Physical Theory of Secular Changes of Climate. 79 
tion increases, because the quantity of snow and ice melted 
. becomes thus annually less and less. In addition, the loss of 
the rays cut off by the fogs lowers the temperature of the air 
; and leads to more snow being formed, while again the snow 
_ thus formed chills the air still more and increases the fogs. 
___ Again, during the winters of a glacial epoch, the earth would 
be radiating its heat into space. Had this loss of heat simply ~ 
lowered the temperature, the lowering of the temperature 
would have tended to diminish the rate of loss; but the result 
18 the formation of snow rather than the lowering of the tempe- 
rature, 
tropics more to the warm hemisphere than to the cold. Sup- 
posing the northern hemisphere to be the cold one, then, as the 
of that hemisphere, more particularly the Gulf-stream, begin to. 
decrease in volume, while those on the southern or warm hem- 
tease. On the other hand, as the ocean-currents diminish, — 
the snow and ice still more accumulate. Thus the two effects, 
_ 4so far as the accumulation of snow and ice is concerned, mu- 
i tually strengthen each other.’ 
a 1s 
187-140 (“Island Life’) he gives a very clear statement of the 
 €lfect of these mutual reactions in the production of glaciation, 
and says that were it not for them it is probable the astronom- 
teal and other causes would not in our latitudes have been suffi-_ 
_ TMust have underestimated their importance as regards the 5 
_ moval of the glaciation. He, however, recognizes the 4 i 
_ that these mutual reactions produce an a ieee effect on t es 
i on, a 
_ Me by means o 
4nd all this again reacts on the northern hemisphere, increasi ee 
_ Yet further the supply of moisture by the more powerful ae 
7 
