...
As things stand, it is manifest that if the above-mentioned white polar
spots of Mars represent snow and ice they should continue to decrease in
size with the approach of summer in those places and increase during the
winter. Now this very fact is observed in the most evident manner. In
the second half of the year 1892 the southern polar cap was in full
view; during that interval, and especially in the months of July and
August, its rapid diminution from week to week was very evident even to
those observing with common telescopes. This snow (for we may well call
it so), which in the beginning reached as far as latitude 70 degrees and
formed a cap of over 2,000 kilometers (1,200 miles) in diameter,
progressively diminished, so that two or three months later little more
of it remained than an area of perhaps 300 kilometers (180 miles) at the
most, and still less was seen in the last days of 1892. In these months
the southern hemisphere of Mars had its summer, the summer solstice
occurring upon October 13. Correspondingly the mass of snow surrounding
the northern pole should have increased; but this fact was not
observable, since that pole was situated in the hemisphere of Mars
which was opposite to that facing the earth. The melting of the northern
snow was seen in its turn in the years 1882, 1884 and 1886.
These observations of the alternate increase and decrease of the polar
snows are easily made even with telescopes of moderate power, but they
become much more interesting and instructive when we can follow
assiduously the changes in their more minute particulars, using larger
instruments.
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