118 THE GLACIER EPOCH OF AUSTRALASIA. 
63 per cent. in summer and only 37 per cent. im winter—do 
not help us to gauge the actual heat received in the winter of 
the glaciated hemisphere, as he has not formed any estimate 
of the known indirect sources of heat which would be received 
by air and ocean currents from the genial hemisphere, but 
the value of which we may have, now, some meas of con- 
ceiving from the study of two regions m nearly the same 
northern latitudes, viz., Labrador and Ireland. 
The former beimg in a glaciated condition owing to the 
influence of the Arctic cold current of water; the latter in a 
genial condition owing chiefly to the influence of the warm 
Gulf Stream, whose heat has been mainly derived from south 
equatorial regions.* While Ecannct but admire the masterly 
and lucid manner in which Sir Robert Ball explains the astro- 
nomical theory, and supports the main conclusions of Dr. 
Croll, I am still disposed to think that in limiting his 
observation, too closely, to the dvect sources of heat and theit 
exact measurement, as regards the glaciated hemisphere, he 
has not sufficiently reflected upon the powerful modifymg 
influences of the indirect supplies received from the genial hemi- 
sphere, nor of the possible changes which might occur in geo- 
eraphical conditions, which might greatly multiply or diminish 
the nominal amount of heat transmitted by the opening of new 
equatorial channels of communication, or by barring former 
channels. Nay more, according to Herschel’s astronomical 
theory, as modified by Sir Robt. Ball, and its expected influence 
npon climate during a period of great eccentricity with the 
winter in aphelion, in the Southern Hemisphere, as at present, 
—it is stated: “In the northern we should have a short but 
very mild winter, with a very long but very cool summer, Z.e., 
an approach to perpetual spring,’ but from Mr. Robt. H. 
Scott’s recent work on Meteorology, we find from existing 
conditions + “ the opposite ts the case, owing to the unequal 
distribution of land and water,’ t and also owing to the fact 
“that in the summer in the Northern Hemisphére ¢he sun’s rays 
fall on the greatest possible land area. Were we havéa complete 
reversal of the supposed influence of the astronomical cause, 
proving that the geographical conditions, which Sir Robt. 
Ball almost ignores as a wecessary concurring cause in the 
initiation of a glacial epoch, has a preponderating effect in thé 
determination of existing climates; and although Sir Robt. 
Ball only admits, to’a certain extent, the modifying influence 
of geographical conditions § and feels the result “a little 
* Dr. Croll estimated that the quantity of heat transferred by the Gulf stream 
from equatorial regions was not less than one-fifth of the entire heat possessed> yy 
the North Atlantic. 
+ Elementary Meteorology, R..G Scott, p. 231 
t Ibid, p. 230. 
§ The Cause of an Ice Age, p. 134. 
