230 DR, LOUIS VESSOT KING ON THE PROPAGATION OF SOUND IN THE FREE 
Fig. 1. Small model of the diaphone sectioned to show details of construction. 
The principal dimensions of the diaphone tested at Father Point are as follows:— 
Piston .—Outer diameter 4^ inches; diameter of driving head 6 inches. Weight 3^ lbs. The piston 
contained 10 ports inch wide at intervals of inch. Amplitude of piston vibration at 25 lbs. 
pressure, about O'15 inch; frequency, 90 complete oscillations per second; ports twice opened during a 
complete vibration, giving rise to sound-wave of pitch 180. 
Trumpet .—Conical semi-vertical angle 6°'5; diameter of large opening 16| inches ; diameter at piston 
inches. Slant length to edge of piston 4 feet 10 inches. Over all length 0• 66 x wave-length. 
Resonance frequency of trumpet 180 complete vibrations per second 
Note .—In the Father Point diaphone (1903 model) the exhaust from the driving cylinder discharges 
into the trumpet. In later designs, as that shown in fig. 1, the exhaust (which is out of phase with the 
main sounding air) is discharged into the atmosphere outside of the trumpet, thereby improving to some 
extent the acoustic output. The writer is indebted to Mr. J. P. Northey, of Toronto, for the above 
information and for the loan of the sectioned model from which the photograph reproduced above was 
made. For further details of the apparatus see Northey, J. P., United States Patents, No. 736, 42$, 
August 18, 1903; No. 879,190, February 18, 1908; No. 973,960, October 25, 1910; No. 1,016,187, 
January 30, 1912. 
