imagining each particle to be a little nucleus to an
atmosphere of heat, or electricity, or any other agent, we are still not
likely to be in error in considering the elasticity as dependent on
_mutuality_ of action. Now this mutual relation fails altogether on the
side of the gaseous particles next to the platina, and we might be led to
expect _a priori_ a deficiency of elastic force there to at least one half;
for if, as Dalton has shown, the elastic force of the particles of one gas
cannot act against the elastic force of the particles of another, the two
being as vacua to each other, so is it far less likely that the particles
of the platina can exert any influence on those of the gas against it, such
as would be exerted by gaseous particles of its own kind.

627. But the diminution of power to one-half on the side of the gaseous
body towards the metal is only a slight result of what seems to me to flow
as a necessary consequence of the known constitution of gases. An
atmosphere of one gas or vapour, however dense or compressed, is in effect
as a vacuum to another: thus, if a little water were put into a vessel
containing a dry gas, as air, of the pressure of one hundred atmospheres,
as much vapour of the water would _rise_ as if it were in a perfect vacuum.
Here the particles of watery vapour appear to have no difficulty in
approaching within any distance of the particles of air, being influenced
solely by relation to particles of their own kind; and if it be so with
respect to a body having the same elastic powers as itself, how much more
surely must it be so with particles, like those of the platina, or other
limiting body, which at the same time that they have not these elastic
powers, are also unlike it in nature! Hence it would seem to result that
the particles of hydrogen or any other gas or vapour which are next to the
platina, &c., must be in such contact with it as if they were in the liquid
state, and therefore almost infinitely closer to it than they are to each
other, even though the metal be supposed to exert no attractive influence
over them.

628. A third and very important consideration in favour of the mutual
action of gases under these circumstances is their perfect miscibility. If
fluid bodies capable of combining together are also capable of mixture,
_they do combine_ when they are mingled, not waiting for any other
determining circumstance; but if two such gases as oxygen and hydrogen are
put t