Chapter IV

OUTLINE OE THE PHYSICAL AGENCIES WHICH LEAD TO SECULAR
CHANGES OF CLIMATE.

Eccentricity of the Earth’s Orbit; its Effect on
Climate.—Glacial Epoch not the direct Result of an
Increase of Eccentricity.—An important Consideration
overlooked.—Change of Eccentricity affects Climate only
indirectly.—Agencies which are brought into Operation
by an Increase of Eccentricity.—How an Accumulation
of Snow is produced.—The Effect of Snow on the Summer
Temperature.—Reason of the Low Summer Temperature of Polar
Regions.—Deflection of Ocean-currents the chief Cause of
Secular Changes of Climate.—How the foregoing Causes deflect
Ocean-currents.—Nearness of the Sun in Perigee a Cause of
the Accumulation of Ice.—A remarkable Circumstance regarding
the Causes which lead to Secular Changes of Climate.—The
primary Cause an Increase of Eccentricity.—Mean Temperature
of whole Earth should be greater in Aphelion than in
Perihelion.—Professor Tyndall on the Glacial Epoch.—A
general Reduction of Temperature will not produce a Glacial
Epoch.—Objection from the present Condition of the Planet
Mars 54

CHAPTER V.

REASON WHY THE SOUTHERN HEMISPHERE IS COLDER THAN THE NORTHERN.

Adhémar’s Explanation.—Adhémar’s Theory founded upon a physical
Mistake in regard to Radiation.—Professor J. D. Forbes on
Underground Temperature.—Generally accepted Explanation.—Low
Temperature of Southern Hemisphere attributed to
Preponderance of Sea.—Heat transferred from Southern to
Northern Hemisphere by Ocean-current the true Explanation.—A
large Portion of the Heat of the Gulf-stream derived from the
Southern Hemisphere 81

CHAPTER VI.

EXAMINATION OF THE GRAVITATION THEORY OF OCEANIC
CIRCULATION.—LIEUT. MAURY’S THEORY.

Introduction.—Ocean-currents, according to Maury, due to
Difference of Specific Gravity.—Difference of Specific
Gravity resulting from Difference of Temperature.—Difference
of Specific Gravity resulting from Difference of
Saltness.—Maury’s two Causes neutralize each other.—How,
according to him, Difference in Saltness acts as a Cause 95

CHAPTER VII.

EXAMINATION OF THE GRAVITATION THEORY OF OCEANIC
CIRCULATION.—LIEUT. MAURY’S THEORY.—(_Continued._)

Methods of determining the Question.—The Force resulting from
Difference of Specific Gravity.—Sir John Herschel’s Estimate
of the Force.—Maximum Density of Sea-Water.—Rate of Decrease
of Temperature of Ocean at Equator.—The actual Amount of
Force resulting from Difference of Specific Gravity.—M.
Dubuat’s Experiments 115

CHAPTER VIII.

EXAMINATION OF THE GRAVITATION THEORY OF OCEANIC
CIRCULATION.—DR. CARPENTER’S THEORY.

Gulf-stream according to Dr. Carpenter not due to Difference of
Specific Gravity.—Facts to be Explained.—The Explanation of
the Facts.—The Explanation hypothetical.—The Cause assigned
for the hypothetical Mode of Circulation.—Under Currents
account for all the Facts better than the Gravitation
Hypothesis.—Known Condition of the Ocean inconsistent with
that Hypothesis 122

CHAPTER IX.

EXAMINATION OF THE GRAVITATION THEORY OF OCEANIC
CIRCULATION.—THE MECHANICS OF DR. CARPENTER’S THEORY.

Experimental Illustration of the Theory.—The Force exerted by
Gravity.—Work performed by Gravity.—Circulation not by
Convection.—Circulation depends on Difference in Density
of the Equatorial and Polar Columns.—Absolute Amount of
Work which can be performed by Gravity.—How Underflow is
produced.—How Vertical Descent at the Poles and Ascent at
the Equator is produced.—The Gibraltar Current.—Mistake in
Mechanics concerning it.—The Baltic Current 145

CHAPTER X.

EXAMINATION OF THE GRAVITATION THEORY OF OCEANIC
CIRCULATION.—DR. CARPENTER’S THEORY.—OBJECTIONS CONSIDERED.

_Modus Operandi_ of the Matter.—Polar Cold considered by Dr.
Carpenter the _Primum Mobile_.—Supposed Influence of
Heat derived from the Earth’s Crust.—Circulation without
Difference of Level.—A Confusion of Ideas in Reference to the
supposed Agency of Polar Cold.—M. Dubuat’s Experiments.—A
Begging of the Question at Issue.—Pressure as a Cause of
Circulation 172

CHAPTER XI.

THE INADEQUACY OF THE GRAVITATION THEORY PROVED BY ANOTHER
METHOD.

Quantity of Heat which can be conveyed by the General Oceanic
Circulation trifling.—Tendency in the Advocates of the
Gravitation Theory to under-estimate the Volume of the
Gulf-stream.—Volume of the Stream as determined by the
_Challenger_.—Immense Volume of Warm Water discovered by
Captain Nares.—Condition of North Atlantic inconsistent with
the Gravitation Theory.—Dr. Carpenter’s Estimate of the
Thermal Work of the Gulf-stream 191

CHAPTER XII.

MR. A. G. FINDLAY’S OBJECTIONS CONSIDERED.

Mr. Findlay’s Estimate of the Volume of the Gulf-stream.—Mean
Temperature of a Cross Section less than Mean Temperature
of Stream.—Reason of such Diversity of Opinion regarding
Ocean-currents.—More rigid Method of Investigation necessary 203

CHAPTER XIII.

THE WIND THEORY OF OCEANIC CIRCULATION.

Ocean-Currents not due alone to the Trade-winds.—An Objection
by Maury.—Trade-winds do not explain the Great Antarctic
Current.—Ocean-currents due to the System of Winds.—The
System of Currents agrees with the System of the
Winds.—Chart showing the Agreement between the System
of Currents and System of Winds.—Cause of the Gibraltar
Current.—North Atlantic an immense Whirlpool.—Theory of Under
Currents.—Difficulty regarding Under Currents obviated.—Work
performed by the Wind in impelling the Water forward.—The
_Challenger’s_ crucial Test of the Wind and Gravitation
Theories.—North Atlantic above the Level of Equator.—Thermal
Condition of the Southern Ocean irreconcilable with the
Gravitation Theory 210

CHAPTER XIV.

THE WIND THEORY OF OCEANIC CIRCULATION IN RELATION TO CHANGE
OF CLIMATE.

Direction of Currents depends on Direction of the Winds.—Causes
which affect the Direction of Currents will affect
Climate.—How Change of Eccentricity affects the Mode
of Distribution of the Winds.—Mutual Reaction of Cause
and Effect.—Displacement of the Great Equatorial
Current.—Displacement of the Median Line between the Trades,
and its Effect on Currents.—Ocean-currents in Relation to the
Distribution of Plants and Animals.—Alternate Cold and Warm
Periods in North and South.—Mr. Darwin’s Views quoted.—How
Glaciers at the Equator may be accounted for.—Migration
across the Equator 226

CHAPTER XV.

WARM INTER-GLACIAL PERIODS.

Alternate Cold and Warm Periods.—Warm Inter-glacial Periods
a Test of Theories.—Reason why their Occurrence has not
been hitherto recognised.—Instances of Warm Inter-glacial
Periods.—Dranse, Dürnten, Hoxne, Chapelhall, Craiglockhart,
Leith Walk, Redhall Quarry, Beith, Crofthead, Kilmaurs,
Sweden, Ohio, Cromer, Mundesley, &c., &c.—Cave and River
Deposits.—Occurrence of Arctic and Warm Animals in some Beds
accounted for.—Mr. Boyd Dawkins’s Objections.—Occurrence
of Southern Shells in Glacial Deposits.—Evidence of Warm
Inter-glacial Periods from Mineral Borings.—Striated
Pavements.—Reason why Inter-glacial Land-surfaces are so rare 236

CHAPTER XVI.

WARM INTER-GLACIAL PERIODS IN ARCTIC REGIONS.

Cold Periods best marked in Temperate, and Warm Periods
in Arctic, Regions.—State of Arctic Regions during
Glacial Period.—Effects of Removal of Ice from Arctic
Regions.—Ocean-currents; Influence on Arctic Climate.—Reason
why Remains of Inter-glacial Period are rare in Arctic
Regions.—Remains of Ancient Forests in Banks’s Land, Prince
Patrick’s Island, &c.—Opinions of Sir R. Murchison, Captain
Osborn, and Professor Haughton.—Tree dug up by Sir E. Belcher
in lat. 75° N. 258