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.
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