You
may remember what I told you in October, 1876, about Venus, how
astronomers have learned that the vapor of water exists in
her atmosphere. The same method has been applied, even more
satisfactorily, to the planet of war, and it has been found that he
also has his atmosphere at times laden with moisture. This being so,
it is clear we have not to do with a planet made of materials utterly
unlike those forming our earth. To suppose so, when we find that the
air of Mars, formed like our own (for if it contained other gases the
spectroscope would tell us), contains often large quantities of the
vapor of water, would be as absurd as to believe in the green cheese
theory of the moon, or in another equally preposterous, advanced
lately by an English artist--Mr. J.T. Brett--to the effect that the
atmosphere of Venus is formed of glass.
There is another theory about Mars, certainly not so absurd as
either of those just named, but scarcely supported by evidence at
present--the idea, namely, advanced by a French astronomer, that the
ruddy color of the lands and seas of Mars is due to red trees and a
generally scarlet vegetation.
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