CORRESPONDENCE 271 



that it was sufi&cient to cause an extensive glaciation, and the privilege of 

 finding the exact extent of change comes within the scope of astronomy. 



This view of the subject was primarily written to be translated into 

 French in the interests of M. Marcel Baudouin — a convert of my first convert 

 Dr. Allen Sturge — whose studies of the dolmens and menhirs of Brittany 

 and their orientations impressed him so much with the need of an astro- 

 nomical interpreter that he informed me that he would have had to invent 

 an explanation on these lines, had Dr. Sturge not brought Drayson to his 

 notice. Again, Mr. Hadrian Allcroft has lately, in the April number of the 

 Nineteenth Century, argued that the astronomical date given for Stonehenge is 

 on other considerations far too distant in time, and that the date is really some- 

 where about 500 B.C., and not 1680 b.c, as given by Sir N. Lockyer, who 

 bases his calculations on the orientation of the Hele stone, which he states 

 to be 23° 54' 30". If de Horsey's curve is consulted for this obliquity, it 

 will be seen that this cuts the date-line at about Mr. Allcroft's figure. 



This is far from exhausting the surprising results in the department of 

 archaeology accruing from a study of the Drayson polar movement. Mr. 

 Barley, whose letter to Science Progress of July 1920 provides extraordinary 

 strong evidence for Drayson based on his figures for the solar apex, has 

 lately discovered that the Great Pyramid, from its geographical position and 

 from the orientation of its passages, constitutes a gnomon by which to 

 measure the epochs of a great cycle of Precession ; and that the outcome of 

 this interpretation is an almost exact agreement with the cardinal points 

 of Drayson's cycle. These facts should act as a spur to geologists to assure 

 them that with further endeavour the same light will guide them into all truth 

 regarding the glacial periods. 



Whatever astronomers may now say, or certain geologists may imagine, 

 there are now sufficient grounds for asserting that an ice period occurred 

 geologically lately, and was still holding sway in the temperate zones con- 

 temporaneously with times of which we have fragmentary historical records, 

 as found in the seats of the ancient civilisations of Assyria and Egypt. 



We need only consider what is merely a truism that it is the tilt of the 

 earth to its orbit round the sun which alone produces the phenomena of 

 summer and winter. If the obliquity becomes greater, the contrast between 

 them is more marked ; ice margins would be extended during the winter, while 

 the summer, though hotter, would not suffice to melt the whole of the winter 

 accumulation ; glaciers would thus creep further and further down the valleys, 

 and the process continuing would give rise to permanent ice-sheets oblit- 

 erating regions once supporting abundant life. 



The present signs denote that the same factors are in operation, but in 

 the converse direction. The obliquity is decreasing ; the ice is retreating 

 rapidly at both poles, and seemingly a critical point in the process has been 

 reached which enables us to observe a general decrease of severity in the 

 winters of temperate latitudes over large areas, emphasising, as will be shown, 

 the fact that we are stiU in process of emerging from a glacial period. 



Now it is a fact, not a theory, that the obliquity has been decreasing, 

 certainly for 3,000 years, i.e. since iioo b.c. It is also a fact, in accordance 

 with the above, that the fringes of the polar ice-caps have been retreating of 

 late ^ to the extent of thirty-six miles in forty years in the South Arctic, with 

 a corresponding melting of the confines of polar ice in Alaska, and elsewhere 

 in the north. There is probably some cumulative effect of various factors 

 which makes itself felt intermittently, because for many years the Swiss 

 glaciers, with the exception of two unimportant ones, have been steadily 

 shrinking .2 This quick retreat of glaciers began about 1850, so that it seems 



^ And not only lately, as will be shown further on. 



* The recent advance of the Grindelwald glacier, I think, must be due to 

 some new affluent diverted from its original course. 



