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RADIATION. 1 9 3

tained a certain amplitude, the mutual jostling of the atoms
produces quicker tremors, and the light-giving waves fol-
low as the necessary product of the heat-giving ones.

11. Absorption of Radiant IIeat by Vapors
and Odors.

We commenced the demonstrations brought forward in
this lecture by experiments on permanent gases, and we
have now to turn our attention to the vapors of volatile
liquids. Here, as in the case of the gases, vast differences
have been proved to exist between various kinds of mole-
cules, as regards their power of intercepting the calorific
waves. While some vapors allow the waves a compara-
tively free passage, the minutest bubble of other vapors,
introduced into the tube already employed for gases, causes
a deflection of the magnetic needle. Assuming the ab-
sorption effected by air at a pressure of one atmosphere to
be unity, the followng are the absorptions effected by a se-
ries of vapors at a pressure of one-sixtieth of an atmos-
phere:

Name of vapor. Absorption.
Bisulphide of carbon. . . .. .. .. . . . . .. . . 47
Iodide of methyl . . . ........................ 115
Benzol ................................... 136
Amylene .................................. 321
Sulphuric ether ............................ 440
Formic ether .............................. 548
Acetic ether ............................... 612

Bisulphide of carbon is the most transparent vapor in
this list; and acetic ether the most opaque; one-sixtieth
of an atmosphere of the former, however, produces forty-
seven times the effect of a whole atmosphere of air, while
one-sixtieth of an atmOSphere of the latter produces six
hundred and twelve times the efl’ect of a whole atmos-
phere of air. Reducing dry air to the pressure of the acetic

9

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