142 Corresjwndence — Hev. 0. Fisher. 



coE-i^ESiFoisrzDiKiisraE. 



DE. CEOLL'S THEOEY OF THE ICE AGE. 



Sir, — As Mr. Cnlverwell's articles in the Magazine and the 

 review of Dr. James Geikie's new edition of "The Great Ice Age " 

 have recalled attention to Dr. Groll's celebrated theory, it may 

 be interesting to your readers to hear the opinion of the great 

 astronomer Adams upon the question. In turning over some old 

 letters only yesterday I came upon one dated 28th February, 1866, 

 which I received from him on the subject, in which, after some 

 remarks upon Herschel's art. 184, of which he says he is " not 

 inclined to think there is much in it," he wrote : " I do not myself 

 believe in the change of eccentricity of the earth's orbit being a 

 cause of climatal changes on the earth. The effect, if any, would 

 depend only on the square of the eccentricity; and this always 

 remains so very small, that I believe the effect on the earth's mean 

 temperature would be almost insensible. Depend upon it, geologists 

 who look in this direction for the cause of Glacial epochs are 

 entirely on the wrong tack. It seems to me much more likely that 

 the actual act of emission of heat from the sun is variable, than that 

 the change of eccentricity of the orbit should have any sensible 

 effect." 



If this be the case, CroU's theory is reduced to Adhemar's, who, 

 in his Revolutions de la Mer, 2nd edition, 1860, published his view 

 that Glacial epochs were caused by the mere alternate presentation 

 of the north and south poles of the earth to the sun, owing to the 

 precession of the axis ; no reference being made by him to changes 

 of eccentricity. It is remarkable that CroU did not know of 

 Adhemar's work when he first published his theory. I had heard 

 two friends talking about it at a meeting of the Geological Society, 

 which led me to buy the book, and finding no allusion to Adhemar 

 in Groll's papers, I drew his attention to it. 



In what I have now written I do not wish it to be thought that I 

 am expressing any opinion of my own upon the subject, but I think 

 these matters of ancient history may prove of interest to your 

 readers. 0. Fisher. 



Haelston, Cambridge, 7th February, 1895. 



PEOFESSOE HULL AND THE CAMBEIAN AGE OF THE 

 CHAENWOOD CLASTICS. 



Sir, — T do not think that Professor Hull's letter in last month's 

 Geological Magazine will do much to convince students of the 

 older rocks that the Charnwood elastics are of Cambrian age. He 

 relies chiefly upon the authority of Sedgwick and Jukes. The 

 views of these eminent men on matters coming within their know- 

 ledge would undoubtedly carry great weight with the younger 

 generation ; but it would be the height of rashness to suggest that 

 they would have continued to adhere to their opinion had they 



