266 J. Croll—Examination of Wallace's Modification of the — 
* 
these causes we must reckon a diminution of the force of the Gulf- 
Stream, or its being diverted from the northwestern coasts 0 
Europe; and what we have to consider is, whether the alteration 
from a long cold winter and short hot summer, to a short mild 
winter and long cool summer would greatly affect the amount of 
ice if the ocean-currents remained the same. The force of these 
currents are, it is true, by our hypothesis modified by the increase 
or diminution of the ice in the two hemispheres alternately, and 
they then react upon climate; but they cannot be thus changed 
till after the ice-accumulation has been considerably affected by 
other causes.” —p. 148. 
There are some further reasons assigned, which will be con- 
d 
recognized by Mr. Wallace in the above quotations, as well asin 
astronomical agénts is to set and keep 'the physical agencies in i 
pee 8 
* ‘Climate and Time,’ chap. iv; American Journal of Science, Oct» 1883; 
Phil. Mag. Oct., 1883. eee ig — eee 
