Not many years ago the planet Mars, which is the next one outside
of us, was supposed to have a surface like that of our earth. Some
parts were of a dark greenish gray hue; these were supposed to be
seas and oceans. Other parts had a bright, warm tint; these were
supposed to be the continents. During the last twenty years much
has been learned as to how this planet looks, and the details of
its surface have been mapped by several observers, using the best
telescopes under the most favorable conditions of air and climate.
And yet it must be confessed that the result of this labor is not
altogether satisfactory. It seems certain that the so-called seas
are really land and not water. When it comes to comparing Mars
with the earth, we cannot be certain of more than a single point
of resemblance. This is that during the Martian winter a white
cap, as of snow, is formed over the pole, which partially melts
away during the summer. The conclusion that there are oceans whose
evaporation forms clouds which give rise to this snow seems
plausible. But the telescope shows no clouds, and nothing to make
it certain that there is an atmosphere to sustain them. There is
no certainty that the white deposit is what we call snow; perhaps
it is not formed of water at all.
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