Searles V. Wood, Jun, — The Climate Controversy, 389 



from the length of the minor axis, each hemisphere receives an 

 equal quantity of heat during any one year ; the greater contiguity 

 of the sun in perihelion being compensated by the more rapid 

 motion of the earth in its orbit at that time, and vice versa. 



Mr. Murphy has, since this theory was first advocated by Mr. 

 Croll, endeavoured to show that the occurrence of the aphelion 

 points during the winter season would have the opposite effects 

 to those attributed to it by Mr. Croll ; and that it is to the occur- 

 rence of the aphelion in the summers of either hemisphere during 

 periods of great excentricity that the glaciation of such hemisphere 

 is to be attributed. Mr. Murphy has lately brought forward another 

 paper, in which he seeks to establish this point ; but as it is not yet 

 published, I shall avoid the chance of misrepresenting his views in the 

 mean time by confining myself to merely calling attention to them. 



Mr. Croll admits that the position of the aphelion point would not, 

 of itself, produce any sensible effect on climate, even with the maxi- 

 mum of possible excentricity, which he gives as making a difference 

 between the sun's distance in aphelion and perihelion of 14,212,700 

 miles ; but he contends that when the cumulative tendency of ice 

 and snow and the operation of the great ocean currents are taken 

 into consideration, the true and principal cause of the changes which 

 have occurred in climate has been the combined operation of the 

 position of the aphelion and the varying excentricity of the orbit. 



As regards this alleged tendency of ice and snow to accumulate 

 at the pole of that hemisphere near the mid- winter of which the 

 aphelion point occurred during periods of a high degree of excen- 

 tricity, Mr. Croll argues that the increased heat of the sun in 

 summer, due to the corresponding occurrence of the perihelion at 

 that season, would be neutralized by the absorption and reflection 

 by ice and snow of a large part of the heat so received, and by the 

 creation of fogs which would intercept the rays. With respect to 

 absorption, Mr. Croll argues that 142° Fahr. are absorbed in melting 

 one pound of ice, and completely lost, so far as raising its tempera- 

 ture is concerned, by reason that they are consumed in tearing 

 asunder the molecules against the forces of cohesion which bind 

 them together into the solid form. Is not an equal quantity of heat, 

 however, liberated to raise the temperature of the surrounding air 

 when congelation returns ? With respect to the rays reflected, Mr. 

 Croll does not tell us what becomes of them. The}^ must, it is to 

 be assumed, be absorbed by the atmosphere ; but in what way the 

 icy region is prevented from indirectly receiving the benefit of them, 

 when so absorbed, he does not attempt to show. 



With respect to the fogs. Sir Charles Lyell urged that there 

 were no sufficient data to assume, as Mr. Croll did, that the inten- 

 sity of the sun in a clear sky, which would first melt the ice, would 

 afterwards be sufficiently overcome by fog to check and almost 

 prevent further melting, in spite of the continued supply of exces- 

 sive heat during summer; but Mr. Croll has since collected instances 

 of the prevalence of snow storms and fogs in the Arctic and Ant- 

 arctic regions, and endeavoured to show that it is to these causes 



