408 PROBABLE EFFECT OF PRECESSION. 



the Antarctic continent," the very existence of which is denied 

 by, and is indeed incompatible with the theory of M. Adhemar, 

 while it is necessary to that of Sir C. Lyell. 



It must, I think, be confessed that the existence of Victoria 

 Land, Enderby's Land, and other coasts, as well as the great 

 volcano of Mount Erebus, are unfavourable to the theory 

 advocated by M. Adhemar, so far at least as he applies it to 

 explain the present remarkable distribution of land and sea ; 

 and it must also be remembered, as tending to show that the 

 geographical distribution of land and sea has more influence 

 on climate than M. Adhemar is disposed to admit, that 

 according to his theory the southern hemisphere ought at the 

 present time to be, as a whole, far colder than the northern, 

 which, however, is not the case. 



Although, then, there can be no doubt that astronomical 

 changes would, to a certain extent, affect our climate in the 

 manner indicated by M. Adhemar, those best qualified to 

 form an opinion do not consider that the cause assigned by 

 him would by itself be sufficient to account for changes so 

 great as those which have taken place. The effect produced 

 increases, however, with the excentricity of the earth's orbit. 

 The form of this orbit is always altering ; as it approaches to 

 a circle, the effect produced by precession and change of 

 position of perihelion diminishes, while on the other hand it 

 increases as the orbit elongates. At present the excentricity 

 of our orbit is only O'OICS, that is to say, the orbit is nearly 

 circular ; but there have been periods when it was much more 

 elongated, and when consequently the extremes of tempera- 

 ture dependent on precession and the position of perihelion 

 must also have been much greater. 



Mr. Croll and Mr. Stone have calculated the excentricity 

 for the last million years, and Mr. John Carrick Moore has 

 worked out the effect upon our climate, assuming other things 

 to remain unchanged, in the four last columns of the following 



