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also raises an excessive quantity of vapour and cloud, which iscarried by upper aerial currents towards the polar regions,there again to increase the fall of snow.
We have not space in which to discuss this question at anylength (and we are aware that a good deal may he said against,as well as in favour of Dr. Croll’s theory), hut we must confessthat it may he very fairly maintained, that the Earth ’s greaterdistance from the Sun during the southern winter does reallycause the cold of the southern arctic zone, and of the southernwinter as a whole, to exceed that of the northern hemisphere.It is also strongly urged in support of this opinion, that, eveuif all possible allowance he made for the configuration of landand water, or for the action of ocean currents, and for theeffects of the existence of a great southern antarctic continent,there nevertheless appears to he no other sufficient explanationof the decidedly greater accumulation of snow and ice whichis met with by mariners who have sailed towards the southpole; so that, although it has been found possible to reach alatitude of more than 83|° north,* the nearest approach to thesouth pole as yet attained is hut little beyond 78°t of southlatitude.
Assuming this to be the result of an eccentricity of - tT V inthe Earth ’s orbit, we may easily understand that a considerablyincreased eccentricity would, in all probability, produce agreatly enhanced effect of a similar kind. And it has beencalculated • that some 210,000 years ago the eccentricityequalled about 31 times its present value, and that it hasvaried according to the subjoined table:— ■
The eccentricity of the Earth ’s orbit J is at present . '0168
20,000 years ago it was . . . . . . ‘0188
40,000 „ it had a minimum value . ; . "0109
100,000 „ it was ..... ’0473
200,000 „ .-0569
300,000 „ .-0424
400,000 it was almost exactly the same as now . . "0170
* By Captain Markham (second in command of Sir G. Nares’ expedi-tion), and Lieutenant Parr, in 1876.t By Sir J. C. Ross, in the expedition of 1839-43.
I Some additional values are given in Beckett’s “Astronomy without