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

THE GLACIAL PERIOD. 33
of 160,000 years; and that 80,000 years have elapsed since the
close of the third or the last period. According to Dr. Croll the
Glacial epoch in the Pleistocene period must, therefore, have
begun 240,000 years ago, and ended, followed by the Post-Glacial
period, about 80,000 years ago. During this long period of 160,000
years, there must have been several alternations of mild and severe
climates, according as the winter in a hemisphere occurred when
the earth was at perihelion or aphelion in its orbit, which hap-
pened every 10,500 years during the period. But as the cold epoch
can be at its maximum only during the early part of each period,
according to Dr. Croll's theory, the last epoch of maximum glaciation
must be placed 200,000 years ago, or about 40,000 years after the
commencement of the last period of maximum eccentricity.
The reliability of these elaborate calculations has, however,
been questioned by astronomers and geologists alike. Sir Robert
Ball, who supports Croll in every other respect, has himself re-
frained from making any astronomical calculations regarding the
maximum value of the eccentricity of the earth's orbit, or the
time when the last Glacial epoch should have occurred, or when
the next would take place. "I cannot say," he observes, "when
the last (Glacial epoch) took place, nor when the next may
be expected. No one who is competent to deal with mathe-
matical formulæ would venture on such predictions in the
present state of our knowledge."* Prof. Newcomb of
New York, another astronomer of repute, in his review of
Dr. Croll's Climate and Time, has also pointed out how in the
present state of astronomical knowledge it is impossible to
place any reliance on the values of eccentricity computed
for epochs, distant by millions of years, as the value of
this eccentricity depends upon elements, many of which are
On the Cause of an Ice Age, p. 152.
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