PAPERS ON CHEMISTRY AND PHYSICS 



olo 



ing of the American Physical Society in December, 1919, 

 in which he clearly demonstrated the distorting etfects 

 of bent tubes and straignt horns on sonnd waves. Al- 

 thongh this diaphragm mounting was designed before 

 Professor Foley's paper was read, the author was very 

 careful in the designing to avoid air pockets of any sort. 



The inertia of the moving parts of the mounting is 

 probably smaller than that of any diaphragm mounting 

 heretofore used in soimd-wave analysis. The only 

 masses involved are, the mass of three or four silk fibers 

 3 cm. long, the mass of the mirror 0.154 cm. long, 0.0435 

 cm. wide and of microscopic thickness, and the mass of 

 the small specks of shellac used to mount the mirror. 



The spring used was made by T\inding Xo. 40 steel wire 

 on a brass cone of small dimensions. The period of any 



Figiire 2. 



spring is a function of its diameter and the elasticity 

 of the material used. The diameter of each turn of wire 

 was dift'erent from that of any other; therefore each 

 turn had a different period and the spring as a whole 

 was aperiodic. While in use a small tuft of cotton was 

 placed insi^le the spring to damp out sidewise vibrations. 

 The other details of the set-up may be seen easily from 

 the diagram, Fig. 2. This device was found to be very 

 sensitive as is demonstrated by the photographs taken 

 with it in Fig. 3. This is a series of curves taken to 

 show that the diaphragm as used was sensitive to even 

 the faintest overtones. Wave A is the sound wave of an 

 open organ pipe. Several overtones can be found in the 

 wave. Wave B represents the sound wave produced by 

 two tubes sounding together, no resonator being used 



