In Fig. 24 we illustrate the Diaphone in the Hope-Jones organ built for Aberdeen University, Scotland. The action is as follows: Wind from the organ bellows enters the pipe foot F, and raises the pressure in the chamber C. The air in the chamber will press upon the back of the valve V, tending to keep it closed. It will press also upon the bellows or motor M, and as this bellows has a much larger area than that of the valve, it will instantly collapse, and, through the medium of the tail piece T, will pull the valve V off its seat and allow the compressed air in the chamber C to rush into the resonator or pipe P. Owing to the inertia of the column of air contained in the pipe P, a momentary compression will take place at the lower end of the pipe, and the pressure of the air inside the motor M will, in consequence, be raised. The motor having now increased pressure both sides, will no longer keep the valve off its seat, and the spring S will open the motor and close the valve. The compression caused by the admission of the puff of air into the lower parts of the pipe P will be followed by the usual rarefaction, and as this rarefaction will exhaust or suck the air from the inside of the motor M, the valve will again be lifted from its seat, and the cycle of operations will be 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.