OBJECTIONS TO M. ADH^MAR'S THEORY. 407 



the southern at that of greatest cold ; and as 630 years have 

 since elapsed we ought to find some evidence of subsequent 

 change. 



As regards the southern hemisphere, M. Adhemar points 

 out that the great southern glacier has considerably retreated 

 since the time of Captain Cook, but it is in the northern 

 hemisphere that he finds the greatest evidence of alteration. 

 He dwells much on the increase, during the last few centuries, 

 of the Swiss glaciers, and of the ice in Greenland, and points 

 out that the cultivation of the vine does not now extend so 

 far northwards as was once the case. M. Adhemar, then, 

 considers that the last epoch of greatest cold must have been 

 11,120 years -ago, since which time the climate of our hemi- 

 sphere gradually improved up to the year 1248, when it was 

 most genial, and after which it has, in his opinion, gradually 

 commenced again to deteriorate. Sir Charles Lyell,* however, 

 does not think that this change, " which could hardly produce 

 more than a difference of half a degree Fahrenheit between 

 the cold of the present winter and that of 1248, would be 

 appreciable." He adds that the whole effect which can be 

 produced by secular astronomical changes must "always be 

 very subordinate to the influence of geographical conditions."-)- 



Sir John Herschell j also is " very far from supposing it 

 competent" to account for so great an alteration. Moreover, 

 it is remarkable as showing how far we are from possessing 

 the data necessary for any satisfactory conclusions, that while, 

 as we have seen, M. Adhemar regards the enormous cupola 

 of ice at the South Pole as the reason for the almost entire 

 absence of land at that Pole, Sir C. Lyell, on the other hand, 

 states as a fact, that the chief cause of the intense cold of 

 high southern latitudes is "the vast height and extent of 



* Principles of Geology, 1867, J Outlines of Astronomy, 1858, 

 vol. i. p. 278. p. 235. 



t Ibid. vol. i. p. 243. 



