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The next point to be regarded was a matter of far greater importance.
From indications afforded by the barometer, we find that, in ascensions
from the surface of the earth we have, at the height of 1,000 feet, left
below us about one-thirtieth of the entire mass of atmospheric air, that
at 10,600 we have ascended through nearly one-third; and that at 18,000,
which is not far from the elevation of Cotopaxi, we have surmounted
one-half the material, or, at all events, one-half the ponderable,
body of air incumbent upon our globe. It is also calculated that at an
altitude not exceeding the hundredth part of the earth's diameter--that
is, not exceeding eighty miles--the rarefaction would be so excessive
that animal life could in no manner be sustained, and, moreover, that
the most delicate means we possess of ascertaining the presence of the
atmosphere would be inadequate to assure us of its existence. But I
did not fail to perceive that these latter calculations are founded
altogether on our experimental knowledge of the properties of air, and
the mechanical laws regulating its dilation and compression, in what may
be called, comparatively speaking, the immediate vicinity of the earth
itself; and, at the same time, it is taken for granted that animal
life is and must be essentially incapable of modification at any given
unattainable distance from the surface. Now, all such reasoning and from
such data must, of course, be simply analogical. The greatest height
ever reached by man was that of 25,000 feet, attained in the aeronautic
expedition of Messieurs Gay-Lussac and Biot. This is a moderate
altitude, even when compared with the eighty miles in question; and I
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