ecame quickly
heated, and so warmed the air. Hence, if Mr. Croll be correct, a period
of high eccentricity would certainly produce a climate in the Northern
Hemisphere such as characterized many of the mild interglacial epochs as
long as the earth passed its perihelion point in Winter.

We have so far only considered the Northern Hemisphere. As every one
knows, while we have Winter, the Southern Hemisphere has Summer. So
at the very time we would enjoy the mild short Winters, the Southern
Hemisphere would be doomed to experience Winters of greatly increased
length and severity. As a consequence, immense fields of snow would be
formed, which, by pressure, would be changed to ice, and creep away as
a desolating glacier. It is quite true that the short Summer sun would
shine with increased warmth, but owing to many causes it would not avail
to free the land from snow and ice.

As Mr. Geikie points out, "An increased amount of evaporation would
certainly take place, but the moisture-laden air would be chilled by
coming into contact with the vast sheets of snow, and hence the vapor
would condense into thick fogs and cloud the sky. In this way the sun's
rays would be, to a large extent, cut off, and unable to reach the
earth, and consequently the Winter's snow would not be all melted away."
Hence it follows that at the very time the Northern Hemisphere would
enjoy a mild interglacial climate, universal Spring, so to speak, the
Southern Hemisphere would be encased in the ice and snow of an eternal
Winter.

But the earth has not always reached its perihelion point during the
Winter season of the Northern Hemisphere. Owing to causes that we need
not here consider, the earth reaches its perihelion point about twenty
minutes earlier each year, so if it now passes its perihelion in Winter
of the Northern Hemisphere, in about ten thousand years from now it will
reach it in Summer, and in twenty-one thousand, years it will again be
at perihelion in Winter. But see what important consequences follow from
this. If during a period of high eccentricity we are in the enjoyment of
short mild Winters and long pleasant Summers, in ten thousand years this
would certainly be changed. Our Summer season would become short and
heated; our Winters long and intensely cold. Year by year it would be
later in the season before the sun could free the land from snow, and
at length in deep ravines and on hill-tops the snow would linger through
the bri