Physical Theory of Secular Changes of Climate. — 87 
I have, on the contrary, maintained that the more severe the 
glacial condition of the one hemisphere, the warmer and the 
more equable would necessarily be that of the other; for the 
very same combination of causes which would tend to cool the 
one hemisphere would necessarily tend to warm the other. 
he process to a large extent consists of a transference of heat 
from one hemisphere to the other. Consequently the one 
hemisphere could not be heated without the other being cooled, 
or the one cooled without the other being heated. The hotter 
the one, the colder the other, and the colder the one, the hotter - 
the other. It therefore follows that the more severe the glacial 
conditions, the warmer and more equable must be the inter- 
glacial warm periods. But, according to Mr. Wallace, there 
could be no warm interglacial periods, either in temperate or 
polar regions, except during the commencement and toward 
the close of the Glacial epoch. 
elore, however, proceeding to examine in detail the steps 
by which he arrives at this modification of my theory, it will: 
be as well that the reader should have a clear and distinct 
knowledge of what that theory really is, and what it professes 
to explain. These I shall now briefly state in the most general 
terms, for misapprehension in regard to the main features of the 
theory lie at the root of most of the objections which have been 
urged against it. 
General Statement of the Theory.—Ist. It is not professed that 
the theory will account for the condition of climate during 
all past geological ages. It treats mainly of the cause of 
glacial epochs; and one of its essential elements is that these 
epochs consist of alternate changes, to a greater or less extent, 
of cold and warm periods; or, in other words, that glacial 
epochs must consist of alternate glacial and interglacial periods. 
The chief, though not the sole, aim of the theory is to account 
and Tertiary periods being inconsistent with my theory, the 
fact is, as we shall see by and by, that this theory affords the 
} given. oo 
2d. The theory is not that a high state of eccentricity will 
Recessarily produce a glacial epoch. No misapprehension has | 
