"
In regard to the lunar atmosphere, it may be said, in a word, that even
those who advocate the existence of vegetation and of clouds of dust or
ice crystals on the moon do not predicate any greater amount, or greater
density, of atmosphere than do those who consider the moon to be wholly
dead and inert. Professor Pickering himself showed, from his
observations, that the horizontal refraction of the lunar atmosphere,
instead of being less than 2 sec., as formerly stated, was less than
0.4 sec. Yet he found visual evidence that on the sunlit side of the
moon this rare atmosphere was filled to a height of four miles with some
absorbing medium which was absent on the dark side, and which was
apparently an emanation from the lunar crust, occurring after sunrise.
And Messrs. Loewy and Puiseux, of the Paris Observatory, say, after
showing reasons for thinking that the great volcanic eruptions belong to
a recent period in the history of the moon, that "the diffusion of
cinders to great distances infers a gaseous envelope of a certain
density.... The resistance of the atmosphere must have been sufficient
to retard the fall of this dust [the reference is to the white trails,
like those from Tycho], during its transport over a distance of more
than 1,000 kilometers [620 miles]."[20]
[Footnote 20: Comptes Rendus, June 23, July 3, 1899.]
We come now to a brief consideration of certain peculiarities in the
motions of the moon, and in the phenomena of day and night on its
surface.
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