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two white caps which are seen at the planet’s
poles. W. Herschel attributed these caps to
ice and snow, and the dates of his observa-
tions indicated a melting of these ice-caps
in the Martian summer.
˜
SchrAter attributed the other markings
on Mars to drifting clouds. But Beer and
˜
MAdler, in 1830-39, identified the same dark
spots as being always in the same place,
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