As things stand at
present, we may find a miniature image of these conditions in the
flooding that is observed in our streams at the melting of the Alpine
snows.
Travellers in the arctic regions have frequent occasion to observe how
the state of the polar ice at the beginning of the summer, and even at
the beginning of July, is always very unfavorable to their progress.
The best season for exploration is in the month of August, and September
is the month in which the trouble from ice is the least. Thus in
September our Alps are usually more practicable than at any other
season. And the reason for it is clear--the melting of the snow requires
time; a high temperature is not sufficient; it is necessary that it
should continue, and its effect will be so much the greater, as it is
the more prolonged. Thus, if we could slow down the course of our season
so that each month should last sixty days instead of thirty, in the
summer, in such a lengthened condition, the melting of the ice would
progress much further, and perhaps it would not be an exaggeration to
say that the polar cap at the end of the warm season would be entirely
destroyed. But one cannot doubt, in such a case, that the fixed portion
of such a cap would be reduced to a much smaller size, than we see it
to-day. Now, this is exactly what happens to Mars. The long year, nearly
double our own, permits the ice to accumulate during the polar night of
ten or twelve months, so as to descend in the form of a continuous layer
as far as parallel 70 degrees, or even farther.
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