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270 J. Oroll—Examination of Wallace's Modification of the 
one and remove it from the other. Consequently the same — 
total combination of causes which will produce an accumula — 
tion of ice on either hemisphere when the winter solstice isin — 
aphelion will produce a melting of that ice when the solstice — 
moves round the perihelion. 
_ Another impossible condition assumed. — ‘‘ What we have to 
consider,” says Mr. Wallace, “is whether the alteration from 
a long cold winter and short hot summer, to a short mild win- 
ter and long cool summer, would greatly affect the amount of | 
ice if the ocean-currents remained the same.” Here, again, we 
have an impossible state of things assumed. It is assumed 
that, notwithstanding the change from an aphelion to a_perihe- 
lion winter, the ocean-currents would still remain the same. 
And it is asked, would the. astronomical causes in this case 
remove the glaciation. I would be disposd to say that they 
would not. 
diminish to any important extent unless some geographical or : 
physical change first occurs.” The first thing required to altech 
perature of the polar and equatorial areas” for any increase | 
