Book-bot.com - read famous books online for free

Is Mars Habitable? by Alfred Russel Wallace
page 34 of 89 (38%)
under identical conditions. The speed of these molecular motions has
been ascertained for all the chief gases, and it is found to be so great
as in certain cases to enable them to overcome the force of gravity and
escape from a planet's surface into space. Dr. G. Johnstone Stoney has
specially investigated this subject, and he finds that the force of
gravity on the earth is sufficient to retain all the gases composing its
atmosphere, but not sufficient to retain hydrogen; and as a consequence,
although this gas is produced in small quantities by volcanoes and by
decomposing vegetation, yet no trace of it is found in our atmosphere.
The moon however, having only one-eightieth the mass of the earth,
cannot retain any gas, hence its airless and waterless condition.

_Water Vapour cannot exist on Mars._

Now, Dr. Stoney finds that in order to retain water vapour permanently a
planet must have a mass at least a quarter that of the earth. But the
mass of Mars is only one-ninth that of the earth; therefore, unless
there are some special conditions that prevent its loss, this gas cannot
be present in the atmosphere. Mr. Lowell does not refer to this argument
against his view, neither does he claim the evidence of spectroscopy in
his favour. This was alleged more than thirty years ago to show the
existence of water-vapour in the atmosphere of Mars, but of late years
it has been doubted, and Mr. Lowell's complete silence on the subject,
while laying stress on such a very weak and inconclusive argument as
that from the tinge of colour that is observed a little distance from
the edge of the diminishing snow-caps, shows that he himself does not
think the fact to be thus proved. If he did he would hardly adduce such
an argument for its presence as the following: "The melting of the caps
on the one hand and their re-forming on the other affirm the presence of
water-vapour in the Martian atmosphere, of whatever else that air
DigitalOcean Referral Badge