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RADIATION. 20 7

which rendered a body competent to intercept the waves
of ether, rendering it competent in the same degree to gen-
erate them. Perfumes were next subjected to examination,
and notwithstanding their extraordinary tenuity, they were
found vastly superior, in point of absorptive power, to the
body of the air in which they were diffused. We were led
thus slowly up to the examination of the most widely
diffused and most important of all vapors—the aqueous
vapor of our atmosphere—and we found in it a potent
absorber of the purely calorific rays. The power of this
substance to influence climate, and its general influence
on the temperature of the earth, were then briefly dwelt
upon. A cobweb Spread above a blossom is sufficient-to
protect it from nightly chill; and thus the aqueous vapor
of our air, attenuated as it is, checks the drain of terrestrial
heat, and saves the surface of our planet from the refriger-
ation which would assuredly accrue, were no such sub-
stance interposed between it and the voids of . space. We
considered the influence of vibrating periodand molecular
form on absorption and radiation, and finally deduced, from
its action upon radiant heat, the exact amount of carbonic
acid expired by the human lungs.

Thus in brief outline were placed before you some of
the results of recent inquiries in the domain of Radiation,
and my aim throughout has been to raise in your minds
distinct physical images of the various processes involved
in our researches. It is thought by some that natural
science has a deadening influence on the imagination, and
a doubt might fairly be raised as to the value of any study
which would necessarily have this effect. But the experi-
ence of the last hour must, I think, have convinced you
that the study of natural science goes hand in hand with
the culture of the imagination. ThroughOut the greater
part of this discourse we have been sustained by this
faculty. We have been picturing atoms, and molecules,

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