repeated as
long as the wind supply is kept up. A series of regular puffs of wind
will thus be delivered into the lower part of the resonator or pipe,
resulting in a musical note.

Figs. 25, 26, 27 represent the first Diaphone heard in a public
building in this country, namely that of a model sounded in St.
Patrick's Cathedral, New York City, in 1905. In this form of Diaphone
the pressure of air operating the Diaphone has been varied between 10
inches and 500 inches, without perceptible variation in the pitch of
the note emitted.

[Illustration: Figs. 25, 26, 27. Diaphone in St. Patrick's Cathedral,
New York]

Referring to Fig. 25, the chamber WW is supplied with air under
pressure whenever the organist presses a key or pedal calling into use
this particular note. The pressure of air enters through the circular
engine supply port S, thus raising the pressure in the chamber C and
forcing in an upward direction the aluminum piston P through the medium
of the division D (colored black), which forms a portion of the
aluminum piston.

When the lower edge of the piston has risen a certain distance it will
uncover the circular engine exhaust port E, and will allow the
compressed air to escape into the atmosphere. At this moment the rise
of the piston will have closed the engine supply port S.

The momentum acquired by the piston (see Fig. 27) will cause it to
travel upward a little further, and this upward travel of the division
D will cause a compression of air to take place at the foot of the
resonator or pipe R. This compression will be vastly increased through
the simultaneous opening of the eight circular speaking ports SP.

The pressure of the compressed air at the foot of the resonator E will
now by acting on the upper surface of the division D depress the
aluminum piston until the engine supply port S is again opened.

By this time the compression at the foot of resonator R will have
traveled up the pipe in the form of a sound wave, and will have been
followed by the complementary rarefaction. This rarefaction on the
upper side will render more effective the pressure of the compressed
air again admitted through the engine supply port S on the underside of
division D.

It will be seen that this cycle of operations will be repeated as long
as the organist holds down his pedal or key admitting compressed air to
the chamber W.

As the aluminum piston P is very light and is in no way impeded in its
movem