paraUel of latitude. The species thus obaerved (the
hawk'a-bill turtle), fumiahes tbe homy plates usually known in commerce as
tortoise-shell, but the principal fishery of these ammals is in tbe Moluccas,
and other islanda of the Indian Arobipelago, and the islands of the West
Indies ; the former, however, being the most important, since tbe shell ia
the most valuable. The green turtie, used for food, is a apecies inhabiting
the tropical pai-ts of the Atlantio Ocean, and attaina a large aize, often

DISTRIBUTION OF ANIMALS IN SPACE. 365
weighing six or seven hundredweight. The fresh-water tortoise is very
abundant in North America, where there are fifteen species determined ; the
land tortoises, on the contrary, are chiefly African, although there are several
European species.
The Crocodiles aie divided into three groups — named respectively. Alli
gators or Caymans, tme crocodUes, and Garials or Gavials. The firat group
are exclusively American, and' have a vride range of distribution, extending
from the United States, in lat. 32° 30" north, through Cenfral America, and
southwards into BrazU and Paraguay, in lat. 31° south. They are amphibious,
chiefly inhabiting the estuaries of great rivers, and rarely leaving the fresh
water. They are very fierce, but chiefly prey in the night, and the South
American species are considered less dangerous than those of the Mississippi.
The African crocodUes extend from Congo to Senegambia on the west, and
Egypt on the east, the common crocodUe of the NUe being disfributed
over nearly the whole river disfrict, and throughout Nubia and Abyssinia.
The Aaiatic crocodUe, or Garial, extends from the north-western coaat of
Ausfraha, through the Indian Archipelago to Hindustan, where it is exceedingly
abundant in the Ganges and other great rivers. The Lizards (including the
monitors, iguanas, chameleons, bUnd-worms, and true lizards) range some
what more widely than the former group, and many of them, as the chame
leons and monitors, are absent in America. The Chameleons form an interest
ing African and Asiatic group, extending over many parts of the south of
Europe. The Geckos and Iguanas are greatly multiplied in BrazU, but range
also in other countriea. The Monitora are chiefly Aaiatic ; and one, sometimes
caUed the land crocodUe, chiefly inhabits Africa and the Indian Archipelago.
A neariy aUied genua ia found in Guiana, where it attains the length of aix
feet. The Skinka are diatributed like the Iguanaa, being chiefly abundant in
Africa and South America ; but there are ten apecies inhabiting Europe.
The Serpents are totaUy abaent from the ialanda of the Paciflc, and most
widely diafributed in the adjacent islands of the Indian Archipelago — a very
remarkable fact in the general diatribution of animals. It is also well worthy
of careful attention, that although many apecies of the order are widely
dispersed in various parts of temperate Asia and Europe, no species is
common to Asia and America. AusfraUa is almost vrithout representatives,
(there being only eleven species in aU, and these pecuUar,) and Japan has six
species, also peculiar. America and Asia, between the fropics, preaent by far the
largeat number of apecies, and Africa is remarkably poor in species, although
the few that there are seem very widely spread. Of the two divisions of
serpents, the harmless and the venomous, the number of species of the former
ia three and a-half timea as great aa the latter, but vrith the exception of
weatem Europe and Madagaacar, scarcely any country is without some
apeciea of both.
The Frogs extend further than any other reptiles towards the polar
regions, reaching in Finland nearly to the Umit of perpetual ground-frost.
In the New World, however, some of them extend even beyond this line in
Greenland and British America, existing on the bank%of the Mackenzie
Eiver, up to the sixty-seventh degree of north latitude, where the mean
temperature is not more than seven or eight degrees Fahrenheit, and where
the cold in winter is so excessive, that the thermometer sometimes sinks to
more than 90° below the freezing point of water. In the southem hemisphere
a frog was found by Mr. Darwm in latitade 50° south, on the banka of the
river Santa Cruz.
Within the fropics Crocodiles and Boas are found on the Andes of Quito,
at an elevation of 3000 feet ; and a remarkable reptile, the Axolotl, occurs in
Mexico at the height of 8000 feet. In the Alps there is a frog Uving in
the vicinity of the snow-line, and various other reptUes of the same order
between 4500 and 6000 feeti In the Pyrenees, the common frog is found at
8000 feet.
If we take the distribution of individuals we shaU find by far the most

366 PHYSICAL GEOGRAPHY.
abundant locaUty to be the Island of Java, after which BrazU, the southem
States of North America, the Island of Sumafra, the Celebes, Egypt, South
western Europe, and North-eaatem India may be mentioned aa the places
where reptUes chiefiy abound.
iS3 Distribution ofthe Maeine Veetebeata. — This group includes the
whale tribe, the seals, and a single genus of reptUes, in addition to the vaat
and important claaa of true fiahes. The whalea form two groupa, the herbi
vorous whales (^eLamardin and Dugong) and the ordinary whales, including
the Dolphin, the Porpoise, the Narwahl, the Cachalot, and the Balama, or
Whalebone whble. All theae suckle thefr young. The lamantin, or sea-cow,
is chiefly Umited to the mouths of rivers m the hottest parts of the Atlantic
Ocean, the American species being distinct from the Amean, but both occa
sionaUy attaining the length of fifteen feet and upwards. The dugong inhabits
the Indian Ocean, and there ia also an aUied genus found in the Pacific. The
spouting whales are very widely spread through the various parte of the
great ocean, but there is no famUy of mammaUa more difficult to obaerve, in
spite of thefr frequently gigantic size. Amongst them the dolphin is seen in
almost every latitude, and the porpoise is ahnost as widely spread, bnt par
ticular species appear to be, and probably are, very much more limited. The
Grampus is the largeat species of this group, and abounds both in the
Atlantic and Pacific Ocean. The Cachalot and Balsena are, however, much
larger, attaining the length of from sixty to seventy feet, and the Eorqual (a
whalebone wrhale) has been met vrith having a totsil length of as much aa one
hundred feet. The former appears to range from the limite of the Arctic
nearly to the Antarctic Ocean, but thefr chief resort is in the deepest parts
of the warmer seaa near the tropica. The whalebone whales are chiefly
found in the colder seaa, but appear to travel to warmer latitadea in aearch
of food. The Seal tribe present a number of species of which the common seal and
the morse are the best known; they are both chiefiy confined to the polar
seas and desert islands in high latitudes, but some of them have a very wide
range, especiaUy in the southem hemisphere.
The distribution of the frue fishes, Uke that of the marine mammalia, is
chiefiy known aa far only as regards the species used by man. Thus, the
cod, the herring, the salmon, the pUchard, &c., have naturaUy atfracted
attention, and thefr habits of migration and the nature of the spots they
select for feeding ground, are tolerably weU known, but of the vast multitade
that herd on the various shores of the different counfries in the world, or
that dweU concealed from observation in the deeper parta of the open ocean,
it is scarcely possible to determine at present their true geographical or
climatal Umits, or the law of .thefr disfribution.
Of the varioua natural tribea of these animals, some are certainly migra
tory and some conatantly confined to narrow limite, but the greater number
have a wide, although by no means indefinite range. The former pass from
one ichthyological province to another, according to the season and the
abundance of food, or the necessities of breeding; but these provinces,
although indicated, have been only partiaUy determined. The most exten
sive includes about forty degrees of latitude on both sides of the equator, in
the Pacific, and this ia fianked by the northern and aouthern portiona of the
great ocean. The Atlantic presente a similar division, and there are many
local and peculiar marine faunas in the great bays and gulfs near the mouths
of great rivers, in the principal inland aeas, and in the various rivers
themselves. Somewhat more than eight hundred and fifty apeciea of fishes have been
described from European seas, rivers, lakes, and coasts, of which two
huudred and ten inhabit fresh water, and of the whole number two hun
dred and sixteen are Britiah, and as many as four hundred and forty-
four of the marine species are Mediterranean. Comparatively few of this
number extend to America, stiU fewer are foimd m the Eed Sea, and

DISTRIBUTION OF ANIMALS IN SPACE. 367
scarcely any reach to the Indian seas. It is remarkable, also, that the Black
Sea, which communicates dfrectly vrith the Mediterranean has a distinct
fauna, and the Caspian another, also pecuUar to itself. The great lakes of
Central Asia and of North America, most of the great fropical rivers in both
continente, and many other smaUer areas of water, appear to be more or less
isolated. Although, in number of species, the southem seas of Europe and the
warmer parts of the Atlantic are richer than the more northem disfricts, this
ia by no meana the caae with regard to individuals, or even the fribes moat
uBeful to man; and, indeed, in thia matter, there seema a certain balance
struck between the cold and warm regions ; for whUe Italy and the aouth
supply fruits and vegetables in enormous abundance, the northern shores
and banks are eagerly watched for countiess myriads of fish, which are dried
and exported as food for the inhabitants of warm countries. Thus the banka
of Newfoundland, and the Dogger Bank, in the North Sea, where there is
shoal water and shelter, are crowded with cod in the month of February to
auch an extent, that in the latter locaUty as many as sixteen millions of fiah
have been caught in one place within a few weeka, and in the former, the
produce of the fiahery for a single season has amounted to forty thousand
tons weight. The pilchard, in point of numbers, is still more remarkable, as
it has been eatimated that, on one occaaion, twenty-five mUliona of fish
(ten thousand hogsheads) have been taken on one shore in one port on a
sinrie day.
It ia by no meana the caae, however, vrith theae and many other fishes
which migrate from one sea or part of a sea to another, that they can readUy
fransport themselves to great distances. The confrary is rather the fact, as
the pUchard and the herring are reaUy limited to very narrow areas of sea,
although appearing only at particular seasons, when impeUed by instinct to
the shores for the purpose of spawning; and ao with othera, where the migra
tion is rather in vertical than horizontal space.
The limits of distribution of fish in vertical space seem to be very strictly
defined. Some swim always near the surface, and, like the fiying-fish,
appear to rejoice in exposing themselves to the afr, whUe others are still
more nearly amphibious, and, Uke eels and an Indian species of perch, can
transport themaelves for some distance on land, or attach themselves to the
shelter afforded by particular trees growing near water. Others, again, are
httoral, inhabiting shores in moderate depth of water; but others, although
found near shore, are, like the plaice and many fiat fish, always buried in
the mud or moving at the bottom. Many others, again, rarely or never
approach the shorea, but remain constantly in deep water ; amongat theae
are the aharks. Mr. Yarrell has remarked, ' that those fish which swim
near the surface of the water have a high standard of respfration, a low
degree of muscular irritability, great necessity for oxygen, die soon — almost
immediately when taken out of the water — and have fiesh prone to rapid
decomposition. Mackerel, salmon, trout, and herrings are examples. On
the confrary, those fish that Uve near the bottom of the water have a low
standard of respfration, a high degree of muscular irritabUity, and less
neceaaity for oxygen; they austain life long after they are taken out of the
water, and thefr flesh remains good for several daya. Carp, tench, eela, the
different aorts of skate, and aU flat fiah may be quoted.'*
With tenacity of life is connected the exfraordinary power observed in
aome fiahea of enduring exfremes of temperatare, and thus the gold fish, a
native of China, not only Uves, but thrives to excess, in water whose, tem
perature is constantly as high as eighty degrees Fahrenheit. Other species
have been found in hot springs in various counfries whose temperature
ranges between 110° and 130° Fah., and Humboldt and Bonpland perceived

* Yarrell's Britisli Fishes, 1st edition. Introduction, p. xiii.

368 PHYSICAL GEOGRAPHY.
fishes thrown up aUve from the bottom of a volcano, in South America, along
with water and heated vapour, the thermometer showing a temperature within
two degrees of the boiling point of water. The enduring power of fishes with
regard to cold is, perhaps, stUl more remarkable, for Mr. Jesse speaks of a
gold fish frozen with the water, in a marble basin, into one solid mass of ice,
and yet, within a few hours of the ice having been thawed, the fiah recovered,
and was soon as Uvely as uaual. The carp alao, to which the gold fish ia nearly
alUed, is well known to have remarkable power in this respect ; and perch, as
well as other fishes, are weU able to sustain the congelation of the water
surrounding them, vrithout permanent injury.
154 Distribution of the Inveetebeata and AETiOTri.ATA. — The Inverte
brate animala are not lesa remarkable in thefr peculiarities of habit, and the
limitation of their nataral range, than the more highly organized groups
afready considered ; and though aome of them, as the Sepias, or cuttle fish,
range freely in all parta of the ocean, or hke the butterflies, flit about in the
afr and proceed Uke bfrds to distant countriea, others are far more Umited, and
exhibit few capabUities of extenaive or distant range. Thus, whether we con
sider the flying species, those which inhabit the surface or soU of the land, or
the enormously larger and more important group, the marine invertebrata,
we everywhere find natural limits of range, botii in horizontal and vertical
space, the increase of depth in the sea answering to greater elevation on land.
The Articulata, including insects, crustaceans (crabs and lobsters), and
worms, are distributed in comparatively narrow and limited areas, so that a vast
number of apecies have been determined, often differing very shghtly from each
other. In high latitades, insects are very few, both in apecies and indiriduals,
except during the short summer period, wtien certain tribea, as mosquitoes,
fleas, and others, multiply with enormous rapidiiy, and prey upon aU larger
animals. In North Europe, and, indeed, in Europe generaUy, the number of
species is much larger, and the variety far greater, and this increases as
we advance towards the equator, but diminishes again in fropical Africa,
whUe South Africa, the African and the Indian islands, are aU richly suppUed
with these animals, althongh by no meana to such an extent aa Cenfral
America, which perhapa in some parts may be regarded as the tme mefro-
poUs of the class. Beetles, however, generaUy, are much more abundant in
temperate than in fropical climates, and this is especiaUy the case in the
northern hemisphere.
The causes that seem chiefly to affect the distribution and range of
insects are — first, food ; secondly, temperature ; thfrdly, prevaiUng wmds ;
and fourthly, elevation above the sea. With regard to the first, aa aome
insects feed upon Uving vegetables, these are necessarUy limited to the range
of such plants, and uauaUy become infroduced by man into thoae distant
countries into which the plants are conveyed. More than two-thfrds of the
whole number of species are conaidered to be thus dependent dfrectiy on the
vegetable kingdom. Temperature also acts indfrectiy by modifying the
nature and amount of food, and in this way, aa weU as by immediate action
on the animals themselves, produces a conaiderable change. It ia, however,
pretty certain that extremea of temperatare have chiefiy to be regarded in
considering the dfrect action of climate, as where tiiere is considerable summer
heat many of theae creatures wUl easUy vrithatand the action of the greatest
reduction of temperature, even in the polar regions. The common mosquito,
the flea, and the common fly, are examples of this.
Mountain chains form natural barriers to the passage of most kinda of inaecta.
As an example of the extent to whieh insecte are sometimes multiphed;
and, therefore, of the way in which they may be said to affect the aspect of
any fauna, we need only refer to the foUowing account of the condition of
some of the great rivers of fropical Anierica, and the swamps near thefr
mouth. According to Humboldt, ' there is no rest in theae apots at any
hour of the day or night, or at any season of the year, so that whole districts
are absolutely "left desert from tbe impossibUity of enduring life under such

DISTRIBUTION OF ANIMALS IN SPACE. 369
torture. New species foUow one another with such precision, that the time
of day or night may be known accurately from their humming noiae, and
from the different sensations of pain which the different poiaoua produce.
The only reapite ia the interval of a few minutea between the departure of
one gang and the arrival of thefr successors, for the apecies do not mix. On
eome parte of the Orinoco, the afr is one dense cloud of poisonous insects to
the height of twenty feet. It ia singular that they do not infest rivers that
have black water, and each white sfream is peopled with its own kinds ; though
ravenous for blood, they can Uve without it, as they are found where no
animals exist.'
In BrazU, the quantity of insects is ao great in the woods, that thefr noise
may be heard in a ship at anchor some distance from the shore. The torrid
zone not only produces the most noisy, but the most brilliant and the most
powerfiU insects. Amongat the former are the butterflies of Africa, the East
Indies, China, and America, which rival the lustre of metals in thefr colours ;
and here also the forests, peopled witb mUUona of fire-fiies of various kinds,
present to the eye an appearance almost Uke that of an immense confiagra
tion. The Termes, or white ants of Africa, buUd soUd hUlocks, and in the course
of an incredibly short time can remove every particle of fiesh even from the
carcass of an elephant; they are so destmctive in South America, that there
is said to be not a manuscript in that country a century old. Spiders also,
although there are more species in Europe than elsewhere, attain a gigantic
size only in hot counfries, where, as in Guiana, a species is found large enough
to catch and devour bfrds.
The migration of insects, Uke that of bfrds, is necessarUy obscure to a
certain extent, but fribes of Locusts are known occasionaUy to transport
themselves from one counfry to another, in a maaa ao denae and ao large as
to form a visible cloud in the afr, darkening the aun'a Ught, and making with
the beating of thefr wings a sound which is said to resemble the distant
murmur of the aea.* The main body when thus compacted, sometimes
proceed to great distances, crossing the Mozambique Channel from Africa to
Madagaacar (a distance of 120 mUes), and proceeding occasionaUy from Barbary
into Italy. Many other inaecta are remarkable alao for the great diatancea
of thefr fiight, and the vaat multitudes coUected together for thia purpoae.
The Crustaceans, which are alao Articulata, include a number of marine
speciea, cbiefly httoral, beaidea many from the freah water, and some that are
terrestrial. In the Polar seaa they are found in great abundance, though the
number of apeciea ia very limited ; and in the equatorial regions, whUe they
are no less numerous, they preaent a greater diversity of form, attain a
larger size, and exhibit in the highest perfection those peculiarities of
atmcture by which the several groups are characteriaed. The Land-craba are
chiefly remarkable in the table-lands (Ghats) of the peninaula of India, and
in the Weat Indies. In the former country they arc troublesome, and
indeed dangerous, by thefr extensive burrowings, but in the AntiUes are
eaten as food.
The Annelids, like the Crustaceans, include inhabitaints of the land, of
fresh water, and of both ahaUow and deep ocean. Some alao, as the Earth
worms, Uve permanently beneath the aurface of the Earth. They occur in
aU climates, but are not able generaUy to wander far from the specific cenfre
to whieh they belong. The marine species are chiefiy httoral.
155 Distribution of the Mollusca and Eadiata. — The MoUusca are
regarded as, on the whole, of lower organization than the Articulata, although
they include amongst them one group (Cephalopoda) which approaches the

* ¦ A fire devoureth before them ; and behind them a flame bumeth : the land is ae the garden
of Eden before them, and behind them a desolate wildemess ; yea, and nothing shall escape
them. . . . Like the noise of chariots on the tops of mountains shall they leap, like the noise of
a flame of fire that devoureth the stubble, as a strong people set in battle array.' — Joel, ii 8 — 5
BB

370 PHYSICAL GEOGRAPHY.
Vertebrata very closely. They are chiefiy marine, although there are many
fresh-water and terrestrial species. The aquatic species are found in all
seas from the poles to the equator, but generaUy at moderate depth, some
burying themselves in sand or mud, others in indurated clay, and some bur
rowing into limestone rocks. Many species delight in quiet sunny nooks
on the margin of fresh-water pools, others in rapid and mighty rivers, and
others, again, in the depths of the ocean, but aU are exceedingly dependent
on local condition. We caimot better give an idea of the nature of the
distribution of these and other lower animals, than by quoting the foUowing
summary from the admfrable memofr by Profeaaor Edward Forbea on the
jiUgean Invertebrata.* Profeaaor E. Forbes divides the portion of sea to
which his observations were chiefiy confined into eight regions of depth,
each characterised by its pecuUar fauna ; ' certain species in each are found
in no other, several are found in one region which do not range into the
next above, whUst they extend to that below, or vice versd. Certain
species have thefr maximum of development in each zone, being most
prolific in indiriduals in that zone in which is thefr maximum, and of which
they may be regarded as especiaUy characteristic. Mingled with the true
natives of every zone are sfragglers, owing thefr presence to the action ofthe
secondary infiuences which modify distribution. Every zone haa also a more
or less general mineral character, the sea bottom not being equaUy variable in
each, and becoming more and more uniform as we deacend. The deeper zones
are greatest in extent, the first or httoral zone extending only to two fathoms,
the second from two to ten, the thfrd from ten to twenty, the fourth from
twenty to thfrty-five, the fifth thence to fifty-five, the sixth to seventy-nine,
the seventh to one hundred and five, and the eighth to two hundred and
thirty fathoms ; below this, at a depth of about three hundred fathoms,
there are supposed to be no Uving animala.' It must not be imagined that
exactly simUar regions are to be met with in every sea, that there are always
the same number, or that the limits of animal life are invariably the same as
iu the .3]gean Sea. We take this as the best example that has been hitherto
worked out, and there is no doubt of there being aome determinable order of
distribution in most other seas, whether confined or open.
The indications as to cUmate or disfribution which may be drawn
from the examination of the Testacea -wiU be found to vary, not only
according to depth, but also from the nature of the ground. A comparison
of the various ammals of the lowest zones with those of the higher, exhibits
also a great distinction in the hues of the speciea ; those from great
depths being generaUy white or colourlesa, whUe those from the higher
regions exhibit more usually brUUant combinationa of colour. The chief cause
of this is no doubt the increased amount of light above a certain depth, but
the nature of the feeding-ground and the food must also exert a modifying
infiuence. Every species has two maxima of development in space, one in depth,
and another in horizontal area ; and in each we find a species at first repre
sented by a few indiriduals, which become more and more numerous tiU
they reach a certain point, after which they graduaUy diminish, and at length
altogether disappear. Sometimes the genus to which the species belongs,
ceases wdth its disappearance, but not unfrequently a succession of sinular
species is kept up, representative, as it were, of each other. When there
is such a representation, the minimum of one species usuaUy commences
before that of which it ia the representative has attained its corresponding
minimum. Forms of representative species are simUar, and often only to be
diatinguished by critical examination. When a genua includea several groups
of forms or sub-genera, we may have a double or friple series of representa
tions, in which case they are generaUy paraUel.

• Reports of tlie British Associatian for tlie Advancemen} ofScimce, Cork, 1848, pp. 1S4 & 172.

DISTRIBUTION OF ANIMALS IN SPACE. 371
' The consideration of the representation in space forms an important
element in our comparisons between the faunas of distinct seas in the same
or representative paraUels. The analogies between species in the northern
and southern, the eastern and westem hemispheres, are instances. But there
is another application of it, which I would make here. The preceding tables
and Uat afford indications of a very interesting law of marine distribution,
probable a priori, but hitherto unproved. The assemblage of cosmopolitan
species at tlie water'a-edge, the abundance of pecuUar climatal forma in the
higheat zone where Celtic apecies are scarce, the increase in the number of
the latter aa we descend, and when they again diminish, the representation of
northem forma in the lower regions, and the abundance of remains of
Pteropoda in the lowest, with the general aspect of the associationa of species
in aU, are facte which fairly lead to an inference, that parallels in latitude are
equivalent to regions in depth, correspondent to that law in terrestrial
distribution which holds that parallels in latitude are representative of
regions of elevation. In each case the analogy is maintained, not by identical
species only, but mainly by representative forms ; and, accordingly, although
we fitnd fewer northem speciea in the faunaa of the lower zones, the number
of forms representative of northern species is so great as to give them a much
more boreal or sub-boreal character than is preaented by thoae regions
where identical forms are more abundant.'*
The laws of distribution of Mollusca and Eadiata are not yet so distinctly
made out as those affecting the Vertebrata generally, but they appear, from
what has been said above, to be of very similar nature. Certain seas present
innumerable multitudes of some species, which do not extend beyond certain
weU-marked, if not narrow Umits ; other seaa are equaUy remarkable for a
mixtare of groups, and an abaence of definite character. These points at
first seem to present difficulties almost insuperable to the proper working out
of the various laws, for the exceptions are both numerous and unexpected.
It is only when we include the element of time, and consider the laws of
succession as weU as distribution, that we find the explanation of such
apparent anomaUes ; and that the apparent disorder and confusion result in
order, and a more diatinct apprehenaion of the unifrv of plan and aystem
throughout nature. We now proceed to examine briefly the evidence of auch
aucceasion and representation in time, and thus connect the present history
of the Earth vrith that past history, which, in the caae of organized beinga,
is now recognised as a distinct science under the name of Palaeontology.

* Professor E. Forbes, ante cit.

BB 2

372
CHAPTEE XII.
DI8TEIBUTI0N OF OEGANIC BEINGS IN TIME.
S 156. Nature of organic remains, and proof of the existence in the Earth's crust of fragmenta
of Plants and Animals belonging to Species now extinct. — 157. Distributiou of extinct
Afammalia in time. — 158. Distribution of extinct Birds. — 1-09. Diatribution of extinct
Keptiles. — 160. Distribution of extinct Fishes. — 161. Distribution of extinct MoUnsca. —
162. Distribution of extinct Articulata. — 163. Distribution of extinct Eadiata. — 164. Dis
tribution of extinct Plants.
l^ATUBE of Organic Bemains, and Proof ofthe Existence in the Earth's
JJl Crust of fragments of Plants and Animals belonging to Species now
extinct. — Moat of the numeroua depoaita met with in different parts of the
Earth are, as we have already intimated, loaded with the remains of plants
and animala of various kinds, but chiefiy those of the sea, accumulated
contemporaneously vrith the inorganic materials of the beds themselves, and
therefore in most cases sfrictiy indications of the actaal condition of the sea
bottom within a given area, and during a limited period. These remains,
therefore, afford materials for a history of the past condition of Ufe on the
globe, and they afford indeed the most distinct information concerning this
history. Tbey are caheA. fossils ; and the use of this word is now limited to
such organic remains, as being of aU things that are dug out of the Earth
those of greatest interest to man in his efforts to penefrate into the past.
The foasUs that have been found appear to be diatinct in aU the esaential
characteristics of species from the recent animals and vegetables of the same
district; and this is the case, whether we regard the Uving representativea,
or those lately embedded in auperficial deposite, or whether we look into
thoae deeper and more metamorphoaed beds, which from thefr poaition
beneath a vaat mass of fosaiUferoua afrata, are manifeatiy of great age when
compared with the existing creation.
Every particular group of deposits in aU parts of the world is more or less
distinctly characterised, not only by ite pecuhar mineral character, but also,
and far more distinctly, by the groups of^ species which together make up its
fossU fauna and flora. These usually differ much less in any two adjacent
conformable beds than in others which are separated by intermediate bands,
whether such intervening maases contain organic remaina or are deatitate
of them ; and they are also more ahke then than when the beds are not
paraUel to, or have immediately succeeded each other, but have been
disturbed between the completion of the lower and the commencement of the
upper series.
GeneraUy it may be regarded aa a law deduced from obaervation, that
the species of animals characterising any one geological period have either
originated during this epoch, or have then attained thefr maximum develop
ment in number. It also appears that species were on the whole more widely
distributed at the time when the older rocks were being deposited than they
are now ; that the departure from a given type or form is greater the farther
back, or older, the formations that we refer to ; and lastiy, that the remains
of animala found in the older rocks exhibit by degrees, as we refrograde in
order of tirae, a larger preponderance in number of invertebrated over that
of vertebrated apecies, tUl at length we reach formationa in which no
remaina are foimd higher in organization than the moUuaca.
The ffrat of theae laws — that whieh involves the statement that 'fossiU
are characteristic of formations,' is one which is of great importance, aa it

DISTRIBUTION OP ORGANIC BEINGS IN TIME. 373
involves two very distinct and startling assumptions — that the fossU remains
found are those of animals and plants, of which not only the individual but
the species is now dead, or extinct from the Earth, and that there has been
not one only, but a long succession of creations of species to supply the place of
those that have from time to time thus become lost. The former assumption
has been so fuUy proved in every work on Geology and Palaeontology ; is so
clearly Ulustrated by the absence now of species once common, aud their
replacement by others ; and agrees ao weU with the probabiUtiea of the case,
that we must here take it for granted. The occasional loss of species, genera,
and even famiUes, from thefr place in creation is now recognised by every
naturaUst, and we only refer to the subject to complete the line of argument.
The successive creation of groups of species to repeople the Earth when old
ones have departed seems, nowever, far more questionable, and it is more
reasonable and more conaiatent with the facts that are known on the subject,
that we ahould assume the infroduction to have been very gradual, species
after species, aa occasion aeemedto require. Aa in the different countenances
of various indiriduals of our own race, there is a distinct expreaaion in each
indiridual, which identifiea him, although aU are of one apeciea and posseas
innumerable pointa in common, so in the representative species of some
important genus, we see the same kind of resemblance and difference ; and
so also in the group of speciea of a certain epoch, we may recogniae a
physiognomical character, which yet admits of these species being replaced
in other groups by indiriduals reaembUng them, but not at aU to be miataken.
The tme meaning of the law aeems, therefore, to be, that taking each forma
tion as including a group of depoaita, formed under simUar or very slowly
changing cfrcumstances for a certain duration of time, and repreaented in
different parta of the world at that time by other species having similar
resemblances and differencea to thoae which are found to affect a fauna or
fiora now in different geographical areaa, we may perceive by careful study
that amount of unity of character which vrill enable us to recognise the group
of apecies and distinguiah it from that found in other beds that are con
temporaneous, even when there exists no other evidence of their con
temporaneity. The actual limitation of a group of species to a particular
group of beds has not, we beUeve, been at aU satisfactorUy proved with
regard to any one case.
The second law, ' that species belonging to more ancient periods had a wider
geographical disfribution than those now living,'* is also to be understood as
true only in a general sense, and with many limitations and apparent
exceptions. We shaU, indeed, find in particular cases, that species of mani
feat importance are spread much more vridely in older rocks than their
representatives are now, or have been since; and as thia ia the caae with large
groups of those species which must themselves be regarded as higMy
characteristic, in particular instances the law may so far be regarded as
established. It has been mentioned as a deduction from the operations of
thia law obaerved in varioua ways, that the temperature of the Earth's surface
has undergone change, and this, indeed, may have wetf happened from those
numerous alterations that we know to have taken place vrith regard to the
relative level of land and water, and the absolute quantity of land above the
water. We beUeve the weight of evidence in this question does not prepon-
derato in favour ofthe -riews of those who beUeve the Earth to have cooled down
from an incandescent state since organic beings were infroduced on its surface.
The thfrd law enunciated is, tiiat the more ancient the formation, the
more widely do its fossU contents depart from the existing type ; and this is
reaUy the simple expression of facta, made out by numerous long continued
and carefol obaervations in various parts of the world, and may, therefore, be
fiiUyreUed on.
The fourth and last of these laws asserts, that the faunas of the most

See Piotet's PaUontologie, vol. i. p. 73.

374 PHYSICAL GEOGRAPHY.
ancient formations are, cceteris paribus, numericaUy richer in animals of low
organization, and chiefly in Mollusca, than thoae of more recent deposits; but
this — although in one sense the mere statement of a fact which cannot now
be questioned, since all obaervations up to the present time have tended to
confirm it — ia yet not to be reoeived without some quaUfication. It may be
said, indeed, as an answer to any theory of development, or of the exiatence
of a scale of beings gradually approaching perf'ection, that although it is trae
in the ancient epoch, that only the remains of fishes are found amongst
invertebrata, and that even these at length disappear, yet the faunas even of
the earliest periods are by no means imperfect, and we ought not to be hasty
in assuming the abaence of the more perfect typea in the older rocka, merely
because we have not yet discovered any remains of them. This is well
exemplified in the case of many parts of the world at present ; for putting
aside the preaence of man, we find the fauna of Aaia apparently auperior to
that of Europe, if we regard merely the exfreme point of organization, since
in the former continent we have the Orang-otang, and in the latter acarcely a
single ape, and few carnivorea of large size. According to this rule, indeed, the
fauna of New HoUand would indicate a condition of the Earth gi-eatly lesa
developed than that of any other country, aince the only mammals are
didelphine; but it is clear, that a very false notion of the general condition
of the Earth's surface at the present time would be obtained by the most
careful consideration of the organic remains found in the islands of the
Indian ArclUpelago, and the Pacific Ocean.
In point of fact, neither the Eadiata, the Articulata, the Crustacea, the
MoUusca, nor fishes, were at all imperfectly represented or developed in
ancient times, and ever since their ffrat appearance, the members of theae clasaea
of animala have posaeased the same degree of perfection as thefr modem repre
sentatives. It is a mistake to auppoae that the early faunas, generaUy, were
composed of animals less perfect than the recent ones, although no doubt
the highest point to which organization has reached, has risen during suc
cessive geological periods, so that whUe cephalopods, or fishes, first formed
the superior limit of organization, these were afterwards surpassed by reptilea,
and these also, after an interval, by mammals.
Two courses are open to us in this attempt to communicate a true notion
of the distribution of animals^ in time. We might either take the various
periods, or the natural groups of species, as the means of representing the
absolute facts determined. Although, however, a correct idea would be best
obtained by a combination of tbe two methods, we propoae here to give
only an outUne of the various tribes of animals as thev are represented
in the faunas of different periods, leaving the other division of the subject
to be studied in works devoted expressly to Palseontology.*
157 Distribution of extinct Mammalia in time. — Organic bodies generaUy
are only preserved in sfrata, so far as they present hard and comparatively
indestructible portions in thefr skeletons, and since most of the mammals,
birds and reptUes, are land animals, while the greater number of deposits
are of marine origin, the disfribution of these is ^so limited to such deposits
as have originated either near land or near the mouths of great rivers.
Amongst Quadrupeds, the teeth offer at once the hardest and the most
distinctive characters, and these can rarely be miataken, and are aeldom
injured materiaUy by long exposure to decay.
Amongst aU the mammalian and bird remains that have occurred, but
few belong to those rocks which ai-e callcd secondary, and none at aU to the
Pala3ozoic group. With a very remarkable exception, occm-ring in the
Stonesfield Slate (one of the beds of the lower OoUtes of England), no true
quadrupedal remains so old as the chalk have yet been obtained.
The remains of mammals are, therefore, almost confined to the rocks of
* See The Ancient World, by the author of this treatise, where an attempt has been made
to give a popular and connected view of the Eartirs organic history.

foi

DISTRIBUTION OP ORGANIC BEINGS IN TIME. 375
the tertiary period, but are there very abundant. They include species of all
the natm-al orders, vrith the exception of man, and no fossils that have been
found reqidre the formation of new orders.
Of Quadrumana, the number of remains that have been found is small,
butthey offer matter of great interest for the comparative anatomist. Several
species have been determined from India (lat. 30° N.) from the tertiary
rocks of the SewaUk hiUs, one of them of gigantic size, and at least as large aa
an Orang-otang. In Europe, also, the order is represented, one apeciea
having been found in France (at Sansans, in 43° N. lat.), which is described
as intermediate between the gibbons and solemn apes; and two species in
England, in the older tertiary beds of the London Clay, whioh appear to
belong to the group of Macacques (macacus). Eemains of Monkeys, of
rigantic aize compared with the exiating apeciea of that continent, have been
ound also in BrazU.
The remains of Bats (Chiroptera), have been found scarcely more abun
dant than monkeys, and they are conflned hitherto to the insectivorous
group. Of these one species is mentioned by Professor Owen, from the older
tertiary sands of Kyson (Suffolk), where the monkeys' remaina occurred, and
another is known (also older tertiary) from the Paris Basin. A single
species is described from CEningen, in newer tertiary schists, and fragments
of several species, some of them not extinct, have been found in caverns in
England, Belgium, and elsewhere. A few species have been determined
from the cavern remains of BrazU.
The Insectivora present some extinct and some recent species in a fossU
state, but considering the almost universal distribution of some tribes at
preaent, and the aquatic habits of many of the species, it is perhaps remark
able that the extinct forms should be so very few, and so exceedingly rare
as we find them to be. One species of Hedgehog, one of Shrew, and one of
Mygale, have been found at Sansans, and an extinct genus nearly aUied to the
mole, but as large as the hedgehog, was associated with the gravel animals
whoae remains are fouud at Bacton, on the Norfolk coast of England.
One of the most interesting of aU the mammalian fossUs found in the
OoUtic beda of Stonesfield, and already aUuded to aa affording eridence of the
great antiquity of mammsla on the Earth, haa been referred by Profeaaor Owen
to this order of Inaectivora, under the name of Ampliitherium. For the
evidence on this subject we must refer to Professor Owen's beautiful work
on the British Fossil Mammals, p. 29.
There are many more species of Carnivora found fossU than of those
ordera yet referred to. Of the Plantigrade group, a considerable nuniber of
species, and, indeed, several new genera, have been described from remains
found in caverns and other superficial deposits. Of the moat remarkable
and intereating ia the great Cavern bear ( U. Spelceus), whoae bones abound
in many large caverns in Germany, and are met with also in England. Other
species are known from Cenfral France, Algiers, BrazU, and the Sewalik
bills, aU, however, of the tertiary, and many of the gravel period. Species
of Badger, Weasel, Glutton, and Coati, have also beentfound fossU.
The Digitigrade Carnivora are represented by fossUs from most of the
tertiary deposits. In the Paris Baain and other older tertiaries, we have the
Dog (Canis) represented by two or three extinct species, while the Genette
and the Otter exhibit one, and the cat tribe (Felis) several.
The middle tertiaries, however (chiefly in France and the Ehine VaUey),
contain more both of species and indiridual remains than the older, and the
newer many more than both together, far the most remarkable and moat
interesting of the group belonging, in fact, to the gravel, except those which
have been met with in India, and of these the age is somewhat doubtful.
Of gravel fosaUa obtained from England, and belonging to this group, we
may enumerate ihe Felis spelcsa, or cavern tiger; the Macliairodus, a gigantic
carnivore ofthe moat ferocioua habits and of great strength; a WUd cat, the
Cavern hyaena, the Wolf, Fox, and some others of existing or closely aUied

376 PHYSICAL GEOGRAPHY.
species. Besides tbe cavern hysena, other species occur in deposits of the
same age in India and Brazil, and this is the case also with the genua
Felis, of which no less than six species have been described by Lund from
the BrazUian caverns, varying in size from that of the jaguar to dimenaions
something less considerable than those of the domestic cat, and presenting
some curious anomaUes. The Amphibia are only at present knovm in a
foasU atate by two or three species of Seal, one found at Angers, one in the
terta'ary marls of 0.anaburgh, and others on the shores of the Mediterranean.
Fragments of a fossil Morse (Triehechus) have also been described, and
various bones of Whales, both in thia country and North America.
The fribe of Bodents, although represented in a fossil stato by many
species, has not been very much stadied. They have been found in the
gypsum beds of Montmarfre, in the middle tertiary beds of Auvergne, or
in the dUuvial depoaita of cavema and osseous breccia. Asia and America,
as well as Europe, have yielded such remains, and many of those in more
recent beda are vrith difiiculty diatinguished from existing species. Of the
various tribes of these animals we find Squfrrels and a apeciea of Myoxus in
the older tertiaries, and an Arvicola, a Hamster, and others, in Auvergne and
at Epplesheim. The Beaver, and an extinct and nearly aUied, but gigantic
species (P genua) (Trogontherium) are found in the newer tertiary, and many
others occur in the gravel, among whioh, in Europe, may be reckoned repre
sentatives of most of the chief existing European genera, and in America a
multitude of new species closely aUied to the forms at preaent existing in
that continent.
The Buminants, infimtely important to man, and now exfremely abundant
in individuala, varieties, species, and genera, did not present the same prepon
derance during the later tertiary periods, andwere, it would seem, exceedingly
rare during the earUer part of this last portion of our Earth's history.
Many species, very nearly aUied to the group and distinctly repreaentative
of it, are referred to the order of Pachydermata, and thoae that remain
are confined to the gravel or newest part of the period, except, indeed, that
the deposits of India prove thefr existence in that counfry at a much
earlier period. The Indian species include two Camels, and a thfrd occura
in Siberia. One or two species of Moschus (musk-deer), species of Antilope,
Cervus, Bos, Bubalus, and others, are found in the same locahty. In
addition to these, there has been found another and very remarkable genus
(Sivatherium), now quite extinct, in which the head is not only provided with
horns, Uke other true ruminants, but no less than two pafr appear (includinof
both those now characteristic of principal natural groups of the order), and
with these are associated peculiarities of the skeleton, apparentiy indicating
a very close approach to the pachyderms, and especiaUy tne elephant.
The ruminants of the diluvial period in England, and of the caverns of
BrazU, and other parta of the world, include numerous species, very nearly
alUed to those now indigenous in the same districts, but othera as remarkably
distinct. Thus, the gigantic Irish elk and several apeciea of Cer\-us (deer)
afford admirable examples of the former, and the existence of remains of a
Giraffe in Central France not less sfriking evidence of the latter condition.
The diatribution of the Pachydermata duriug the tertiary period is
especiaUy interesting, aa it is chiefly from this order that the most striking
and characteristic, and even representative forms, seem to have been obtained
during the earliest part of the tertiary period. The extinct speciea are also
intereating, since, in many cases, they fUl up gaps now existing in the order,
and connect this with the not very simUar gi-oupa of Euminantia, Eodentia,
Carnivora, Cetacea, and MarsupiaUa. The lacunte thus filled up show how
complete the scheme of nature is, and they show also, that during one part,
at least, of the Earth's history, and over an extensive portion of the surface,
one group of quadrupeds preponderated, and included animala having aU
varietiea of habit, just as, at tho present time, tho marsupial tribe is developed
in Australia, almost to tho exclusion of other races,

DISTRIBUTION OF ORGANIC BEINGS IN TIME. 377
The most ancient forms of Pachyderm^ are those described by Cuvier
under the name Palceotherium, Anoplotherium,, Anthracotherium, Hijraco-
therium, Lophiodon, &c. These gave place to Dinotherium, Bhinoceros, &c.;
and theae again to Mastodon, Elephant, other apeciea of Bhinoceros, Hippopo
tamus, &c., in the Old World, accompanied (not replaced) by Macrauchenia,
Toxodon, and others, in South America. In India, there were besides these a
number of very curious species, forming an exceedingly rich fauna, to which the
order Pachydermata furnished the greatest number of species, and appears
most to affect the phyaiognomy. We need not here deacribe the peculiarities
of these singular animals, as they wUl more properly come under.considera-
tion in the next chapter. In England, of about twenty mammals distinctly
made out from the older tertiary bods, more than twelve are Pachyderms ;
but from the deposits of more modern date, although the number of mammals
is very much more considerable, there are but seven from the gravel beds,
seven from caverns, and three from the alluvium, and this relative prepon
derance in the older rocks of the period seema universaUy observable,
although it is most strikingly the case in the beds found near Paris and those
of the London Basin. It is worthy of remark, that the physiognomy of the
fauna is very greatly affected by thia order in the older tertiariea, not only
because there are so many representative forms of the other, and more
recently developed natural orders of quadrupeds, but because the multitude
of individuals as weU as species, and the largest and most important of the
quadrupeds, were ofthis kind.
The Edentata are now almost confined to South America, only a few
representative forms extending to Asia and Africa. Thefr distribution in
ancient times was apparently not very different so far as geographical area
ia concemed, aa the fossU remaina have hitherto been found only in the
preaent metoopoUs of the order. The extinct species arc, however, extremely
different in form and magnitude from the existing ones, presenting some of
the moat exfravagant departures from existing types yet met with, so that
though the number of speciea ia not large, their investigation becomea a
subject of great intereat. The remains of the gigantic repreaentations of
the Sloth and ArmadiUo range, however, more widely than the species now
characteriatic, at leaat one genus (Megalonyx) having reached as far north
as Vfrginia, IT.S., whUe others extended far down into Patagonia. There
are two principal groups, one represented by the Megatherium, Mylodon,
Megalonyx, Scelidotherium, Ccelodon, and Sphenodon, the corresponding
existing genus being the Sloth. The other group contains Glyptodon,
Hoplophorus, Paehytherium, Chla/im/dotherium, and two others, wmch all,
more or leas, reaembled the Armadillo. One or two fragments of bones from
the Plata have been doubtfcUly assigned to animals of which the Ant-eater is
the modem type. Most of the genera above-named are confined to a single
apecies, and they are all of the very recent tertiary period.
Aa the Edentata are chiefly found foasU in America, where the exiating
forma appear, so the order Marsupiata, at present characteristic of Auatralia,
ia that to which the greateat number of mammalian, remains of the same
counfry must be referred, and few occur elsewhere. There is, however,
,one remarkable exception in the Stonesfield Slate, where a Didelphine
species has been discovered accompanying the Insectivorous mammal before
deacribed. With this exception, and a couple of species in the older
Tertiaries of London and Paris, aU the extinct forms are AusfraUan, and
include Kangaroos, some of them of gigantic dimensions, and a Wombat.
They occur in caverns, chiefiy in WelUngton VaUey, about 200 mUes north
west of Sydney, New South Wales.
158 Distribution of extinct Bieds. — The remains of bfrds occur but rarely,
and are usuaUy very imperfect. Footmarks, however, have been found which
it is difficult not to refer to animals ofthis kind, in rocks of very ancient date,
and thus the class of birds may be referred back much further in date than
the mammals. Impressions of bfrds' feet occur in tho red sandstone of

378 PHYSICAL GEOGRAPHY.
Connecticut, United Statea, and in beds of simUar mineral composition, and
belonging to the oldest portion of the secondary series in England and
Germany. The former have been generaUy deacribed aa carboniferoua ; the
latter are certainly from the newer red aandatone, above the magnesian
limestone. The eridence on which the correctaesa cf thefr reference to bfrds
may be considered to rest, arises from the shape, which requfres that the
animal that made them should have been a biped — that the feet should have
been tridactyl or three-toed, the middle toe much the longest, and each
terminated with claws, and that sometimes there waa a fourth abort toe
behind. It cannot be regarded aa impossible that reptUes may have been ao
consfructed as to leave impreaaiona ofthis kind, and aa few remains of bfrds'
bones have been found in other rocka of the secondary period,* but Uttle
evidence conceming these animals is obteined tUl we examine the older
tertiary beda of the Paris Basin. There, however, and in the London Basin,
and again m numerous other tertiary rocks where cfrcumstences were favour
able for thefr preservation, such indications are found aa leave no doubt that
Bfrds accompanied the Pachyderms, Carnivorea, aud other repreaentativea
of the class MammaUa, in tolerable abundance. The older tertiaiy speries
include a Vulture from the London Clay, a apeciea referred donbtfoUv to the
Eing-fisher fribe (Haley onidie), and a small wading bfrd from beds ofthe same
age, besides several related more or less closely to the PeUcan, Sea-lark, Curlew,
Woodcock, Owl, Buzzard, and QuaU, from the Paris Basin. The newer tertiaiy
beds have also suppUed several apeciea ; and in the gravel, or in caverns, there
have been found remains of species of Eaven, Lark, Pigeon, Duck, and Snipe.
In South America, and especiaUy in BrazU, where caverns have been ao
effectuaUy aearched for foaaU remains by M. Lund, there have been found
fragments of several bfrds, amongst which may be mentioned two Ostriches
much larger than existing American species ; whUe in New Zealand other
remaina have been found in great abundance, diatinctiy referable to an extinct
and gigantic race of wingless birds — the prototypes of the smaU Apteiyx, at
present characteristic of the same island. Many species of these have been
described, and various genera named to include them.
159 Distribution of extinct Eeptiles. — The disfribution of reptilea in
time ia a matter of great importance to the Geologist, inasmuch as these
animals seem reaUy to have been the chief inhabitants of the Earth during the
middle period of its existence, and thefr remains are not only more abundant,
but more perfect, and also more distinct from the exiating representative
species— at least so far as the continent of Europe is concemed — ^than any of
those hitherto considered. It is here first that new orders requfre to be
defined, to include species far removed in habit and structure from known
forms, and some of these are so strange that description can hardly exaggerate
the auigular departure from aU we are in the habit of considering.
If the reader refer to the Ust of orders of Beptilia in a prerioua page,
he wUl find three mentioned as not existing now iu a recent state, and
known only by organic remains, found in rocks cbiefly of ancient date. In
addition to these three, however, aU the existing orders have some fossU
representatives, and some of them a considerable nimiber, contained in
genera which can no longer be recognised as including recent forms. We
proceed to consider briefly the disfribution of the different species of fossU
reptiles in time.
The most ancient reptiUan remains are those which accompany the sup
posed birds' footprints m the Cai-boniferous (P) sandstone of Connecticut.
We find also various footprints in these rocks whieh have been referred

One specimen was found by M. Von Meyer in the cretaceous slates of Claris, having the
lorm and general charactoi s of passerine birds. Another specimen, fl-om the Wealden beds of
Kent, IS referred very doubtfully to albatross, and a large wading bird has been determined from
lilgate lorest, (also Wealden.)

DISTRIBUTION OF ORGANIC BEINGS IN TIME. 379
chiefly to Chelonia (turtles and tortoises), and aimilar markings have some
times been described as fossU footsteps in the sandstones of ancient date in
our own island.
The most ancient actaal bones of reptUes hitherto discovered occur in the
magnesian limestone beds of the neighbourhood of Bristol, but it may be
pennitted to doubt whether these are not rather of the secondary than the
PalEeozoic period. In the middle beds of New Eed Sandstone in Cheshfre
and Warwickshfre, many very interesting fragments of bones have been
met vrith besides footprints, aU tending to prove that at that period many
reptUes existed, varied in form and dimensions, and belonging probably either
to the Bafrachian or the Lacertian order. Beds near the Cape of Good Hope
(South Africa) have yielded also fossUs which partly from independent
geological eridence, but cbiefly from the character of these remains them
selves, are regarded as older secondary. Numerous footprints in the New
Eed Sandstone seem beyond a doubt reptilian.
The rocks of the secondary period form a perfect necropolis of the reptUian
tribe, and in the Lias, wbich succeeds the New Eed Sandstone, we find a multi
tade of remaina oi ihe Ichthyosaurus and Plesiosaurus, the chief representatives
of the order Enaliosauria. Theae remarkable animala, which were apparently
sfrictiy marine in thefr habits, and even more thoroughly adapted for aquatic
existence than the cetacean mammals, were singularly abundant in the
argiUaceous bed afready aUuded to, but continued, not only by the preserva
tion of the genus, but in some cases by identical species, through the whole
ooUtic series into the chalk, receiring an additional genus during the deposit
of the newer ooUtic rocks. In the lower OoUtes (Stonesfield Slate, already
more than once referred to for its fossUs) the order Dinosawria also appears,
and ia represented by the carnivoroua and gigantic Megalosaurus, which appears
to have continued where cfrcumstances admitted, and in the newest part
ofthe OoUtic period (Wealden) was accompanied by the Iguanodon (a herbi
vorous genua, alao gigantic), and iheHylceosaurus. Not only, however, were
these two remarkable orders of marine and land saurians first presented
during the middle part of the secondary period, but they were accompanied
by the Pterosauria or Flying saurians, a race yet more unlike existing forms
and the inhabitanta of the afr. The only genus yet deacribed by these
animals (PterodcuityT) appears first in the Lias, but was continued like the
marine tribe into the Chalk, and presents, Uke the others, a conaiderable number
of speciea. It ia chiefly in England and Western Europe that these remains
have been found, since there the ooUtea are chiefly developed, and seem to
have been accumulated under the most favourable conditions.
The order of Croeodilia, or maUed saurians, was richly represented in the
secondary period. Of the three dirisions (those of which the vertebra are
bi-concave, convexo-concave, and concavo-convex, respectively), the first
contains the Teleosaurus, a kind of gavial, extending from the Lias into the
Middle OoUtea, and another genus, also ooUtic, besides two generic forms
(Suchosaurus and Goniopholis), both Wealden. The second (convexo-concave)
contains several apeciea, the older ones occurring in the Lbwer OoUtes, and the
newest in the Wealden ; whUe the thfrd (concavo-convex) includes aU the
existing crocodUes : one doubtful cretaceous species, several of the tertiary
period, from the London and Paris Basins, and some of the middle tertiary
deposits of Cenfral France.
We have afready referred to the Lacertians, as containing the most
ancient representative forms of the great Eeptilian class. Besides those
already mentioned, there is another New Eed Sandstone species, referred to
a distinct genus (Cladyodori), wliUst the Geosaurus is found in the Solen-
hofen (Upper OoUtic) beda, besides two or three genera met with in the chalk,
of which that caUed Mosasaurus is the best kno-wn. The Leiodon is
nearly aUied.
The Chelonians, recognised by numerous foot-prints in the older rocks
and New Eed Sandstones, are distinctly exhibited, by fragments, in a fossU

380 PHYSICAL GEOGRAPHY.
state, in the ooUtic beds, but they are almost confined to the Stonesfield slate
in England, though on the continent of Europe some of the other ooUtic
rocks have yielded aimilar indications. In the Wea,lden rocka more numerous
and characteriatic fossUa of this kind appear, and, Uke the others, they ^-'- —

to the emydian fribe, inhabiting marshy and swampy places. The true
fresh-water turtles are found in the triassic rocks and lias, and in aeveral
tertiary deposits. True marine turtles (Chelonians) have been found in the
Portland and Purbeck rocks, and in various tertiary strata, especiaUy of the
older part of the period.
The fossU remains of Serpents (Ophidia) have not been found in rocks
older than the London Clay, and only a few species have been deacribed
from that locaUty. Theae animals appear to have had gigantic repre
sentatives during the older tertiary period in Great Britain, but since then
have disappeared from these parts of the world, or at least have left only a few
species of comparatively small aize. The Bateachians, also, once presenting
very remarkable forma, approximating them to the CrocodiUans, have not of
late exhibited any aberrant forms. Fragmente of frogs and salamandera are
found, occasionaUy, in tertiary rocks, but few striking deviations have been
seen amongst the more recently deposited fossUs from the most ordinary
exiating tjrpes.
i6o Distribution of extinct Fishes. — Most of the deposite containing
fossUs having been formed under water, it is not astonishing that a very
large proportion of the organic remains preserved should have belonged to
marine animals ; and thus it foUows, that although rarely so characteristic,
or in themselves so valuable for determination, the remaina of marine
animals afford, from thefr number and preponderance, the principal means
of becoming acquainted with the ancient conditions of hfe on the globe.
Fishes, as the most highly organized of marine animals (except, indeed,
Cetaceans, whose remams are rare and comparatively unimportant) thus
asaume an importance in Palseontology, whioh they do not possesa in general
Zoology. We have spoken above of the division of fishes into four orders, according
to the structure of their scales. Of these four orders, two are absolutely
confined to the rocks of the Cretaceous and Tertiary periods and existing
seas. The other two are also stUl represented, but by comparatively few
species, and these, vrith the exception of the Squaloid, or S Siark famUy, not
the most important ones. It thus happens that the termination ofthe Oohtic
(including the Wealden) period, exhibits the most perfect break in the whole
series, so far as this class of animals gives e-ridence, and two famiUes of fishes
(the Stargeons and Eays) also take thefr rise at the commencement of the
secondary period, whUe the Hybodonts disappear at ite termination. It is
worthy of note, that not only are the fishes of the Palaeozoic period limited
to two of four of the nataral orders, but they are confined to one group
of these, characterised by the continuation of the vertebral colunm into
the upper lobe of the caudal fin, producing a much more considerable deve
lopment of that part, and thence caUed Heterocercal. These, which were
abundant during the Palfeozoic or Older fossUiferous period, then became
very rare ; the rocks of the secondary series chiefiy present homocercal fishes,
or thoae which have the caudal fin equaUy developed, and proceeding entfrely
from the extremity of the vertebral column, or at least have very few that are
of the other kind.
Of the different groups of Fiahea, the Acanthodians and Dipterians (two
famUiea of Ganoids, nearly aUied to the Lepidoids), and the Cesfracumts
(Placoids), were firat introduced, and have been found together in the Old
Eed Sandstone (Devonian) rocks, and the latter also, though very rarely, in
Silurian rocks. The number of species iu the older rooks is not con
siderable, but graduaUy increases towards the newer beds, and becomes
rather numerous iu the Carboniferous rocks, several complete genera
being introduced aud lost during tiie interval. Amongst these are tho

DISTRIBUTION OP ORGANIC BEINGS IN TIME. 381
singularly formed Cephalaspids, the Ptericlithys, the Coceosieus, and others
among the Lepidoid group, and also several Sauroid fishes, as Diplopterus,
Megalicthys, and others, whUe in the Magnesian Limestone, where the
PaliBOZoic rocks terminate, and the Heterocercal fish cease to be exclusively
present, the Pygopterus, Acrolepis, and some other genera of Sauroids, with
the Palceoniseus (Lepidoid), make thefr appearance, but are not continued into
the secondary rocka.
Taking the difi'erent famiUea of fiahes, and commencing with the Lbpi-
DOID ffanoida, we find that the heterocercal genera, of which there are six
(not including the Acanthodians and Dipterians), include four absolutely
confined to rocks not newer than the Carboniferous, and two (Palceoniseus
and Platysomus) only just extending into the trias. There are stiU remaining
the whole tribe of homocercals, including ten genera and many species, which
are exceedingly common, and highly characteristic of the Uas and some
newer oohtic beds, extending in one instance (Lepidotus) into the chalk. The
has may, however, be regarded as the metropolis of this group ; at leaat
thirty-two apecies being known in the Enghsh oeds alone, and many others
occurring in the Uas on the Continent. Of the different genera, Gyrolepis is
carbomferoiis and triassic; Dapedius and Tetragonolepis almost exclusively
haaaic ; Lepidotus -widely distributed throughout the secondary period ; and
Pholidoporus chiefly Wealden.
The Saueoid, like the Lepidoid famUy, is widely spread among fossUi
ferous rocks, and the Ccelacanths, in some reapect analogous, may be
considered as having a simUar diafribution in time. The heterocercal genera
range between the Old Eed Sandstone and the Trias; one genus (Saurichthys)
being triassic exclusively, and others confined to the old red and carboni
feroua rocka. Of the Coelacantha there are also several carboniferous and
older genera, Megalicthys being the most remarkable.
The homocercal Sauroids are chiefly oohtic, where the number of apecies
is exceedingly large. The famUy of Ptcnodonts are almoat aU oolitic, but
may be conaidered to range from the triaa to chalk. The Sclerodeems,
another famUy, ia found in cretaceous rocks, but extends and ia chiefly
common in the older tertiaries. The Accipenseeides (Stm-geons) include
one suppoaed Uaa genus, and one from the London Clay, besides the exiating
Sturgeona. The order of Piacoids, divided into seven families, is represented in a
fosaU atate by genera refemed to every famUy but one (Cyclostoma). Of
theae, the moat important among existing fishes are those least abundant in a
fossU state, and the converse is also true, the Cestracionts having only a
few Uving speciea, whUe the Eays and Saw-flah are rare among extinct forms.
The oldest placoid flshes are Cesfracionts, but the greatest development
ofthe famUy seems to have taken place about the close ofthe carboniferous,
and commencement of the secondary period, and they are now represented
by a single species. The Hybodonts commenced in the carboniferoua period,
and extended only to the cretaceoua rocka ; but like the Cestracionts, the
chief species are triassic and ooUtic. Of sharks (Squaloids), there are
representative forms from the commencement of the c&,rboniferous to the
eriating period, the cretaceoua rocka generaUy containing perhapa the greatest
number, although many teeth are found, and some of gigantic size, in the
middle tertiary series. The rays and saw-flsh have been found only ij
tertiary rocks, but the Chimeroids appear to have extended over a much
wider range, remaina ha-ring being found occasionaUy in the carboniferous
limestone. The Ctenoid and Ctcioid ordera of Agassiz, include a veiy large propor
tion of aU existing flshes, but not a single species older than the chalk. The
Perch famUy amongst the former, and the Scomber and other families, of
which the carp, the pike, and the herring are now well known genera, are
those chiefly represented in the ancient seaa. It is remarkable, however, that
the fosaU species are usuaUy of distinct generic character, and not unfre-

382

PHYSICAL GEOGRAPHY.

quentiy form into a group or sub-famUy, showing some more or less striking
peculiarity. Thus, tiiere is a distmct group of perch-Uke fishes in the creta
ceous rocks, having more than seven rays to the branchiostegous ray, and dif
fering absolutely m this pomt of sfructure from the existing species. So
also tiie Sparoid fish (Dentex, &c.) are found only fossU ui the Monte Bolea
(older tertiary) beds. Most of the other Ctenoid, as weU as the Cycloid
fishes, are represented either by a few species of known genera, or by genera
now altogether extinct. Many more are found in the tertiary than the
cretaceous rocks, and the beds of Monte Bolca are especiaUy rich in indiriduals
as well as species. The foUowing tabular statement of the distribution of
fossU British species determined by M. Agassiz some years ago, wUl, if not
quite accurate, give atleast a useful idea of the subject. It must he observed,
that the number of British tertiary species is exceedingly smaU, compared
with that from other countries.
Table I. — Grouping of the Species qf British Fossil Fishes.
Cycloids 
Ctenoids 
Placoids —
Cestracionts ...
Hybodonts
Sharks 
Rays 
Chimeroids

Table II. — Distribution of British Fossil Fishes in the Principal Groups
of Formations.

nera.

Species.

Genera.

Spedes

.. 86

Brought forward ..

. 341

.. 31
GiNOms —
Lepidoids 
. 27 .
. 116
13
.. 83
Sauroids 
. 25 .
. 74
5
.. 48
Coelacantbs 
. 10 .
. 27
11
.. 26
Pycnodonts 
. 84
7
.. 24
Scleroderma 
. 6
9
.. 43
Sturgeons 
. 2
341
Total species ..
. 650
o.t5
Total Species.
'ii
1
1
1
i
11
^1
1 1
23
f 8
m
1
n
¦si11
i o
i
s
U
CA
rt
u
Ci.
>.;
CQ
o
a,
ca
CD
o
u
Paleozoic
7 Silurian . . .
7
7
69 Devonian . . .
7
3
10
34
13
12
59
170 Carboniferous .
34
63
10
1
,,
ins
M
14
14
62
49 Permian . . .
1
10
11
24
10
3
1
..
38
Second AET.
63 Triassic series .
6
7
11
ir<
40
.¦i
R
1
q
93
12S Lias 
11
5
5
2
2
S5
m
41
1
1
1
103
,^
202 OoUtic series . .
19
10
.¦i
n
i!
16
r,7
37
."iR
3
49
M.'S
2* Wealden series .
7
1
4
1
13
7
4
11
155 Cretaceous series
16
1
29
5
51
5
3
2
20
6
36
19
49
Tebtiaet.
92 Older Tertiary!
(London clay) i
••
-•
10
19
3
32
••
10
1
11
12
37
i6i Distribution of extinct Mollusca. — Ofthe varioua natural groups of
mollusca, or sheU-bearing anunals, which have left behind them diatinct
indicationa of a former state of existence, the Cephalopoda are among the
most remarkable and abundant, especially in the older and middle series of
• The species of Placoids thus designated, are determined only from Ichthyodornlitcs,
except in some cases, (especially on the Silurian list,) where they have not yet been referred
with certainty to any natural family, and may be either Placoids or Ganoids.
DISTRIBUTION OF ORGANIC BEINGS IN TIME. 383
rocks. The Gasteropoda, of which the limpets and whelk are examples, and
which now include the large fribe of univalve sheUs, are also well indicated by
a vaat number of species, while the Conchifera (the bivalved-shell animals)
are presented in a number of difierent forms, graduaUy approximating those
of exiating species as they approach our own times, but afiording m the
older rocks generaUy a smgular preponderance of the group called Bka-
CHioPODA, repreaented now by the Terebratula.
Beginning vrith thoae of higheat organization, we find the remaina of
Cephalopoda of aimple and long extinct forms in the most ancient of fosUi-
ferous rocks. The genus Orthoceras, and others nearly aUied, (Gomphoceras,
Cyrtoceras, Phragmoceras,) are thus enormously developed inthe SUurian and
Devonian rocks, whUe Nautilus, Clymenia, and afterwards Goniatites, present
numerous Devonian and Carboniferous species, and a singular preponderance
of individuals greatly aflTecting the physiognomy ofthe fauna. The nautUus,
retaining its general form and structure, waa in the secondary period accom
panied by the numerous members of the genus Ammonites, which, attaining
a maximum of development in time towards the latter part of the period,
entirely died out before its close. PecuUar forms of the sheUs of these
animals are to a very remarkable degree characteristic of particular beds or
groups of beds, and thus in the ohaJk, the form which at first was a com
paratively aimple spfral, became greatly varied, and often exceedingly
diff'erent from the normal type. The genus Belemnites, although rather less
widely diffused, contains aome of the moat doubtful and least recognisable of
aheUs, partly from the great simpUcity in the external surface and form, and
partly from the varietiea of groweth and accident to which it was subject. No
less than twenty -five genera of ancient Cephalopoda have been determined, of
which only two are now Uving, (Sepia and Nautilus,) and but three additional
ones can be found in aU tertiary deposits hitherto known. There are nine
genera Palseozoic, (seven of them from the lower rocks,) fifteen are lower
secondary, and six upper secondary. Of aU the genera, Anmionites is that
most abundantly represented ; and it has been found convement and useful
to separate its very numerous species into no less than twenty-one groups,
forming seven dirisions of the genua, characterized chiefly by the ahape of
the back of the ahell. Thia diriaion ia conaidered to be natural and gives
proof of marked modificationa of form, having reference to epochs of time.
It was infroduced by Von Buch, and has since been slightly modified by
M. A. D'Orbigny.
The species of Gasteropodous MoUuaka, found in the oldest or SUurian
rocks, are comparatively few, and are difficult to determine accurately,
although many have been referred to exiating genera. The weU-known
genua Natica, the patelUform Capulus, and the Chiton, are considered to be
truly represented in these ancient rocks, but with these there are a number
of others, more or less reaembUng Littorina, Nerita, Patella, Trochus, Turbo,
and Turitella. There are many others to be added to the hst.
Taking, however, a vrider range, we find amongst the principal genera of
these univalve moUusks, only ten acknowledged, and flve doubtful ones, in
the whole lower Palaeozoic group of rocks, and only sixteen admitted, and
ten doubtful in the upper Palseozoic series, most of the genera in the older
being also included in the newer rocks. Of these, all vritiiout exception are
marine, some being Uttoral or inhabit shaUows, but most of them occurring in
deep water. In the lower aecondary rocks we have sometimes thirty-six
genera, and in the upper secondary forty-six, whUe throughout the tertiary
rocks the order is represented in 108 genera, including a number of terresfrial
and fresh-water species.
The CoNCHiFEEA, or bivalve moUusks, are very scarce in a fossU state in
the oldest fossiliferous rocks, and exhibit some singular and long extinct
fonns. The Avicula and Pecten are the first known genera distinctly reco
gnisable, but vrith them are associated several others, that have been doubt-
y, and in many cases wrongly, referred to such groups as those which now

384 PHYSICAL GEOGRAPHY.
include the cockle, the rnya, the muacle, &c. It is in the carbonU'erous Ume
stone that shells of this kind first become common, and Ireland is especiaUy
rich in specimens. The species of Arcacece are especiaUy characteristic of this
among the ancient formations, and in the stiU newer depoaita of the Oohtic
period, where foasU shells of all kinds are unusuaUy abundant, this famUy is
nearly approximated to the existing diriaions. Beaidea these, we have also
in the OoUtes species of Corbula, Porina, the Mytilacece, the Veneridce, the
Lucince, Astarte, Lima, and Crenatula. ' The genera most developed in
British strata are, Pholadomya, oi which nineteen species are enumerated,
Modiola (17), Area (23), Nucula (11), Trigonia (13), Astarte (22), Cardinia
(12), Cardium (12), Isocardia (11), Pecten (31), Lima (23), Gervillia (10),
and Ostrea including Gryphcea (33). Some genera, of which there are few
species, are also highly characteristic, as Pema (2), Pholas (2), Panopaa
(several), Opis (2), Myoooncha (1), Lysiomassa (4), Hippopodiwm (1), and
Corbis (3). In the fresh-water beds of the Wealden numerous weU-marked
species of Zinio occur, with Cyclas and Dreissena. The British cretaceoua
fossUs of this famUy have considerable relations with OoUtic forms, and in
some iew instances (as Gervillia aviculoides) appear to be identical. The
greater number occur in the Greensand, or Lower cretaceoua aeries, and
indicate the formation of theae beda to have been in shaUower water than
that in which the chalk waa depoaited. The genera greatly developed are.
Area (12), Nucula (11), Trigonia (12), Venus (17), Inoceramus (17), Ostrea
¦with Gryphcea (20), Lima (12), Pecten (14). The presence of tme species of
Crassatella, Cyprina, Cardita, Solen and Spondylus, is worthy of note.
Pholadomya, Panopcea, Corbis, Corbula, Isocardia, Anomia, Avicula, Ger
villia, Plicatula and Pecten, have weU-marked repreaentationa among
British crestaceous fossUs. Thetis is a remarkable genua ofthis period."*
The Eocene or older tertiariea contain a vast number of apecies referable
to knovra genera, but aU, or almost aU of them are now extinct. In the upper
tertiaries, a larger proportion of existing species is met with, and the pre
vailing and characteristic forms assume a much closer resemblance to thoae
found in the vicinity of the spot containing auch groupa. There are also
many generic forms of theae sheUs in foreign beda, not known in our own
counfry, and there appears to be a grouping which graduaUy resembles that
now observable. Many species found fossU on our own shores and belonging
to newer tertiary deposits, have also been met with imder other cfrcumstancea
and in diatant spots, atUl living.f
The general character of the bivalves of the middle part of the tertiary
series in England is Mediterranean, or rather Lusitanian, and of the newer
part, mixed Mediterranean and northern, whUe stiU newer beds occur which
are eaaentiaUy northem, and even arctic.J
The remarkable aheU-bearing animals caUed Bbachiopoda, although
somewhat rarely represented in exiating aeaa, must at one time have ^ayed
a most important part in the animal economy, and even greatly affected
the physiognomy of many ancient and now extinct faunas. They aeem to have
been the earliest introduced of aU moUusca, some species of Lingula being
the oldest fossUs known. They soon and greatiy increased, and the typical
forms of genera, and more important groups, were at once amongst the
most abundant, and the most remarkable of the forms of organic life of
which any remains are left.
Of these animals more than 100 species have been determined from
British Silurian beds alone, the genus Ortliis (50 species) being most

• See the descriptive letter-press attached to the Palicontologioal Map, by Prof. E. Forbes,
lu Johnston's Physical Atlas.
t This is the case also with the univalves, as a remarkable Fmus, (F. coatiarius,) long sup
posed to be confliu'il to the fossil beds on the cast const of Englaud, has lately been found
occupying a definite position as a recent species on the coast of Spain.
t E. Forbes, ante cit.

DISTRIBUTION OP ORGANIC BEHSTGS IN TIME. 386
remarkable. Lepioena (20 species) is also characteristic, and Pentamerus is
confined to this group of rocks. Spirifer, Terebratula and Atrypa, Orbicula
and Crania, and a few Producti have also been described. In the Devonian
period Spfrifer increases, Strigoceplialus replaces Pentamerus, Productus
mcreases, Orthis decreaaes greatly, Leptoena continuea, and Calceola (a new
genua) ia added, and is exclusively of this period. In the carboniferous rocks,
Spirifer and Productus, and Chonetes^th Terebratula, include almost the
whole number of Brachiopods, which, fiowever, are enormously preponderant
in number of individuals in many disfricts. In the Permian rocks the whole
group has fallen back mto a few unimportant representatives, thirty-seven
apecies only being kno-wn.
The genua Terebratula is in a high degree characteristic of the -whole
secondary period, and only a few Spirifers, with Crania, Lingula, Orbicula,
Magas, and others, interfere with its presence. In the tertiaries, the
sheUs of Brachiopods are almost as rare as in existing seas. A remarkable
and anomalous extinct group, which under the name Budistes have attracted
much attention, but have not been satiafactorUy explained, are pecuUar to
the rocka of the newer secondary period.
162 Distribution of extinct Aeticulata. — Of this great and important
class, now repreaented by ao many thousand species of insects, Cirrhipeds,
Annelids, and Crustaceans, but few remains, comparatively speaking, have
been found in a fossU atate. Some ofthe few, however, exhibit great intereat.
Of Cruataceans, the famUy of Trilobites, now totaUy absent, aeems to
have been eminentiy characteristic of Palaeozoic formations. There are
several groups, chiefly from the Silurian or lower part of the Palaeozoic
aeriea, and the apecies that occur in the Devonian and Carboniferous rocks,
are for the most part few in number, and not remarkable for any fuU repre
sentation of indiriduals, or any marked peculiarity of form, with the exception,
indeed, ofthe genera Brontes and Harpes (Devonian), and Griffithides (Car
boniferous). Many other Crustaoeana appear in the carboniferous rocks,
but they have not been found in sufiicient abundance to afiect the general
character of the group of fossUs.
The Oohtic rocks, and indeed aU the rocks of the secondary epoch, from
the Lias to the Chalk, present numerous and interesting Crustacean remains,
many of them pecuUar, but aU approximating much more to the existing
forms than the Trilobites do. The Lias contains several species resembling
the lobster and prawn, and these as weU as species of crabs, &c., are continued
and multipUed in the oolites of England, and the upper ooUtic beds from
which the celebrated lithographic slate of Solnhofen, in Bavaria, is obtained.
Other Crustaceans, both crabs and lobsters, or rather representatives of these
tribes, are found occasionaUy in the lower cretaceoua beds. The London Clay,
and other tertiary beds, both in England and elsewhere, contain remains of
varioua apeciflc forma stUl more nearly allied to the inhabitants of the adjacent
seas. Some speciea of smaU Crustaceans of lower organization, ( Cypris, &c.),
have been met vrith abundantly in various parts of the newer palaeozoic, the
secondary, and tertiary aeries. ^
Insects have left remains in various rocka, but they are generaUy too Ul
preaerved to enable ua to diatinguiah any very important characters. In the
coal meaaurea the body of a acorpion, the remains of wings of flies, and the
wing-cases of some beetles have been described, and in the Lias and lower
Oohtes numerous fragments, generally imperfect, have been the objects of
careful examination by Mr. Westwood.* The newer OoUtic and the W ealden
deposits present other examples, but it is difficult to refer to fragmenta so im
perfect by very diatinct specific charactera. In tertiary deposits the remains
of such animals become much more abundant, but are chiefly conflned to a
few localities. The tertiary beds of Aix, in Provence, and of CEningen, the
hgnites of the neighbourhood of Bonn, and the amber-bearing deposita on the
* See Brodie's liistory of Fossil Insects in the Secondary Rods of England,
CO

386 PHYSICAL GEOGRAPHY.
shores of the Baltic, are the most remarkable andjproUfic, and have yielded
results of some importance to the Entomologist. The foUowing eight principal
orders of insects are represented in a fossU state — Coleoptera (beetles), Ortho-
ptera (locuats), Newroptera (dragon-fly), Hymenoptera (Ichneumon-fly), Hemi-
ptera (lady-bfrd), Lepidoptera (butterfly), Diptera (fly), Thysamowra (Podura).
Eemains of Annelida are not wanting in afossU state, but the animals ofthis
tribe being aoft, only a few and imperfect indications are usually preserved.
In the oldest SUurian rocks, marks have been found which have been referred
to worms, and it is not unlikely that simUar indications might be found in
rocks of almost aU ages.
Many worms incase themselves in stone, and thus the sheUy tubes
in which the animal once Uved are very permanent. Since, however, at
present, very difi'erent species are found to inhabit tubes not to be diatin
guished from one another, it ia clear that not much stress can be laid on eridence
derived only from data so Uttle important. The genera Serpula and Ditrupa
are of almost universal occurrence, and probably include a large number of
extinct species in aU parts of the world and of almost aU geological dates.
163 Distribution qf extinct Radiata. — Of these animals, the Echino-
dermata and the Zoophyta form the two most important groups, and we have
in addition to these, the Amorphozoa, containing the sponges, of which many
are found in a fossU state. Many weU marked and peculiar forms occur in a
foasU state in rocks of aU periods, and many natural famUies, once enormously
abundant, have either entfrely disappeared or dwindled down to the most
insignificant dimensions.
Of the Echinoderms the most ancient group is that of the Cystidea, closely
aUied to another group, the Crinoidete, which, as weU as the former, is abun
dantly presented in a fossU state, but very rarely by any existing speciea.
The Cyatideana include a number of genera aU (vrith one doubtful exception)
Silurian, but the Crinoida are more vridely diflused, althongh these alao appear
to have commenced their existence at the very earUest infroduction of life,
and attained thefr maximum of development during the Carboniferoua period.
A. new and peculiar group (Pentacrinus) replacea tbe older forma in the Lias,
and by varioua species continues into the Chalk. Other, but not numerous,
species are also found, the free-swimming forms commencing, and graduaUy
displacing the attached Crinoids. In addition to the Crinoids, the orders of
OphiuridcB and .Asteriadce (star-fishes) commenced in the oldest period, but
appear to have obtained thefr chief development much later. Star-fishes and
true Ophiuras, as weU as Crinoids, have thus a vride range of distribution in
time among the large and not unimportant group of animals to which they
belong, and in the newer partof the Palaeozoic period they began to be accom
panied by Echinidas (sea eggs). The remaining groups of Echinodermata
present no hard parts by wmch thefr form can be preserved to future ages,
and there is thus no evidence of thefr existence in a fossU state.
The Zoophyta, amongst which are included corals and a multitude of
smaU animals having calcareous skeletons, besides many others which have no
solid framework, afford abundant indications of their former existence in
rocks of aU ages. It appears from the result of observations on these, that
• little if any change has been made in the plan of zoophytic organization
since the beginning of geological time ; that wUiilst some genera have passed
away and new ones have taken their places, the earhest forms were as perfect
as their successors, indeed, among the very earhest, the most perfect forms of
zoophytes play as important a part as the most rudimentary. Most of the
genera are remarkable for thefr great duration in time, and this apphes also
to agreat many species both during Palaeozoic and Tertiary epochs.'*
There are two diviaions of Zoophytes buildmg solid habitations, one of
which, the Bryozoa, does not really belong to the dass, but on account ofthe

E. Forbes, in Physical Atlas, ante cit.

DISTRIBUTION OP ORGANIC BEINGS IN TIME. 387
exfreme simUarity of the stony frameworks constructed by its members, they
cannot be dissociated from the trae polyps consfructing corals. Of this
dirision as of the other (the Polyps), there are examples in SUurian rocks
where the genera Eschara, Flustra, and others are found. In the same rocks
are Favosites and Chcetetes, Petraia, Catenipora, and Aulopora. These, with
Strombodes and Syringopora, give a marked character to the oldest fosaUi
feroua limestones of the SUurian period. Many ofthe SUurian species extend
into Devonian rocks, although many others diaappear and are replaced by
new forma, and Astrcea, afready introduced, becomea there more abundant.
Gyathophyllum, lithodendron, and Lithostrotion occupy an important place,
and with Gorgonia attain a maximum in the subsequent or Carboniferous
rocks, which are remarkable for the large proportion of coralline limestone
ofwhich the lower division ia made up.
The PalsBozoio zoophytes are quite distinct as a group from the apecies
found in rocks of the secondary period, and some forms, as Graptolites,
are altogether pecuhar to the older epoch. In the lower and middle Oolites,
a conaiderable number of corala occur, Astrcea being eapeciaUy rich in apecies
and indiriduals, though Turbinolia is almost equaUy remarkable. In the
cretaceous rocks there are many smaU corals, most of them Bryozoa, which
have not been much examined, and in tertiary formations the number of
species is very large, but the condition of the seas in which they Uved appears
to have greatly differed from that of more ancient periods.
The fosaU Amorphozoa include chiefly sponges aud spongiform bodies, the
lowest in organization of aU that have been determined. There are a few
SUurian and some Devonian species, whUe others have been observed also in
carboniferous rocks, but some of the German locahties of OoUtic rocks are far
more remarkable than older beds for the preaence of such remains. A large
number of forms have been described both there and in the newer or creta
ceous rocks, the moat remarkable genua among the latter being Ventriculites,
which occura abundantly among the chalk ninta. Tertiary sponges have
been described by MicheUn and others.
There stiU remain to be mentioned the two large and doubtful, but not
uninteresting, groups, the Foraminifera and Infusoria, which must be referred
to the Zoophyta, and wbich, although no doubt introduced very early and
occurring fossU in Devonian rocks, begin to be important in the newer part
of the palaeozoic period, especiaUy in Ilussia. Other species have been found
in the lias and oohtes, a large number in cretaceous rocks, and an almost
infinite multitude in rocks which are perhaps intermediate in age between
the secondary and tertiaiy, as weU as in the older tertiary rocks of various
parta of Europe and North America. Most of the fossU infusorial animalcules
of which remaina have been found are in tertiary rocks of comparatively
modem date.
164 Distribution of extinct Plants. — The remains of planta are, aa might
be expected from the character of most of the deposits, either entfrely absent,
or confined to a few spots, and only in rocks far removed in point of time.
Thus we find such remains chiefly in the rocks of thf carboniferous period,
but also in the older ooUtic rocka in the "Wealden and in tertiary deposits.
The oldest forma of vegetation are very diatinct from thoae since infroduced,
and show a remarkable preponderance of fema, both arborescent and others —
at least, thia is the case with the carboniferous fossUs : and although some
species have been referred to Devonian rocks, and fiicoids are foimd occasion
ally in SUurian Umestones and schists, the reaUy important groups are only
known in beds associated with coal. With the ferns of this period are dico
tyledonous frees aUied to pines, and these in the newer beds are accompanied
by Cycadem and trae Coniferce, which ranged plentifuUy during the secondary
penod in England and Europe. The fossif plants of the London Clay are
closely aUied to some groups now conflned to the East Indian Islands, and
probably indicate a warmer climate than at present, and avery difi'erent
disfribution of land. CO 2

388

CHAPTER XIII,
ETHNOLOGY.
§ 165. General nature and meaning ofthe science of Ethnology.— 166. On specific character.—
167. Divisions and mode of treatment of the subject. — 168. External structural peculiarities
of the human race. — 169. Intemal structural peculiarities. — 170. Principal varieties of
the human race, and their arrangement into distinct groups. — 171. Natural geographical
limita of distribution. — 172. Language. — 173. Modification of the races of men. —
174. Mixture of races. — 175. Influence of man on other animals. — 176. Influence of man
on inorganic nature and on the vegetable kingdom. — 177. Eflfect of inorganic nature on
man. — 178. Statistics of the human race. — 179. General conclusion.
/~^ENEBAL Nature and Meaning ofthe Science of Ethnology. — No
\jr account of the Earth, its inhabitants, and its history — ^professing to
explain the modiflcations of its surface, and record the revolutions and
changes it has undergone — ^would be in any sense complete without including
some notioe of the human race and its distribution in various countries, and
at various times. The study ofthis department of Natural Ilistory has been
designated Ethnology, and the object in the present chapter is to give an
outhne of the science so named. We muat, however, neglect many pointa
of intereat, eapeciaUy those which are connected with the personal and social
quaUties of the human race, for these in no way affect that natural-histoiy
view which solely belongs to Physical Geography.
Considered as a race infroduced upon the EMi;h at a certain period of its
history, the human famUy preaenta to the careful and phUosophic observer
an irmnite variety of problems, diflicult and compUcated in the highest
degree. Hitherto these problems have received but little attention compared
with their real importance, and tbe growing interest felt in reference to
them within the last half century has hardly yet spread to the mass of
society, who are apt to shelter themselves under doubtful histories, and the
general but vague ideas derived from very imperfect knowledge. The most
that we can here attempt, however, wiU be to state a few of the problems,
and point to the various attempts made for thefr solution or Ulusfration.
The subjects that offer themselves for consideration in the strictly
natural-history study of the human race, are chiefly those coimected with
colour and other external peculiarities, intemal structure, language, and
inteUectual development. These aU involve to some extent positive facts,
and hence we may, vrith some satisfaction, discover by thefr means the
degree of affinity that may exiat amongst the principal dirisions of men; but
the real importance and relative value, even of these facts themselves, can
only be appreciated by careful study.
It may perhaps be considered, that the inquiries of chief importance, and
those which, when answered, promise the greatest resulta, have reference to
(1) the speciflo identity of those various races of men which diff'er most from each
other, and which being found inhabiting disfricts naturaUy distinct, may be
regarded to some extent as typical races — (2) the degree to which mixtures
of theae racea can produce other and permanent varietiea — (3) the extent to
which such mixtures as have been afready produced can be fraced back—
(4) thc absolute period during which the human race has been actuaUy
present, not only on the globe in general, but in particular countries — and
(5) the true amount of mfluence that man, in an uncivUized or civiUzed
state, has upon the diatribution of other famiUea of his own kind, and upon
other organic beinga. These ai-e points fafrly within the inquiry of the
natm-aUst, and demand therefore notice in this place.

ETHNOLOGY. 389
166 Spedfic Character. — In considering such points we are forced to pay
some attention to another question that has long been a source of dispute —
namely, what is to be imderstood by the term species, and how far varietiea
may extend without reaching to apecifio difference. In man, aa in other
animala of high and complex organization, capable of adapting themaelvea to
great changes of temperatm-e and cUmate, living at one time under the
burning raya of a fropical aun, and at others enduring a three or four months
perpetual night and frost near the poles, there must occur many modifications
of habit at least, if not of structure, which manifestiy involve no departure
from the normal type. But because this is the caae, we are by no meana
justified in assuming that such differences of habit can involve real and
permanent modification of structure, for such a conclusion could only with
propriety be admitted, if it were supported by many analogies derived from
other natural-history facts, dfrectly bearing upon the point. Too Uttle
attention haa often Tbeen paid to natural-hiatory and common-aenae viewa
on thia aubject, and to the laws of analogy and affinity of diatribution and
linutation of species of other animals, in deciding on the probable origin of
the human race, and the date of thia event.
It haa, indeed, been usual to assume, as the definition of species, that
' the faculty of procreating a fertUe offspring constitutes identity of speciea,
and that all differences of sfructure and external appearance compatible
therewith, are solely the effects resulting from variety of cUmate, food,
or accident, consequently are forma of mere varieties, or of races of one
common species.'* It may, however, be safely asserted, that any argument
conceming the origin of the human race derived from this deflnition is
ricious, for the whole point in question is assumed, and there seems no doubt
that several of those groups of other animals best determined, and moat
universaUy aUowed to be distinct, may naturaUy breed together, and do
produce hybrids capable of continuing a race, and exhibiting some pecuUarities
of each of the tribea from whioh they are derived. Thua, varioua tribea of
wi\.A.felidiB breed with each other ; goats breed vrith sheep ; common cattle
vrith the Zebu, and other well marked species; and the common hare with the
rabbit, and alao vrith the hares of other countries, exhibiting examples of no
alight importance, where fertile hybrids have been produced by mixtures of
weU marked species, although new races have not been established. In aU
theae cases, as, indeed, in any single famUy of any animal, a certain amount
of mixture of blood is requfred to keep up a healthy race, and it may even
be necessary to revert to the original stock for such purpoae, but this does
not interfere with the important conclusion that auch mixtures of species are,
to a certain extent, natural and are essentiaUy proUflc.
In spite of this, notwithstanding such occasional exceptions to the usual
steriUty of hybrids, it ia atUl, however, very clear, that there must be some
prorision in the constitution of organized beinga tending, under ordinary
circumatancea, to keep breeda distinct, and prevent the amalgamation of really
natural groups. In other words, though apeciea may not be atrictiy determin
able by the test of unfertile hybrids, there stUl are tine specific distinctions
preserved unbroken and unmixed vrith singular tenacity. It is of the highest
importance for naturaUsts to determine, if possible, the nature of these
diatioctiona, and how far any of them are universaUy appUcable ; but we are
bound to admit that thoae who puraue the higher departments of PhUosophical
Zoology, have as yet faUed in assisting the progress of natural history by the
discovery of any such charaoteristica.-f-

* Hamilton Smith, Natural History ofthe Human Species, p. 114.
t We quote from a very recent work by Alexander Von Humboldt the following additional
evidence on this subject of the fertiUty of hybrids :— ' The Canadian bison can be trained to
agricultural labour. It breeds with the European cattle, but it was long uncertain whether the
hybrid was fruitful. Albert Gallatin, who, before he came forward in Europe as a distin
guished diplomatist, had obtained, by personal inspection, great knowledge of the uncultivated

390 PHYSICAL GEOGRAPHY.
167 Divisions and Mode of Treatment ofthe Subject. — ^Ethnology, there
fore, or the physical history of the human race, cannot obtain from general
natural history a decisive answer, even to thoae inquiries which properly and
neceaaarUy belong to that acience ; and it therefore caUa for asaiatance from
many other departments of knowledge. In the preaent outline, we may vrith
advantage conaider, first, that portion of the physical view of the human
species which is more directly connected with zoology, comparative anatomy,
and comparative physiology. "When in this way some idea is communicated
of the more elementary facts, we may proceed to consider very generally
those points of comparative phUology, and afterwards of general human
history, which bear upon the questions we have to discuss. Having thus deter
mined the natural-history facts of our race, it wUl be useful to consider the
influence of the human apecies on inorganic and organic nature, and con
versely the influence of external nature on the human famUy under various
cfrcumstances of temperature, climate, and civilization. It is tme that in
this sketch many detaUs of great importance may be omitted, whUe, on the
other hand, opportunities -mil he afibrded for lamenting the almost total
abaence of great claaaea of facts ; but perhaps also this may be useful in
dfrecting attention to the present state of knowledge on so important a
subject. 168 External Structural Peculiarities of the Hu/man Bace. — Those
marked pecuUarities of men that are continued from generation to generation
without change, and seem at length to be absolutdy unchangeable, relate
chiefly to colour, hafr, and external form, but also include some atriking
anatomical characters of great importance. Thus, permanent varieties in
stature, in the proportions of the limbs, in the form of the pelvis, and in the
form and proportions of the cranium, are so numerous and distinct aa to
separate at once the different famUiea of men into aeveral groups.
The earUest recorded accounts that have survived the destruction of
written documents and oral fradition, seem to point to the existence of races
of men attaining in former times more gigantic dimenaiona than at present ;
and however exaggerated and diatorted the accounta may be, they yet aeem
aufficient to juatify a conclusion, that the early conquerors in Asia Minor, and
Southem as weU as Northern Europe, may have exceeded the original races
in respect of height, as much as they certainly did in vigour of character
and physical energy. The only race, however, that can now be referred to as
showing any distinct evidence on the subject is that which has been described
in Patagonia, and which, Uke others, must soon give way to the encroachment
of the white man ; but stUl showing superiority of form when compared, not
merely with the stunted and Ul-developed Puegians about them, but even
when placed side by side with Europeans of full vigour and ample propor
tions. This is stated by aU travellers of credit, and must certamly be
admitted. Many instances, however, are on record of individuals in aU
countries attaining even a more conaiderable stature ; and amongat them we
may mention the case of a Swede, one of Frederick the Great's gigantic
guards, described by Haller as being eight and a half feet high, whUe several
Irishmen have been known to attain the height of seven to eight feet ; and
one, whose skeleton is now in the Museum of the CoUege of Surgeons, and
who died, aged twenty-two, in 1783, measured eight feet four inches.
Notwithstanding these exceptions of individuals and races, there is cer
tainly no evidence of any great deviation from the average standard that

parts of the United States, assures ns that ' the mixed breed was quite common flfty years ago
in some of the north-western counties of Virginia j and the cows, the issues of that mixture,
propagated like all others.' ' I do not remember,' he adds, ' the grown bison being tamed, but
sometimes young bison calves were caught by dogs, and were brought up and driven out with
the European cows.' At Monongahela, all the cattle were for a long time of this mixed breed,
but complaints were mado that they gave very littlo milk.' We beUevo no one ever questioned
the speciflo distinctions between the Europeiui breed of cattle and the bison.

ETHNOLOGY. 391
cannot weU be referred to local circumstances, but as Uttle doubt can there
be that various races do present diff'erent average stature. Thus, the Pata
gonians, inhabiting the southern exfremity of South America, are beyond all
question an eminently taU race, whUe the Bosjesmans of the Cape of Good
Hope, and the neighbouring counfry, are as strikingly below the average
stature. Nor is inteUectual cultivation by any means concemed in this
matter, since the native AusfraUans, the nearest in point of low intellectual
powers to the South African dwarfish tribes, are, on the confrary, a tall race ;
whUe the stunted Fuegians, the race nearest in position to the lofty Pata
gonians, and the Caffres, inhabiting the country near the Bosjesmans, differ
but httle in civiUzation from thefr dwarf neighbours.
Although it is certain that great differences in stature are capable, under
favourable cfrcumstances, of producing permanent varieties without reference
to climate, yet it has been considered that this latter also may have some
effect. The point is one of some Uttle importance, especiaUy in considering
the average height of races taken fafrly from a sufficient number of
observations; but facts are wanting to found any certain argument with
reference to this subject.
If there is difficulty in judging of unity of race by the average stature, it
wiU readUy be understood that other dimensions are stUl less useful in this
respect. A considerable difference, however, may be traced in the development
of varioua races, though insufficient tojustify important generalizations.
Other external characters of the human race are found in the form of
particular parts, some tribes having the head fiattened in a remarkable
maimer, otners having the bones of the exfremities more or less developed,
some possessing thick lips, othera smaU ears, others high cheek bones, whUe
a vaat variety of less important differences characterise particular groups,
according to some temporary or local cfrcumstances. Many of these depend
directly on intemal sfructure, whUe others, such as colour, are excluaively
auperficial, although sufficientiy important to require careful and minute
attention. The nature and condition of the hafr afford other external charac
teristics of singular value, and thus hafr and colour are uauaUy considered as
the most dfrect and ready means of grouping the different varieties of the
human race into large natural famiUes.
The pecuUarities of colour presented in man are chiefiy four — white,
yeUow, red, and black, but each of theae admits of a vast variety of shades.
The white is often varied with deUcate shades of pink, and passes also into
tawny and oUve coloured. The yeUow passes into copper coloured on the
one hand, and black, on the other. The copper colour also admits of many
varieties, and even black ia often presented of different shades in the various
members of the same great natural famUy. AH theae colours are Uable to
what are caUed albino varieties.
Of the whole population of the world, a very large proportion, including
almost aU the inhahitanta of tropical countries, exhibit tints of colour
approximating them more or less closely to black. These have generaUy
black hafr and dark eyea, the hue of the skin being leps decided than that of
the hafr and iris. Where the black is combined with red, as in the indigenous
copper coloured races of America, the hafr does not cover any part of the
face, and in aome parta of Africa the hafr ia not only black, but is crisp,
woolly, and short, presenting very marked and permanent characteristics.
The white and yeUow varieties of men generdly present a fair complexion,
assuming a red or tawny tint on exposure to sunlight, and accompanied by
hafr of Ught brovra, aubum, yeUow, or red colour, and eyes either grey,
azure blue, brown, or some shade of yeUowish or greenish brown, or greenish
yeUow. These colours of the eye are often found in individuals not presenting
the frue characteristics of skin and hafr, but in great masaea of men not exhi
biting recent mixture of race one prevailing tint may generaUy be recogniaed.
The term albino is appUed to mdiridual cases occurring from time to time
in aU countries, although chiefly noticeable among Negroes, owing to the

392 PHYSICAL GEOGRAPHY.
marked contrast then preaented to the ordinary condition. The characteristic
of this variety is, that the hafr and skin are perfectly white, without a tinge
of colour, and the fris of the eye red. Eaces of albmos have been described
in some parts of the interior of Africa, but they probably do not extend to
more than a few famUies in particular -vUlages. The persons thus charac
terized are frequently the offspring of parents whose other chUdren do not
present the same peculiarities. _ _
Before concluding this account of external structure, it is necesaary to
refer to varietiea of form preaented by the face, and eapeciaUy the Ups and
noae, whioh are amongat the more dfiatinctly marked characteristics in the
Negro race, the Chineae, the Malaya, and aome of the Americans. The form
ana position of the ears is also a point worthy of remark.
169 Internal Structural Peculiarities. — The form and proportions ofthe
human cranium exhibit differences ao marked, and ao greatly affecting the
intellectual development and capacity for civUization of the inhabitanta of
diff'erent countries, that the assistance of anatomy in this matter is of the
highest importance to the progress of Ethnology, and lately also it haa been
found that pecuUaritiea of structure correaponding to these are to be met
with in the figure and proportiona of the pelvis. It is necessary, therefore,
to consider the facts that are most important in each case.
The cranium is a hoUow bone pecuUar to vertebrated animals, and forma
the protective investment of the brain, on which it is moulded, and the form
of which, in warm-blooded animals, it represents. It contains in its waUs
the organs of hearing, and contributes to form the orbits of the eye, the
nostrUs, and the face. It is buUt up of eight bones which are not finnly
connected tiU some time after birth, so that there is a certain amount of
flexibUity, admitting of great change of general form and proportions by
continued artificial pressure.
The ffrst attempt to point out distinctive characters in skuUs was that of
the anatomist Camper, who based his conclusions on the shape of the akuU
and the measurement of the angle (caUed the facial angle) included between
two linea, one drawn from the paaaage of the ear to the baae of the noae,
and the other slanting from the forehead to the most prominent part of tbe
upper jaw-bone. This angle was thought to afford a measure ofthe capacity
of the fore part of the slmU and of the size of the corresponding portion of
the brain, and in this way the skuU of Em-opeans when measured gave an
angle of 80°, that of a Ealmuk 75°, and that of a Negro only 70°. He alao
observed that there are forms of the head in which the angle appeared to be
greater than it is in the European, and others in which it is less than in the
Negro, the former being the ideal heroic heads ofthe ancient Grecian deities,
and the latter being animala of inferior organization, the ape having the
greateat angle, but not exceeding 64°. It must, however, be remarked, that
in this measurement the apparent gradation from the Negro to the ape is
not real, as if the skuUs are taken from animals of full age in which the
dentition is complete and the jaws completely developed, the angle is not
more in the orang or satyr than 30°, and in the tooglodyte only reaches 35.
In the comparison of skulls, one important point has also aometimea been
overlooked — namely, the form of the base of the skuU, on which dependa
much of the general measurement of the anglea.
Besides the facial ande, there are other points of diff'erence aeen in
comparing the skuUa of different racea; for whUe some skuUa are round and
symmetrical, with a broad smooth forehead, others, again, are square, or
nearly so, othera pyramidal, othera nai-row and lateraUy compresaed; whUe
11 tbese varieties naturaUy induce very marked external pecuUarities corre
sponding to them. Almost aU the anomalous and even monstrous diver
gencies from the normal type in man are capable of being fransmitted to
posterity, aud thus tbe races amongst whom flatness of the head or any
other deformity ia regarded aa a beauty, exhibit the corresponding form
in the heads of very young infimts, even when no mechanical pressure has
been induced.

ETHNOLOGY. 393
One of the most important varieties in the structure of diff'erent races
consists in a pecuUar conformation of the pelvis, and tliis has recently been
the subject of careful investigation by Dr. VroUk, of Amsterdam, who has
examined and described minutely the detaUs observable in skeletons of
Europeana, Negroea, and Javanese of both sexes, a female ofthe Bosjesmans
race, and a person of mixed breed.
The important result of these investigations aeems to be, that, although
the proportions of the bones in this region in Europeans are very different
in the two sexes, the difference is much greater between the male and female
Negro, the former exhibiting remarkable strength and density, whUe the
latter, in the same race, combmes lightness of substance and delicacy of form
and structure. The Javanese of both sexes appear to possess a pelvis of
pecuUar hghtness of substance and smaUness of size, while the female
BoBJesman exhibits, in a most exaggerated form, the narrowness and elonga
tion remarkable in the Negress, and apparently approaches to the structure
ofthe chimpanzee and the orang.
Other observations on the pelvis, by Professor Weber, woiUd tend to
show that all varietiea of form in the pelvis may be described as belonging to
one of four kinds — the oval, the round, the square, and the wedge-shaped, of
each of which examples are found in most countries. The form that is most
usual among Europeans is the oval, that of the Americans the round, that of
the Mongols the square, and that of the different racea of Negroea the oblong.
Other structural pecuUarities are seen in the bones of the extremities,
which in the Negro and some uncivihzed races are comparatively elongated
and sfraggUng, crooked and badly formed. Thus the tibia and fibula in the
Negro are more convex in front than in Europeans, the calves of the legs very
high, the feet and hands fiat, the heel-bone flat and continued nearly in a
sfraight line with the other bones ofthe foot, and the foot itaelf remarkably
broad. The fore arm is also much longer in proportion to the body than in
other races, and the head ia placed further backward on the vertebral column.
170 The Principal Varieties of the Human Bace and their Arrangement
into Distinct Grmups. — Although the pecuUaritiea mentioned in the preceding
aection are none of them sfrictiy confined to special races, stUl they are so far
characteristic that by thefr meana we can -with some degree of reason speak
of the white, black, copper-coloured, and other races, without fear of being
misunderstood, and we may also subdivide tbese into wooUy-hafred, black-
hafred, beardless, and others. But when connecting these so far natural
f roups with those which, according to the records of human history, have
welt in, or emigrated from, special countries, there are immediately intro
duced various elements of confusion, preventing any possibUity of subdivision
into tribes without the assumption of so much, that fiction soon takes the
place of fact. It is evident that the space devoted to the subject of
Ethnology in these chapters vrill by no means admit of the discussion of any
riews, and we can only put before the reader, as a conclusion, the arrange
ment that haa seemed most convenient and most useful.
Among the various pointa of difference that might be assumed to aaaiat in
the arrangement of the tribes of men, the form of the skull, combined with
the colour of the akin and hair, the texture of the hafr, and the form and
proportiona of the pelvis, agree for the most part uu marking at least three
groups posseaaed of the extremea of difference in these reapecta, and not ill
aupported by hiatoric teatimony. It has, indeed, been usual to admit of five
principal or typical stocks of this kind, but,. perhaps, two of these are more
properly considered aa aub-typical, at leaat m the present condition of our
knowledge. The three groups thus suggested may be called the Caucasian,
or bearded type ; the Mongolio, or beardless type ; and the woolly-haired, or
Negeo type. The Europeans generaUy may be considered aa repreaenting
the former; the Tartara, Chinese, and other inhabitants of Central Asia, the
native tribes of America, and the inhabitants of Australia, the second; and the
Africans the thfrd.

394 PHYSICAI- GEOGRAPHY.
The characteristics of the three principal ty^ies may be thus described :—
1. The Caucasian Type. — This lypical group has received its name from
the idea of its having originated in the mountains ofthe Caucasus, whence it
has spread in Europe and Asia. AH the civUized nations of the West belong
to it, and it has generaUy obtained absolute domination when famUies
have migrated to diatant countries. It admits of many and very important
subdiriaions. The races thus designated are for the most part white, bnt include tribes
of almost every shade towards absolute blackness. The hair is abundant on
the head, varying from the deepest brown, and even black, to auburn, yeUow,
and fiery red, and becoming grey vrith age. In aU the races, the mjdes have
decided beard, often spreading over the upper Up and fringing the sides of
the face, being, in such case, crisp, curly, or undulating, ancTnot lank. The
hafr usuaUy harmonizes vrith the complexion, and that of the head and face
have nearly the same colour.
The skuU ofthe Caucasian tribes is larger in proportion than in the others
— ^it is oblong and rounded, and the facial angle rises from 75° to nearly 90°.
Its volume amounts to from 75 to 109 cubic inches. The mouth is amaJ],
the teeth vertical, the Ups graceftd and not tumid, the cheek bones not
projecting, the chin fuU and round. The shoulders are ample, the chest
broad, the ribs firm, and the loins weU tumed ; the thighs and the calvea of
the lega symmetrical, and the whole frame constructed for the endurance of
toU, and with physical powers equal to the intellectual organization, com
bining more than any other race sfrength of limb with activi^, and enduring
vrith ease the greatest vicissitudes of cUmate and temperature.
The people thus characterized include the inhabitants of the great river-
vaUeys of Southern and Westem Asia, and aU the inhabitants of Europe,
except the Laplanders, the Finns, the Magyars, and some other eastem tribea.
A large part of North America and many portions of South America are also
now peopled with the descendants of the Westem Europeans who have
migrated in a civiUzed atate.
2. The MoNGOLic Type. — The races that belong to this class differ both
from the Caucasian and Negro stock in many highly important phyaical and
inteUectual qualities. The skuU is smaU, the facial angle 70° — 80°, the
contents of the cerebral chamber 69 to 83 cubic inches ; me face is flat, the
cheek bones projecting lateraUy, the eyes smaU and obUquely placed ; the
hafr coarse, lank, and olack ; the beard scanty, not curly, and not covering
much beyond the chin. The nose is smaU and pointed, and the month well
formed. The colour of the skin yeUow of all shades, rarely passing into
white, on the one hand, or black, on the other. The typical races are square
of body, low in stature, haring the trunk long, the exfremities comparatively
short, and the wrists and ankles weak.
The people chiefly exhibiting these pecuUarities of structure are the
Cenfral and Northem Asiatics, the Finns and Laplanders in North Europe,
and the Magyars of Hungary. The Chinese and Japanese, and the various
Tahtar tribea are the moat numerous and characteristic of these races at
present. The Esquimaux also belong to them.
The Indian fribes inhabiting North America approach the tme Mongols,
and may be regarded as subtypical, presenting some points of resemblance to
the aberrant tribes of Caucasians. In these, however, the colour is more
deeply red or copper-coloured, the cheek bones more rounded and not pro
jecting lateraUy, the face broader, the forehead low, and the skuU less
pyramidal. Another remarkable and very large natural group, the Malays, may be also
considered as forming a connecting link between the Mongol and Caucasian
typea. The Malay fribea have generally a smaU head, measuring from 64 to 89
cubic inches — the forehead is low, the face flat and broad, the nose short, the
mouth wide, and the uppcr jaws projecting. The hafr is generaUy coarse,
tho skin vai-yiug in colour from cleai- brown to dai-k dove, the beard scanty,

ETHNOLOGY. 395
and the frame sUght, except when a mixture with Caucasian blood can be traced.
As a people, they are apt to be treacherous, implacable, and ferocioua, and
they are chiefly confined to the coaat, and some of the islands of the Indian
Ardiipelago, excluding parts of Papua and some parts of AustraUa.
3. The Negbo Type. — The wooUy-haired stock properly designated by
thia name predominate in Africa. They present many marked pecuUarities,
amongst which may be mentioned a small facial angle, varying from 65° to
70°, a amaU head lateraUy compressed, a narrow depressed forehead, a broad
cmshed nose, a protruding lower jaw, a vride mouth with thick Ups, and large
aohd teeth, with the incisors placed, not vertical, but obUquely forwards.
Besides these characteristics, we find the hair frizzled, coarse, and though not
reaUy wool, simulating the appearance of it. The body is often exfremely
muscular, and exhibits perfect physical development, but the humerus is
ahorter, and the fore arm proportionably longer than in Caucasian skeletons.
The legs and feet are inelegant, the wrists and ankles robust, and the hands
coarse. The akin ia generaUy dark-coloured, but very often jet black. In-
teUectuaUy, they do not occupy a high poaition among the races of men,
thought being habituaUy dormant, and there being in most cases an almost
peuiUe love for musical sounds. An important and highly interesting
branch of this variety occurs in Westem Aaia, in what is sometimes caUed
the Semitic race, including the Assyrians and Babylonians, now almost extinct,
the Jews, the Arabs, and the Ethiopians.
All these weU marked varieties of the human race, and a large number of
others less distinctly characterised, have certainly been in existence on the
Earth for a very long period, since in paintings and sculptures made by the
Egyptians more than three thousand yeara ago they were as sfrongly
indicated as at this day. It is certain, too, that the diff'erences are not entirely
caused by climate, if, indeed, they are at aU dependent on that as an agent,
but we are not at present in a condition to explain the real origin of the
peculiarities of structure observed, or refer them to any reasonable and
probable aource.
171 Natural Geographical limits of Distribution. — The various tribes
of men, in diff'erent countries, appear in most cases to have had definite
limits, corresponding to those of certain groups of animals, and although
indiriduals and hordes have wandered to distant countries, and settUng there,
have exposed themselves to the influence of diff'erent climatea and habita,
they have yet retained thefr peculiarities of stmcture. It is therefore
important to consider, as far as possible, the chief groups in relation to the
country where they now exist, or whence they have migrated.
The Arabs and the Egyptians are two examples of contiguous races
belonging to the same famify, but exhibiting marked diff'erencea, the former
occurring in Aaia, and the latter in Africa; the former adjacent to the
civilized countries of the East, among whom the Hindoos, the Persians, the
Armenians, and others, are well known examples; whUe the latter border on
the Negro fribes. Dr. Prichard has remarked, that ' though inhabiting, from
tune immemorial, regions in juxtaposition and almost, contiguous to each
other, no two races of men can be more sfrongly contrasted than were
the ancient Egyptian and the Syro- Arabian races : one nation fuU of
energy, of restless activity, changing many times thefr manner of existence,
—aometimes nomadic, feeding their fiocks in desert places, now settled and
cultivating the Earth, and filling their land with populous vUlages, and
towns, and fenced cities, — ^then spreading themselves, impeUed by the love of
glory and zeal of proselytism, over distant countries ; the other reposing ever
m luxurious ease and wealth, on the rich soU watered by thefr slimy river,
never quitting it for a foreign cUme, or displaying, unless forced, the least
change in thefr position or habits of Ufe.'* The differences thus indicated

• Frichard's Kalural History of Man, 3rd edition, p. ISO.

396 PHYSICAL GEOGRAPHY.
were carried out also in detaU, and nearly correspond to the conditions of the
two countries in aU respects of Physical Geography, and thus it is, that the
natural configuration of a district may and does exercise an important
influence ontiie growth and development of the human race therein.
It has been customary to consider the diff'erent races of men as proceeding
originaUy from certain lofty mountain chains as thefr original habitat, and in
this way the Caucasians and the Mongols have been so named, because the
one race waa supposed to be derived from the lofty mountain chain of the
Caucasus, between the Black Sea and the Caspian, and the other from the
loftier chain of the Altai, peopled in its higher plains by the Mongols. So
also the Negroes have been supposed to be derived from the southem face of
the Atlas mountains. This view, however, is not supported by facts, at least
so far as history oan adduce them. It ia more probable that the principal
racea have flourished and obtained thefr pecuUarities in great river vallCTs, aa
that of the Euphratea, the Indua, the Gangea, the NUe, the rivera of (Suna,
and othera in the Old World, or in great fertUe plaina, or extensive fraota
of country, abounding in herda of deer and cattle ; whUe othera have
adapted themselves to cfrcumatancea in smaUer areas, and formed fishing
tribes, hunting fribes, or mountaineers of various degrees of interest and
importance. To trace the geographical range and limits of each race now recogniaed
as aboriginal, would occupy too much space, and we must refer the reader
for such information to the work of Dr. Prichard, afready quoted, and to that
of Colonel HamUton Smith, recently pubhshed. On the Natural History
qf the Human Species. It wUl be useful to Ulusteate the subject by a few
examples, drawn from the distribution of races in Europe, and especiaUy in
those counfries in whioh we, as EngUshmen, muat feel the greateat intereat.*
It is now almoat universally admitted, that the European nations are a
seriea of colonies of what is caUed the Ai\?sit^ race, but under what cfrcum
stancea, and by what path they originaUy paased into Europe, can only be
a matter of conjecture. It has been considered probable that the northem
nations of Europe took thefr way through the regions which Ue to the north
ward of the Caspian, reaching in thia manner the mouth of the Danube, and
spreading then towards the north. The ItaUan, HeUenic, and Dlyrian races,
on the other hand, probably arrived by a different route— namely, through
Aaia Minor and across the Bosphorus.
Of the different European nations, which may be regarded as derived
from branches of one original stock, we must look upon those which were
driven most to the weat as the oldest, and thus begin vrith the Celtic nations,
including two branches, one represented by the Irish, Scotch, and Manx, and
the other by the Welah and Bretona, and the early inhabitanta of Spain.
Next in order comes the Germanic family, consisting of the Northmen,
ancestors of the Icelanders, Norwegiana, " Swedea, and Danea ; and the
Teutonic atock, in its three subdivisions of Saxon, German, and Gothic.
Next are tribea inhabiting Lithuania; and then the Slavonic race, ofwhich
there are two branchea, the Weatem or Proper Slavic, including the Polea,
Bohemians, and tribea near the Baltic, and the Eaatern branch, compre
hending the Eussians, Servians, and other aUied famUiea.
South Europe aeema to have modified the migrating races in a different
way, and presents the old Italians, the Tuscans, &e Thraoians, the Arnaouta
and Albanians, and the ancient HeUenic race.

• Wliile these sheets were passing through tbe press, a work has been published by Dr.
Latham, ( The Natural History of the Varieties of Man, I vol. Svo,) which may safely be recom
mended to the student as the soundest and oleai-est enunciation of the most advanced and
scientific viewa of Ethnologists.
t The name ' Aryas' is the ancient national designation both of the Pei-sian and Indian
branch of the great Asiatic source of the races that now overspread Europe and Southern Asia,
and the dei-ived races have thence been called ' Arian.' The name was adopted by the Medes,
and has been handed down by the Greeks.

ETHNOLOGY. 397
It atfll, however, remaina doubtful whether theae races, whose history can
be to a certain extent fraced, and which present diatinctly their relations to
each other, and to the original stock, were reaUy the earhest tenants of these
counfries. The more probable hypotheais is, that there were stUl earlier
tribes, and in the case of our own counfr-y there is not wanting distinct evidence in
proof of ita having been the habitation of man very long before the earUest intro
duction of that fribe of Celts who have often been regarded as the first settlers,
Ifwelook to the eridence that exists concerning the actual distribution
of these races, we shall find them greatly but not entfrely Umited by moun
tains and rivera; each tribe seems to have had a nucleus in the newly
discovered, or newly conquered tract, whUe from this nucleus they at first
diverged to occupy a certain area, and finaUy migrated in part to carry the
advance that had been made in civiUzation to a freah apot, where the higheat
advance that had been made in the mother country served aa the starting point
for the young hordes. Thus it is, that in mountainous countries we stUl find
kingdoma and portions of highly civUized countries, presenting in their popu
lation the most marked diff'erences, and even contrasts, whUe over other far
larger but level tracts, a perfect uniformity and monotony of national cha
racter prevaUs, often exceedingly unfavourable to the progress of civUization.
It has already been stated, that the Caucasian tribes occupy aU Europe,
with the exception of Finmark, Lapland, and part of Hungary . They also
now occupy part of North Africa, Persia, the whole of India, the United States
and British possessions of North America, a very large part of South America,
and many portions of AuafraUa. A part of South Africa, and a multitude of
islanda in the Pacific Ocean, have also been colonized by them in recent times,
and thua the Westem Caucasian varieties are now spread over the globe, and
have in many caaes almoat driven out the original races.
When we regard the whole Earth, and consider what is known of the
physical geography and cUmate in every country, there wUl often appear
some distinct natural reason for the spread of particular races in the
dfrections we may frace them. Thus, the Caucasians occupy, and have
occupied for a very long period, the great fertile vaUeys and plaina of the
temperate zone, and the more habitawe counfriea in the torrid zone, at least
ao far aa the Old World is concemed ; whUe the Negroes have been chiefiy
confined to the waste and unfertUe deserts and other lands of tropical
and Southern Aftica ; and the Mongols to the table-lands, mountains, and
vaUeys of Northem Asia, America, and AustraUa. The greatest popu
lations are generaUy found on the banks and moutha of rivera, on the ahorea
of gulfs and great inland seas, and thence the races have generaUy ex
tended up the country, foUowing the course of the streams, and strictly
limited by great and rapid rivers, which have thus proved effectual natural
barriers. Men, indeed, in a natural state, are subjected to laws of disfri
bution Uke other animals — they spread where means of subsistence and
shelter offer themselves, they multiply in the most favourable spots, they
atop where there ia no longer any inducement to go on ; but thia ia not the
caae when racea become able by mechanical ingenuity to overcome natural
difficultiea ; and thus the spread of civilized nations, 'and their limits of
diatribution, offer no parallel^ and are bounded by no such checks as those
which, up to a certain point in cultivation, have proved absolute. StUl, early
impressiona have never yet been effaced. Penefrating through the aurface
on the smaUest occasion of extraordinary excitement, we are able to perceive
the marked national characteristics in almost every people, whether we look
at races derived from a multitude of sources like our own, or those com
pounded only of two or three — whether we regard the half-breeds between the
Negro and Caucasian, or the Caucasian and MongoUc, or look at the nearly
pure descents of the higher castes of the Hindoo. Government has no power
of uniting races whose blood is different — language may conceal for a time,
but cannot obliterate these permanent characters; and for at least thfrty
centuries there have been as weU marked and important distinctions between

398 PHYSICAL GEOGRAPHY.
the bearded and the beardless man, the red man and the white, and the tme
Ethiopian and the Negro, aa there are at this day, vrhUe the essential points
of distinction are as clear now as they were at that distant period.
172 Language. — Of aU characteristics presented by the diff'erent
races of men, and depending on the higher or inteUectual part of his nature,
none ia more useful in determining disputed points as to the origin of parti
cular tribes than the careful atudy and comparison of the words and
grammatical construction employed to express the wants and feelings of our
nature. The study of language must, therefore, go hand in hand with that
of physical pecuUarities and human history, and though, as we shaU see, not
absolutely to be depended on or trusted, when it affords only negative
results, or to be taken without hesitation even when resemblances can be
traced, stUl it must always have great weight in the mind of any unprejudiced
person. It is generaUy agreed, that the most extensive relations between
languages, and those least likely to be effaced by time and foreign inter
course, are the fundamental lawa of conatmction, both in words and sentences.
Construction, indeed, or the rules which govem the relations of words in
sentences, seems especiaUy enduring and constant, since simUarity in this
respect prevaUs through whole classes of languages which now have few words
in common, though they appear originaUy to have had more. But beyond this,
there is a cognate character in words themaelvea, which aometimes pervadea
the entire vocabulary of a whole family of languages, the words being formed
in the same manner and according to the same artificial mle. Thia ia Ulua-
frated in the monosyUabic structure of the Chinese and Indo-Chinese lan
guages, while a remarkable instance of grammatical analogy is to be found in
each of the two systems of the Indo-European languages, of which the Greek
and EngUsh are respectively examples.
It has, indeed, been doubted whether analogy of stmcture alone ia
sufficient to prove community of origin of different languages, when unsup
ported by simUar words, as it would seem that languages reaUy descended
from the same stock must exhibit their origin in both ways. It is, however,
certain that such words may be very few in number, as wiU be seen if we
compare the Welsh and Kussian tongues, which are singularly unlike in this
respect ; whUe, on the other hand, a large number of words being infroduced
does not prove the languages to be of cognate origin. The eridence to be
deduced from verbal analogies depends, however, much on the classes of worda
in which auch analogy is to be traced, and the words that resemble each other
in languages derivea from the same stock are very different from thoae
borrowed after the two languages are formed. There is, for example, a Mnd
of domestic vocabulary in the first case, which includes the simplest famUy
relations, 'father,' 'mother,' &c., together -with the names of various parts of
the body, of the most essential and manifest material and visible objecta, and
of domeatic animala, besides some verbs expressive of universal bodUy acts,
many personal pronouns, and the numerals, at least to a certain smallextent.
On the other hand, there are worda belonging to a certain degree of
civiUzation, and connected with the aimple arts (e. g. to plough, to weave, to
sew, &c., and the names of weapons, tools, and dress), which are often common
to nations whose domestic vocabularies are different, and different when the
domestic vocabulary is nearly the same. It vrill also be evident that many
words indicative of inteUectual improvement, moral cultivatioi, reUgion, and
other matters, wUl be occasionaUy borrowed by a nation during its progress
in civiUzation, and often from people who from any accident have influence,
although they may belong to a different stock. Thus, the New Zealanders wiU
acquire a multitude of EngUah worda, although no relation may be fr-aceable
between the roots of thefr languages and the EneUsh, nor its earher and
domestic vocabulary.
The varioua languagea of the Earth have been grouped mto four:—
1. IJie Indo-Jiuropean languages. 3. The Tm-anian, or languagea of High

ETHNOLOGY. 399
Asia, and other regions to be pointed out. 3. The Chinese and Indo-Chinese,
a monosyUabic and uninflected language. 4. The Syro- Arabian, or Semitic.
The Indo-European languages are the national idioms of all those races
who at the time of Cyrus became, and have ever since continued to be, the
dominant nations of the world, except where Mahommedan fanaticism has
recovered for the Mongol and Negro races some sway over the weaker divisions
ofthe Indo-European tribes. There are many groups of these languages, each
group including a large number of dialects. The eastern group comprehends
the ancient Persian idioms, the Sanskrit and the Pali of India. The western
group, the Greek, the old lUyrian or Albanian, the old ItaUc language
excluding the Etruscan, the old Prassian, the German, the Slavonian, and
the Celtic : these are all very diatinct and of very ancient date.
Now, it becomea very naturally a question, since no one conquering
nation could introduce at once so many languages, whether the diff'erent
nations were kindred fribes of some primitive stock, and derived the analogies
of thefr speech from some common language which had graduaUy deviated
from original identity by variations at m-at merely of dialect, but gradually
increasing ; or whether the facts wiU admit of any other explanation. It
seema clear, that there is no other, and, indeed, there ia internal evidence in
the Indo-European languages themselves, sufficient to prove, that they did
giyw by gradu^ dialectic development out of one common matrix. ' Any one
who possesses competent knowledge of these languages, and considers the
nature of thefr relations to each other, the fact that the original roots are for
the most part common, and that in the great system of grammatical inflection
pervading aU these languages there is nothing else than the varied
development of common principles, must be convinced that the differences
between them are but the result of the gradual deviation of one common
language into a multitude of diverging dialects, and the ultimate conclusion
forced upon us is, that the Indo-European nations are the descendants of one
original people, and consequently, that the varieties of complexion, form,
stature, and other physical quaUties which exist among them are the resulte
of deriation from an originEd type."*
The groups of languages referable to the second great famUy of European
and Asiatic nations, differ in some fundamental points from that of the Indo-
European race, and asaiat in this way to support tbe conclusion, which is
indeed forced upon ua by other evidence, that these racea had overrun many
parta of Europe, very far to the west, long before even the oldest of the
races now existing were at aU introduced. The languages are remarkable as
haring nouns nearly or whoUy without inflexion or variation of case,
number, or sex, which can only be expressed by appending additional words,
and exhibiting these auxUiaries, and any possessive and relative pronouns
of other languages as suffixes, or syUables placed after the words which they
modify. Of aU the tribes possessing these languages, two only, vrith the exception
ofthe Finns and Lapps, have effected a lodgment in Europe in such a way as
to _ perpetuate to the present time any physical evidence of thefr former
existence. These are the Magyars and the Basques. There are also phe
nomena in the Finnish, Lappish, and Celtic languages, which appear to render
probable a former admixture vrith races which are now totaUy extinct.
Another famUy of languages belonging to the great continent is the
Chinese, which, with its vanous Indo-Chinese dialects, consists of mono
syUabic roots, not becoming dissyUabic by conatmction. These languages
are not only incapable of inflexion, but do not admit the use of particles as a
supplement to this defect, the position of words and sentences being the

» ' Eeport on Ethnology,' by Dr. Prichard, in the Reports of the British Association for tlie
Admmeement of Science, for 1847, p. 243. It is right to state that the substance of this section
on language is borrowed from Dr. Frichard's Eeport.

400 PHYSICAL GEOGRAPHY.
principal means of determining thefr relation to each other, and the meaning
intended to be conveyed.
The Syro-Arabian languages are a very ancient and important group,
wbich appear to have been apoken from the very earUest timea by the varioua
nations inhabiting Aaia to the weatward of the Tigris. They also extended
widely, and at a very eariy period, into Africa. The principal Aaiatic idioms
are the Chaldaean, the Hebrew, and the Arabic. Besides theae are the
Abyssinian dialects, the old Libyan dialects, and some others in Africa.
It appears probable from the preaent state of our knowledge, that only
two races of people and two languages exiat in the vaat regiona of Southern
Africa. These are the Hottentots, in the most southem parts, and the great
nation alUed to the Kaflrs of the eastern coast. They belong to one famUy,
aU their languagea being dialects of one speech.
Central Negroland presents a multitude of languages or dialects which
alao have relations with each other sufficiently marked to induce us to regard
them aa being of one common origin.
The languages of the ialanders of Polynesia are considered to offer
resemblances, vvhich cannot bo the effect of casual intercourse, but are essen
tial affinities deeply rooted in the construction.
In America, the northem exfremity is peopled by the Esquimaux, whose
language is known, and extends from Asia. Southwards, to a considerable
distance, two great famUiea of native languages are presented, one on flie
eaatern, and the other on the western side ; whUe stUl further southwarda, and
as far aa Mexico, the Cherokees and other Indian fribes form a group -with a
distinct tongue. In. Mexico are two principal and many less important
languages, whUe South America contains a vast variety of different tribes,
whose languages have been grouped into three, many of them, however,
being very littie known.
It may here be obaerved, that although languages, as inteUectual creations
of man, and closely entwined with hia whole mental development, bear the
stamp of national character, and as such are of the highest importance in
the recognition of the simUarity or diversity of race, they yet present many
illusions to be guarded against, as weU as a rich prize to be attained. Positive
ethnological studies, supported by profound historical knowledge, teach ns that
a degree of caution is required in these investigations conceming nations and
the languages spoken by them at particular epochs. Subjection to a foreign
yoke, long association, the influence of a foreign reUgion, a mixture of races,
even when comprising only a smaU number of the more powerful aud more
civUized immigrating race, have produced in both continents simUarlyreeurring
phenomena — namely, in one and the same race, two or more entfrely diff'erent
famiUes of languages; and in nations differing widely in origin, idioms
belonging to the same linguistic stock. Great Asiatic conquerors have been
most powerfuUy instrumental in the production of sfriking phenomena of thia
nature.* 173 Modification of the Baces of Men. — It is an important consideration
that m many countries, where there has been no recent influx of diff'erent
tribes, and where no cauae of change is perceptible but the slow and gradual
advance of civUization, and the progress of inteUectiial and moral develop
ment, there has yet been a very considerable modification of the physical
charaoteristioa of the prevaUing races. It is desfrable to consider how far thia
may have acted in past times with other portions ofthe great human famUy.
Civilization may, and in some caaes does, produce two effects, as it not
only occasionaUy modifies the existing race, but also drives before it and
destroys lesa powerful, although indigenous tribes. Thus, if aa seems pro
bable, from the comparison of language, and from the occurrence of bones
ot men in places now covered up by deposits containing other human bones of
great antiquity, there were originaUy MongoUc fribes over a great part or
• Humboldt's Cosmos, Col. Sabine's translation, '1846,) vol. i p. 364.

ETHNOLOGY, 401
the whole of Europe, including the British Islands, and if, as it is equally
certain in Western Europe, and in the British Isles, there are no present
indications of the race either in structure or appearance, we must conclude
that the advancing and conquering nation haa deatroyed tho indigenous
tribes, without permitting the blood of the two races to become mingled.
Examples of physical change in a race during the progress of civUization are
seen in Germany, where tiie accounts given of the physical characteristics
of the inhabitants only a few centuries ago oblige us to beUeve that the
prevailing colour of the hair was then yellow or red, and that of the eyes blue.
Without any further admixture of blood from a dark-coloured race, this has
now undergone much alteration, for the prevalent colour, not only in the large
towns, where mixture of blood may have been the cause, but also throughout
the coimtry, is certainly very different. With regard to this subject we may
also refer to the authority of Dr. Prichard, who says, in his work on the
Natural History of Man, dready quoted, ' I can assert from my own observa
tion that the Germana are now in many parta of thefr country far from a
bght-hafred race. I have seen a considerable number of persons assembled
in a large room at Frankfort on the Maine, and observed, that except one or
two EngUshmen, there was not an indiridual amongst them who had not dark
hafr. The ChevaUer Bunsen has assured me that he has often looked in vain
for the aubum or golden locks and the light cserulean eyes of the old
Germans, and never verified the picture given by the ancients of his country
men tiU he visited Seandinaria ; there he found himself surrounded by the
Germans of Tacitus.'*
It appears indeed beyond question, that not only the Teutonic race, but
even the Celtic have imd.ergone much change in this respect, for there seem
to be abundant fraditions asserting the prevalence of yellow, and even white
hafr among the people of that race, anciently inhabiting Ireland, Scotland,
and Wales. Now, it is certain that the present Highlandera are by no
means a yeUow or red haired people generaUy, although some districts present
this characteriatic. The prevalent characters in most part of the north of
Scotland are dark brown lank hafr, with a fafr complexion and grey eyea.
Since the mixtures that have been moat common in all the westem nations
have consisted of Celtic and Teutonic blood in some form, we thus have no
reason in this respect for the change of colour. It must be referred partly,
perhaps, to a modification of climate effected by di'ainage and the removal of
forests, partly to different food, and partly to the different condition in which
men now Uve.
The influence of a race of men migrating into a new country wUl neces
sarily differ in some respects, according to the circumstances under which
they appear and are received. Conquest and simple colonization may, for
example, produce different results, but stUl it appears from the experience of
past times, and even of very recent immigration, that the more civiUzed race
will generally prevaU, and not only so, but will graduaUy desfroy the
aborigines of the newly visited tract. The traces that are seen in various
ways of the existence of a race of men in Europe befoie the present Indo-
European race was introduced, are so slight, and have apparently produced
sp little physical change, that they must be almost neglected in any con
sideration of this kind, and thus the new race must be regarded as having
quite driven out and destroyed the earUer one. When we find a few fribes
Btm retaining thefr places and natural characteristics in some mountain
fastnesses, as the Basques in the Pyrenees, we see more clearly the possi
biUty of such extinction of races, and may recognise the cfrcumstances under
which it is possible.
Of aU cases of incursion presented in history, those of the HeUenic race
into Italy from the south, and subsequently of the Teutonic race from the

• Prichard, ante cit, p. 197.
DD

402 PHYSICAL GEOGRAPHY.
north, and that of the Scandinavian branch of the same great famUy to
Northern France and Britain, are the most remarkable and the most dis
tinctly traceable. Others had occurred in earlier times in Asia, conceming
which we know comparatively Uttle that is definite, and a simUar great
experiment is now being tried m America, and also in AustraUa, New Zealand,
and some of the other islands of the Pacific. In China, however, incursions
have been made, the reault of which ia different, as there the conquering
tribes, insufficient in number and inferior in cultivation, have only succeeded
by superior physical energy, and have obtained the government without
changing the people.
The lost races of antiquity naturaUy present many points of great interest,
especially when from time to time thefr memory is recalled by the discovery
of remains due to their labour or their ingenuity. Thus the Babyloniana
and Assyrians, the ancient and aboriginal tribes of Greece and the Etruscans,
and the much later inhabitants of Lycia, nations which had attained to some
/degree of civUization, and amongst whom the arts of constmction and
sculpture were reaUy and very succeaafuUy cultivated, have so far tended to
modify succeeding and long subsequent generations of men, that we naturaUy
inqufre into the cfrcumstances of^ thefr destmction. They appear before ua
aa races of civUized men destroyed by barbarians; and although from theae
barbaric conquerora greater, more highly cirilized, more inteUectual, and
more important nations have often ariaen, atUl the first change was that of
destruction effected by physical force against aU the advantages of inteUectual
superiority. While, also, some of these nations — including several formerly
inhabiting Asia Minor — were utterly desfroyed and thefr citiea buried in
heaps of ruins, others, as the Jews, have surrived, though aa wanderers
over the earth ; whUe the Egyptians have retained thefr name and thefr place,
although all the advance once made by them in civiUzation haa relapsed into a
monotonous and hopeless state of ignorance and slavery.
The events of the last two centuriea have shown that the influence of
civilized men determinately and permanently occupying a country may, as
in North America, tend to the absolute extermination not only of tribes, but of
many aboriginal races, and the day is perhaps not far distant when the so-caUed
American Indians shaU cease to exist, every effort ha-ving faUed to induce them
to adapt themselves to the cfrcumstances forced upon them, and no real advance
ha-ring been made in the modification of the race by the admixtm-e of tribes
or the infroduction of civUization. Total extermination is manifeatly a
possible event vrith regard to a whole people, even where room is left for
thefr existence, when they are encouraged to adapt themaelvea to new
conditiona, and when no check is put upon them beyond that degree of
encroachment which would demand only a change of habit to render it
- ,*

174 Mixture of Baces. — In various parts of the world cfrcumstances
have enforced a considerable mixture of tiie great natural families of men,
and although there is some reason to believe that this mixture is not in
itself natural, yet as it results in the production of such modified charac
teristics as may in the end form real groups, it becomes right to consider
here some remarkable instances of the kind where the misture of race has been
complete, and where the two fribes combining are distinctly recognisable.
The extreme cases of mixture that can occur are, of course, those of
different members of the three typical classes — namely, the Caucasian with
the Negro or Mongolio, and the Mongol with the Negro. The mixtures of
typical Caucasian, Negro, and MongoUc tribes with Americans and Malays are

• There is, however, an apparent exception in the case of the Cherokee nation, who are
described as settling in villages, and giving up their wandering habits for the arts of civilization.
The Indian tribes iu some parts of North America, and especially in Canada, seem also to have
cultivated the land to somo extent, as within the historic period an Indian town stood sur
rounded by corn fields on tlie sito now occupied by tho oity of Montreal.

ETHNOLOGY. 403
mtereatmg in the next degree ; and many caaes of admixture of the early
derived races, such as Celtic, Teutonic, and Sclavic ; Hindoo, Arabic, and
Egyptian ; or mixed Em-opean with mixed Asiatic races of the same original
stock, are scarcely less interesting or important in an ethnological view.
Dr. Prichard has put it forward as his decided conviction, that races of
men, of whatever kind, are equaUy proUfic, whether marriages be contracted
between indiriduals of the same or of the most dissimUar varieties, and he
adds, ' If there is any difference, it is probably in favour of the latter.'*
America is a counfry where mixtures of the Indo-European race of
various famUies (Spaniards, Portuguese, EngUsh, German, Dutch, and French,
and even Jewish,) have been effected, under tolerably equal and favourable
circumstances, -with the American Indians of various tribes, and vrith many
fribes of. Negroes from the cenfre and west of Africa; and it has been calcu
lated by M. Eugendas, (Voyage dans le Brezil, Paris, 1835,) that out of a
population of upwards of thfrty mUlions in various parts where settlements
have been made, the proportion of mixed races is as much as fifteen per cent.,
that of the various Negro tribes being eighteen, of native Indians twenty-
aeven, and of whites of aU kinds forty per cent.
Since the mixture of races appears in some cases to hkve produced a
reaUy new and intermediate stock, it may be weU to mention the instances
ofthis kind before proceeding to the subject of mixed racea where there is
stUl a doubt as to the permanence of unity of character of the produce.
Among the instances of new tribes formed by the mixture of two weU
marked races, that of the Griquas, or Griqua Hottentots, ia mentioned by
Dr. Prichard, as having been the result of the intermarriages of the early
Dutch colonists of South Africa with the aboriginal Hottentots, whUe the
so-called Cafusos form another race derived from the mixture of the native
Americana of BrazU with the Negroes imported from Africa. The former
tribes are a powerful and marauding race, Uving on the borders of the colonial
territory on the banks of the Gareep or Orange Hiver, along a distance of
aeven hundred mUes. Some of them are thriving agriculturists, and others
are coUected into a large community settled under Morarian missionaries.
The Cafusos exhibit very remarkable phyaical pecuUarities. They are
deacribed by Spix and Martina (Beise durch Brazilien) aa being alender and
muacnlar — of a dark copper and copper-brown colour — ^baring an oval coun
tenance, vrith high cheek bones, but not so broad as the Indians ; broad and
flattened nose, neither tumed up nor much bent ; broad mouth, with thick but
equal Ups, which, as weU as the lower jaw, project but Uttle ; black eyes,
intermediate in position between that of the Indians and the Negroes, and
excessively long hafr, half curled at the end, and rising almost perpendicularly
from the forehead to the height of a foot or a foot and a half.
Another remarkable mixed race is seen in New Guinea along the northem
coast, and in some adjacent islanda, obtained from the mixture of Negro with
Malay blood. Theae ' Papuans,' as they have been called, have large bushy
masaea of half-woolly hafr, measuring from two and a half to three feet in
cfrcumference, and the people have for this reason been caUed ' mop-headed.'
Thefr skin is deep brown, the hafr black, the nose broad, and the Ups thick,
and the shape ofthe skuU approaches that of the Malays.
The mixtures of white vrith negro blood in America offer many pecuUarities
worthy of notice. The first issue of the European and African (called mulatto)
is a medium in colour, figure, and even in moral quaUties ; the colour being
yeUow, brown, or ta-wney, according to the complexion of the father,
(mnlattoa derived from the marriage of a black man with a white woman are
comparatively rare,) the hafr curied and black, the iris dark, and the race
superior in cleanliness, capacity, activity, and courage, to the NeCTO. The
Buccesaive addition of European blood is considered to restore aU European

* Prichard, ante cit, p. 18.
D d2

404 PHYSICAL GEOGRAPHY.
qualities in the third generation, and the same number of generations is
required to reduce the race to the original Negro. In the aecond atage, the
terceron — the produce of Europeana and mnlattoa — ^the hafr and features are
European, and the former has no wooUy curl, but the skin has a sUght brofvn
tint, although the cheeks are red. The next generation, the chUdren of the
European and the terceron (called the quadroon) are undistinguishable from
whites. An interesting variety ia obtained by the mixture of European with native
Indian blood in South America. The offspring in this case ia caUed mestizo,
and haa the hair black and straight, the colour almost pure white, and the
skin peculiarly transparent, the iris dark, the beard smaU, the extremities
also smaU, and the eyes placed somewhat obUquely.
Among the various races of men, it is weU worthy of notice, that the
mixtures that most readUy take place seem rather at the wUl of the lower
than the higher race — the Negro woman willingly cohabiting with the white
man at his pleasure, although the white woman rarely intermarries with the
Negro man. It is also the case that the beardless or the wooUy haired tribes
acqufre a Caucasian expreaaion of beauty from a first intermixture, whUe
very often both stature and form excel that of either type ; and in another
case, in the second generation, the eyes of the Mongols become horizontal,
and the face oval. The crania alao of the Negro stock immediately expand
in thefr hybrid offspring, and the impression on subsequent generations is
more durable than when the order is reversed.*
175 Influence of Man on other Animals. — There are perhaps many
instances to be found in nature, where, owing to some local peculiarity of
climate or vegetation, one race of animals multipUes to the injury or exter
mination of another, or is modified to adapt itself to altered circumstances
It is only man, however, who is able to avaU himself at wUl of the serrices of
his feUow-creaturea, and can induce them to change thefr place of habitation,
their habits, and their natural tendencies, when snch change conduces to his
comfort or luxury. We must here consider a few of the casea where thia
modification is most decided, to understand fuUy the position of man in the
scale of creation.
In establishing himself in a new coimtry, the colonist wfll naturaUy
endeavour to avail himself of the existing and indigenous animala, to infroduce
others most useful and necessary for his purposes, and to desfroy those
species from which he can expect no advantage, and which may injure the
producta he desirea. In addition to thia, and whilst infroducing new animala
and vegetables, he introduces also unwittingly others which depend on them
for sustenance, and thus also tend to modify existing races.
The tribes of animals most useful to man, and which have been most
generaUy domesticated, are, the dog and cat among carnivora ; the ox, sheep,
and goat among ruminants ; the swine and horse among pachydermata;
the rabbit amongst rodents. Each of these offers many facts showing the
possibUity of change in external form, and even internal stmcture, to a very
remarkable degree, when exposed to the infiuence of civiUzation.
The dog as the companion of man in almost aU counfries has undergone
changes so considerable, that it is now equally difficult to decide whether
there was reaUy but one original stock, or whether the numerous races are
only fertUe hybrids. Of all the dogs, that of AusfraUa lives in the wUdest
and most natural state, and approaches in the sfructure of the skull most
nearly to the wolf, exhibiting Uttle sagacity, and being scarcely obedient to
man. The Danish dog and mastiff come next in this reapect, and are suc
ceeded by the terrier and the hound, in whose skuUs a lai'ger cavity is left for
the brain. The shepherd's dog has a very considerable capacity of cranium,
and in the spaniel and water dog this capacity is stUl greater. These and the

* Hamilton Smith, ante cit., p. 131.

ETHNOLOGY. 405
other varieties differ much in their stature and size, and in the shape of their
ears and taUs, which latter have from sixteen to twenty-one vertebra;, varying
in particular breeds. Some tribes have an additional toe or claw to the hind
foot, and some have additional or false molars. The hafr also varies greatly
in different breeds, being in some almost absent, and in others extremely
developed, either as long sUky or wooUy hafr ; and, in short, the dog presents
aU the varieties of hafry covering of the body met with in the entire class
of mammalia. Now aU these changes and modiflcations of the natural and original
condition of the dog are due to his aaaociation with and employment by man.
He aeoompaniea his maater to aU counfries, hunts with and defends him in
every climate and under aU circumstances, never recurring to the wUd state,
or evincing any desire to recover his Uberty. It is difficult to know which to
admfre most, the phancy and adaptabUity of the servant, or the pertinacity
with which the whole race clings to the inteUectual and moral superiority of
the master.
The ox and the sheep offer difficulties scarcely less considerable, and
present varieties almost as marked as the dog. Whatever we regard as the
source of domestic cattle, and whether they are of one or more original wUd
varieties, it ia certain that they have undergone by domestication such changes
in form, dimensions, structure, hafr, horns, taU, and other important charac
teristics, that they are no longer to be traced back without the greatest
difficulty. The breed of cattle infroduced by the early settlers in South
America has, however, succeeded in covering that part of the western
continent, and is fast destroying many indigenous races. The sheep, also —
one of the most anciently domesticated animals — is one in which very great
varieties are displayed ; and here it is probable that several species nave
become mixed, and that many of the breeds are fertUe hybrids. Some when
fransported to foreign counfries retain their pecuUaritiea more distinctly than
others, but aU seem to undergo great change after a few generations, approxi
mating to the local pecuUarities of form and structure. In this animal, new
breeds have been produced occasionaUy, by taking advantage of individual
peculiarities and deformities, and no doubt the numerous varieties presented
are aU greatly influenced by human agency.
The horae is found wUd in some parts of Asia and Africa, but it ia very
doubtful whether in either case we see the original species, and not a
cultivated race escaped from civiUzation ; and varieties of size, shape, and
colour are so marked, that aU reaemblance is lost by which we can decide the
question of original identity. The swine, if not ao greatly varied, exhibits
proof of change equaUy aatiafactory, some breeds having soUd hoofs, others
very long ears couched upon the back, others a large pendant beUy, and
very short legs, whUe another, found at Cape Verd and other places, has
large tusks, crooked Uke the horns of oxen.
On the whole, it undoubtedly appears that ' domestication effects a much
greater change on the manner of^ exiatence than any removal from one
country to another that can be imagined to take place during the continuance
of the wUd state. Its reaulta are, in fact, more extenaive on the nature of
animala, for domestication is not a casual and temporary change efiected in
an indiridual, but the modification of a race, by which it becomes fitted to
exist under new cfrcumstances.'
The phenomena of variation thus offered, may be grouped under three
heads, involving — ffrst, differences of organic structure ; secondly, physiolo
gical, and, thfrdly, psychological differences.
The diffierences of organic atmcture depend at firat either on an accidental
variety propagated intentionaUy, and tranamiaaible becauae of the tendency
that exiata throughout aU nature to reproduce in the offspring the peculiarities
of his immediate ancestor, or else of some modification directly produced by
change of climate, better and more regular food, and more uniform shelter.
External characters of many kinds connected with the skin, hafr, &o., are

406 PHYSICAL GEOGRAPHY.
easily modified in this way, and even the shape of the head and pelvis, the
proportions of the extremities, length of neck, and other points of stmcture,
admit of great variety.
Physiological varieties or diversities in the intemal constitution are so
frequently met with in individuals, that we can easUy conceive diff'erences
to exist m races long detached from the parent stock, and subjected to the
infiuence of man. Kie average duration of life, the number of the young
produced at a birth, the period of gestation, the changes of constitution
during Ufe, these are points which may be regarded as spedfic ; but even
these yield, though to a smaUer extent, to the effects of civilization and
domestication. This is Ulusfrated by the fact, that the cows of South America
and those of Europe differ in the time of giving mUk.
The habits and instincts of animals present, in the case of every species, a
distinct psychological character, which has been less studied in its general
natural-mstory vjilue than aa a subject of amusement and curiosity. Theae
habits and inatincta are, however, capable of modification in an exfraordinary
degree by association vrith man, and it is weU worthy of notice, that instinct,
to whatever degree it is cultivated in a race, is immediately and ahnost per
fectly fransmitted to the offspring, which accordingly wUl hardly requfre
teaching to perform the same tasks. That this is the case in dogs, especially
sporting dogs, haa been long known; but it is also the same with other
animala, as we are told ' the hereditary propensities of the offspring of the
Norwegian poneya, whether fuU or haJi-bred, are very singular. Thefr
ancestors have been in the habit of obeying the voice of thefr nders, and not
the bridle, and horse-breakers complain that it is impossible to produce this
last habit in young colts ; they are, notwithstanding, exceedingly docUe and
obedient when they understand the commands of thefr maater. It is equaUy
difficult to keep them vrithin hedges, owing perhaps to the unresfrained liberty
the race may have been accustomed to in Norway.'*
On the whole, then, it is clear that man has by domestication, and
especially as he haa himaelf advanced in civilization, very much changed and
modified many fribea of animals, removing them into distant coimtries,
inducing them to accustom themselves to different climates, and fraining them to
habits and inatincts altogether new and pecuUar ; thus encouraging remarkable
modiflcations in form, colour, integument, internal stmcture, and other points
of animal economy, and, at length, permanently fixing numerous varieties,
often more vridely separated than the original type from nearly alUed but
very distinct species.
176 Influence of Man on Inorganic Nature, and on the Vegetable
Kingdom. — Wherever man plants himself, and advances beyond the mere
animal condition, by the exercise of his inteUectual faculties — wherever, in a
word, there is found any trace of civilized man, there we shaU also find that
external nature has undergone some change. Thus, when immigration takes
place to a country covered thickly with vfrgin forests, which have continued in
the same atate for hundreda or even thousands of years, the forests are soon
cut down, and are replaced by fields of waving corn. So where Nature has
left wide stagnant pools, extensive barren tracts, or plains covered vrith
plants useless to man, all these things are readUy changed by his active
exertions, and soon, in consequence of these alterations in condition, the
climate also becomes modified ; this again, as we have afready seen in the case
of Germany and elsewhere, reacting upon the physical characteristics of the
inhabitanta of the district.
In a former chapter, when speaking of the natural limits of disfribution of
certain vegetable and animal species, and the representative forma met with
under simuar conditions of climate in distant counfries, some reference was
made to the power of man in this respect, and his habit of infroducing by

Mr. Knight, quoted in Prichai-d, ante cit, p. 72.

ETHNOLOGY. 407
ai-t many plants and animals into cUmates altogether new to them. This, we
have also had occasion to conaider, as far as animals are concerned, in the
present chapter, and now it is only necessary to recal a few striking facts,
which wiU illustoate the same general law in the case of plants and cUmate.
It is impossible even to imagine the original food of the human race, but
we certainly know that the Banana and the Plantain muat have been in use
from a very early period, since neither of them, from the oldest times of
which we have record, appeared in the state of nature, but only as essentially
altered by cultivation. Very early, too, must men have made the large-
seeded Grasses fributaries to his storehouse, for we know not the time when
any of the plants now used as Bread-corn were transplanted from thefr
native soU and rendered more useful to man.
' A striking phenomenon, which indicates the enormous antiquity of the
culture ofthe Cerealia is that, in spite of many most profound investigations,
we have not yet succeeded in discovering the proper native counfry of the
most important kinds of Com. Not one of the industeiously inquiring
fraveUers in America has ever met there vrith Maize otherwise than culti
vated, or as evidently an outcast from culture. With regard to our European
kinds of Com, we have only very inaccurate indications that they have been
found wUd, here and there, in the south-western counti'ies of Cenfral Asia.
But history proves that those regiona formerly supported so large a popu
lation, and that there existed so high a condition of culture, that the
assumption can acarcely be justified that those Corn-plants now found there are
anything but descendants from plants wbich have escaped from cultivation.*
From our knowledge of the great eastem portion of Asia, we are aware that
in China a dense population can, by a certain degree of industrial culture,
succeed in extirpating every wUd plant, and in clothing tho land exclusively
with vegetables intentionaUy raised. Except some few water-plants in the
purposely flooded rice-fields, the botanist finds scarcely any plant in the
Chinese plains which is not an object of cultivation. Thus, it may not be at
aU impossible that the Cerealia — ^perhaps originaUy (as is the case now witb
so many AusfraUan plants) confined to a narrow region of disfribution, which
was taken possession of at an early period by a strongly developing population
— ^have actuaUy whoUy disappeared from our Earth in the character of
original wUd plants.'f
Other most important and beneficial changes have been produced by human
agency inthe case of various fruit frees (e.^. Apple, Pear, and Cherry), andin
the common table vegetables of temperate climates. Who, for example, could
recognise the Caulifiower, Savoy, and other Cabbages in the dry, nauseous, and
bitter-flavoured Colewort — the undoubted stock of these vegetables; or who,
comparing the cultivated vrith the wUd Carrot, could believe that the one was
derived from the other. In aU these cases, by actual cultivation, man is able
to modify particular planta, and render even those which are apparently
injurious usefiU articles of universal and grateful food.
But much more than this is done — for the work is done on a far larger
acale — by thoae processes of clearing and preparing »for human habitation
to which we have already aUuded. Nor are these processes always successful
in permanently improving the district subjected to their influence ; for we
find in ancient human records, or in those handed down by Nature herself,
sufficient proof that parts of Egypt, Syria, Persia, &o., now burnt up by the
sun, arid from want of water, and aUowing only a very sparing population,
were once clothed with vegetation, weU watered by considerable steeams,
and capable of feeding as many thousands as there are now hundreds.
In confrast we may take the case of the Ehine and the country on its

* Wheat grown from seed obtained from Egyptian mummy cases of great antiquity has,
within the last few years, been cultivated in England. It appears to have some peculiar and
distinctive characters. t Schleiden's Plant, translated by I-Ienfi-ey for the Eay Society, p. 297.

408 PHYSICAL GEOGRAPHY.
banks, where is now raised ono of the finest of European wines, but where in
tho time of Tacitus not even the cherry, much less the grape, would ripen. The
disappearance of the forests commenced and originated the mighty change.
So also, iu other cases,the cultivation of clover, requiring a moist atmosphere,
has passed from Greece to Italy, thence to Germany, and is now fiying still
further towards the Westem Ocean. In Egypt, Pythagoras forbad his
scholars to live upon beans; but no beans grow there now to feed them.
The wine of Mareotis, celebrated by Horace, and capable of inspiring the
guests of Cleopatra, grows there now no longer. The pastures at the foot of
the richly watered Ida — Argos, once celebrated for its breed of horses — ^the
Xanthus, with its hurrying waves— these are aU histories of the past ; they
are reminiscences of what man has done, but they are now no longer
possible. We may conclude this view of the result of human cultivation in the
words of Schleiden adapted from those of Ehaa Fries.*
' A broad band of waste land foUows graduaUy in the steps of cultivation.
If it expands, its cenfre and cradle dies, and on the outer borders only do
we find green shoots But it is not impossible, only difficult, forman, without
renouncing the advantage of culture itself, one day to make reparation for the
injury which he haa infiicted ; he is appointed Lord of Creation. Trae it is
that thorns and thistles, Ul-favoured and poisonous plants, weU named by
botanists rubbish plants, mark the frack which man has proudly fraversed
through the Earth. Before him lay original nature in her wUd but subUme
beauty ; behind him he leaves the desert, a deformed and ruined land ; for
chUdish desfre of destmction, or thoughtless squandering of vegetable
treasures, have desfroyed the character of nature, and man himself flies
terrifled from the arena of his actions, leaving the impoverished Earth to bar
barous races or to animals, so long as yet another spot in vfrgin beauty smUes
before him. Thus did cultivation, driven out, leave the East, and perhaps the
deserts, formerly robbed of thefr coverings ; thus, Uke the wUd hordes of
old over beautiful Greece, this conquest is now roUing with fearfiU rapidity
through America, the eastem countries becoming barren through the demoh
tion of the forests only to inteoduce a simUar revolution into the far west.'
177 Effect of Inorganic Nature on Man. — We have seen that whatever
effect is produced by human agency on the animal and vegetable world, reacts
on the human race in ita tum, and thus at length modifies its physical charac
teristics. But the civilization ofany great natural fanuly of men is an event
which depends on something more than accident, and which is doubtless very
much influenced by the circumstances of external nature, so that it becomes
necessary to consider how far we can fafrly refer many differences that we see
to such external influence as climate, fertiUty, and geographical position.
With regard to aU these points, it seems certain that man, although
perfectly capable of settling and becoming the permanent inhabitant of ahnost
any part of the Earth, yet has not the higher quaUties and powers of his
nature developed except in temperate latitudes ; where his time is neither
entirely and necessarUy dirided between the search for coarae animal food
and thc repose and torpidity induced by exfreme cold, nor, on the other
hand, entirely at his own disposal, in consequence of the abundance of fruits
presented by a too bountiful Nature and always ready at hand when he desires
food. The former ia tho case with the Esquimaux and other tribes of
Northern Asia and America, and the latter occurs in those warm islands and
shores (of which there arc many) where the labour of a day will aupply a week's
food, not only for an individual but for the famUy dependent on him,
q.ud whore the lassitude arising from heat encom'ages almoat total idleneaa.
Tho north tcmperale zone has from the commencement of civUization been
the cradle of aU those races which have had force and energy to conquer,
talents to govei-u, and ingenuity to advance iu (he mechanical and fine arts.

* Sclllddeu's Vlnnl. ante rit., p, 306.

ETHNOLOGY. 409
Difficulties havo always tended rather to excite the powers than to check the
efforts of man ; and, therefore, in the end, those who have had most to do in
thefr contest with Nature have not only done the most, but have taken abso
lutely the highest place, and produced the greatest effect upon their feUow-
men. At aU times, the Chinese have exhibited a certain amount of civiUza
tion, and in ancient times the Egyptians, the Babylonians, the Assyrians, and
the Chaldees, and the Hindoos in the eastern division of the great Indo-
European world — ^more recently the Greeks, and after them the Romans —
and in modern times, the inhabitants of countries stUl further west have taken
the lead, and have carried the arts and sciences to graduaUy increasing
perfection ; but it is important to remember that this has been done in pro
portion as the climate of these countries has undergone change, and that the
improved civilization of the western races has been accompanied, if not
assiated, by a gradual equalization and amelioration of the temperature, the
-frinter becoming leas severe, and the summer longer and more avaUable, even
if the absolute amount of heat distributed in the year has undergone no
considerable alteration. Thua each of the three great natural famiUes of man
inhabiting the temperate zone, have always presented some people of principal
civilization, but those tribes dwelling in tropical countries have not advanced
far, and many of them have never emerged from the darkness of absolute bar-
bariam. And whUe we find the advancmg nations of the weatern hemiaphere
alwaya exhibiting thefr higheat quaUties where a necessity for exertion was evi
dent without a satisfactory result being hopeless, the nations of America before
the discovery of that continent by the Europeans had also attained a certain
though smaU amount of civUization, presenting in some respects a paraUel to
the Assyrians and Egyptians, but not tending, it would seem, to any further
or more uaeful advance, and thus to be compared with the Chinese rather
than the Indo-European race.
Although an important relation certainly exists between the state and
condition of nations and the cfrcumstances of thefr physical geography, the
opinion of M. Victor Cousin can by no means be entertained — namely, that
ii^any coimtry be examined in reference to the latter, it wUl be possiljle to
teU. a priori what is che condition of men in that countey, and what part its
inhabitants wiU act in history. The exceptions to this rule are important,
for they occur in those caaea where a mixture of blood or the immigration of
a diff'erent atock has changed the tendencies ofthe inhabitants. The objects
first to be obtained in a new settlement are food, needful raiment, and sufficient
shelter from the inclemency of the weather. If these are either too eaay or
too difficult of attainment, the development of the race, so far as the exercise
of the higher powers of human nature are concemed, is checked and pre
vented; but if these requfre moderate exertion and caU for ingenuity, and if,
moreover, the race is one of those in which inteUectual advance is the rule,
and not the exception, then may we expect that the very struggUng to over
come difficulties wUl give fresh power and energy, and induce the exercise of
the varioua useful arts and sciences.
178 Statistics of tlie Human Bace. — There are some numerical and tabular
facts regarding the human race in its various natural diviaions, that seem
worthy of notice in this place, as bearing upon the general subject before us.
Thus, the estimated popiuation of the globe, the way in which it is beUeved
that population is distributed, the rate of increase, the limits of increase, the
rektive phyaical development of varioua racea, the duration of Ufe, and other
ainnlar mattera, possess much intereat, and assist us in obtaining accurate
notions with regard to the human race.
According to Balbi, the actual present population of the globe is about
737 miUions, disfributed aa foUows : —
Europe, with its adjacent islands  227,700,000
Asia, ditto  390,000,000
Africa, ditto  60,000,000
America, (North and South,) ditto  39,000,000
Australasia, and other islands of the Pacific ... 20,300,000

410 PHYSICAL GEOGRAPHY.
The number of square mUes of land on the Earth is estimated aa about
5I5 miUions, and, therefore, we have, on an average, about fourteen and a
thfrd persons to a square mUe. To give an idea of the amount of increase
conceivable, we may state that in China it has been eatimated that more than
a hundred peraons, on an average, are planted on each square mUe of that
vast empire, although very large tracts are hopeleaaly barren ; whUe, as the '
population of England and Wales at the last cenaua waa about fifteen
miUiona, and the countriea together contain about 50,000 square mUes, there
are aeen to be with ua not less than 300 on an average to each aquare mUe. Of
the whole population, however, one-thfrd reside in large towna (of 10,000 and
upwarda). The rate of increase of mankind it is not easy to calculate, except in veiy
Umited districts. In the thickly peopled districte of England, the increase in
ten years, ending 1841, amounted in towns to 20-2 per cent. ; in the mral
districta to 11-2 per cent. ; and in the whole population together to 14-4 per
cent. The annual increase may, perhaps, be fafrly estimated as being now
about one and one-third per cent.
Of the whole population of the world, it is thought that about one thirty-
third part (three per cent.) die every year, and that the atock ia during the
same interval increased by somewhat more than a thirtieth (three and a thfrd
per cent). This would give about 23f millions born, and 21^ mUhons dying
in each year. Although, however, the average mortaUty ia reckoned ao high,
the mean average of life in the human race ia much more than thfrty years,
and in spite of the large number of children and young persons who meet
with an early grave, (one-fourth of the infants bom dying before they are a
year old, whUe half the whole number do not attain the age of twenty-two
years,) the mean duration of life muat be considered to amount to from thirty-
eight to forty-two years, according to cfrcumstances.
The number of male children born in civilized countries exceeds that of
females by about one-twentieth part, but in consequence of greater exposure
to accidents, the destruction of life by war, and unhealthy employmente, the
mortaUty of males is greater, and finally the women are more numerous than
men. In Great Britain, at the last cenaua, there was an excess of female
population to the extent of 24fl,181, (being in the proportion of thirty-nine
to thfrty-eight nearly,) although there was during that period an annual
excess of male births in the proportion of twenty to nineteen.
The average number of chUdren to a marriage in Europe varies in different
countries, from three and a half to nearly five and three-quarters, being least
in Northem Europe and greatest in Savoy. It may be considered that the
ordinary proportion in England is four births to each marriage. Perhaps
one cause of the proportion being comparatively small in England is, that
from prudential and other motives, msirriages frequentiy do not take place tiU
somewhat later in Ufe than in many other countries in Europe; but another
and more important one arises from the fact that so large a proportion of the
inhabitants dwell in large towns.
The general proportion between births and deaths taken one year vrith
another, and for a large extent ofthe civilized world, may be considered to vary
between 100 and 150 births for every 100 deaths. It is probable that a larger
proportion than the latter can hardly exist under the most favourable cfrcum
stances, whUe the former can only take place where there are some causes of
unusual and even fearful mortaUty.
The true proportion between bfrths and deatiis for a number of years
cannot at present be determined with certainty, owing to a want of accuracy
in the registrations. In England, however, it is probably as 150 to 100.
With reference to the original peopling of the Earth itself, or of new
countries, it has been calculated that under very favourable circumstances the
human race may bo tripled in about twenty-fom' years. It has, also, been
supposed that the posterity of one malo and female might in three hundred
years, if not interfered with, amount to a population ofabout 4,000,000 of souls.

ETHNOLOGY.

411

The ordinary mortaUty of a country with reference to its whole popula
tion varies, of course, according to the climate and mode of Ufe of the people.
In England (including Wales), it is estimated to amount to about one forty-
sixth, that proportion of the whole population dying annuaUy. In France,
it is estimated at one-fortieth, and in Bussia the same ; while in some selected
spots, as, for example, in North Wales and part of Surrey, it reaches to only
one fifty-fifth.
In England, at the last census, the ages of nearly 16,000,000 of individuals
were returned, thus giving very interesting facts vrith reference to the duration
of human Ufe. We quote this table as given in MaccuUoch's Statistics ofthe
British Empire, (vol. i. p. 424) : —

Population calculated for
July 1, 1841.

Deaths registered in
1841.

Annual mortality :
per cent. j

Ages.
1
1
Persons.
Males.
Females.
Persons.
Males.
Females
Mean.
Males.
Females 1
|i-^r
0-1
429,419
210,507
213,912
74,210
41,444
32,766
17-365
19-726
14^984
6
1-2
429,803
215,493
214,310
27,268
13,987
13,281
6-353
6^603
6^204 1
16
2—3
437,276
218,208
219,068
15,027
7,516
7,611
3-441
3-461
3432
29
3-4
410,077
203,653
206,424
9,914
5,028
4,886
2-422
2^474
2^370 '
41
4—5
401,.555
201,238
200,317
7,164
3,620
3,544
1-786
1^802
1771 ,
60
0-5
2,108,130
1,049,099
1,059,031
133,583
71,595
61,988
6-349
6833
5^860
16
5—10
1,906.576
953,893
952,683
17,868
9,093
8,775
¦938
-955
•922
107
10—15
1,733,652
881,129
852,523
9,116
4,478
4,638
•527
•509
•545
190
15—20
1,588,340
782,425
805,915
12,056
6,604
6,452
•759
•718
•801
132
80—26
1,551,703
724,013
827,690
13,922
6,633
7,289
•900
-918
•882
111
25—30
1,284,020
611,390
672,630
12,889
6,045
6,844
1-OOb
-991
1-019
100
30-35
1,167,954
565,226
602,728
11,414
6,422
6,992
•978
-961
¦995
102
35—40
885,306
435,430
449,876
11,195
5,385
5,810
1-266
1-239
1-293
79
40—45
888,806
435,991
452,815
10,510
5,251
5,259
I •185
1-207
1163
84
45—50
639,202
313,709
325,493
10,244
5,322
4,922
i-m
1-700
1514
62
50—55
634,910
307,435
327,469
10,811
5,673
5,138
1-710
1-849
f571
68
55-60
392,166
189,816
202,350
10,552
6,418
6,134
2^700
2-860
2^640
37
60-65
440,110
209,246
230,862
13,813
7,090
6,723
3-155
3-395
2^915
32
65—70
259,839
120,829
139,010
14,071
6,881
7,190
6-442
5^706
5^178
18
70-75
224,431
104,138
120,293
15,569
7,630
7,939
»974
7341
6^607
14
75-80
120,015
55,653
64,362
14,525
6,992
7,533
12^152
12^586
11^717
8
80-85
70,494
31,136
39,358
11,681
5,358
6,323
16662
17-242
16^083
6
85-90
24,008
10,149
13,859
6,550
2,841
3,709
27^418
28-047
26-790
4
90-95
6,541
2,493
4,048
2,243
898
1,345
34-677
36-091
33-264
a
95-100
1,421
497
924
604
220
384
42-972
44-352
41692
2
too and ¦»
upwards /
249
82
167
UO
29
81
4^829
35^221
48^438
2
AUages
15,927,867
7,783,781
8,144,086
343,847
174,193
169,649
2^160
2238
2'083
46
412 PHYSICAL GEOGRAPHY.
In this table the whole population of England is included, and the laat
column ahowa the mean mortality at any given age. Thus, between the ages
of fifteen and twenty, one person out of every one hundred and thfrty-two
dies per annum. The annual mortality column, read -without regarding the
decimal points, expresses also the number who die each year of any age out
of every hundred thousand.
The mean age of the male population of England, taken from this table,
would be twenty-five and a half years, the young predominating, owing to
the increase in the population, and the higher average of deaths in the earher
periods. If the community were stationary, the mean age ofthe people would
be (cceteris paribus) thfrty-two years, and the mean age of death a Uttle more
than forty -one years.
We have given these latter statistical detaUs chiefly from our own
country, because the information is, we believe, at leaat as fuU and accurate,
and the general result as satisfactory, as is the case vrith any others that have
been published. In many respects, too, they contain positive data not else
where to be obtained, but it is right to add that the Belgian statistics are also
most carefuUy and minutely tabidated.

General Conclusion.
We have now reached the cloae of our work on this great subject
of Phyaical Geography, and it might, perhapa, be thought adrisable to
revert to the main facts placed before the reader, or consider the general
harmony of the subject and the mutual bearing of every part on the whole.
But, in fact, it would be diificult to coUect into a few pages the resulte
of the numerous facts afready presented in a condensed form, and it is
better to give a simple outUne of the advantage that ought to be derived
by the student than endeavour merely to impress upon bim the extent or
the diflSculty of the task. If we look back to the middle ages and notice
the rarity of general information and the difficulty of obtaining it, we may
perceive some excuae for the practical as weU as inteUectual ignorance of
the multitude of that day. They could and did observe isolated facta, of what
ever kind, even as we do now, and the phenomena of nature did not, we may
be sure, then pass unnoticed by the shrewd and thinking men who were in a
nosition to obaerve them. But there were no meana readUy at hand of
"preading and comparing information, and thua, before the invention of
printing, facta were almoat uaeleaa, because they were isolated, and could not
conveniently be worked into that form in which they become materials for
generalization. The discovery of printing gave a facUity for this, and then
' the sparks of information, from time to time struck out, instead of glimmering
for a moment and dying away in obUvion, began to accumulate into a genial
glow, and the fiame waa at length kindled which was speedUy to acqufre the
sfrength and rapid spread of a confiagration.' But although this outbreak
of science, and its sudden and vast expansion, and steady, unremitting
progress up to the preaent time have indeed been marveUous, it is manifest
that there ia stUl much room for further increase when the people of each
countey shaU be sufficiently weU informed on every subject to oring their
powers of observation into useful bearing, and occupy thefr leisure with
distinct investigations of Nature and hor works. It is the accumulation of
knowledge by tiie people indiriduaUy, that must be looked to as the source of
great fnture discoveries, and such knowledge as that presented in the present
volume is chiefiy valuable as it gives useful, correct, and practical information
to those who vrish to learn and are willing to be useful. To quote again
from the beautiful essay by Sir John Herschel, (afready referred to above,)
' It is obvious that aU the information that can possitly be procured and
reported by the most enlightened and active traveUers must laU infinitely
short of what is to be obtained by individuals actuaUy resident upon tho spot.

GENERAL CONCLUSION. 413
TraveUers, indeed, may make coUections, may snatch a few hasty observa
tions, may note, for instance, the disfribution of geological formations in a
few detacned points, and now and then iritness remarkable local phenomena ;
but the resident alone can make continued series of regular observations,
such as the scientific determination of clunates, tides, magnetic variations,
and innumerable other objects of that kind required ; can alone mark all the
detaUs of geological sfructure, and refer each stratum, by a careful and long-
continued observation of ite fossU contenta, to its tone epoch ; can alone note
the habita of the animals of his country and the Umits of its vegetation, or
obtain a satisfactory knowledge of its mineral contents, with a thousand
other particulars essential to that complete acquaintance with our globe, as
a whole, which is begiiming to be understood by the extensive designation of
Physical Geography; besides, whioh ought not to be omitted, multiplied
opportumties of observing and recording.those exfraordinary phenomena of
Nature wluch oflFer an intense interest from the rarity of thefr occurrence, aa
weU as the inatmction they are calculated to aflford. To what, then, may
we not look forward, when a spfrit of scientific inquiry shall have apread
through thoae vaat regions in which the process of civiUzation, its sure
precursor, is actuaUy commenced and in active progress P And what may
we not expect from the exertions of powerful minds caUed into action under
circumstances totaUy different from any which have yet existed in the world,
and over an extent of territory far surpassing that which has hitherto
produced the whole harvest of human inteUect P In proportion as the
nmnber of those who are engaged on each department of physical inqufry
increases, and the geographical extent over which they are spread is enlarged,
a proportionately increased facUity of communication and interchange of
knowledge becomes essential to the prosecution of thefr researches with full
advantage. Not only is this desfrable to prevent a number of individuals
from making the same discoveries at the same moment, which (besides the
waste of valuable time) haa always been a fertUe source of jealousies and
miannderstandings, by which great evUs have been entaUed on science, but
because methods of observation are continuaUy undergoing new improve
ments, or acquiring new facUities, a knowledge of which it is for the general
interest of science should be diflused as vridely and as rapidly as possible.
By this meana, too, a sense of common interest, of mutual assistance, and a
feehng of sympathy in a common pursuit, are generated, which proves a
powerful stimulus to exertion ; and, on the other hand, means are thereby
afiiDrded of detecting and pointing out mistakes before it is too late for thefr
rectification.'* It has been the object of the author to prepare a teeatise which shaU be
uaeful in the way thus aUuded to, and since ' one of the means by which an
advanced state of physical science contributes greatly to accelerate and secure
its further progress is the exact knowledge of physical data,' and that these
data can only be known and made use of to advantage by the help of general
knowledge of natural as weU as mathematical science, he trusts that his
portion of the present work is adapted to advance nscience in the right
dfrection.

Herschel's Preliminary Viscov/rsc, p. SiP.

THEORY OF DESCRIPTION
AND '
GEOGRAPHICAL TERMINOLOGY.

CHAPTER I.
§ 1. Nature and divisions of the subject. — 2. Of positive position. — 3. Of relative position. —
4. Of land and water in extent. — 5. Of land in elevation. — 6. Of water not in motion. —
7. Of water in motion. — 8. Of the natural productions of the surface of the earth.
l^ATUBE and Divisions of the Subject. — Descriptive Geography has for
^V its object to give the Imowledge of the superficial character of the
Earth's surface, and its productions, whether vegetable or animal. It
is, however, impossible to confine it sti:ictly to these things, inasmuch as no
description of either its vegetable or animal productions would be satis
factory if it were not accompanied by the knowledge of the things on
which they depend, as soU, climate, &c., which belong to the department
of Physical Geography, and more especiaUy of man, for whom the preaent
state of the globe was designed, and those works of his by whidi it is
covered. But this involves some historical considerations; for it must be
evident that in the same place may be found the results both of man's
present and past labours. The fisherman's hut stands on the ruins of Tyre,
the black tent of the Arab on those of Nineveh, vegetables fransplanted
formerly may appear indigenous now, and therefore the description of any
country must vary much, according to the time with reference to which it is
given. Descriptive Geography is, nowever, more immediately concemed vrith
the greater and more abiding features of the surface of the Earth; the
dirision of the Earth into kingdoms and states, vrith ite resulte, belongs rather
to PoUtical Geography; the dianges efl'ected by man's residence in particular
places, to Topography; but the latter involves itself with the former ao
intimately that it ca,nnot be aeparated from it, for the knowledge of places
(tottos, a place) includes both thefr natural character, and the efiect of man's
residence in them; the first coming under the head of Descriptive Geo
graphy, and the second under Pohtical; but as Topography descends to
minor detaUs and meaaurements, which have no dfrect or at least apparent
efi'eet on the world at large with which Geography proper concerns itself, and
as the Umits of the present work preclude minute details altogether, the
description of the surface of the Earth may more profitably be considered in
it under two leading divisions : —
1. The Earth's aurface and natural productions.
2. The Earth's surface as afi'ected by the residence of man upon it.
The first, it wUl be observed, is but an extension of what haa been already
freated of in Physical Geography ; the mode in which it is to be freated
must, however, be difi'erent. Science, it is true, is one and indirisible, but it is
presented to our minds under difi'erent phases and in various connexions,
and the unity is preserved, if the principles on whioh it depends are not
violated, even if it be riewed from another aspect.
To describe any given part of the Earth's surface, three preliminary con
siderationa are required: — I. Poaition. 2. Extent, or horizontal contour.
3. Form, or vertical contour.
Poaition is both positive and relative. The first is determined by Mathe-

GEOGRAPHICAL TERMINOLOGY. 415
matical Geography ; the second is the result of extent and form, as has already
been shown in Physical Geography. Extent is dependent on form; but
inasmuch as we are accustomed to obtain our knowledge of the Earth's surface
from ai'tificial globes, maps, and charts, and that which is first appai'ent on
them after the position, is the extent of the countries depicted, it is better in
description to preserve the order in which they are given above.
2 Of Positive Position. — If the globe of the Earth were a perfect
sphere, aud did not revolve in one uniform dfrection, arbitrary means could
alone be resorted to, to determine the position of places ; but being an oblate
spheriod, having its shortest diameter for its axis of revolution, two points
and one cfrcle are at once determinable on its surface. The points caUed the
Poles, at the north and south exfremities of that axis, are so named with
respect to their relative position to a certain point in the heavens, to which
the mariner's compass, by the magnetic power imparted to it, ia dfrected.
(See M. G., p. 6; and P. G., p. 196.) In strict accuracy, a circle drawn round
the Earth equidistant from those points, has its circumference greater than
any other wmch can be deacribed on the globe. (See Chartography, p. 179.)
Thia circle, thus distinguished both in cnaracter and position, is called the
Equator ; by it the globe is dirided into two equal parts or hemispheres,
and another element for the right estimation of the position of any place
obtained. In practice, however, tho difi'erence between this cfrcle ana any
other dravra through two equidistant points on the globe, (haring a longer
diameter between them,) is inappreciahle. As every circle is divided into
360 degrees, cfrcles drawn through the poles, diriding the equator into that
number of parte, or, if the scale admit, subdividing these again into minutes
or other equal parts, wUl form limits by which the position of places may be
ascertained; but aa in a lateral dfrection — i. e. in the line ofthe equator — there
are no fixed pointa like the polea, an arbitrary distinction between these
cfrcles has been necessitated, and this every nation haa natm-aUy made for
iteelf, each reckoning these circlea from aome point apparentlymoat desirable
fi'om local or political connexion. (See Chartography, p. 181.) We, in England,
reckon from Greenwich, because the National Observatory is there ; and
these cfrcles, caUed Meridians of Longitude, numbered from thence, enable
ua to ascertain the distance of any place from the meridian of that place in
degrees ; but aa circles drawn through the same point approach each otber,
aa they approach that point, so although the aame number of degrees are
estimated between each meridian, the length of a degree becomes leas and
lesa in proportion to ita neameas to the polea. It becomes, therefore, neces
sary to limit the number of these cfrclea, or the upper part of globes and maps
would soon become confused by them ; smaU divisions of lateral space must,
on this account, be ascertained on a globe by the use of the brazen meridian
and horizon, or by a graduated scale, or on a map by measurement. Degrees
are thus estimated by inspection, but they may be reduced to mUes by the
rules afready laid down (see M. G., p. 72), or by reference to a table (aee
Appendix A), it being remembered that a degree at the equator is sixty
geographical mUes in length.
The meridians of longitude, or circles drawn througt the poles, are of the
same cfrcumference* — viz., 360 degrees, of sixty mUea to a degree, they are
commonly caUed great circles ; but, as those circles only can be great circles
whioh are drawn through two points equidistant from each other, circles
drawn, dividing them into equal parts, and consequently paraUel to the equator,
must be of less cfrcumference, and gradually decrease as they recede from it :
auch cfrcles are called ParaUels of Latitude — parallel, becauae parallel to the
equator, and of latitude now with iuatice, becauae they are on each side of it.
The name, however, was adopted by the ancients when it waa supposed that
the extent of the Earth from eaat to weat (ita therefore so caUed longitude,)

On the comparative magnitudes of small and great circles. (See M. (?., p. 24.)

416 THEORY OP DESCRIPTION AND
was greater than that from north to south, therefore caUed ita latitude. The
latitude and longitude of any place — i. e. its position on the surface of the
Earth — ^is aacertained by obaerriiif what meridian and paraUel cut each other,
or what minuter diviaions' intersect, where it is situatea.
The position of the Earth with respect to the Sun, its annual and diumal
rotations, afi'ord additional means of estimating position. The apparentpath of
the Sun on the surface of the Earth is indicated by a great cfrcle cuttmg the
equator diagonally, called the EcUptic (see M. G., p. 14) ; the two points equi
distant from each other where the two cfrcles intersect are caUed theEquinoctial
points (see M. G., p. 56), and these for certain periods afi'ord points from whioh
to measure distance in its relation to time and the seasons. The exfreme
distances north and south of the equator to which the ecliptic reaches, mark
the extreme pointa at which the Sun is ever vertical; these are termed
Solstitial : and the zone or belt thus formed round the Earth Umited by
circles corresponding to the 231° of latitude, and oaUed respectively the Tropic
of Cancer and the Tropic of Capricorn, from the signs ofthe Zodiac farthest,
from the equinoctial pointa, is caUed the Torrid Zone, and any place lying
within it is said to be within the tropics. Beyond this, as far north and south
as the 66|° of latitude, the Temperate Zone extends, and from thence to the
Poles, 235°, the Arctic and Antarctic respectively.
In Physical Geography, as has been noted, other zones, having reference
to temperature, cUmate, natural productions, &c., are recogniaed, and aU
these may be appUed to the estimation of the position, but rather relative
than the positive, of places on the surface of the Earth.
3 Of Belative Position. — As aU estimation of position in longitude must
be to a certain extent arbitrary, east and west are only relative terms, and
although position, north or aouth, is capable of more exact definition, yet
when applied to the position of places with respect to each other, they like
wise become relative. A place near the Soutii Pole may be north of another
still nearer that point — may be north of one and south of anotherplace,
or east, or west, or vice versd. This is relative position on the globe. Pfaving
determined the position of the great continental masses, we may, in describing
any place conaider — 1. What poaition it occupies in them, and in which of ite
great natural divisions it is to be found ; 2. To what physical dirision or diafrict
it belongs ; 3. How it ia aflfected by poUtical divisions ; 4. Ite poaition vrith
respect to commerce. Each of these may be again re-considered in a general
or particular relation, in a topographical or resfricted, or a geographical or more
enlarged sense ; and although our object is to avoid topographical detaUa as
much as possible, the description even of counfries, whether considered in
thefr phyaical or poUtical relationa, would be very incomplete were not both
attended to.
Eelative poaition may not only be considered in extent, but in elevation ;
the point of departure for calculation is, by common consent, assumed at the
sea level ; and it may be estimated not only in actual height in mUes, yarda,
or feet, but in regions of temperature also, as already noticed, the temperature
decreasing with the elevation. (See P. G., p. 325.) As, however, this varies,
not only with the elevation, but in proportion as it recedes north or south
from the influence of the Sun's rays, position thus estimated is more especially
relative. Vertical position may be reckoned not only above but below the
level of the sea ; some, but comparatively few, places on the Earth's surface
being thus distinguished.
From the considerations afready entered into in the part on Physical
Geography, it is apparent that the horizontal contom' of the land dependa on
the sea by whioh it ia bounded, while that again is the result simply of
depreaaions in the land ; and thua the form or vertical contour of the Earth's
surface is the origin of all ita superficial diviaions ; it is alao that which is most
apparent to the eye of man; but, on the other hand, the elevationa and
depressions on the Earth'a aurface are, when compared with ita extent,
entirely insignificant.

GEOGRAPHICAL TERMINOLOGY. 417
4 Of Land and Water- in Extent. — The principal dirisions ofthe land are
caUed Continents, those of the water, Oceans. Ofthe former, it was customary
to reckon four, Europe, Asia, Africa, and America ; to these some added a
fifth, Ausfraha. Having regard, however, to the meaning of the word, and
gnided by the practice of modern geographers, the definition already given
(see P. G., p. 216) has been adopted — Continent, that which is connected
'together and continuous. There are therefore only two continents, the Old
and the New — the former containing Europe, Asia, and Africa ; the latter,
America, North and South; to these the terms east and west have been
respectively applied. They are, of course, only relative. The oceans divide
the continents from each other.
Ocean is a word adopted from the Greek, and, from tbe use of its cognates
in languages of simUar origin, seems to embrace ideas of extent and depth,
as weU as of production or generation. Bochart and others suppose it derived
from a Syriac word which signifies to ' encompass.' This is probably conse
quent on the uae of the word among the Greeks, who suppoaed the ocean to
eneompasa the land, as its connexion with production appeara to be the
result of the mythological teansmission of the history of the general deluge.
In its largest extent it is now taken to mean the whole body of water on
the surface of the globe, the surface drainage of those portions entfrely
surrounded by land alone excepted. It haa been usually divided into five
parts, all retaining the general appellation — the Atlantic, the Pacific, the
Indian, the Arctic, and the Antarctic; until lately their respective limits were
very indefinite, but in 1845 the B.oyal Geographical Society of London
appointed a committee to consider the subject, and their report is thus given
in Johnson's Glossary qf Geographical Tei-ms ;*
' That the limita of the Arctic and Antarctic Oceans, respectively, be the
Arctic and Antarctic Cfrcles ; that the limits of the Atlantic on the north and
south be the Arctic and Antarctic Cfrcles, that its western limit be the coaat
of America aa far aouth as Cape Hom, and thence prolonged on the meridian
of that Cape untU it meets the Antarctic Circle ; that its eastern limit be the
ahores of Europe, Africa as far south as the Cape of Good Hope, and thence
prolonged on the meridian of Cape LaguUas, tUl that meridian cuta the
Antarctic Circle ; that the Indian Ocean do extend from India and Persia
on the north to the Antarctic Cfrcle on the south ; that ita western limit be
the shores of Arabia and Africa, as far south as Cape LaguUas, and thence
along the meridian of that Cape to its intersection with the Antarctic Cfrcle :
that its eastern Umit be the west coast of the Birman Empire, and a part of
the Malayan peninsula, the west coasts of Sumatra, Java, Timor, and
AusfraUa, as far as the southernmost point of Van Diemen's land, and thence
continued along the meridian of that point to its intersection with the
Antarctic Circle ; that the Pacific do extend from the Arctic Circle on the
north to the Antarctic Cfrcle on the south ; that its western limit be the east
coast of Asia and of the Island of Sumatra, the northern shores of Java,
Hom, and Timor, and the coasts of Australia, from MelviUe Island, round to
the southem point of Van Diemen's Land, and along its meridian to the
Antarctic Circle ; and that its eaatern limit be the west coast of America and
the meridian of Cape Hom as far as the Antarctic Cfrcle. It was further
agreed, that the Atlantic and Pacific Oceans be subdivided into three portions
— a northern, a southem, and an intertropical — and that the Indian Ocean
have but two divisions, an intertropical and a southern.'
It ia obvious that such questions aa these can only be decided arbifrarily,
for it wUl be observed, that some of the limits given are natural and some
artificial, and as without authority the universal consent of geographers can
scarcely be expected, it is not only within the province of such societies as

* We beg to acknowledge here, once for all, our obligations to this very useful and able
le work.

little work.
BE

418 THEORY OF DESCEIPTION AND
the Eoyal Geographical Society to express an opinion upon them, but
the duty of every geographer to submit his individual opinion to thefr
collective decision. If, however, the universal consent of aU students of this
science is to be hoped for to anything upon ita own merits, it might weU be
to this, for the Umits given are, aa waa to be expected, clear and well defined,
and subject to no reasonable objection.
(The Disfribution of Land and Water, thefr normal shape, &c., are freated
of in P. G., chap, iv.)
Besides these great and more general, the ocean is susceptible of smaUer
dirisiona, dependent like them on the configuration of the land. The
next in extent and importance are uauaUy aaid to be Seaa. The word Sea
ia of very indefinite appUcation, being often convertible with Gulf or Bay.
It ia uaed in contradistinction to land in a general sense, and in its special,
appUed to diriaions of the ocean, but apparently vrithout rule. Some aeaa, aa
the Mediterranean Sea, are very nearly surrounded by land — some more
open, as the sea of Kamschatka. The etymology of the word (from the Saxon
see secge) ia rather auggeative of the former, meaning a repoaitory, basin,
cistern, — ^thia would, however, include the Gulf of St. Lawrence, Hudson's
Bay and Baffin's Bay among the seas. Some lakes have been denominated
seas, as the Caspian, and the Lake of Gennesareth, caUed sometimes the Sea
of GaUlee. It is much to be desfred that some decision was arrived at
in this matter by the Geographical Society. The word Gulf is, as has been
seen, sometimes used convertibly with Sea; it appears to be properly the
intermediate term between that and Bay ; it is derived from the Greek,
Kok-rros, implying hoUowness, depth. Homer uses the word for a bay or creek,
(II. b. ii. I. 560,) and it is explained by Eustathius and Sfrabo to mean a sea
enclosed between two promontories ; it is generaUy esteemed to differ from a
Bay in being deeper than it is broad at its enfranee ; the latter word being
derived from a Saxon root, signifying to bend, (or possibly from byge, an
angle) — any deep bend of the sea should in propriety be caUed a Bay,
and in contradistinction to a Gulf, it shouldt be wider at ite entrance
than in depth ; but this definition wUl not hold good in practice, for then
Baffin's Bay could not be so denominated. In the absence, however, of
any exact definition of theao three terms, the foUowing may be proposed —
a Sea, any deep recess of the ocean which may be entered by more than one
principal channel ; a Gulf, any similar recess, having only one ; a Bay, an
indentation of the ocean, lying open to it. In case, however, of the adoption
of this, or indeed any exact definition, the present namea must be changed.
The Mediterranean and Eed Seas would cease to be so termed, and
Hudson's Bay and Baffin's Bay would become Gulfs or Seas. The term Bight
is synonymous with Bay.
The passages by which a gulf, or such seas as the Mediterranean and Eed
Sea, communicate witb the ocean are called Sfraits — as the Sfrait of Gibraltar.
The tefm strait, occaaionaUy but erroneously used in the plural, is syno
nymous vrith channel, it is appUed to passages between islands, as well as
between the ocean and a gulf, or Mediterranean Sea ; and the words Arm
and Sound are sometimes used for the same purpose ; but the word Channel
is equaUy appUcable to rivers, and arm more properly to deep indentations
having no second outlet. Strait ia the same as straight, and is derived from
words which imply elongation (stretching, sfraining). It is customary to -write
straight when the meaning is dfrect, strait when narrowness is imphed,
apparently without reason. A strait is a narrow passage, and the word has
been appUed to a defile or pasa, between mountaina. The word Sound has a
similar derivation originally, but the Saxon Sund was used for a narrow sea or
swimming. A Sound, is therefore to be diatinguished from a Strait, in not
of neceaaity having a double communication with the ocean, and possibly aa
being of comparatively little depth — being in soundings, which is usuaUy held
to mean a depth of water of not much more than eighty fathoms. (For depths
of Ocean, seo P. G., chap, v.) In the east of Scotiand such indentations or

GEOGRAPHICAL TERMINOLOGY. 419
channels are called Ffrths or Friths, which, if esteemed cognate with the
laiJnfretum, indicate the roughness of the water caused by passing such
narrow channels; on the west coast of Scotland and in Ireland, Lochs, i. e.
Lakes — the primary sense of this word is to shut in or enclose ; and in
Norway, Fiords. A small sfrait is also caUed a Gut. This word is also
applied to the narrowest part of a strait.
The smaUer divisions of the ocean, as they are more immediately related
to the coaat hne, in its minute indentations, so they are best described
in connexion vrith the land. Continental land has been afready referred to
as diriding the continuous surface of the globe into two great parts. All the
minor appeUations given to divisions of land in extent, excepting those which
are properly diminutives, have no relation to size, and are therefore used
equsdly for larger or smaUer portions of the aame character.
In deecribmg land in extent it is desfrable, flrst, to secure an accurate
perception of ite general shape, whether it approaches a square, a teiangle,
or any other mathematical figure, whether it be simple or compound, without
paying attention to the minute indentations of the coast. This may be
c^ed ite normal shape.*
The lines by which this figure is bounded may be measured either from
one exfreme point to another, or a mean may be taken, the latter plan has
been adopted for the descriptive partof this work; thefr contents should next
be ascertained; thia may be done by reducing degrees and minutes of longi
tude and latitude into nules, and proceeding by the rules given, M. G., ch. iv.
§§ 2 — 6, vrith reference to the scale and projection of the map, by which
tiie calculation is made — (see Chartography, p. 178, et seq.) — or by simple
measurement on an artificial globe.
Having thus obtained a general idea of the shape and size of the land tp
be described, it muat be conaidered in detaU, firat marking the larger and then
the lesa important indentations or extensions of the coast-line. The principal
extenaiona of land into the water, for they are appUcable to aU aituations —
are caUed Promontories: the derivation ofthis word from the Latin Promon
torium (^0, before, mo?w, a mountain), indicates first its origin — viz., from the
elevation of the land above the sea level — (this must always be remembered
when the shape of land is conaidered); and aecondly, that it ia more properly
uaed to denote high land. The word Promontory has no reference to aize.
The great southem triangular projections of the continental lands afready
referred to (see P. G., p. 216) are thus named; smaUer ones, of course,
are veiy numerous. There are, however, diminutives used in the description
of projections of very smaU size, — a Point is the low extremity of a Promon
tory, — a Cape (from caput, head) is a projection of the coast, or termination of
a promontory, neither of great elevation nor yet altogether deficient in it.
It may be properly used as a generic term for any projecting land, having
no relation to elevation, or as intermediate between Point and Headland,
the latter always indicating considerable altitude ; a Point of smaU magni
tude is termed a Spit or Tongue; a smaU Headland, a Bluff— this word is
speciaUy localized on the Ohio and Mississippi rivers in America. Foreland
is aynonymous vrith Headland, and the word Ness (i.*e. nose, a projection)
affixed to a descriptive appellation has the same meaning. This word is
localized on the east coast as BUl, having the same meaning as on the south
coast of England. Spits are sometimes foimd below Capes and Headlands.
The word Tongue is usuaUy the diminutive of Point, and applied to a small
extension of low land.
Land projecting into the water, of whatever shape, attached on one side
to a larger maaa, whether continental or insular, is caUed a Peninsula, (from
the Latin, pene, almost — insula, an ialand; in Greek, x^P<rovrja-os, chersonesus.

• Noi-maJ, from norma, a square— 1. c, right angle, or angular measure— hence the use of
the word to eigniiy by rule, on principle, elementary.

E £ 2

420 TIIKORY OP DESCRIPTION AND
land— island.) This word appUes to any teact bounded on three sides by
water. It is a mistake to auppoae that aU peninsular tracta of land are united
to the main land by au isthmus; some are, it is true; but that which we oaU
the peninsula, — viz., the countnes of Spain and Portugal, aa being the most
important peninaula with respect to England, is not. An Isthmus (from the
Greek, ia-6poi; a neck or narrow passage,) is a narrow neck of land connecting
a peninsula to a continent, or two peninsulas together. It is, however, perhapa
more correct to explain the word as meaning a neck of land joining two
peninsulas, as a continent becomes peninsular when thua attached. North
and Soutii America would be islanda if they were not joined by the Isthmus
of Panama, or rather of Central America; but the diminutive aize of some
peninsulas makes the former definition more easy of immediate apprehenaion,
and it is most correct when applied to peninaular tracts in inland seaa, lakea, or
rivers — the detaching ofwhich from the mainland would not alter ita character.
Promontories and Peninaular tracts of land. Points, Capes, and Head
lands derive, as has been noted, their extenaion from thefr elevation above the
water; but land surrounded by it is termed an island, (see P. G., p. 217,)
(from insula, Latin, any detached place or buUding.) It ia obvioua that, if
thia word be taken in its customary acceptation, the two great continental
masses are islands ; its derivation, however, shows this to be incorrect, it
should be a part of something, because detached, Australia has, therefore,
by some geographers been taken from out this category : a glance at the
map wUl, however, ahow that it cannot be aeparated from the Malay Peninaula
and ita appendant islands. A number of islands in near juxtaposition ia
termed a group — many groups form an Archipelago. This word is, however,
more justly applicable to a aea studded with groups of islands. It waa
originally applied to the sea between Greece and Asia Minor ; its etymology
is disputed, but it is probably from apxos, tbat which rules, chief, and
TreXayof, Sea; either because of the Archipelago being the chief or most
important sea to the Greeks, or because the islands command it.* Ialanda
ranged iu a line, whether atraight or curved, are termed a Chain; sueh
frequently connect a group to the mainland, or promontories and peninaulaa
to corresponding portions of the oppoaite coaat. The Aleoutian Islands thus
connect North America with Asia — the West Indian, North with South
America. A smaU island is eaUed an Islet or Ait ; smaUer elevations above
the water-level, if composed of hard material, Eocks — if of soft. Banks.
Eocka when numerous or extended are caUed Eeefs ; when these run paraUel
to the coast, they are termed Fringing reefs ; when they croaa or impede a
passage. Barrier reefs ; when raised by the labour of zoophytea. Coral reefa ;
and these when depressed in the centre, or raised in a circular form, and
inclosing water, are caUed Lagoon reefs or atoUs. Eocks when aerrated, or rising
in aharp peaks, are termed Needles : to these when iaolated, and rising
abruptly from the aea, the term vigia (from the Portuguese, implying a neces
sity for watchfulness) is applied. Low rocka lying horizontaUy, especially
when laminated, are caUed Shelves. Precipitous banks or rocks, whether near
the margin of the water, or enclosed, are termed Clifi's, (from the Saxon,
implying cleavage, i. e. cleft ;) when steep and rugged. Crags, (i. e. broken,
from the Celtic.) Berg is a German word, adopted with reference to the
liiUy banks of streams and elevations supposed to be the result of former
fluvial action ; it is alao applied to masses of ice rising high above the water.
The term Bank is often applied to portiona of the land (either natural
elevations or depoaited by tidea or currents) which are never above the water;
these are also termed Shoals, but shoala are generally aufficientiy near the

* This word was not in use among the Greeks, and seems to have been brought into the
west of Europe in comparatively modern times. It is supposed by some to be the result of
mispronunciation of ^l•fatul¦ TreXayof, the .Esiean Sea; but it seems diflicult to account for the
letter ¦/¦ being entirely dropped, — especially if its use be traced to tlie Italians, the first traders
to that sea after the estabUshment of the Turldsh power.

GEOGRAPHICAL TERMINOLOGY. 421
surface to be dangerous to navigation, which banks are not. The word
Bank has also the more extended signification — the Banks of Newfoundland,
for instance, occupy an enorraous area.
As the larger projections and indentations of the land form the divisions
of water caUed seas, gulfs, bays, &c., so there are particular terms applicable
to those formed by the smaller ; Headlands and capes form amall bays ; tbese,
if nearly surrounded by land, are caUed Harbours (from the verb to harbour),
because tbey afford protection to shipping. Where protection is afforded from
all winds, the harbour is said to be land-locked ; where partial protection only
is afforded, it is caUed a road or roadstead ; this word is also applied to any
portion of the water where ships may anchor in safety from some winds ; a
emaU harbour is caUed a Haven, (from the Saxon, hcefan, in Welsh, havyn, a
stiU place). If a harbour or haven have on it a town where trade is carried
on, it is called a Port. StiU smaller indentations of the coast are termed
Inlete, Creeks, and Coves. The former is more properly used with reference
to a small strait. The word creek is explained by its etymology from the
Saxon crecea, a crack, and is therefore deeper and more irregular in form
than a cove. Cove is the diminutive of bay, and indicative of an arched form.
If access to a harbour or inlet of the aea, or river's mouth, is impeded by a
ahoal, or bank, or reef, the impedient is termed a Bar, because a barrier ; these
are described according to character and position, whether they are rocky,
sandy, or muddy, shifting or permanent, cenfral or on one side.
The margin of the sea ia called a littoral, coast or shore. The Latins used the
word litus, from the verb lino litum, signifying to overlay, to anoint, for the line
ofthe land which is washed by the aea ; hence our word Uttoral. It ia termed
by saUors the sea-board. The Austrian Provinces on the coast of the
Adriatic are eapeciaUy termed 'littorale.' The word coast is derived from the
Latin co«te, a nb, which was applied to the margin ofthe sea, probably because
it encloses or bounds the sea. The modern acceptation of the word is,
however, somewhat more extended. It is appUed to all land near the
sea, and is aynonymous witb, but more commonly used than littoral ; while
the word shore is applied to the part which is washed by the wavea (yet the
expreasion going ashore is equivalent to landing). Shore is applied to lakes,
but coast is not. The word Coast is also, but with less propriety, used for
the districts adjacent to the boundary or frontier of any country whether
limited by aea or land.
The coaat line is the Une drawn on maps and charts to indicate where land
and water meet. The expression, line of coast, is more general. A coast is
said to be high or low, rocky or sandy, continuous or indented, concave or
convex, fertUe or barren.
The character of the coast is important with respect to the commerce, as
well as the defence of any country, it should, therefore, be always carefuUy
described. This may be done under three heads, as suggested in the Glossary
of Geographical Terms afready referred to, and as, indeed, all land ought to
be described. 1. The outline or plan of the coaat ; 2. The profile; 3. The compoaition.
The first haa reference to extent, the second to elevation, the third is more
properly geological.
The shore is aaid to be shelring or steep-to, according as the angle formed
by it with the water Une is smaU or great.
TV hen shelving, and alternately covered and exposed by the ebb and flow
of the tide, it is caUed a Beach, (possibly derived from the Saxon bee or boc,
equivalent to the Greek ^ayos in the sense of corroding, it being washed away
or altered in form by the waves.) If compoaed of amaU stones, it is termed
shingly, (perhaps from the Greek Sxtfw, to divide.) The adjective muddy is
sometimes united to the word shore— a muddy shore is when a continuous
bank is formed by the current throwing up the mud brought down by the
rivers, as on the coast of Guiana; this, as wUl be seen, frequently alters
the course of the mouths of the rivers themselves.

422 THEORY OF DESCRIPTION AND
The action of water in wearing away parts of the coast of the sea, or
shore of a lake or river, exposed to its influence, is termed (from the Latin)
abrading or abrasion. (See P. G., p. 254.)
Wben the water forced by the tide, or wind, or e-ren by a current,
over rocks or shoala, foams and roars, the term Breakers is applied to it, and
sometimes, but incorrectly, to the rooks or shoals. When, in Uke manifer,
it breaks dfrectly on the shore, the word Surf (? from the French sur-fait).
The flow of water in one direction is caUed a Current, when forced rapidly
between paraUel ledges, or reefs of rocks, or sandbanks, a Eace. When the
tide wave, compressed in a narrow channel, rises with great rapidity and a
terrible noiae, it is caUed (from the Saxon) a Bore. (See P. G., p. 233.)
This is to be observed in the exfremity of the Bristol Channel, the Bay of
Fundy, and, more or less, in aU simUar situations, aspeciaUy where exposed to
the direct action of the tidal wave. When by the force of the tide or current
pressing the water diagonaUy against the snore, or between rocks or banks,
a cfrcular dfrection is given to it, or where a sinular effect is produced by the
meeting of two currente, or by deep holes producing a downward suction, this
ia termed an Eddy ; in the latter caae, when very large and powerftd, it is
caUed a Whfrlpool. These words are used indifferently with respect to both
salt water and fresh, to lakes and rivers, as weU as the ocean.
.15 Cf Land in Elevation. — Under the appeUations which have been
explained are included all that relates to extent of land, and by which it may be
described in that relation. This is, however, rather apparent than real, being,
as before observed, entfrely dependent on contour, or the elevation and deprea
aion of its surface ; but as the level of the sea is the apparent limit of the land,
all beneath it belongs more properly to the division of Marine Hydrography.
From the horizontal profile of the land, description must proceed to that on
which it depends, the vertical profile. From the level of the aea the land rises
irregularly. The highest elevations appear to man much more considerable
than they reaUy are; he judges of them by thefr relative proportion to himself
and the limited sphere of his own observation, and not vrith reference to the
globe on which they are raised. When thefr height is estimated by this
rule, it wUl appear that though on the elevation of the land aU ite other
superficial features depend, as weU aa thoae of the water by which such large
portions of it are covered, yet that they are relatively very inconsiderable.
Eunchinginga, which is now generally considered to be the highest mountain
in the world, is about 28,177 feet in height ; the mean diameter ofthe earth is
7912 mUes ; but estimating the greatest elevation on the surface of the globe
at 30,000 feet, and the diameter at 8000 mUes, to make the relation more
apparent, the proportion wiU be as 30 to 42,240, or 1 to 1408. Mr. De Morgan,
in his very able work On the Use ofthe Globes (c. in.), gives the foUowing cdcu-
lations vrith reference to the irregularitiea ofthe Earth's surface : — ' The Earth
is reaUy a sUghtly flattened sphere, having the axis passing through the shortest
of all its diameters. The shortest radius, or semi-diameter, being half the axis,
is 3949 mUes. The longest, which belongs to the great cfrcle having the enda
of the axis for its poles (caUed the equator), is 3962 mUes. On a globe of
eighteen inches in diameter, this difference of thfrteen mUes would not amount
to so much as the thirtieth of an inch, and it would be altogether useless to
take any account of it. (See Chartography, p. 179.) We shaU then suppose
the Earth to be a sphere, with the mean semi-diameter of 3956 mUes, so mat,
roughly speaking, 1000 mUes are 2^ inches, (more accurately 2'275 inches.)
The mountains are not represented; one of thirteen mUes high (and we know
of none auch) would not prick the fingers through the vamisn with which the
globe is covered, which, therefore, much more than represente a universal
deluge. Suppoaing the atmosphere to be forty miles high, it would nowhere
rise a tenth of an inch from the globe." With such knowledge, the incon
siderable relation of the higheat elevations to the size of the globe need not
be insisted on, but in thefr relation to Phyaical Geography, and to man, they
are of the greateat importaueo. The tendency of water to seek its level makes

GEOG«APHICAL TERMINOLOGY. 428
the position and quantity, as weU as character of the watera of the globe,
dependent on its contour ; every conical projection, every ridge, in short,
every elevation of what sort soever it may be, becomes a watershed;
and that knowledge of the height, slope, and dfrection of the various
watersheds of the Earth's surface the first step to its general contour.
The word watershed in geographical definition, impUes the Une by which
any waters are divided from each other, and the watershed of any counfry
is no doubt such a Une ; but as every slope sheds water, and many rivers
have thefr rise on slopes below the main watershed, some further dirision
of the word, some classification of the districts to which it is applicable,
appeara highly desfrable. As this does not seem to have been ever attempted,
the foUowing ia offered as a suggestion :
That there is a line in every country, which may be termed its principal
watershed, wUl not be disputed ; every country has some one district, usually
in the dfrection of its greatest length, more elevated than another, from the
sides of which the waters coUected from snows, dews, rain, and springs,
pour dovm, until they are received into the basin of some inland water, or at
last into the sea; this may, therefore, be properly termed its primary water
shed ; but, as the mountains of the world cannot be satisfactorUy considered
except in thefr relative connexion, the highest ranges extending through the
freatest length of the continental masses, the term primary watershed should
e confined to these ; beyond them othera of leas conaiderable elevation are
found, the slopes of which are presented towards the primary watershed and
form with it deep hoUowa, into which thefr united watera are poured, whUe
from the oppoaite slope the watera coUected deacend in a different dfrection.
These may, not inaptly, be termed secondary watersheds, as paying the
tribute of part of their waters to the primary, and forming the inferior Umit
to the principal river baains ; whUe others rising beyond may be caUed
tertiary. It wiU be obaerved that this classification affords not only a
systematic diviaion of the elevated land, but alao of the watera of the globe ;
aa appertaining to any of ita parta, rivers having their rise in the primary water-
sheda may also recAve a similar designation, as may thefr basins ; others may
be termed secondary or tertiary, according to thefr position and the watersheds
to which they belong.
The highest elevations on the surface of the Earth are caUed Mountains,
but this term is appUed to elevations varying from less than 3000 to more
than 28,000 feet, and it has long been a difficulty in geography to find an
accurate definition for this word, which, derived from the Latin mons, (quasi
(joi/of, as standing alone,) was appUed originaUy to very inconsiderable
elevations. Mountain and Mount appear to differ from each other in the
latter being single, and the former, possibly, coUective ; many mounts
may assist m forming a mountain ; but in the lower elevations the words
mountain and hUl are used aynonymously, as we say, the Welsh hUls or the
Welsh mountains. Some have proposed to confine the word HUl (Saxon,
from a root signifying elevation, or, poaaibly, to hide,) to summits not rising
more than 1000 feet above the level of the sea. Ifi this were done, some
claaaifioation of mountaina beaidea that of elevation above hUls, would stUl be
neceaaary. Others have been disposed to regulate the appUcation of the term
by the geological structure of the elevation m queation, eateeming mountaina
the effect of upheaval, hUls of denudation, but this could scarcely be a test
of its geographical propriety ; for the same reason the connexion between
the clasaification proposed and the geological characteristics which may be
traced in its divisions, is not more enlarged upon, but taking the primary,
secondary, and tertiary watersheds of the Earth as mountains, and all others
as bills, we shaU find the former ranging, on the average, above, and the
latter below, 2000 feet. In landa detached from the great continental
maaaes the mountains may be classified with the chains of which they are
extenaiona, and thus opportunity -wUl be afforded not only for systematic
arrangement but systematic comparison. Undulating grasay hills are in

424 THEORY OF DESCRIPTION AND
England called Downs ; undulating sand hUls, in some locahties Dunes— words
of kindred origin with the EngUsh down as opposed to up.
To describe the configuration of the land in its varymg contour, many
terms have been adopted by geographers. A more or less corneal summit ia
caUed a Peak; a connected. Une of summits, a Eidge, or Eange; to such, if
they present many peaks, the term serrated (from the Latin serra, a saw
in Spanish sierra,) is applied. Crest is a general term for the highest part
of a mountain. A Pasa is, as the meanmg of the word would suggest, the
place between the peaks, or higher elevations, where a mountain-chaui is pass
able. Pasaes are usuaUy at the angle formed by one part of a chain with
another, or of a main chain with its spurs or branches, and consequently
beino- at the head of valleys, are also (as wiU be seen) at the head waters of
rivers. The word Branch is, however, more applicable to a river than a
mountain. A pass was sometimes by the ancients caUed a gate, (by the Greeks,
¦nvXaiv, pylon,) aa it is now by the Spaniards ; port is used on the Pyrenees,
pertuis on the Jura; its French equivalent is col, narrow; a pass, or portion
of a pass, more narrow than the rest, ia termed a Gorge. This term belongs
more properly to the channels of the upper waters of the smaUer feeders of
rivers and mountain torrents. It differs from a Defile in being alwaya
near the summit of a mountain, whUe the latter name is applicable to
any narrow passage between precipitous rocks, especiaUy if long and
winding. AU these terms appertain to mountaina.
Both mountaina and hUls are the boundariea of vaUeys. The term VaUey
may be appUed to any depression on the surface of the globe. The largeat
vaUeys form the beds of the great oceans. Seaa, bays, gulfs, &c., are aU vaUeys
below, or partially below, the level of the sea. VaUeya, in the common accep
tation of the word, are those depressiona which are observable above the
aea level, and which form the beds of rivers and basins of inland seaa,
lakes, &c. They wiU naturaUy class themselves vrith the watersheds to
which they belong. Those wMch Ue between the primary and secondary
ranges, aud form the beds of the principal rivers, wiU be classed first.
In Europe, for instance, we find four principal vaUeys, those of the
Danube, the Ehine, the Ehone, and the Po. VaUeys have been dirided
(see Johnson's Glossary, pp. 44, 45,) into principal, whether longitudinal
with, or transverse in thefr dfrection to, the mountain-chaina by which they
are bounded; lateral vaUeys, those of inferior order, which join the principal;
high, or mountain vaUeys ; and low, or vaUeys of the plains. These terms,
however, are rather descriptive epithets, and explain themselves, but do not
afford any regular classification. Apart from thefr relation and position with
respect to mountain-chains, vaUeys differ from each other in depth and shape
as well as extent. The most important distinction to be remarked ia, whether,
as is most usual, a valley graduaUy expands from ite upper exfremity to its
mouth, or is bounded and partiaUy enclosed by lateral ridges, or even so
surrounded aa to afford no outlet for ita watera. In the latter case, it was
proposed by Malte Brun to caU the lakea which auch vaUeys usuaUy contain
Caapians. The word vaUey is from the Latin vallis. VaUum seems to have
been appUed indifferently to the ditch or the palisade, by which the Eomans
surrounded their camps. Vale is the diminutive, and is more properly uaed
with reference to the undulating depressions between hiUs. The word inter
vale is used in America to signffy the teacts of rich aUurial land often found
in valleys; it haa occasioned some difficulty, and has been variously explained.
Dugald Stewart esteems it equivalent to ' inter vallos Spatium,' the space
between the palisades, and remarks that, having been &st used to denote
a Umited portion of longitudinal extension generaUy, it became afterwards
more usually applicable to portions of time.
VaUeys seem to demand a double classification ; firat, with reference to
poaition ; secondly, as to character ; the latter being in no manner dependent
on the former. Valleys containing their onn system of waters are found
below the level of the sea aa weU aa on high mountains, whUe those which

GEOGRAPHICAL TERMINOLOGY. 425
have only a narrow outlet may contain either a river or a lake. This, how
ever, offers a characteristic sufficiently weU deflned. VaUeys may therefore
be described as lake or river vaUeys ; these, again, as longitudinal or cfrcular,
confined or open. The term basin might have been used with much pro-
priefy for enclosed valleys, had it not been adopted to expresa tbe whole
surface drained by any system of waters (see P. G., c. v., pp. 233, 239.) The
word basin (possibly from the Greek fiaa-is,) adapted from bassin, (Fr. basin
or bowl,) haa been defined (Johnson's Glossarv, p. 10) as a more or loss
extensive, and more or leaa concave portion of the Earth'a aurface cfrcum-
Bcribed on aU sidea, or on all but one, by wateraheds, and formed of all the
slopea whose watera are received into a common receptacle, whether this be a
river, lake, or inland sea. Basins may be classified as lacustrine or fluvial,
equivalent to lake vaUeys and river valleys. The word is alao applied to
vaUeya below the level ofthe sea, and may be Oceanic or Mediterranean. A
fluvial basin may be either the confluence of aU the vaUeya which unite thefr
tributary waters in one stream, or each valley by itself ; or, in general terma, it
may be appUed to any weU-defined dfrection of the courae of a river formed
by lateral shorea from the main watershed, thus it is not unusual to say,
speaking of a river, 'the baain of ita upper watera.' Lacuatrine basins are,
more properly speaking, those which contain caspians, or lakes which have no
outlet for thefr waters, but it is not confined to them.
The watersheds are then the limits of the basins, the character of
which determines that of the waters which are fou-nd in them ; but not
unfrequently sloping at a very smaU angle with the level of the sea,
they spread out into extended tracts, to which various names have been
given descriptive of thefr character, but varying with the locaUty and
the language of the inhabitants. The worda plateau (from the French)
and table-land have been afready apphed (see P. G. p. 223) to fracts of
conaiderable elevation and of small mclination. These may be on the tops
of mountains or on thefr sides; plains are to low land what plateaux are
to high land. The whole aurface of the globe may be divided into hiUs,
valleys, and plains ; but very vridely extended vaUeys, as in North and Soutii
America, become plains, from the extent being more than commensurate vrith
the height of their watershed. Plains may be crossed by hills, may be undu
lating or fiat, fertUe or sterile, wet or dry ; if green and even partiaUy fertile,
they are in North America caUed Prafries — i. e., meadows. These are
claaaified as dry and roUing, or wet ; to the latter, perhaps, the term Savannah
would be most properly appUed, for damp grassy plains are so called in America.
On the confrary. Llanos are, like the former, dry ; such are to be found in all
parts of the world near large rivers alternately fertUe and arid. To the south
ofthe river Amazon, they are caUed Pampas, a word used indiscriminately for
the raised surface of the great plains wmch extend from that river to the
Straits of MageUan. The former appeUation is more prcmerly confined to the
vaUey ofthe Orinoco ; the latter to that ofthe La Plata. In South-eastern and
Asiatic Eussia, similar teacts are termed Steppes, (from step,harven, Euss.) The
term desert is usually appUed to vaat fracts covered withisand. These, however,
have not an unvaried character, fertUe apots are occasionally met with wherever,
from any cause, water is present. AU these tracts derive thefr appeUations
from thefr leading features. The word wUderness differs from desert, in
being applicable to land covered with spontaneous and abundant vegetation,
as well as to wild barren spots, among rocky mountains, as in the peninsula
of Arabia. In India, a wUdemess (usuaUy found in moist places) is caUed
a Jungle. Plains covered with low plants are in France termed Landes ; in
Germany, England, &c.. Heaths, from the plants most commonly found on
them. Land having ite surface saturated with water, ' which from the con
cave form and impermeable nature of the bottom does not chain away,' is
termed a Swamp or Bog ; the latter, of Celtic derivation, indicates ita binding
and tenacious character, the former (Saxon) its spongy nature. The term bog
is generaUy thought to imply a peat formation, wMe swamp is used more

426 THEORY OP DESCRIPTION AND
generaUy. Swamps may have frees growing in them (cedar swamps are
common in America). Marsh is from a Teutonic root, and nearly allied to
moor ; it has generally a flow or rivulet running through it ; by some, marsh
is thought to be the generic term, and is alao used vrith reference to meadows
occaaionally overflowed by the sea, or under a system of salt-water irrigation,
which are called salt marshes. Fen is applied generaUy to low moist lands.
Having explained the terms used in describing land in its vertical contour
and varymg character, we proceed to those used with reference to water
above the level of the ocean. The water on the face of the Earth is either
at rest or in motion.
6 Of Water not in Motion. — Dew and rain falling, and snow melting in
water, on the surface of the globe, coUect in hoUowa, or trickle down in rilla ; or
again flltered through ita superficial strata, form Springs, (see P. (?., pp. 209,
211, 238.) Small bodies of water coUected in hoUows are caUed Pools or
Ponds, the former when they are fiUed with rnnning water, the latter when
isolated, though a very small pond is often caUed a pool. The bed of a river,
when partiaUy dry in summer, often presents a aeries of poola ; theae would
be erroneously termed ponda. A large pond is a amaU lake. Theae are not
the converae of islands, inasmuch as they are not always, nor indeed very
frequently, surrounded entfrely by land, as islands are by water, but receive
into and emit water from them. Lakes may be described in position, from the
watershed to which they appertain. In character — they are of four kinds : —
Ffrst. Those which neither receive nor teansmit water, i. e. which are
neither fed by nor are the source of steeams — such lakes are more commonly
found in mountainous countries, are generaUy of smaU dimensions. Lagoons
are sometimes simUar in appearance, but owe thefr existence to the infiltration
of water from, or the overflowing of, either the sea or rivers; they are therefore
usually found in low landa. Lagoons are for the most part shaUow, frequently
dry up in summer, not unfrequently at one time connected, and at another
disconnected from thefr parent waters. This is the case at Holyrood Pond,
St. Mary's Bay, Newfoundland, the enfranee to which being formed in
winter by the force of the waves, is annually stopped up by shingle in the
summer, and affords the inhabitants a plentiful supply of fish, which are thus
placed at their mercy : it was formerly an arm of the sea, and many sunUar
lagoona are formed by the blocking up of small harbours, creeks, and
channela by sand or shingle. Lagoona, though havmg thua an apparent
relation to, are not to be arranged in the first class of lakes. Lakes and
ponds being the result of surface drainage ; lagoons, of overflow or infil
tration. Lakes, ofthe second class, are those which receive into, but do not emit water
from them, These are usuaUy salt and brackiah, often found in mountainoua
districta, high above the level of the aea, not unfrequentiy the reault of vol
canic action; sometimea below the level of the sea, as Lake Asphaltites in
Palestine, erroneously termed the Dead Sea, and the Caspian. Lakes of this
olasa are the receptacles of inland systems of waters and rivers which do
not communicate with the ocean, (see P. G., p. 218.) The thfrd class is
formed of lakea which do not apparently receive, but emit thefr waters; some
do so by subterranean channels, as Lake Copais in Beotia did, and Lake Jouxin
does. Lakes of this class are usuaUy found at the head of rivers, especiaUy in
the pasaes of the primary mountain chains, frequentiy, as in the Eocky Moun
tains, at the sources ofthe Saskatchevan and Frazer's rivers, and in the Alps at
thoae of the Inn and the Po, in immediate proximity to each other, whUe thoae
rivera which issue from them faU down the opposite slopes of the watershed.
The word Portage, i. e. carrying-place, is apphed to the land between two such
lakes, aa also between any streams or lakes, or the passage round a waterfaU
or rapid, where it is necessary to carry boats or canoes and launch them again,
to continue the inland navigation. The fourth class is the most numerous,
consiating of lakea which both receive waters into and emit waters from them.
These are common in the middle and lower courses of great rivers. When

GEOGEAPHICAL TERMINOLOGY. 427
foUowing each other in succession, or clustered together, the same terma,
chain and group, are used which apply to ialands. A chain of small lakes
linked together by a riyer or stream, is caUed by the Germans a chaplet
river. "Where, in America, a river in its tortuous course forms a deep and
•wide extending bend, the same term is applied which we use in simUar cases
with respeot to small streams; it is called an Eddy; this is correct; for
great and smaU are only relative terms, and both are the result of the aame
kind of action, only on a different scale.
The water of laies is subject to the same definitions and description as
that of seas and oceans ; the irregularities of thefr outline are expressed in
the same terms, but the word shore is more generally used to express the
margin or border of a lake than coast. Some lakes have, as has been
noticed, the level of thefr waters below that of the sea, but the majority are
raised above it ; many, however, have the bottom of thefr basins below that
level. Lakes in Scotland are termed lochs. The term lacustrine is appUed
to whatever belongs to, or is connected vrith, a lake, as Lacustrine basin, &c.
7 Cf Water in Motion.— Water running down the sides of mountains, bills,
or other sloping grounds, coUecting in small channels, forms EUis, Sfreama,
or Eivulets; the former is from the German, meaning a groove or channel
(or possibly from the Scandinavian strila, ryller, to run or glide), the latter
the diminutive of river. Steeam is Saxon, and uaed as a generic term for
water in motion, whether salt or fresh, vrithout reference to magnitude on the
cause of motion.
Sfreams which flow into other waters are termed affluent, when they
flow from them effluent. Tributary steeams are those which conteibute
thefr proportion to any lake, river, or collection of waters. It has, however,
been Juatiy remarked, that ' a tributary is not necessarily an affluent, though
an affluent must be tributary," for an affluent may receive the waters of other
sfreams, and convey them to one common recipient, to which they would aU
be tributary, whUe to it they would be affluent.
The term effluent is equivalent to branch, which is not applicable to an
affluent; the branches which rejoin the parent stream are caUed ' ana'
branchea ;* those which at the moutha of rivera encloae and diride friangular
tracta of land, to which from the NUe the term delta (the Greek A) haa been
apphed, are caUed deltic branchea ; thoae which divide a delta into ialanda,
but return again into a deltic branch, not flovring dfrectly into the sea, ana
deltic ; those which connect two rivers together, conjunctive branches ; and
thoae by which water from the main steeam is drained off into marshy or
sandy places, drain branches.
The terms convergent and divergent ahould be appUed to waters flowing
into or out of a river when thefr character is not known ; it is obrious that
the one may be an affluent or an ana branch, the latter a deltic, drain or ana
branch ; these terms are, therefore, important in the exploration and the
description of countries imperfectly known. When a river spreads into two
branches, it is aaid to bifiircate, (bis, twice, and furcus, a fork, Latin, a
pleonasm.) A biforoation is uauaUy a branch, and Oonfined to the aame
baain as its parent stream; but in some cases, as in that of the Caaaiquare,
by which the waters of the Orinoco are connected with those of the Maranon
or Amazon Eiver, it connects two basins together. This term has, but
vrithout necessity, been appUed to mountains. The junction of sfreama is
termed thefr confluence, (confluo, to flow together;) thia frequently gives
local appeUations to places ; in Welsh, names beginning vrith Aber indicate
such a position.
The difficulty of classifying elevations of land and of applying the

' Ana, said to be a contraction of anastomosing, anastomosis being in medicine the inoscu
lation ((7ra^a, a mouth, Gr.) of vessels together, or of veins with arteries. Thie is, how
ever, unnecessary, for ava, in composition, signifies 1)ack again, or in retum, and such branches
bring back again the waters which they before had takeu away.

428 THEORY OF DESCRIPTION AND
names used to express them, has been already noticed. The difficulty ia as
great with respect to running water. Estimated by comparison, many rivera
ahould have diminutivea applied to them. Compared to the Amazon, the
Thamea is but a brook, yet here the Thamea is an important river. The
difBculty is, however, capable of the same solution. The classification of
watersheds gives at once a classification of rivers. A river (from rivus, Latin,
a channel) is a coUection of small streams or rivulets; many smaU rivers
may combine to make one large one. The use of the word is not, therefore,
confined to a mam stream any more than it is dependent on proportion.
That from wbich a river takes its rise, whether spring, lake, swamp, or glacier,
is called its Source. Most rivers have more than one source, and aa in the
case ofthe Misaiasippi, the name ofthe least importance ia aometimea aelected to
designate the whole. The principal source is to be aacertained by its elevation,
distance from the mouth, and by the volume and character ofthe water it contri-
b'ates. The junction of a stream with the recipient of its waters, whether river,
lake, sea, or ocean, is termed its Mouth. This ia, however, only appUcable
as opposed to Source, for some rivers fiow through lakes and marshes.
Eivers can have many sources, and may have several mouths, but the words
can only be used with reference to thefr exfremities. The mouth of a river
is also called, from the French, ita embouchure. This word is appUcable to
the mouth of a river, whether it be in a lake or in the aea ; but when, flowing
into the sea, the mouth of a river ia modified by and aubject to the infiuences
of the tides, it is termed an .ffistuary, a name derived either dfrectly from
cEstus, the tide, or from cestuo, to boil, (Latin, implying restleasnesa,) and thus
indicative of the effect of the tidal wave meeting the current of the river.
The expression, Courae of a stream, impUes ita dfrection, ite current, the
motion of its watera. This varies much in different rivers and in different
parts of the same river, and is a marked and important feature to be noted in
aU, especiaUy its rapidity as indicative of the elevation of its source.
Flurial, fluriatic, and fluriatUe are adjectives, expreaaive of formation
from, or connexion with, a river, aa flurial delta, fluriatUe lagoon, fluviatic
formation; the firat is most appropriate.
Eivers whioh have their rise in the primary wateraheda of the globe have
themaelves the same appeUation. This class wUl be found to include aU tbe
largest rivers in the world. The secondary watersheds wUl give thefr appel
lation to the rivers which are derived from them, and the more narigable
portion of rivers wUl usuaUy be found without thefr limits, and so on, but
no classification or distinctive appeUation has yet been suggested with
reference to the character of rivers. This is yet a desideratum, (see John
son's Glossary, on the word Biver, p. 39;) some approach to it has, however,
been made by dividing the course of rivers into three parte — the upper,
middle, and lower. This, however, can only be done satisfactorUy when a
river is connected with more than one watershed. There is, however, another
clasaification, which is most important, in considering the globe in reference
to man — rivers are navigable or not, A narigable river may be so from the
sea, or only inland, or both; its navigable character may be consequent on its
natural depth, or the effect of the tidal wave ; in any case the consequences
will be important to the counfry through which it fiows.
The carity in which a river fiows is called ite Channel; the bottom ofthe
channel its Bed; the sides its Banks; (bank, Saxon, a bench, mound, or pUe,)
both are of importance in the description of a river. The first regulates its
depth; if rocky and broken, it forms a rapid or fall; if level and extended
so that it may be passed on foot, a ford. The banks may be sloping or
steep, rocky, or fertile: if sloping, the waters may be extended; if steep, and
especially when approaching the perpendicular, they wUl be confined, and
not unfrequently the compression of water between high rock produces appa
rently a fall of water. This in North-west America is called a Caiion, from a
Spanish word meaning a cylinder, or bore. The bed and banks of rivers
vary much in different parts of their courses, and are dependent on the

GEOGRAPHICAL TERMINOLOGY. 429
profile and character of the country through wbich they flow. Sudden
irregularities of the surface produce some of the most important features in
the description of rivers — the fall of water over rocks. To characterize this,
various names have been given. A Cataract is a large body of water pre
cipitated from a considerable height ; the word (derived from the Greek,
KarapaKTos) implying force, violence, power. A Cascade is a small cataract.
In cascades the water sometimes descends by successive leaps. A Leap is
the faU of water, unbroken, from an inconsiderable height. A Force ia the
result ofthe narrowing of the bed of the atream ; it differs from a caiion in
being of less extent. Of aU these the generic term is Fall, which has no
reference to character, elevation, or volume of water, being applied indif
ferently to a mountain stream and to the Niagara, to the FaUs of WUberforce
and ofthe Clyde.
8 Ofthe Natural Productions of the Surface ofthe Earth. — In the descrip
tion of the characteristics of different parts ofthe Earth's surface — the oppoaite
features of fertUity and sterility have been already noticed, — these not only
involve, of necessity, aU the intermediate stages of vegetable productiveness,
but the kind as weU as quantity of the vegetable produced. FertUity
is always the result of moisture, m river or lacuatrine baains by the waters
they contain; it is so even in the smaller, as when in deserts either a
depression of the surface, a quaUty of soU more capable of retaining mois
ture, or the preaence of a apring, produces those oases (habitable, from the
Coptic) in which the confrast of the verdure they present, and the refresh
ment they afford with the arid waste by which they are aurrounded, ia ao
gratefal to the traveller. Inplains, vegetation is kept up by the plentiful
dewa which faU upon them. The vaUeys are, aa has been noticed, connected
together by their head waters being in the gorges or passes of the mountains,
often in close proximity. Plains are always passable.
Animal life depends on the nature as well as the quantity of vegetation,
and thus man partakes of tbe characteristics of the soil which gave him bfrth.
Not only, then, shall we find the proportion and relation of land and water
depending on the contour or proffle of the former, but the vegetation, and
consequent on that, the animal life ;* and laatly, the human beinga whose
exiatence depends upon them, and whose character is modified by them,
not less than by the communication which can be maintained between different
parta of the earth; the consequent diapersion of mankind over ita aurface;
and the subsequent apread of civUization and religion. From the considera
tion ofthe horizontal proffle ofthe Earth's surface, it was natural to proceed
to its vertical ; the next step is the knowledge of its productions, which
leads as naturally, as it does imperceptibly, to that of its inhabitants. Among
those productions, it wUl, however, be necessary to include some minerals,
especiaUy gold, iron, and coal, as haring exercised a dfrect and powerful
influence over the progreaa of population in the world.
These subjects have been treated of generally as a part of Physical
Geography; it is not necessary here to enter more into detaU, and to
explain the terms employed in the description, as in the case of land and
water. They being generaUy weU known, and not» belonging solely to
Geographical Description, while some have technical or local appUcation,
which will be noted in the proper place ; of some, aa prafriea, savannahs,
silvas, heaths, &c., notice has afready been taken, (aee P. G., p. 218 to 225.)
In this place, therefore, they need only be referred to. The word
Foreat (of a Latin or Celtic origin, but in any caae from a root signifying
to depart, and hence in the Eomance languages equivalent to strange,
foreign) is applied, in Geography, to an extensive tract of land covered with
trees. In law and custom in this country, tracts of land which have had
those rights, under the laws for the preservation of game, whioh entitled
them to the appellation, were and are stiU called forests, though some-

• See sections in Physical Qeography on distribution of vegetables, &c.

430 THEORY OF DESCRIPTION.
times vrithout trees ; hence barren tracts, as Exmoor, obtain that name.
The Saxon term Wood, which has naturaUy no relation to size, is now used
to imply a smaller extent of surface covered with trees than is meant by
forest. In the description of forests and woods, the most important consi
deration ia the character of the teeea of which they are composed, to what
uae the timber they produce can be appUed, whether it ia capable of
supplying the wants of man, and therefore whether it invites man to its
own destruction and extends his influence over the face of the Earth with
commerce and civilization. These are, perhaps, more influenced by the forests
of the globe than by anything elae, for though the path acrosa plaina ia
open for man and beast, and the head watera of rivers dfrect to the practi
cable pasaes of the mountains, yet an easier and more dfrect path is
afforded by the aea, by which the ncheat and most productive soU, the allu
vium about the lower course of the rivers, is brought into use, and the moutha
of rivers connected together, as thefr basins are by the mountain pasaea ; to
avaU himaelf of this faciUty, man requfres ships, and thus maritime nations
have perhaps owed thefr possession of that most desfrable characteriatic to
the preaence of timber fit for ship-buUding. It was so vrith Hfram and his
Phcenicians, it is so with us and our American brethren. Forests being
inhabited by beasts of chase, producing also a race of hunters ; aa plains
feeding cattle are inhabited by Nomaifi (from the Greek, vefuo, to mride,
distribute, and thence to wander and to feed cattle.) In Uke manner soils
capable of producing cereal plants, or others fitted for the food of man, have a
tendency to locate men upon them. Hence citiea have firat sprang up in
fertUe vaUeya.
It has already been shown (see P. G., ch. 10. § 129) that limite are
aaaignable to the productiona of most vegetables — these Umite encloae fracta
caUed zonea, and vary, aa haa been ahown, from poaition and elevation ; both
have reapect in some degree to climate and soU. It haa been noticed that
the cereal plants, with some other species, as weU as the domesticated
animals, have foUowed man in his progress over fhe globe. They should,
therefore, be noticed in connexion vrith bim and his works ; apart from him
those only of indigenous character ought to be noticed. Tet where he has
not been, the character of the indigenoua vegetable and animal Ufe ia an
index of what he may, with ease and propriety, infroduce into any country ;
and not unfrequently the pecuUarities of animal and vegetable Ufe affect tbe
habits and character of man to an infinite degree. The moss of Lapland,
and the reindeer, from which it takes its name, and whose food it is ; the
camel and the horae, the date-free and the coffee-plant of South- Weatem Asia ;
the Uama of South America, and the bread-fruit-tree of Polynesia, may be cited
as marked examples, aU probably indigenous, aa the horse, sheep, and cattle of
America and Australia, and the potatoe of Ireland, are exotic. The limite
of some of these and simUar natural agents affecting the life of man, both
social and political, wUl be found clearly defined in the atias adapted to thia
work, and m most phyaical atlases. From it, in connexion with the chapters
on Physical Geography, aufficient general information may be obtained on
this subject ; ita appUcation in detaU must form part of the description of
different countries, and wUl be considered as it affects them separately.

431

CHAPTER II.
1. Of political geography. — 2. Of historical antecedents. — 3. Ofthe distribution ofthe human
race. — 4. Of geographical statistics. — 6. Of the order to be observed. — 6. Ofthe civil
divisions of the world. — 7. Of the civil divisions of countries. — 8. Of religious divisions. —
9. Ofthe dominant religion. — 10. Of religious sects. — 11. Of religious statistics. — 12. Of
the industrial geography of countriea. — 13. Of industrial divisions. — 14. Of occupation. —
16. Of the pastoral. — 16. Of the agricultural. — 17. Of the manufacturing. — 18. Ofthe
commercial.
OF Political Geography. — PoUtical Geography has been defined (see
Admiralty Manual of Scientiflc Enquiry — Geography, p. 129) as including
• aU those facts which are the immediate consequences of the operations of man
exercised either on the raw materials of the Earth, or on the means of his
intercourse vrith his feUow-creatiires.' This corresponds to the division
already made — namely, ' the effect of man's residence on the Earth ;' and this
may with propriety be, in the widest and most comprehensive sense, termed
pohtical. It has, however, been customary to apply the term poUtical prin
cipaUy to the geographical divisions and limits of empfres, kmgdoms, and
states, their laws, mode of government, &c. ; but as the polity of some
countriea has a reUgious, of others a commercial basis ; as in some countries
the religious system is separate and detached from the civil, in others a
mihtary rule has been superimposed upon previously exiating ciril and
religious institutions ; as in one country one predominates, and in another
country another ; the adoption of this vrithout subdivision does not seem
Ukely to conduce to a clear understanding ofthe subject. Man in his works,
, aa apparent on the Earth, may perhapa be moat usefuUy considered in three
relations — rehgious, ciril, industrial.
2 Of Historical Antecedents. — ^As in few cases, if in any, the geographical
limits ofthe three dirisions wUl be found to coincide with each other, the arbi
trary dirision ofthe Earth by its rulers having generaUy been made to suit
present intereste: seldom, if ever, the phyaical teatures and natural relations of
countries, or what is equaUy important, thefr natural divisions, stUl less the rela
tionship or dissimilarity of thefr inhabitants: in abort, the intereat of the few
having been consulted, and not that of the many, it wiU appear necessary to
look back on the history of counfries and thefr inhabitants, in order that their
preaent anomalous condition may be understood ; for not uncommonly it wiU
be found that, in consequence ofthe different cfrcumstances in which they have
been placed, and the different rule under which they have existed, races
similar in character and origin are found in very different stages of progress ;
so different, indeed, that they present no outward indications of thefr relation
ship. It ia naturaUy the part of Geography to show how these changes have been
affected by the physical character of the countries which the people in whom
they are observable have inhabited ; of History, to inquire into the political
causes properly so caUed. Yet these two branches of the subject cannot be
entirely separated, the physical may depend on the political; despotism,
whether civil or religious, may prevent the gifts of God from being tumed to
account : anarchy may desfroy what has already been raised by the industry
of man ; the fertiUty of Egypt has since the time of Joseph been the cause of
the oppression of its people ; the desolation of many parts of Italy is the
consequence of the dominion of Eome, whether imperial or papal, commencing
with its rise, and continuing to the present time. If, therefore, we would
comprehend the present condition of the surface of the Earth, an historical
inqufry into the changes which have taken place upon it during ' recorded
time' must precede its description. This wUl afiect different parts of the

432 THEORY OF DESCRIPTION AND
world in various degrees. Of the past history of many parts little ia known ;
of aome, nothing. Yet even where little is known, indications are not wanting
of the importance of the past, Of thia, the remains of an extinct race recently
discovered in the valley of the Misaiasippi wUl afford sufficient evidence.
Our knowledge of the ancient world is, for the most part, confined to the
accounts of tke Hebrew, Grecian, Eoman, and Alexandrine vn-iters, and
limited to the extent of their information, the boundaries of the Peraian,
Macedonian, and Eoman empfres, with the inroads and incursions of their
rulers on the neighbouring countries, and the discoveries of Phoecinian,
Cathaginian, and Bgjrptian mariners; and on this account, as weU aa
becauae ita application is principaUy in iUustration of their history. Classical
G>eograpliy must assume a more topographical form, and wiU be presented
in the first place and by itself, that it may form a satisfactory baaia for
further inqufry. In it, however, aa of universal significance, the division
and dispersion of mankind, and their effects upon the world, cannot be
fully treated of, although they may be noticed. A general sketch of theae
great infiuencea must therefore precede the consideration of the poUtical state
of the world in modern times, as that must be preluded by a general descrip
tion of the features and character of its surface ; and the same method must
be followed in detaU with reference to every separate counfry ; whenever it
is desirable or possible to extend it so far ; the poUtical inquiry wUl then
foUow easily and naturaUy.
3 Of the Distribution of the Human Bace. — To the various famiUes of
the human race, their physical and mental characteristics, and the natural
laws to which they are aubject, general reference haa been made in the chapter
on Ethnology (see P. G., p. 388). This has of late years taken its place as a
separate science, and it is not therefore now the province of Geography to enter
into the philosophy ofthe aubject, with respect to man as an animal, but to state
what ia known of the present localization of his species, and the geographical
causes which have led to it. The former has been described generaUy, and must
be more particularly detailed with respect to every counfry as it comes under
review. The latter vriU be found chiefly in the configuration of land in elevation
and extent, directing migration into certain natural channels, of which the
primary watersheds afford general indications ; those of the Old World, sepa
rating the north from the south, and concentrating the energies of varioua racea
round the great Mediterranean basin, thua uniting them all in one common
progreaa ; whUe thoae of the New World, far removed from its eastem limit,
rendering the entire continent acoessjible by the mighty streams coUected
from their lengthened slopes, have given facUities for the diffusion of the
races of the Old World, developed in physical and mental energies by con
centration and coUision, over its surface.
The use of the various paths of migration has, however, depended on the
power of man to avail himself of them. The great plains offered facUities
of migration to the pastoral inhabitanta of the ancient world, to w hom the
seas were impassable. The coasts ofthe inland waters were therefore peopled
long before communication existed between tbem. The vaUeys of the head
waters of rivers were always, and are now, the only practicable paths acrosa
the primary watersheds ; by them, therefore, the stream of migration has been
permitted to pasa, and by them communication ia maintained. The valleys of
the great rivers have, therefore, received inhabitants from their upper as well
aa their lower entrances. The proximity of a primary watershed to the
coast may, aa in the caae of Africa and America, entirely cut off one portion of
a continent from communication with the other for many yeara, and therefore
cauae conaiderable difference in the character of thefr population ; this is more
over also affected by the varying physical characteristics of the countries
themselves, which are again consequent on thefr vertical contour ; and thus it
also happens that the commercial exchanges and consequent intercourse of
countries is often rather with distant people than with thefr neighbours.
Since the development of navigation, comraerce has been principaUy

GEOGRAPHICAL TERMINOLOGY. 433
carried on by means of the sea ; the old paths of inter-communication have
been therefore abandoned ; modern science has discovered means of cheap and
rapid transport over the land, and we may thus fafrly expect to see them
re-opened. Their disuse caused the decrease of population and civUization in
the districts through which they passed, their restoration wUl cause their
le-peoplement and enrichment ; and thns Syria, the valley of the Euphrates,
Asw Minor, Persia, the Balkan, may before long be again important to the
world, ^a Egypt has afready become, and as we see Central America, Upper
Californhk and Texas are becoming.
As tiie general disfribution ofthe human race over the surface ofthe earth has
been consequent on its larger physical features, so has the local arrangement
been lyit&the presence of agricultural or mineral wealth. Agricultural districts,
not requiring a large population, or the possession of the knowledge of mecha
nical power in any great degree for thefr cultivation, have been early peopled.
Itis to the presence of mineral wealth, and the development of manufactures
and commerce, that the congregation of numbers in smaU disfricts is owing ;
hencewe find the greatest accumulation of men in masses at the mouth of rivera,
in harbours, and where natural paths of communication intersect, dfrected by
the necessities of commercial intercourse, or in mineral disteicts. In ancient
times, the presence of gold, copper, and tin exercised great infiuence on the
difliision of population, and the extension of commerce. To the former is attri
butable the firat efforte to unite Greece with the eastem shores ofthe Baltic in
commercial intercourse, of Solomon to carry Phoenician trafficacross the Isthmus
of Suez ; the commencement of the era in which we live was marked by the
discovery of the gold-producing counteies of the New World, to which a
constant sfream of emigration has been since directed, and in our own day
California, and possibly AustraUa, may owe thefr population to the same cause.
Tin and copper have carried the ships of Carthage to England, and the ships
of England to the Indian seas, AusfraUa, and America. But since the use of
machinery and the appUcation of steam as power, coal and fron have exercised
the greatest influence in this respect. Nor is the providence of God in
directing the distribution of the human race limited by the supply of the wants
cf man,tiie prorision for the cure ofhis diseases has its peculiar influence upon it.
Even in savage coimtries among the natives, as among the beasts of the field,
periodical visits to mineral springs have always been observable, and in civUized
countries men have always congregated and cities been buUt around them or
in thefr immediate vicinity, whUe, too, in smaller degree, even salubrity of
atmosphere and beauty of scenery have influenced this localization.
Tlus distribution, as has been already noticed, being irregular both in space
and time, it vriU be found to affect PoUtical Geography in aU its dirisions.
The dril hmits, divisions, and polity of countries ; the industrial habits of
their people; and thefr relations with others, whether distant or neighbouring,
and aperiaUy their reUgious faith and its outward expression, wiU be found to
vary accordmgly.
4 Qf Geographical Statistics. — In aU the dirisions of Political Geo
graphy, and the inquiries consequent upon their consideration, the province
of Statistics must of neceasity be trespassed upon. Geography relating to, or
rather combining together, aU sciences in thefr relations to the Earth and to
man; as in the case of Geology, Meteorology, Ethnology, or any other, so in
Statistics, whUe the application and results of the science wiU be taken advan
tage of, they vrill be dealt with generaUy and not in detaU. In none perhaps are
the details so uncertain, in none, perhaps, the general results more satisfactory,
more conclusive, or more useful. Materials for statistical calculations exist
only in cirilized countries, and may, in fact, be considered as no smaU proof of
advanced civilization : thefr character will vary with that of the people to whom
tiiey relate, and be especially influenced by thefr habits and mode of life.
They may be more easily attainable in some countries in the reUgious, in
others in the civU or industrial divisions. In most countries, even the very
savage, mUitary statistics can be procured : their existence by themselves is
FF

434 THEORY OP DESCRIPTION AND
perhaps to be considered the flrst advance in civil polity ; soUtary tribes on
the shores of the Polar Sea, of New Caledonia, Afnca, AusteaUa, and Terra
del Fuego, alone existing vrithout it. Industrial statistics, whether agricul
tural, commercial, or manufacturing, occupy the second place ; social, medical,
and educational, the thfrd and most advanced ; but the latter of these are
closely aUied to reUgion, and reUgious statistics are evidently independent of
advanced civilization. Educational statistics -wUl be found to depend rather on
the character of the reUgion of any country, than either ite influence or the
extent to which that influence is systematized, from which the statistical
accounts of it must in the main result; possibly the most systematic and
thoroughly organized form of reUgion the world has perhaps ever known, the
Eoman catholic, may be found to have retarded civilization m exact proportion
to its domination over its members, the exact and regular working of ite
machinery, and the consequent amount of statistical knowledge attamable
respecting it.
Statistical inquiry, as relating to PoUtical Geography, comprises aU calcu
lations of number ; under the head CivU, the amount of population in the
various divisions ; the proportionate number of representatives, if any ; of
militia, miUtary, or naval force ; of taxes, and other pubUc burdens and con
tributions, may be considered : under that of Industrial, the proportion of
population to surface ; the numbers employed in various trades and occupa
tions ; the products of agriculture, mines, manufactures, and commerce :
under that of EeUgious, the numbers and proportion of the various secte into
which the people may be divided. The Statistics of Education and Science wUl
belong to either or all, according to the country under consideration; in
Prussia, for example, neither the indusfrial nor reUgious can be considered apart
from the civil. In all, however, care should be taken not to extend the inqufry
beyond its geographical relation.
5 Cf the Order to be observed. — Of the three divisions which have been
recognised, we have placed the EeUgious first, as being in a great measure
independent of the other two ; it may be convenient to maintain this order in
general description, and to vary it in particular, to take first a general survey
of the extent and influence of the different faiths professed by the people of
the Earth, and independently of thefr civU- relations, and then to describe
more particularly the religious divisions consequent upon them ; for whUe, on
the one hand, the principal reUgious systems of the world extend themselves
vrithout reference to pohtical divisions ; on the other, the ecclesiastical poUty
may be diatinct from, and independent of, the civU ; yet in separate countries,
and under distinct govemments, it naturally adapte itself to the civU dirisions ;
and in exceptional cases, when it does not, they wiU probably be found the
best, if not the only means by which its Umits may be deflned. Particular
religious belief often attaches itself to particular races, the civil divisions of
countries are not unfrequently the consequences ofthe localization of distinct
races, and in this way, again, the reUgious and ciril divisions may be found to
coincide. In the consideration, therefore, of PoUtical Geography in detail, the fol
lowing sequence of its divisions ahouldbe observed : civil, rehgious, industrial ;
civU, from the Latin, civilis — i. e., appertaining to citizenship, that which
belongs or relates to citizens, or its complement — ^the state.
6 Of the Civil Divisions ofthe World. — The larger ciril divisions of the
Earth's surface are dependent on the arrangements made by the great human
societies whioh inhabit them for thefr government, and receive various names,
most of which are now used without being limited by strict etymological
propriety. The first in rank and importance should be, and in some instances
are, termed empfres. These are govemed by an emperor, in whom is_ con
cenfrated the authority of the whole, (as the word ' imperator,' first appUed to
the generals ofthe Eoman armies in tiie provinces who were the representatives
in them of the power of the state, seems to imply.) This word was adopted by
those who claimed similar authority to that exercised by the Eoman emperors

GEOGRAPHICAL TERMINOLOGY. 435
whether in Italy, Eastern Europe, France, Germany, or Eussia. Its import is
now very various ; it is used equaUy with reference to Eussia, Austria, BrazU,
China, and the Island of Hayti, all ofwhich are governed by a ruler styling
himself emperor. It is sometimes supposed to express the agglomeration of
many separate kingdoms, states, or provinces, imder one supreme head ; but
in this case Great Britain and her dependencies would be the largest and
most important empfre at present in the world, if not that the world has
ever seen. This appUcation of the term ia teue with reference to Eussia
and Austria, and partiaUy of BrazU, or more correctly, the BrazUs. Great
Britain is often termed an empfre, but its monarch has not assumed the title
corresponding to that designation.
Eingdoms, counteies ruled over by a king or queen, (Saxon, cyng cynig,
German, konig, implying miUtary rule,) stand next in rank to empires ; yet some
kingdoms, as those of Great Britain and France, being of equal, if not superior
importance to any existing empfres, there is no steict propriety in the sequence.
The term monarchy (from the Greek, fiovor apxos, monarch — i. e. sole ruler)
ia appUed equaUy to empfres and kingdoms where the supreme power is
concenfrated in an individual. Monarchies may be hereditary or elective,
despotic or limited; the latter are frequently termed constitutional, because
the constitution, to which both the monarch and his subjects have subscribed,
defines the limite of his power and their obedience. In despotic monarchies,
the vriU of the sovereign is law; in limited monarchies, the law is above aU
wUl, and the power of the government is di-rided between the supreme ruler
and the assembled representatives of the other power or powers by which that
ofthe monarch is limited. ParUaments, chambers of peers, senators, deputies,
diete, or other names, are appUed to these assembUes. They differ much in
thefr constitution and powers; some are hereditary, as the House of Lords, in
England; otiiers elective, as the House of Commons. Different qualifications
are also requfred for thefr members. These varieties of constitution belong
to the poUtical history of the world. PoUtical Geography, however, of
necessity concerns iteelf vrith the great principles on which these varieties
are based, as indicative of the origin of the families of mankind in which they
are found; the physical character of the countey in which they have been
educated; or of that in which they are located.
A limited monarchy is, perhaps, to be considered as the agreement of the
three great elemente of govemment — the executive, the deUberative, and the
suggestive. The first is involved vrith the monarchical principle, the second
with the aristocratic, the thfrd vrith the representative. The first expresses
the vriU — tiie second, the mind — ^the third, the body of the people. When the
first predominates, and in proportion to its predominance, the monarchy
becomes more and more despotic ; the ruler a tyrant, in the original accep
tation ofthe term, (from the Greek, rvpawos, implying the rule of an indivi
dual according to his own wUl — i. e., without law;) when the second preponde
rates, and in proportion to its preponderance, oligarchical, (from the Greek,
oKiyos apxT), the rule of the few;) when the latter, democratical, (from the
Greek, 8ijjiioy, the people, and Kpareos, to rule — i. e., the .rule of the many.)
In different counteies and among different races, we find tendencies to
different exfremes, as wiU be hereafter noticed.
It wiU appear in the sequel that these principles develop themselves
co-extenaivefy vrith corresponding reUgious and mdugtrial conditions of
society, and may be considered partly as consequences of them, partly as
resnltmg from the physical organization of the races adopting them, and
partly from the physical character of the country they inhabit, as inducing
the corresponding conditions referred to.
Simple despotism appears fraceable to the congregating of men in masses :
when in cities, as the consequence of democratic ascendancy ; among
nomad races, of warlike and migratory tendencies requiring a leader. The
former is observable in the Gfre^c cities and colonies ; the latter, among the
Mongul races. The monarchical principle, on the other hand, appears rather
F F 2

436 THEORY OP DESCRIPTION AND
the extension ofthe patriarchal, the king originally having simUar jurisdiction
to that of a father of a famUy; it is generaUy found in connexion with tribal
and aristocratic inatitutiona, and haa its further development in the constitu
tional monarchies of Europe, especiaUy in England. Among the ancients, it
is to be found among the earliest inhabitants of Greece, the Persians, the
Etruscans, probably the Egyptians. It is at present confined almost entirely
to the races which have been styled Indo-Germanic or Arian (aee P. G., p. 396),
of which the Anglo-Saxon is the type. With tribal distinctions, classification
of trades and employments, social divisions, as of caste in India, local govern
ment, guilds, and municipal institutions, are traceabie, as weU as a tendency
to connect these divisional authorities, whether ciril, religious, military, or
commercial, with property and tenure of land. The fammes in which they
are found have, therefore, agricultural tendencies, and have taken the lead at
a comparatively late period in the history of civUization, thefr development
being slow, their tenacity proportionately great.
Democracy naturally develops itself among commercial and manufacturing
communities; its first necessity is numbers confined to a Umited space: the
apparently exceptional case presented by the United States oi America is so
only in name, the government of that country being of a mixed character.
The word republic, (from the Latin, res publica, commonwealth,) in ite
ordinary acceptation, impUes a govemment dependent on the wiU of the
people ; it is, therefore, properly a democratical form of constitution. Yet
Eome, under the empfre, was a despotism with republican forms; it had been
previously an oligarchy under similar conditions. The word state (from the
Latin, status, condition,) may be applied to any country haring supreme
authority within itself; it is generally used with reference to smaller political
bodies, especially those united together for mutual advantage; such are those
of Central Europe attached to the German empire, such the United States in
North America.
The word colony may be appUed either to a detached province of an
empire, kingdom, or state ; a city founded in a foreign country, but preserring
its connexion by tradition at least with its parent; or a body of men emi
grating from one countey to establish themselves m another. Great Britain
has Iier colonies in the firat sense in North America, AusteaUa, and New
Zealand; in the second, at Aden; in the third, in her emigration and colonizing
companies, the first bodies of emigrants sent out by tbem being often so
called. The second was the application more common among the Greeks
and Eomans; the third has been very general in aU ages. In this sense tbe
Flemings founded colonies in England, the EngUsh and Scotch in Ireland,
the Germans in Hungary and Spain.
The word capital should be applied to those cities in which the govern
ment of the country is carried on.
7 Of the Civil Divisions of Countries. — GeographicaUy considered, we
find under thia head —
1st. The limits or boundaries of the country under consideration; tbe
character of the frontier line thus presented, whether natural or artificial;
the relation to and points of connexion with the counteies by which it is
surrounded. These should be considered under this division simply with
reference to their general government, and they may have either a miUtary
or commercial relation. Artificial frontiers have hitherto requfred barriers
against armed aggression or contraband trade, far more numerous and expen
sive than natural frontiers. We cannot violate the arrangemente made by
the Great Creator of the universe without suflering by our foUy, and the evU
effects of this error are perhaps more apparent and more felt in the character
of the people bordering on such a frontier, than in the expense incurred in
maintaining it.
Not the least important portion of the frontier of any country is its sea
board, if it have one. The possession of this gives freedom of action and
comparative freedom from aggression on that quarter; opens direct commu-

GEOGRAPHICAL TERMINOLOGY. 437
nication witii countries far distant; and enlarges the sphere of political action
It IS the happmess of this countey to possess no other, and to it she owes
probably much of her poUtical as weU as her commercial importance.
As on an inland frontier the Unes of fortresses and other artificial defences
should be syatematicaUy described, so, on a maritime, the ports and harbours
.available for the outfit and shelter of fieets, the dockyards and arsenals
situated upon them, with thefr relative capacity and importance, as well as
the natural or artificial defences ofthe coast, should be carefuUy noted.
The points of connexion between neighbouring countries must depend on
the natural or artificial means of communication which exist. Eivers, canals,
raihoads, or great miUtary roads, such as are found in Germany, wUl there
fore come under this head ; unless, as in England, most frequently, they have
been constructed entfrely for the purposes of commercial intercourse.
2nd. The general divisions of the empire or state : if the former, the
states of which it is composed first, and then as in the latter when considered
separately ; the larger and more important diviaion affecting its polity,
vrnetiier judicial, miUtary, or financial, as in different nations. These greater
dirisions obtain different names, and as these names are not always applied
with strict reference to thefr meaning or etymology, and indeed are often
hiatorical — ^i. e., the legaciea of former ages, and indicative of divisions made
origmaUy for other purposes than those for which they are at present used —
it IS better to consider them all as local terms, and explain them as their
uae becomes necessary. These first great divisions relating to the general
and central government wUl probably be found susceptible of subdivisions —
for example, in England we fiid firat, the division into Shfres and Counties,
and these again subdivided into Hundreds, Tithings, &c., or Pariahea, which
are again formed into Unions, and as in mUitary affairs, the larger divisions
arranged in Districts.
The cities and towns wUl be susceptible of the same classification. The
metropoUs (from the Greek, mother city) belongs, as we have seen, to the
first class, as do fortresses, arsenals, and public dockyards ; whUe the prin
cipal tovms of the larger divisions must be placed in the second.
It is difficult to distinguish exactly between a city and a town. The appel
lation may be consequent either on law or custom. Blackstone, in the Intro
duction to his Commentaries on the Laws of England, deflnes a city as ' a town
incorporated, which is or hath been the see of a bishop,' and he distinguishes
between borough and other towns. ' A borough,' he says, ' is now understood
to be a town either corporate or not, that sendeth burgesses to parliament. Other
towns there are to the number (Sir Edward Coke says) of 8803, which are
neither cities nor boroughs ; some of which have the pririlege of markets, and
some not, but both are equaUy towns in law.' From the context it appears,
that he considered tithings, to-wns, or vUls, to be marked by the possession of
a church and the celebration of divine service, the sacraments, and burials;
towns or tithings, subsequently called vills, consisted of ten freemen ; demi-viUs
of flve, and hamlets of less than five. (See Spblman's Glossary.) These
divisions, as weU as their extension to hundreds, and again to counties and
earldoms, being of Saxon origin, and the civil being so intimately connected
with the eccleaiaatical, vriU show not only that in these acceptations they
are originally to be confined to England, but that iu them they cannot
be now used even here, much less in any other country, and that their
application must be governed by custom and analogy. The word town is
derived from the Anglo-Saxon, tynantun; in the Dutch, tuyn, an enclosed
place. The word vUl (from the Latin, villa, a country-house, and having its
apphcation originaUy so confined) has, in modern times, been extended, as in
Anierica and the British Colonies, to considerable fracts of land caUed
townships. Geography of course concerns itself principaUy with the limits
of the divisions, and the localities of the cities and towns ; their uses belong
to PoUtical History. It will be necesaary, however, to enter sufficiently into
this part of the subject to make the character of the divisions inteUigible.

438 THEORY OP DESCRIPTION AND
8 Cf Beligious Divisions. — It has been afready noticed (see section 5)
that the religious divisions of the world have no direct connexion with the
poUtical, although they have vrith those wbich are consequent on similarity of
race. In modem Geography, these are few, eaaUy defined, and extensive in
thefr operation.
They may be characterized in principle as Monotheistic and Polytheistic,
it being now generaUy admitted that no nation or society of men can be
sfrictiy termed Atheistic ; and Chevalier Bunsen does not hesitate to name
religion and language as being the first facts that may be predicated of
any nation.
Of the monotheistic systems the principal are Christianity and Maho-
medanism, to these may not improperly be added Buddhism, and that of the
nations inhabiting America when it was discovered by Europeans. If this
classification be adopted, more than two-thfrds of the inhabitante of the
world may be considered as worshippers of one God. In aU these, however,
a tendency towards polytheism is apparent among certain nations and
famUies in connexion vrith a personal, physical, or objective development of
the faith professed. It is leas observable in the Mahomedan than in the
others, because the unity of the Deity is the ftmdamental article of that
creed, but it is found even there in the worship of sainte, and the same
among the Buddhists. It is the cauae of the two great divisions of
Christianity, the Eoman-cathoUc and the Protestant, for in this respect the
Greek Church may be considered protestant.
Christianity being a religion divulged, not for a race, but for mankind,
may and does flourish among aU races and famiUes. It has, however, taken
deepest root among the Indo-Germanic race afready referred to. The Celtic
being the more impulsive, are aU but universaUy Eoman CathoUcs; the
Teutonic, the more thoughtful, as generaUy Protestant. The Greek Church
(the principal characteriatic of which is its entfre dependence on a civUhead —
the Emperor of Eussia) has its principal root among the Sclavonic races,
remarkable for thefr subserviency of disposition. Mahomedanism has pre
vaUed chiefly among the races inhabiting south-western Asia and Africa,
belonging to the Negritic division, as already indicated. (See P. G., p. 395.)
Buddhism is co-extensive in the East -with the Mongul race. The other
religions of the world appear scarcely capable of enlarged classification, being
chiefiy traditionary, and uninteUigible equaUy to those professing them as to
others. 9 Ofthe Dominant Beligion. — Under this head mnst first be noted
the prevalent reUgion, or that recognised by the ciril govemment of the
country, and the principal seats of ecclesiastical power and religious
worship. These must of course obtain under different names, according to
the nature of the reUgion and language of the country. The locahties of
great reUgious meetings or festivals ; of universities or schools devoted prin
cipaUy or entirely to ecclesiastical purposes, or carried on under ecclesiastical
superrision and authority, should also be noted. These may, however, belong
to the subdivision of this subject, foUowing in natural order, in which the
larger ecclesiastical districts of the countey are described. This wUl depend
on the character of the superrision exercised, whether general or sectional;
it may also be local. The national schools of England partake of aU these
characteristics, — they are national as under government inspection, or that
of the National Society ; sectional or diocesan, the clergy exercising so large a
share of thefr dfrection ; local, because in most caaes parochial. It wUI be
obriously impossible to enter into such considerations in detaU; in most caaea
it ¦wiU be possible only to indicate the number, extent, and locaUty of the
minor diviaiona. Under the second head of this, as in the ciril, the chief
towns of the subdivisions may with propriety be noticed, whether bishops'
sees or otherwiae.
10 Of Beligious Sects. — Having considered the leading or dominant
reUgion in ita geographical relation, the sects which may exist in the country

GEOGRAPHICAL TERMINOLOGY. 439
under description must be taken in order of importance ; thefr centre of
locaUty noted, if any ; if not, thefr proportionate distribution. From the
circumstances of artificial division already alluded to, it often happens that of
the same countey politicaUy considered the inhabitants differ essentiaUy in
their reUgious character, and are not unfrequently connected by it more
intimately with their neighbours than -with their countrymen. This may
have an historical explanation, being the result of diff'erence of origin, immi
gration, or otherwise, or it may be consequent on the physical character ot the
countiy : the former is, perhaps, more often the case.
This dirision of PoUtical Geography, as has been noticed, is not unfre
quentiy found closely connected vrith both the others ; especiaUy it wUl be
observed that ciril and religious Uberty walk hand in hand, and that their
natural consequences are the advancement of education, the increase of
agricultural or manufacturing industry, and the extension of trade and
commerce. II Of Beligious Statistics. — In this class, as in the preceding, some
statistical information should be included. The numbers professing the
national creed, and those of the principal sects ; the proportion of numbers to
area, if any secte be localized, should if possible be ascertained, and the
industrial class to which they more particularly appertain should also be noted.
I'rom such facts general conclusions of much importance may be drawn.
Care must, however, be taken that the inferences be correct ; e. g., it might be
correct to say that countries professing the Eoman-catholic rehgion are leas
advanced in civiUzation than those which have protested against it ; it would
be incorrect to attribute this whoUy to the religion, because those countries
which have protested were once ofthe same faith; the answer must be sought
in the connexion between the character of the people and their poUtical and
geographical position, resulting in the one retaining, and the other protesting
againat the faith in question. The cause of reUgious and social advancement
may probably in like manner be found to be the same. In our ovrn
country, the manufacturing and mining districts are said to be strongholds of
dissent from the established reUgion ; it would be equaUy incorrect to refer
this to any pecuUar antagonism to the mode of faith arising out of the
habits ofthe people, or the nature of their occupations ; it should rather be
attributed to the neglect of those districts by the government and the clergy,
except in so far as the kind of labour may influence the development of the
mental or bodUy faculties respectively, as vriU be hereafter shown, or as the
purauit of wealth haa a natiiral tendency to draw men away from religion ;
and thus we find that the employers have taken no care of the spiritual weUare
of thefr workmen, until danger to themselves has arisen from the neglect.
The materials for this division of inquiry into the PoUtical Geography of
the world are very insufficient, no good hiatorical and statistical account of
the reUgions ayatems extant in the world being at present in existence ; even
the aggregate estimate of the numbers professing the great leading reUgions
of the world being very variously estimated, and detaUs being obtainable only
in those countries dfrectly under the influence of the European races, and
even in them they are usuaUy very Uttle to be depended upon.
12 Cf the Industrial Geography of Countries. — The civU and reUgious
diriaions of countries have been described as for the most part rather
arbifrary than natural, thefr connexion therefore with Geography proper is
rather accidental than essential. The thfrd — -riz., the industrial, differs from
the others in this, that the localities in which its great diviaiona are found,
have usuaUy a natural relation to them — i. e., the industrial occupations pre
vailing in them are consequent on thefr physical character. The truth of this
vrill appear on very cursory inquiry. Land suitable for pasturage is seldom
so well adapted, frequently is not at aU suited to agricultural purposes. The
locahties of certain manufactures are dependent sometimes on the presence of
the raw material, often, perhaps, on that which is necessary for its conversion
to useful purposes. Thus the copper of CornwaU and AustraUa is carried to

440 THEORY OF DESCRIPTION AND
the coal districts of South Wales for smelting ; the cotton of America to the
neighbourhood of fron and coal for machinery and fuel. In such cases the
proximity of good ports and harbours, and their connexion vrith the interior
by rapid and easy teanait, both for the importation ofthe raw material and for
the export of the manufactured goods, is indispensable. The rise of such
commercial towns as Glasgow and Liverpool is naturally consequent, as are
the rapid increase of population and the extension of intemal communication.
The influence therefore of mineral wealth is moat conaiderable, and among
minerals, coal and fron, as of most general appUcation, occupy the firat place.
13 Of Industrial Dirisions. — The leadmg sub-dirisions of this part of
Political Geography have been already aUuded to, as — I. Pastoral; 2. Agri
cultural; 3. Manufacturing; 4. Commercial.
These, of course, may frequently be found in close connexion in the same
district, but the character of the district vriU be decided by the predominant
industrial occupation.
Each of these must be considered, not only as to its locality, but its
character; and as the character of the disfrict and consequent occupation
of its inhabitents react upon thefr character, both physical and mental, it
wUl be necessary to consider them in this relation also.
14 Cf Occupation.— The amount of mental effort necessary to dfrect
physical labour varies with the nature ofthe employment. The predominance
of the physical over the mental, or vice versd, wUl produce a development
corresponding to the proportion of those influences in the people subject to
them. Speaking generaUy, labour is not a characteristic of pastoral life ; in
agricultural, flie labour requfred is rather bodUy than mental; in manu
factories, the labour employed is certainly skUled labour, but that often more
the effect of habit than knowledge or mental effort ; and this is especiaUy the
case in such as admit of considerable dirision of labour, more particularly
so when the article manufactured is smaU and made in very large quantities;
in auch, the people employed may be considered rather aa Uvmg machines
than rational agents. Labour incident to commercial pursuits, especiaUy that
of navigation, seems, upon the whole, most conducive to an equal develop
ment of mental and bodUy energies.
But it is not sufficient to consider the nature of the labour to which
different classes are subject, the leisure afforded them must Ukewiae be
eatimated, aa weU aa thefr action and reaction on each other. The effect of
Ieiaure, like that of labour, differs according to its character and extent. In
pastoral Ufe, the labour, if ever conaiderable, is so only after long intervals of
leisure; this leisure is of necessity spent among the works of nature; thefr
contemplation is therefore a general consequence. The motions of the
heavenly bodies mark the passage of time and the retum of the seasons ; the
beauties of the Earth and her productions, and the order and harmony of the
works of creation, produce corresponding ideas in the mind. Among pastoral
tribes and nations, therefore, asfronomy, music, and lyric poefry have been
most frequently cultivated. The prevalence of leisure among them commonly
gives to their relaxation the character of physical labour, and thefr habits of
contemplation and soUtude give self-dependence of character whUe they dispose
the mind for the reception of superstitious rites, or even more to a speculative
faith. It may be a question whether the pecuUarities of thefr Uves do not
offer a serious bar to the reception of polytheism and idolafry.
In agricultural Ufe, the regular and. continuous sfrain on the physical
powers produces corresponding exhaustion; leisure is used for rest, and
enjoyment is customarUy sensum. The physical development is in muscular
strength, the mental ia overpowered by it, the religious beUef assumes a
personal and sensuous character, and becomes often vulgarly and coarsely
superstitioua. In the majority of manufactm'ing cmploymenta, tho leisure is more that
of the mind than the body, thc labom' being rather constant than severe ; and

GEOGRAPHICAL TERMINOLOGY. 441
when the employment aasumes the character which has therefore been called
mechanical, because like that ofa machine, though appUcable to a higher class
of production, the mind may be entirely abstracted from the labour of the
body, and not unfrequently handicraftsmen ply thefr trade with minds
absorbed in mathematical calculations. The more mechanical, therefore, any
emplojrment is, the more the mind may be disengaged, and the more varied
and extensive wUl be the mental pursuits of those engaged in it. Such labour
is also debUitating to the body; a morbid habit is produced. The tendencies
of this class are consequently towards abatruae speculations, mathematics,
phUosophy, poUtics. The shoemaker and the tailor may be the rival poli
ticians of the country vUlage. In disteicts entfrely manufacturing, political
societies and combinations are commonly found. The morbid temperament
consequent on the nature of their employment enlarges real and suggests
imaginary evUs; nervous irritabUity takes the place of muscular strength;
the enjoyments, often sensual, are chiefiy, if not entfrely, of a stimulating
character; the rehgious tendencies are speculative, not imaginative ; their
development, deistic, if not atheistic. These are, therefore, the natural resorts
of the pohtical reformer and the reUgious schismatic.
The labour and leisure consequent on the pursuit of commercial industry
are so varied in thefr character, that in thefr results they may resemble any
or aU the other classes. The saUor may, however, be fafrly taien as the type
ofthis dass. The leisure in his case is simUar to that of a pastoral Ufe,
excepting inasmuch as it wants most of the beauties, whUe it abounds in the
sublimities, of nature; it produces, therefore, a character imaginative and
superstitious, perhaps, but scarcely poetical. The constant realization of danger
makes the recognition of a personal pro-ridence customary in him, but the
equaUy constant conquest of the dangers to which he is exposed, by science,
sEU, courage, and physical power, gives him a mental and bodUy self-depen
dence unequalled, perhaps, by any other. Accustomed to discipline, obedience
ia hia pohtical characteriatic, though, inasmuch as his Ufe is spent almost
entirely apart from civU institutions, he can scarcely be said to have any poli
tical creed.
The conclusions which foUow on these considerations appear, then, to be,
that pastoral life produces a simple, impulsive, imaginative race, possibly
deficient m reasoning powers ; religious, but superstitious, and not idolatrous ;
recognising an immediate connexion with the Deity, and therefore conscious
of iimerent dignity. The poUtical character wUl be tribal, tending to royalty ;
the physical, that of energy rather than strength.
The agricultural wUl be the contrary of this : heavy in body and mind,
sensual in character, his reUgion wUl be gross — his political habit submissive
—his self-dependence that of brute force ; he vriU be the slave of the despot
and worshipper of idols.
The mechanical vriU produce highly-developed reasoning faculties, com
bined with low physical but highly-nervous energies ; the deist and the
democrat. Cities, especiaUy manufticturing, have therefore been the originators
andaupportera of democratic forms of govemment; then of equaUty, productive
of anarchy, as among the ancient Greeks and modern Itahans — the dominion
of one, an empfre, as in the case of Eome and Paris. Commercial cities have
the same general characteristics, softened by more extended intercourse with
the rest of the world ; and in them the saUor often becomes a political tool,
from his habit of obedience and his want of civU associations.
From these it foUows, moreover, that countries possessing the most varied
phyaical features produce, on the whole, the most highly-developed race of
inhabitants. Such are the countries which have borne, and wUl continue to
bear, rule in the earth. Such were Peraia, Greece, Italy ; and such, but in
a far higher degree, is England. (See Gutot's Lectures, c. I.)
15 Ofthe Pastoral. — The true pastoral districta are those which are only
suited to the production of short and sweet herbage, and therefore unfit for
tillage, either from the lightness or superficial nature of the soU. It not

442 THEORY OP DESCRIPTION AND
unfrequently, however, happens that low lands, on which luxuriant grasses
can be produced by irrigation, either natural or artificial, and which could also
be made to bear large crops of other vegetables, are devoted to the rearing of
cattle. These are not properly to be reckoned in the pastoral districta, and
yet they can scarcely be otherwise classed than in them ; and a comparison
must therefore be instituted between districts of such different character as
the downs of Sussex and Hampshfre, the bills of Cumberland and Westmore
land, and the rich vaUeys of Hereford, Somerset, and Devon, and the flats of
Lincolnshfre. Land recovered from, or occasionaUy overflowed by, the sea is often
devoted to the feeding of cattle, the saline character of the herbage being,
for short periods, very conducive to thefr health. This again can scarcely be
considered pastoral, and with the preceding, whUe classed among pastoral
in its productions, may, in the character oi its inhabitante, be rather con
sidered agricultural. •
Pastoral countries generaUy present a nomad population ; in them, cities,
are of course rare, and the pecuhar character of thefr inhabitants is dependent
on that of the animals they rear, and the uses they put them to. Tne Lap
lander who tends his reind.eer to supply the necessaries of life, differs less
from the Arab in this than in the consequences of the cUmate he resides in,
whUe both perhaps differ equaUy from the Gnacho of the Pampas, who rears
his herds of vrild cattle to carry on a teade in hides and horns. Wben
therefore these disteicts come under notice, these peculiarities must be
specified. The portions of the world naturaUy adapted to pastoral Ufe, are
usually found between the primary and secondary watersheds of the conti
nents on the side of thefr least rapid decUvity and greatest extension, and
form a very large proportion of its surface. They are not, however, fitted to
support a popiuation equivalent to thefr extent. From them, therefore, at
vanous times great emigrations have taken place, which have had a marked
effect on the history of the world. Pastoral countries may and usuaUy
have agricultural districts vrithin them; countries not pastoral may have
districts of that character. The influence on the people vriU in the one case
be general, in the other, local. The social Ufe of pastoral countries has been
generaUy of a patriarchal nature, ciril government scarcely recognised ; thefr
commerce usually carried on overland by means of caravans ; thefr poUtical
combinations can therefore never be elaborate or lasting, thefr commerce
never extensive. As the pastoral habit of Ufe appears to have first prevaUed
after the Deluge, so the caravan (a word probably of Persian origm) teade
seems to have been the first in use. We find it so in aU countries in
course of settlement, if suitable to it ; it disappears with the erection of
cities and the estabUshment of roads, and means of more safe and rapid
communication. 1 6 Of the Agricultural.-— The agricultural countries and districte of the
world are, as the name impUes, those which are capable of cultivation by
man, upon whioh he can by manual labour raise vegetables necessary for the
support of life, and essential to the arte and requfremente of civilization.
They are usuaUy found in the vaUeys of rivers ; the richest and most
extensive in the allurial formations about thefr lower course and beyond the
secondary watersheds. Here are to be found the great corn and rice pro
ducing countries, those whioh supply others with the means of subsistence —
the granaries of the world.
In a state of nature, those districts of the Earth which are best adapted
to agricultural purposes are commonly covered with the heavy growth of
vegetable life, often of frees. The character of this growth indicates the
quality of the soil, and the nature of the crop it is most calculated to produce.
The Unit which connects these districts with the commercial and manufac
turing, is suppUed by this cfrcumstance— the agricultural districts requiring
the produce of the manufacturing, whUe these again, not producing food for
a superabundant population, must be dependent on them for it. The identity

GEOGRAPHICAL TERMINOLOGY. 443
of the interests of all men and thefr mutual dependence on each other, thus
appear to be the natural order of creation.
The agricultural districts are those which foUow in course of settlement
on the pastoral. Thefr settiement of necessity raises the question of tenure of
land. The modes in which land raay be held by individuals may be reduced
¦under two heads ; the one in which the occupier is the owner of the soil,
the other in which he pays rent for his occupation. These have been consi
dered respectively characteristic of different races of men, possibly they are
rather distinctive of different stages of progress. Tenure by mUitary serrice,
the basis ofthe feudal system, and one form of tenure by occupation, has pre
vaUed wherever the Indo-Germanic race has been diffused, and by its pre
valence marks it as migratory and aggressive. We first read of rent for knd
in the book of Genesis, where Joseph bought all the land of the Egyptians
for Pharaoh, and let it again to the Egyptians for a fifth part of the
produce. (Gen. xlvu. 24.) These two modes of tenure, producing very dif
ferent effecte on an agricultural population, are important to be noticed in
Political Geography.
It ia, as has been observed, in districts of this character that cities have
first arisen ; in them, man being stationary, property has increased, and
with the increase the mechanical skill of man has been developed to supply
his artificial wants, the result of riches and society ; a marked distinction
thus arises between the dweUers in towns and the agriculturists — a distinc
tion which becomes more marked in proportion to the increase of wealth
andpopulation. The nature of the agricultural produce of any disfrict must have its effect
on the people inhabiting it, not only because of the difference of climate and
soU necessary to the production of different plants, but of the effect which
those uaed for food may have on the physical energies of the people. Thus,
the corn-producing countries wiU be more favourable to physical develop
ment than the rice-producing. It is necessary also to consider whether the
vegetable produce of the Earth be directly employed in manufactures, or
fransported for that purpose, as at present the three great staples, cotton,
flax, and hemp are.
The transport of heavy raw material to a distance, for the purpose of
manufacture, is e-ridence of a great advance in the industry of the countries
engaged, especially that in which it is manufactured. It may also be taien
as an indication that there is a surplus beyond the produce requfred for the
food of the people. The retums vriU, therefore, be in manufactures or
money, and the balance in favour of the country exporting.
17 Cf the Manufacturing. — Manufactures are, in the early stages of
civUization, carried on among a nomad or an agricultural population ; they
become localized when either the dirision of labour for their conduct on a
large scale becomes necessary, or the presence of the raw material attracts
them to any particular place. Since the extensive use of machinery in aU
manufactures, they have had a tendency to gather round the coal and fron
producing disteicts ; the facilities of transport afforde^ by raUroads may have
a tendency to disperse them again. At present, however, these minerals
muat receive special notice in connexion -with the diatribution of manufac
turing industry over the face of the globe.
When the agricultural produce of any district is employed in neigh
bouring manufacture, the one is supported and enriched by the other, but it
more often happens that the increase of manufactures in any district has a
tendency to desfroy its agricultural character. This happens especiaUy
m distncts, the mineral wealth of which is the subject of manufacturing
indust^— and this, if only from the necessity of finding place for the refuse
which has been brought to the surface vrith the deafred mineral. In some
mming districts, the coal in particular, the disposition^ of this rubbish is a
problem often difficult and always expensive in its practical solution. But in
any case, the necessities of a dense population, whether real or artificial, the

444 THEORY OP DESCRIPTION AND
supply of the wants of the poor and the luxuries of the rich, must reduce
considerably the agricultural capabiUties of the district.
It is also a question of importance whether the manufactures of any
countey are for home consumption or for exportation; if the former only, they
must be very limited in extent ; if the latter, they wUl of course be enlarged
to meet the demand made for the article produced. The consequence wUl be,
a return trade and enlarged commercial relations ; and here also a reactionary
tendency may be observed, since much of this retum trade wiU be in agricul
tural produce for the food ofthe manufacturing population.
The congregation of men in manufacturing districte, and the tendency of
these employments to lower the amount of agricultural produce to be
obtained for them, wUl thus compel a teade in articles of food; but as the
food-producing countriea are uauaUy in a low atage of civilization, their con
sumption of manufactured articles is limited, and commerce therefore fiows
in two channela. The presence of mineral wealth is dependent on geological
formation, by it the locahties of certain manufacturea are of necessity
determined ; and here also, as in the other divisions, we see the nature of the
country influencing, if not determining, the character and occupation of ite
inhabitants. 1 8 Cf the Commercial. — Commerce is dependent on manufactures; it is
either internal or external, maritime or over-land. Commerce is the exchange
of surplus commodities ; even where it is carried on vrith a cfrculating medium
on one side, this is strictly teue ; there muat then be a aurplus of money.
Theae exchanges can only be made between places where the surplus is
different. The commercial relations between different parte of the world are,
therefore, determined by the character of thefr productions. Commerce is
therefore, in its geographical disfribution, not the result of accident, but
subject to fixed laws.
The paths of commerce also are regulated by physical causes. The caravan
trade of old was carried, as it is now, over table-lands, deserts, and prairies.
The passes of the mountain chains have directed it first into certain districte,
and brought those thus connected by the head-waters of thefr rivers into early
and most immediate commercial relations. In maritime commerce, islands
and inlets of the sea had an early share, voyages were then made across the
ocean, but even its broad expanse did not give unlimited facUities for traffic.
There also physical difflculties formed barriers, imperceptible indeed, but stiU
effective. Currents and trade-winds dfrected commercial intercourse into
certain channels, from which not even steam navigation has materiaUy
diverted it. The extension of raUway traffic seems, however, Ukely to bring
back much of the commerce of the world into the old overland routes, and
by making speed the first element in the calculation, to invest those parte of
the continental masses that approach nearest to each other with an import
ance they have not enjoyed since the earUest periods of commercial enter
prise, as affording the more immediate means of communicatiou.
From what has been afready aaid, it wiU be apparent, that, aa extent
ia the reault of elevation, or in other worda, the horizontal development
of the land is the consequence of its vertical contom', upon this also
depends the disfribution of animal and vegetable life over the surface of the
earth, the variety of produce of different countriea, their consequent rela
tive value as a residence for man, and the commercial relations wbich may
exist between them, and no lesa the physical development of man himself, his
habits of life, employments, and mode of thought, and hence, in no smaU
degree, the character of hia religioua and political life — upon this alao haa
depended the distribution of mankind over the Earth, both in time and space,
the earher or later peopling of different districts, the som-ce from whence
they have been peopled, and the paths of migration, — these have had thefr own
proper effect on the history of the world, speciaUy in the diffusion of language
and literature — have made the western part of the old continent progressive,
whUe the eastern haa remained stationary, if it has not retrograded.

GEOGRAPHICAL TERMINOLOGY. 445
The presence of minerals and metals has also been shown to be dependent
on the same cause, being found only in certain parts of the geological series.
They are avaUable only when those portions are presented. The rocks which
have been formed by fluvial deposit, and especially the coal measures, could
only have been so formed in entire or partial basins, and their localities have
therefore been determined by vertical contour at the period of their forma
tion ; whUe those minerals and metals which are formed in connexion with
rock of earlier place in the series, are only avaUable for the purposes of man
where they make thefr appearance above or through the others. The localities
of manufacturing and mining industry have therefore been pre-arranged by
the same cause. It has been shown that commercial exchanges are the result
of variety of produce, that this variety ia the conaequence of variety of contour,
that the paths of commerce by land are determined by, and that those by sea
have been, and are now dependent on the same causes. It haa also appeared
that aU theae have a reciprocating effect on each other ; for not only do
manufactures encourage and develope agriculture, if not at home, of necessity
elsewhere, that commerce ariaea and la maintained by the variety of aupply and
demand ; but that different kinda of manufacturea and variety of commercial
intercourae, as weU as of agricultural produce, stimulate and encourage those
with which they are connected ; and thus it becomes apparent that countries
possessing the greatest physical development are capable of the greatest
induatriaf development also. The knowledge therefore of vertical contour
muat be the basis of aU true geographical knowledge, and from the considera
tion of its effects we must conclude that the Great Creator in giving form to
the Earth disposed certain causes to neceaaary enda, and that in thia dia-
poaition he proposed the ends to which he haa adapted the means, and that
we, as parts of his creation, more especiaUy those to whom as his intel
ligent servants he has given the rule and use of his inferior creation, shall
act most to his glory, and best fulffl the conditions of our own existence, when
we dfrect our actions, whether poUtical or social, vrith an inteUigent apprecia
tion of them ; and that his original deaigna and beneficent intentions towards
the world caimot be fulfiUed by us, untU we know, appreciate, and apply to
thefr proper purposes, the capabUities, not of one but of aU countriea, untd
we conaider not only what one country may be made to produce, or what one
people are capable of producing, but how the produce thus obtained wUl
affect other counteies, how advantage may result to others also ; in short, tUl
the good of the many be consulted, instead of that of the few, and we fulfil
generaUy, as well as particularly, the royal law, to do to others as we would
have them do to us.
To this desfred consummation, the knowledge of geography in its highest
relations is necessary. This can only be attained by careful initiation into its
elements. The importance of the end to be attained may weU stimulate to
more laborious and uninteresting investigations than this science requires.

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