REPLY TO CRITICS. 47 



mulation could begin. Prima facie, therefore, high 

 eccentricity will not account for glacial periods." * In 

 the language of Prof. Newcomb, it is as follows : — 

 " During this perihelion summer, the amount of heat 

 received from the sun by every part of the northern 

 hemisphere would suffice to melt from four to six 

 inches of ice per day over its entire surface ; that is, 

 it would suffice to melt the whole probable accumula- 

 tion in three or four days. The reader can easily 

 make a computation of the incredible reflecting power 

 of the snow and of the unexampled transparency of 

 the air required to keep the snow unmelted for three 

 or four months." 



It is assumed in this objection that because the heat 

 received from the sun by an area is more than suffi- 

 cient to melt all the snow that falls on it, no permanent 

 accumulation of snow and ice can take place. It is 

 assumed that the quantity of snow and ice melted 

 must be proportional to the heat received. Suppose 

 that on a certain area a given amount of snow falls 

 annually. The amount of heat received from the sun 

 per annum is computed ; and after the usual deduction 

 for that cut off by the atmosphere has been made, if 

 it. be found that the quantity remaining is far more 

 than sufficient to melt the snow, it is then assumed 

 that the snow must be melted, and that no accumula- 

 tion of snow and ice year by year in this area is 

 possible. To one approaching this perplexing subject 

 for the first time, such an assumption looks very 

 plausible ; but a little reflection will show that it is 

 most superficial. The assumption is at the very outset 

 totally opposed to known facts. Take the lofty peaks 

 of the Himalayas and Andes as an example. Few, I 

 suppose, would admit that at these great elevations as 



* " Geological Magazine," January, 1880/p. 12. 



