no KENNELLY-TAYLOR— EXPLORATIONS OVER [April 22, 



organ-pipe of adjustable pitch, tuned to produce the maximum vibra- 

 tory ampHtude at the center. As shown in Appendix II., the con- 

 stant ^ is then the product of the equivalent mass m and the square 

 of the resonant angular velocity oj^. 



A series of statical measurements were made, by applying small 

 tensions /.„ by means of a calibrated spring, to the center of the 

 diaphragm, and observing, with the aid of the explorer, the central 

 displacements Ws, thereby produced. It was found, as might be 

 expected, that the ratio of /,, to zu., was constant, so long as the latter 

 did not exceed 18 /x,. Moreover, the value of .? obtained from /,s/Ws 

 was approximately the same as that obtained from formula (9), 

 App. II. This static method of finding s, however, is inferior to 

 the resonance method, because precise static measurements are 

 difficult to obtain. The application of electro-magnetic excitation 

 to a steel diaphragm also imposes residual stresses, which make the 

 use of the static method unreliable. 



The Mechanical Resistance r. 



The constant r was measured, with the explorer, by photograph- 

 ing the decay curve of vibration amplitude on a moving photo- 

 graphic film, when the diaphragm was tapped at the center, and 

 allowed to return to the equilibrium position under its own damping 

 forces. It is shown in Appendix II., that the resistance r is twice 

 the natural frequency multiplied by the equivalent mass and the 

 logarithmic decrement. Fig. 10 is a tracing from a photograph of 



Fig. 10. Tracing from Photograph of Decay Curve. Diaphragm No. i. 



the curve of decay. A small camera, represented in Fig. 11, was 

 set up in front of the explorer, containing a photographic film 

 wrapped around a metal drum. The drum was motor driven at a 

 peripheral speed of approximately 4 meters per second, and the 

 shutter was opened at the time of tapping the diaphragm. The 

 logarithmic decrement of this curve is 0.184, at the frequency of 

 824 '—' ; so that with an equivalent mass m of 1.09 gm. the value of 



