1871.] DKATSON GLACIAL EPOCH. 233 



account for it, the author brought forward the following considera- 

 tions : — 



Of the three principal movements of the earth, namely its daUy 

 rotation on its axis, its revolution round the sun, and the slow coni- 

 cal 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 gra- 

 dually 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' 47" from that of the hea- 

 vens. 



Taking this curve as a guide, the author finds that 2000 years 

 ago the angular distance of the two poles was about 24°, giving a 

 climate scarcely different from that now prevailing. 4000 years 

 ago the angular distance would be about 29°, when the climates of 

 high northern and southern latitudes would present much greater 

 seasonal changes than at present ; and these changes woidd go on 

 increasing back to the year 13,000 b.c, at which period the distance 

 between the two poles would be greatest, namely 35° 25' 47". 

 This would bring the arctic circle down to latitude 54° 35' N., that 

 is to a line passing south of Moscow, just north of Berlin, north of 

 Amsterdam, nearly through the middle of Great Britain, and then 

 through Labrador and British Columbia. AU the countries north of 

 these places would be subjected to arctic conditions ; and these would 

 prevail with even more severity than at present in the winter, whilst 

 from the greater elevation attained by the sun in summer that sea- 

 son would be much hotter than at present, the siimmer of the lower 

 arctic latitudes being even tropical in its intensity. These extreme 

 changes of climate would prevail, according to the author, during 

 a period of about 15,000 years ; that is to say, commencing about 

 21,000 years ago, the climate would become more and more extreme 

 up to about 15,000 years ago, and then gradually more and more 

 equable to about 6000 years ago. 



DiscirssioN. 



Prof. Kamsat inquired whether the author's theory involved the 

 recurrence of glacial epochs, and whether he considered the course 

 of the described phenomena to be constant in early astronomical 

 epochs. 



Eev. Osmond Fisheb inquired whether the carve was founded on 

 observed facts, or whether it was obtained from physical considera- 



