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. 5