ommon thickness, to intercept the waves f heat, was carefully
determined. The vapours of the quids were next taken, in quantities
proportional to e quantities of liquid, and the power of the vapours
intercept the waves of heat was also determined.

Commencing with the substance which exerted the least absorptive
power, and proceeding onwards to the most energetic, the following
order of absorption was observed:

Liquids Vapours

Bisulphide of carbon. Bisulphide of carbon.

Chloroform. Chloroform.

Iodide of methyl. Iodide of methyl.

Iodide of ethyl. Iodide of ethyl.

Benzol. Benzol.

Amylene. Amylene.

Sulphuric aether. Sulphuric aether.

Acetic aether. Acetic aether.

Formic aether. Formic aether.

Alcohol. Alcohol.

Water.

We here find the order of absorption in both cases be the same. We
have liberated the molecules from the bonds which trammel them more or
less in a liquid condition; but this change in their state of
aggregation does not change their relative powers of absorption.
Nothing could more clearly prove that the act of absorption depends
upon the individual molecule, which equally asserts its power in the
liquid and the gaseous state. We may safely conclude from the above
table that the position of a vapour is determined by that of its
liquid. Now at the very foot of the list of liquids stands _water_,
signalising itself above all others by its enormous power of
absorption. And from this fact, even if no direct experiment on the
vapour of water had ever been made, we should be entitled to rank that
vapour as our most powerful absorber of radiant heat. Its
attenuation, however, diminishes its action. I have proved that a
shell of air two inches in thickness surrounding our planet, and
saturated with the vapour of sulphuric aether, would intercept 35 per
cent. of the earth's radiation. And though the quantity of aqueous
vapour necessary to saturate air is much less than the amount of
sulphuric aether vapour which it can sustain, it is still extremely
probable that the estimate already made of the action of atmospheric
vapour within 10 feet of the earth's surface, is under the mark; and
that we are indebted to this wonderful substance, to an