eric conditions, is not a reliable
mode of measurement. It is easily understood that a cubic foot of air at
sea-level will contain a great many more atoms than a cubic foot of air
will at the top of a high mountain; or, to state it in another way, a
cubic foot of air at sea-level will occupy much more than a cubic foot
of space 10,000 feet higher up. Suppose, then, that the amount of heat
held in a cubic foot of air at sea-level remained the same, as related
to the number of atoms. In its ascent we shall find that at a high
altitude the same number of atoms that were held at sea-level in a cubic
foot have been distributed over a so much larger space that the sensible
heat is greatly diminished or diluted, so to speak. It was an old notion
that heat would hide itself away in fluids under a name called by
scientists latent heat. This theory has been exploded, however, by
modern investigation.

If we place some substance that will inflame at a low temperature in the
bottom of what is called a fire syringe (which is nothing but a cylinder
bored out smoothly, with a piston head nicely fitted to it, so that it
will be air-tight) and then suddenly condense the air in the syringe by
shoving the plunger to the bottom, we can inflame the substance which
has been placed in the bottom of the cylinder. In this operation the
heat that was distributed through the whole body of air, that was
contained in the cylinder before it was compressed, is now condensed
into a small space. If we withdraw the plunger immediately, before the
heat has been taken up by the walls of the syringe, we shall find the
air of the same temperature as before the plunger was thrust down. This,
however, does not take into account any heat that was generated by
friction.

Let us further illustrate the phenomenon by another experiment. If we
suddenly compress a cubic foot of air at ordinary pressure into a cubic
inch of space, that cubic inch will be very hot because it contains all
the heat that was distributed through the entire cubic foot before the
compression took place. Now let it remain compressed until the heat has
radiated from it, as it soon will, and the air becomes of the same
temperature as the surrounding air. What ought to happen if then we
should suddenly allow this cubic inch of air to expand to its normal
pressure, when it will occupy a cubic foot of space?

Inasmuch as we allowed the heat to escape from it when in the condensed
form, when it