ating fork, the sound does not cease. The second fork has taken
up the vibrations of its neighbour, and is now sounding in its turn.
Dismounting one of the forks, and permitting the other to remain upon
its stand, I throw the dismounted fork into strong vibration. You
cannot hear it sound. Detached from its case, the amount of motion
which it can communicate to the air is too small to be sensible at any
distance. When the dismounted fork is brought close to the mounted
one, but not into actual contact with it, out of the silence rises a
mellow sound. Whence comes it? From the vibrations which have been
transferred from the dismounted fork to the mounted one.

That the motion should thus transfer itself through the air it is
necessary that the two forks should be in perfect unison. If a morsel
of wax not larger than a pea be placed on one of the forks, it is
rendered thereby powerless to affect, or to be affected by, the other.
It is easy to understand this experiment. The pulses of the one fork
can affect the other, because they are _perfectly timed_. A single
pulse causes the prong of the silent fork to vibrate through an
infinitesimal space. But just as it has completed this small
vibration another pulse is ready to strike it. Thus, the impulses add
themselves together. In the five seconds during which the forks were
held near each other, the vibrating fork sent 1,280 waves against its
neighbour and those 1,280 shocks, all delivered at the proper moment,
all, as I have said, perfectly timed, have given such strength to the
vibrations of the mounted fork as to render them audible to all.

Another curious illustration of the influence of synchronism on
musical vibrations, is this: Three small gas-flames are inserted into
three glass tubes of different lengths. Each of these flames can be
caused to emit a musical note, the pitch of which is determined by the
length of the tube surrounding the flame. The shorter the tube the
higher is the pitch. The flames are now silent within their
respective tubes, but each of them can be caused to respond to a
proper note sounded anywhere in this room. With an instrument called
a syren, a powerful musical note, of gradually increasing pitch, can
be produced. Beginning with a low note, and ascending gradually to a
higher one, we finally attain the pitch of the flame in the longest
tube. The moment it is reached, the flame bursts into song. The
other flames are still