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But it must be borne in mind that these large numbers
depend in part upon the extreme feebleness of the air; the
power of aqueous vapor seems vast, because that of the air
with which it is compared is infinitesimal. Absolutely con-
sidered, however, this substance, notwithstanding its small
specific gravity, exercises a very potent action. Probably
from 10 to 15 per cent. of the heat radiated. from the earth
is absorbed within 10 feet of the earth’s surface. This
must evidently be of the utmost consequence to the life of
the world. . Imagine the superficial molecules of the earth
trembling with the motion of heat, and imparting it to the
surrounding ether; this motion would be carried rapidly
away, and lost forever to our planet, if the waves of ether
had nothing but the air to contend with in their outward
course. But the aqueous vapor takes up the motion of the
ethereal waves, and becomes thereby heated, thus wrapping.
the earth like a warm garment, and protecting its surface
from the deadly chill which it would otherwise sustain.
Various philosophers have speculated on the influence of
an atmospheric envelope. De Saussure, Fourier, M. Pouil-
let and Mr..Hopkins have, one and all, enriched scientific
literature with contributions on this subject, but the con-
siderations which these eminent men have applied to atmos-
pheric air, have, if my experiments be correct, to be trans-
ferred to the aqueous vapor.

The observations of meteorologists furnish important,
though hitherto unconscious evidence of the influence of
this agent. Wherever the air is dry we are liable to daily
extremes of temperature. By day, in such places, the sun’s
heat reaches the earth unimpeded, and renders the maxi-
mum high; by night, on the other hand, the earth’s heat
escapes unhindered into space, and renders the minimum
low. Hence the difference between the maximum and min-
imum is greatest where the air is driest. In the plains
of India, on the heights of the Himalaya, in central Asia, in

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