10 E. P. Cukenoell — Theory of the Ice Age. 



No doubt, if there were a fall of anything like 45° F. in the mid- 

 winter temperature of Great Britain, there would be a great increase 

 in the fall of snow ; as it is, I have shown that there would be none 

 worth speaking of — nothing that would not be melted by a couple 

 of soft winter days, 



(E) We now come to a point on which Croll insists at great 

 length, namely, that summer heat is less effectual in melting winter 

 snow than winter cold is in producing it. I might pass this by as 

 I have passed (D) by, on the ground that there would be no snow 

 to melt, but the question is so important from a climatic point of 

 view, and so much of the evidence seems strongly opposed to 

 Croll's view, that it is worth examining the matter at some length, 

 especially as Croll's view on this point is almost as necessary to 

 the astronomical theory as the views already dealt with in (C). 



According to Croll (pp. 58-60), there are three separate ways 

 whereby accumulated masses of snow and ice tend to lower the 

 summer temperature, viz. : — 



First, by direct radiation. No matter what the intensity of the 

 sun's rays may be, the temperature of snow and ice can never rise 

 above 32°. Hence their presence tends by direct radiation to lower 

 the temperature of all surrounding bodies to 32° 



[Here follow illustrations as to the summer cold in Greenland 

 and the high Alpine regions ; also the statement that if India were 

 covered with an ice-sheet, its summers would be colder than those 

 of England.] 



Second. Another cause of the cooling effect is that the rays which 

 fall on snow and ice are, to a great extent, reflected back into space. 

 Even those which are not reflected but absorbed, do not raise the 

 temperature, for they disappear in the mechanical work of melting 

 the ice 



Third. Snow and ice lower the temperature by chilling the air and 

 condensing the vapour into thick fogs . . . which would effectually 

 prevent the sun's rays from reaching the earth, and the snow in 

 consequence would remain unmelted during the entire summer. 



Here follow several pages of illustrations of cold climates, those 

 of Greenland and Hudson's Bay in the Northern Hemisphere, and 

 South Georgia, Sandwich Land, South Shetland, Straits of Magellan, 

 and other places in the drift-currents coming from the Antarctic 

 regions. Thus Croll's examples are all open to the fatal objection 

 that they are selected from regions where the sun-heat has to 

 contend, not only with the ice or snow actually on the ground, 

 but with cold di-ift-currents which bear great masses of ice and 

 snow from the Polar regions. 



A question of this kind cannot be settled by such an eclectic 

 method. It is not by taking all the cases which at first sight may 

 appear favourable to the view we desire to uphold that we shall 

 arrive at the truth. No doubt there are regions exposed to cold 

 currents of Arctic or Antarctic origin which are very much colder 

 in summer than we should expect from the sun-heat corresponding 

 to their latitudes, just as there are regions where, owing to warm 



