92 DISCUSSIONS IN CLIMATOLOGY. 



the climate was throughout uniformly warm or sub- 

 tropical, this would not prove that the theory was 

 wrong, unless it could at the same time be shown that 

 the necessary conditions demanded by the theory did 

 then exist. But instead of this supposed condition of 

 climate during Secondary or Tertiary periods being 

 inconsistent with my theory, the fact is, as we shall 

 see by and by, that this theory affords the only rational 

 explanation of such a state of things which has yet 

 been given. 



2nd. The theory is not that a high state of 

 eccentricity will necessarily produce a glacial epoch. 

 No misapprehension has been more widespread or 

 more difficult to remove than this. From the very 

 commencement I have maintained that no amount of 

 eccentricity, however great, could produce a glacial 

 condition of things ; that the Glacial Epoch was the 

 result, not of a high state of eccentricity, but of a 

 combination of Physical Agencies, brought into 

 operation by means of this high state*. As an example 

 of this misapprehension, how frequently has 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 removed 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 theory, eccentricity alone ought to 



* For this reason I prefer to term the theorj 7 the Physical Theory 

 rather than the Eccentricity Theory, as it has been called by some 

 writers. 



