Chapter I: Preface

In the following pages I have endeavoured to give a full and concise statement of the facts and arguments adduced in support of the theory of Secular Changes of the Earth’s Climate. Considerable portions of the volume have already appeared in substance as separate papers in the Philosophical Magazine and other journals during the past ten or twelve years. The theory, especially in as far as it relates to the cause of the glacial epoch, appears to be gradually gaining acceptance with geologists. This, doubtless, is owing to the greatly increased and constantly increasing knowledge of the drift-phenomena, which has induced the almost general conviction that a climate such as that of the glacial epoch could only have resulted from cosmical causes.

Considerable attention has been devoted to objections, and to the removal of slight misapprehensions, which have naturally arisen in regard to a subject comparatively new and, in many respects, complex, and beset with formidable difficulties.

I have studiously avoided introducing anything of a hypothetical character. All the conclusions are based either on known facts or admitted physical principles. In short, the aim of the work, as will be shown in the introductory chapter, is to prove that secular changes of climate follow, as a necessary effect, from admitted physical agencies, and that these changes, in as far as the past climatic condition of the globe is concerned, fully meet the demand of the geologist.

The volume, though not intended as a popular treatise, will be found, I trust, to be perfectly plain and intelligible even to readers not familiar with physical science.

I avail myself of this opportunity of expressing my obligations to my colleagues, Mr. James Geikie, Mr. Robert L. Jack, Mr. Robert Etheridge, jun., and also to Mr. James Paton, of the Edinburgh Museum of Science and Art, for their valuable assistance rendered while these pages were passing through the press. To the kindness of Mr. James Bennie I am indebted for the copious index at the end of the volume, as well as for many of the facts relating to the glacial deposits of the West of Scotland.

JAMES CROLL.

EDINBURGH, _March, 1875_.

CONTENTS.

CHAPTER I.

INTRODUCTION.

PAGE
The Fundamental Problem of Geology.—Geology a Dynamical
Science.—The Nature of a Geological Principle.—Theories
of Geological Climate.—Geological Climate dependent
on Astronomical Causes.—An Important Consideration
overlooked.—Abstract of the Line of Argument pursued in the
Volume 1

CHAPTER II.

OCEAN-CURRENTS IN RELATION TO THE DISTRIBUTION OF HEAT OVER
THE GLOBE.

The absolute Heating-power of Ocean-currents.—Volume of
the Gulf-stream.—Absolute Amount of Heat conveyed by
it.—Greater Portion of Moisture in Inter-tropical Regions
falls as Rain in those Regions.—Land along the Equator
tends to lower the Temperature of the Globe.—Influence
of Gulf-stream on Climate of Europe.—Temperature of
Space.—Radiation of a Particle.—Professor Dove on Normal
Temperature.—Temperature of Equator and Poles in the Absence
of Ocean-currents.—Temperature of London, how much due to
Ocean-currents 23

CHAPTER III.

OCEAN-CURRENTS IN RELATION TO THE DISTRIBUTION OF HEAT OVER THE
GLOBE.—(_Continued._)

Influence of the Gulf-stream on the Climate of the Arctic
Regions.—Absolute Amount of Heat received by the Arctic
Regions from the Sun.—Influence of Ocean-currents shown by
another Method.—Temperature of a Globe all Water or all
Land according to Professor J. D. Forbes.—An important
Consideration overlooked.—Without Ocean-currents the
Globe would not be habitable.—Conclusions not affected by
Imperfection of Data 45