_The Magnitude of the Atmosphere._
The total quantity of air of which our atmosphere is composed is
another of the arbitrary magnitudes of our terrestrial system; and
we may apply to this subject considerations similar to those of the
last section. We can see no reason why the atmosphere might not
have been larger in comparison to the globe which it surrounds;
those of Mars and Jupiter appear to be so. But if the quantity of
air were increased, the structure of organized beings would in many
ways cease to be adapted to their place. The atmospheric pressure,
for instance, would be increased, which, as we have already
noticed, would require an alteration in the structure of vegetables.
Another way in which an increase of the mass of the atmosphere
would produce inconvenience would be in the force of winds. If the
current of air in a strong gale were doubled or tripled, as might
be the case if the atmosphere were augmented, the destructive
effects would be more than doubled or tripled. With such a change,
nothing could stand against a storm. In general, houses and trees
resist the violence of the wind; and except in extreme cases, as
for instance in occasional hurricanes in the West Indies, a few
large trees in a forest are unusual trophies of the power of the
tempest. The breezes which we commonly have are harmless messengers
to bring about the salutary changes of the atmosphere, even the
motion which they communicate to vegetables tends to promote their
growth, and is so advantageous, that it has been proposed to
imitate it by artificial breezes in the hothouse. But with a stream
of wind blowing against them, like three, or five, or ten, gales
compressed into the space of one, none of the existing trees could
stand; and except they could either bend like rushes in a stream,
or extend their roots far wider than their branches, they must be
torn up in whole groves. We have thus a manifest adaptation of the
present usual strength of the materials and of the workmanship of
the world to the stress of wind and weather which they have to
sustain.