88 J. Oroll—Examination of Wallace's Modification of the 
been more widespread or more difficult to remove than this. 
F very commencement I have maintained that no 
amount of eccentricity, however great, could produce a glacial 
Soares of things; that the Glacial epoch was the result, not 
ee tate of eccentricity, but of a combination of physica 
the present condition of the planet Mars been adduced as 
evidence against the theory. The eccentricity of Mars’ orbit is 
at present greater than that of the Earth’s even when at its 
superior limit; and its southern winter solstice is not far re- 
moved from aphelion. It is therefore maintained that, if my 
theory of the cause of the Glacial epoch be correct, the southern 
hemisphere of Mars ought to be under a glacial condition, and 
the northern enjoying a perpetual spring—and this, as is well 
known, is not the case. Here it is assumed that, according to 
the e theory, eccentricity alone ought to produce a glacial epoch, 
‘irrespective of the necessary physical a aie We know 
with pariainty that those physical conditions which, according 
to the theory, were the direct cause of the ‘Glacial epoch on our 
globe, cannot possibly exist on the planet Mars.t Just take 
one example ; either the properties of water on the planet Mars 
or the conditions of its atmosphere must be totally different 
from those of our earth; for were our earth removed to Mars’s 
distance from the sun, our seas would soon become solid ice 
and we could have neither snow nor rain , ocean-currents, nor 
any of the necessary conditions for secular change of climate. 
This is doubtless not the present state of Mars; but the reason 
of this can only be that the physical and meteorological con- 
ditions of the planet must be wholly different from those of 
the ear 
of aqueous vapor, or in the condition of our sons 
ket effectually prevent the possibility of a glacial epoch 
rring on our earth, notwithstanding a high state of eccen- 
siete, we need not wonder that the planet Mars is not in a 
state of glaciation. But the eccentricity of Mars, though high, 
is still far from its superior limit, and the planet may yet, for 
anything — we know to the contrary, pass through a 
Glacial e 
3d. pete: prevailing misapprehension is the ee 
that the theory does not recognize the necessity for geograph- 
ical conditions. In reading “ Island Life” one might be apt to 
suppose that one of the chief points of difference between Mr. 
Wallace and myself is that hewegards geographical dawibation 
* For this reason I prefer to term the theory the soe labia rather than 
the Eccentricity Theory, as it ~ been called by som 
+ See ‘Climate and Time,’ p. 7 
