Page 230 - Lokmanya Tilak Samagra (khand 2)

CHAPTER II

THE GLACIAL PERIOD

Geological climate-Uniform and gentle in early ages-Due to
different distribution of land and water-Climatic changes in the
Quaternary era~The Glacial epoch-Its existence undoubtedly proYed
-Extent of glaciation-.-\t least two Glacial periods-Accompanied
by elevation and depression of land-:\Iild and genial Inter-Glacial
climate even in the Arctic regions-Various theories regarding the
cause of the Ice Age stated-Lyell's theory of geographical changes
-Showing long duration of the Glacial period-Croll's theory-Effect of
the precession of the equinoxes on the duration and intensity of seasons
-The cycle of 2r,ooo years-The efrect enhanced by the eccentricity
of the.earth's orbit-:\Iaximum difference of 33 days between duration
of summer and winter-Sir Robert Ball's calculations regarding the
average heat received by each hemisphere in summer and winter-Short
and warm summers and long and cold winters, giving rise to a Glacial
epoch-Dr. Croll's extraordinary estimate regarding the duration of the
Glacial epoch-Based on the maximum value of eccentricity of the
earth's orbit-Questioned by astronomers and geologists-Sir Robert
Ball's and Newcomb's view-Croll's estimates inconsistent with geologi-
cal evidence-Opinions of Prof. Geikie and :vir. Hudleston-Long
duration of the Glacial period-Summary of results.

The climate of our globe at the present day is characteris-
ed by a succession of seasons, spring, summer, autumn and
winter, caused by the inclination of the earth's axis to the plane
of the ecliptic. When the North Pole of the earth is turned
away from the sun in its annual course round that luminary, we
have winter in the northern and summer in the southern hemi-
sphere, and vice versa when the North Pole is turned towards
the sun. The cause of the rotation of seasons in the different
hemispheres is thus very simple, and from the permanence of
this cause one may be led to think that in the distant geological
ages the climate of our planet must have been characterised by
similar rotations of hot and cold seasons. But such a suppo-
sition is directly contradicted by geological evidence. The in-
clination of the earth's axis to the plane of ecliptic, or what is
technically called the obliquity of the ecliptic, is not the sole
cause of climatic variations on the surface of the globe. High
A. 2