ses are not generated by the pendulum." And finally, Daniell says:
"A vibrating body, _before it can act_ as a sounding body, must produce
alternate compressions and rarefactions in the air, and these must be
well marked. If, however, the vibrating body be so small that at each
oscillation the surrounding air has time to _flow round_ it, there is at
every oscillation a local rearrangement--a local flow and reflow of the
air; but the air at a distance is almost wholly unaffected by this."

Now, as Prof. Carter has shown by experiment that a tuning fork _while
still sounding_ had only an amplitude of swing of 1/17000 of an inch, and
only traveled an aggregate distance of 1/33 of an inch in one second, or
one inch in 33 seconds, surely such a motion is neither "swift," "fast,"
nor "vehement," and is unquestionably much "slower" than the motion of a
pendulum. We have only to consider one forward motion of the prong, and
if that motion cannot condense the air, then no wave can be produced; for
after a prong has advanced and stopped moving (no matter for how short a
time), if it has not compressed the air, its return motion (on the same
side) cannot do anything toward making a compression. If one such motion
of 1/17000 of an inch in 1/512 of a second cannot compress the air, then
the remaining motions cannot. There is unquestionably a "union limit"
between mobility and compressibility, and unless this limit is passed,
mobility holds sway and prevents condensation or compression of the air;
but when this limit is passed by the exercise of sufficient energy, then
compression of the air results. Just imagine the finger to be moved
through the air at a velocity of one foot in one hour; is it possible
that any scientist who considers the problem in connection with the
mobility of the air, could risk his reputation by saying that the air
would be compressed? Heretofore it was supposed that a praeong of a tuning
fork was traveling _fast_ because it vibrated so many times in a second,
never stopping to think that its velocity of motion was entirely
dependent upon the distance it traveled. At the start the prong travels
1/20 of an inch, but in a short time, _while still sounding_, the
distance is reduced to 1/17000 of an inch. While the first motion was
quite fast, about 25 inches in a second, the last motion was only about
1/33 of an inch in the same time, and is consequently 825 times slower
motion. The momentum of the prong, the amou