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it is farthest from the solar centre. But there is another 
element which combines with what is called, the eccentucity 
of the orbit. Winter and summer are not caused by our being 
farther from the sun in the one than in the other ; but by that 
motion of the earth which shortens, or, as we may say of 
polar regions, blots out the winter's day, and lengthens the 
day of summer. In polar latitudes, the sun shines on the 
surface of the globe during the whole twenty-four hours of the 
summer's day, and is not seen at all in winter. It is on the 
effect of this, which arises from the turning away of the polar 
surface from the sun, that Mr. Croll chiefly depends for the 
proof of his theory. The radiations of heat must be excessive 
from the polar surface, when it is dark and at its greatest 
distance from the sun— when, too, because of its slow motion, 
its winter is at the longest. This loss of heat (as Mr. Croll 
argues) will not be compensated by the sun's nearness m 
summer ; for the shortness of that season, from the swiftness 
of the earth's motion, in proportion to the length of the 
winter, will prevent all that would otherwise make the summer 
warm/ Put, then, these two things together— let the northern 
winter occur when the earth is farthest from the sun, and, 
consequently, the summer when it is nearest the winter will 
then be excessively severe, and the short summer, not even 
usually warm. This, Mr. Croll thinks, will cause a glacial 
period over great part of the northern hemisphere. Now, let 
the case be reversed — the short winter occurs when the earth 
is nearest the sun in space, and the long summer when it is 
farthest away. The consequence of this will be greatly 
lessened radiation in winter, and the equalizing, to a great 
extent, of that season and the summer in northern regions. 
These opposite combinations of the earth's position, m relation 
to the source of heat, account, according to this view, for 
regularly recurring periods of extreme winter cold, combined 
with proportionally small summer heat, such as will fail to melt 
the winter snow, and periods when the summer and winter 
are lost in constant spring. Could we confine our reasoning to 
astronomical theory, and leave out other considerations of a 
geooTaphical nature, Mr. Croll would, we think, make out a 
pretty strong case by his argument for a “ glacial 'period , 
during the time when the winter occurs at our greatest 
distance from the sun. But this is not the problem which is 
of greatest importance, as we are constrained to view the case, 
that has respect to a hot climate sufficient for palms and 
turtles in our northern latitude. Mr. Croll does not attempt 
to make out this. He has difficulty in making out a period 
fit even for the ferns of the coal-measures, when winter occurs 
