On the probable Cause, Date, and Duration of the Glacial Epoch of Geology

Abstract

A fter referring to the evidence of the occurrence of a Glacial Epoch, and to the various hypotheses which have been proposed to account for it, the author brought forward the following considerations:— Of the three principal movements of the earth, namely its daily rotation on its axis, its revolution round the sun, and the slow conical movement of its axis of rotation round the poles of the ecliptic, the third is, in the author’s opinion, the cause of glacial epochs. The angular distance of the pole of the ecliptic and the pole of the heavens is at all times the exact measure of the obliquity of the ecliptic, or the extent of the Arctic circle upon the earth. There is evidence that during the last 2000 years these two poles have gradually decreased their angular distance, so that, while the pole of the heavens moves round some curve at the rate of about 1° in seventy-two years, it approaches the pole of the ecliptic at a variable rate, at present about 46″ in a century. The author had calculated from the recorded positions of the pole of the heavens during the last 2000 years, the curve traced by this pole with relation to the pole of the ecliptic. He found it to be a circle, the centre of which is 6° from the pole of the ecliptic, and 29° 25′ 4.7″ from that of the heavens. Taking this curve as a guide, the author finds that 2000 years ago the