thousandth of a second, according to the suddenness and violence
of the explosion; then elasticity restores the air to its original
condition and everything is just as it was before the explosion. A
thousand detonations can produce no more effect upon the air, or
upon the watery vapor in it, than a thousand rebounds of a small
boy's rubber ball would produce upon a stonewall. So far as the
compression of the air could produce even a momentary effect, it
would be to prevent rather than to cause condensation of its
vapor, because it is productive of heat, which produces
evaporation, not condensation.

The popular notion that sound may produce rain is founded
principally upon the supposed fact that great battles have been
followed by heavy rains. This notion, I believe, is not confirmed
by statistics; but, whether it is or not, we can say with
confidence that it was not the sound of the cannon that produced
the rain. That sound as a physical factor is quite insignificant
would be evident were it not for our fallacious way of measuring
it. The human ear is an instrument of wonderful delicacy, and when
its tympanum is agitated by a sound we call it a "concussion"
when, in fact, all that takes place is a sudden motion back and
forth of a tenth, a hundredth, or a thousandth of an inch,
accompanied by a slight momentary condensation. After these
motions are completed the air is exactly in the same condition as
it was before; it is neither hotter nor colder; no current has
been produced, no moisture added.

If the reader is not satisfied with this explanation, he can try a
very simple experiment which ought to be conclusive. If he will
explode a grain of dynamite, the concussion within a foot of the