120 KENNELLY-TAYLOR— EXPLORATIONS OVER [April 22, 



Summary. 



1. The distribution of amplitudes over small circular telephonic 

 diaphragms, under simple impressed vibrations, has been measured, 

 it is believed for the first time, by means of a new and specially 

 constructed vibration-explorer. 



2. The simple vibrations of the small steel circular diaphragms, 

 used in telephonic receivers, appear to belong to the fundamental 

 mode, within the ordinary telephonic range of intensity and fre- 

 quency up to 2,000 '—', with the distribution of impressed forces 

 here described. 



3. The explorations have confirmed the working theory of the 

 velocity-circle diagram for such vibrations, and have afforded means 

 of determining the three constants ni, r and s, in that theory, for 

 acoustically excited vibrations. 



4. In the resonant condition, exploration is somewhat uncertain, 

 owing to slight instability in the vibratory behavior of the dia- 

 phragm. 



5. The distribution of forced amplitude at varying radial dis- 

 tances, has been found to compare well with the Rayleigh theory 

 of freely vibrating plates, when good flat clamping around the edge 

 can be secured, and with acoustic excitation. The coefficient of 

 equivalent mass appears to be 0.183 for such a case. With electro- 

 magnetic excitation, the amplitude distribution may be very different 

 and the coefficient is ordinarily increased. 



6. Loading a diaphragm with a small mass at the center, de- 

 creases its natural frequency, and tends to reduce the amplitude of 

 vibration at the center, with a relative increase at outlying points; 

 so that the equivalent mass of the diaphragm, considered by itself, 

 is apt to be changed. 



7. A means is suggested, based on the velocity-circle diagram, 

 for comparing the acoustic intensities of organ-pipes of different 

 pitches. 



8. The distribution of amplitudes over the surface of a steel re- 

 ceiving-telephone diaphragm, with bipolar electromagnetic excita- 

 tion, was found to be of fundamental mode, but with a tendency to 

 form two maxima, one over each pole. 



9. In some small, thin, glass diaphragms, three modes of vibra- 



