; and a vibration is in
consequence produced; which with the great facility, which elastic
fluids possess of forming eddies, may explain the production of sounds
by blowing through a fissure upon a sharp edge in a common organ-pipe
or child's whistle; which has always appeared difficult to resolve;
for the less vibration an organ-pipe itself possesses, the more
agreeable, I am informed, is the tone; as the tone is produced by the
vibration of the air in the organ pipe, and not by that of the sides
of it; though the latter, when it exists, may alter the tone though,
not the note, like the belly of a harpsichord, or violin.

When a stream of air is blown on the edge of the aperture of an
organ-pipe about two thirds of it are believed to pass on the outside
of this edge, and one third to pass on the inside of it; but this
current of air on the inside forms an eddy, whether the bottom of the
pipe be closed or not; which eddy returns upwards, and strikes by
quick intervals against the original stream of air, as it falls on the
edge of the aperture, and forces outwards this current of air with
quick repetitions, so as to make more than two thirds of it, and less
than two thirds alternately pass on the outside; whence a part of this
stream of air, on each side of the edge of the aperture is perpetually
stopped by that edge; and thus a vacuum and vibration in consequence,
are reciprocally produced on each side of the edge of the aperture.

The quickness or slowness of these vibrations constitute the higher
and lower notes of music, but they all of them are propagated to
distant places in the same time; as the low notes of a distant ring of
bells are heard in equal times with the higher ones: hence in speaking
at a distance from the auditors, the clear sounds produced in the
larynx by the quick vibrations of its aperture, which form the vowels;
the tremulous sounds of the L. R. M. N. NG. which are owing to
vibrations of certain apertures of the mouth and nose, and are so
slow, that the intervals between them are perceived; the sibilant
sounds, which I suppose are occasioned by the air not rushing into a
complete vacuum, whence the vibrations produced are defective in
velocity; and lastly the very high notes made by the quickest
vibrations of the lips in whistling; are all heard in due succession
without confusion; as the progressive motions of all sounds I believe
travel with equal velocity, notwithstanding the greater or less