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 movement or swing, the speed of its vibration, and consequently the pitch of the note emitted, will be governed by the length of the resonator or pipe R. The tone given by this particular form of Diaphone possesses a peculiar sweetness in quality, while the power is limited only by the pressure of air used to operate it. [Illustration: Fig. 28. Diaphone in the Auditorium, Ocean Grove, N. J.] In Fig. 28 we give an illustration of the form of Diaphone used in the Hope-Jones Unit organ at the Auditorium, Ocean Grove, N. J. P is a pallet controlling the admission of air into the body of the pipe P|1|. M is a motor adapted for plucking open the pallet P through the medium of strap _s_. The box B is permanently supplied with air under pressure from the bellows. When the valves V and V|1| are in the position shown in the drawing, the Diaphone is out of action, for the wind from the box B will find its way through the valve V (which is open) into the interior of the motor M. When it is desired to make the note speak, the small exterior motors M|1| and M|2| are simultaneously inflated by the electro-pneumatic action operated by depressing the pedal key. The valve V will thereupon be closed and the valve V|1| be opened. As the pressure of air inside the motor M will now escape into the pipe or resonator P|1|, the motor will collapse and the pallet P will be opened in spite of the action of the spring S which tends to keep it closed. The wind in the box B will now suddenly rush into the lower end of the pipe P|1|, and by causing a compression of the air at that point will again raise the pressure of the air inside the motor M. The pallet will thereupon close and the cycle of operations will be repeated--thus admitting a series of puffs of wind into the foot of the pipe P|1| and thereby producing a musical tone of great power. As the valve V|1| is open, the sound waves formed in the pipe P|1| will govern the speed of vibration of the motor M. It will thus be obvious that the Diaphone will always be in perfect tune with the resonator or pipe P|1|, and that the pitch of the note may be altered by varying the length of the pipe.