In the first
experiment, the sudden doubling of the space causes the ether also to
expand, inasmuch as the sides of the vessel prevent the instantaneous
passage of the external ether. In the second, both vessels are full, one
of ether, and the other of air mixed with ether; so that there is no
actual expansion of the space, and consequently no derangement of the
quantity of motion in that space.

LAW OF SPECIFIC HEAT.

From this view it is evident that the specific heat of elastic fluids
can only be considered as approximately determined. If equal spaces
possess equal momenta, and the ethereal or _tomic_ matter be inversely
as the weight of the atomic matter in the same space, it follows that
the product of the specific gravities and specific heats of the simple
gases should be constant; or that the specific heats should be inversely
as the specific gravities,--taking pound for pound in determining those
specific heats. If we test the matter by the data now afforded, it is
best to obey the injunction, "_In medio tutissimus ibis_." In the
following table, the first column are the values obtained by Regnault;
in the second, the former values; and in the third, the mean of the two.

Gases. Reg. specific heats. Former specific heats. Mean.
Atmospheric air, .237 .267 .252
Oxygen, .218 .236 .227
Nitrogen, .244 .275 .260
Hydrogen, 3.405 3.294 3.350

The specific gravities of these gases, according to the best tables in
our possession, are:

Specific gravities. Mean. Products.
Atmospheric air, 1.0000 x .252 = .252
Oxygen, 1.1111 x .227 = .252
Nitrogen, 0.9722 x .260 = .252
Hydrogen, 0.0745 x 3.350 = .249

As might be expected, there is a greater discrepancy in the case of
hydrogen.

If we test the principle by the vapor of water, we must consider that it
is composed of two volumes of hydrogen and one volume of oxygen, and
that one volume disappears; or that one-third of the whole atomic
motion is consumed by the interference of the vibrations of the ether,
necessary to unite the atoms, and form an atom of water. We must
therefore form this product from its specific gravity a