r Physical Theory of Secular Changes in Climate. 268 
Arr. XXXI—Ezamination of Mr. Alfred R, Wailace’s Modifi- 
cation of the Physical Theory of Secular Changes of Climate ; 
by JAMEs Crott, LL.D., F.RS. 
[Continued from page 93.] 
4 Iy the examination of Mr. Wallace’s main argument, I shall _ 
_ __ Consider it, first, in relation to physical principles, and, secondly, 
™m relation to geological and paleontological facts. 
L Physies in relation to Mr. Wallace's Modification of the Theory. 
; 
: 
: _ The grand modification, that during the height of the glacial 
= epoch the snow and ice would not disappear when precession 
g brought the winter solstice round to perihelion, I have already 
. siven in Mr. Wallace’s own words. As the reasons which he 
assigns for this modification are very briefly stated by him, I 
___may here give them also in his words. 
2 ter describing the state of Northeastern America and the 
North Atlantic, to which I have already alluded, he says: 
foetal epoch), can we suppose that the mere change from the 
istant sun in winter and near sun in summer, to the reverse, 
could bring about any important alteration—the physical and geo- 
hical causes of glaciation remaining unchan, For, cer- 
ainly, the less powerful sun of en though lasting some- 
ms to me = 
ation has been brought about by high eccentricity combined with 
favorable geographical and : 
iti 7 may a, 41 
_ bination it is doubtful whether extreme glaciation would ever occur), 
but these ice-sheets cannot, I believe, increase or diminish to any ce. 
ot extent unless some geographical or physical change first 
eres. ee LOO | cs 
= Again,—“ It is quite evident that during the height of the lacial | ee 
i there was a combination of causes at work | : 
oS ae of Northwestern Europe and Eastern America b 
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