वेदों की प्राचीनता एवं काल-निर्णय / ओरायन (लोकमान्य बाल गंगाधर तिलक - खगोलीय वैदिक शोध)

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
proved—Extent of glaciation—At least two Glacial periods—
Accompanied by elevation and depression of land—Mild 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 21,000
years—The effect enhanced by the eccentricity of the earth's
orbit—Maximum difference of 33 days between the 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 the eccentricity of the earth's orbit
—Questioned by astronomers and geologists—Sir Robert Ball's
and Newcomb's view—Croll's estimates inconsistent with
geological evidence—Opinions of Prof. Geikie and Mr. Hudleston
—Long duration of the Glacial period—Summary of results.
THE climate of our globe at the present day is characterised 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 hemisphere, 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