442 KENNELLY, TAYLOR— PROPERTIES OF 



K2 into approximate coincidence with that of K^. Under these 

 conditions, the phenomena of absorption, at or near resonance, can 

 be readily observed. It has been possible in this manner to check 

 the causes and essential characteristics of telephone-diaphragm ab- 

 sorption. 



Absorbing Influence of the Amplitude Measurer on the 

 Vibration of a Diaphragm. 



It was observed in the course of the preceding tests, in which 

 the amplitude measurer was successively on and off the receiver, 

 that the application of the device, apart from the warping effect of 

 its clamps, slightly diminished the diameter of the impedance circle. 

 In one case, this diameter, without the explorer, was 100.6 ohms, 

 and with the explorer 92.5, all other conditions remaining un- 

 changed. In other words, the application of the amplitude meas- 

 urer reduced the vibrational velocity and vibrational amplitude about 

 8 per cent., without appreciably affecting the other constants of 

 the instrument. This shows that when precision is needed, the 

 motional-impedance circle should be taken with the amplitude meas- 

 urer both on and off successively. The difference between the two 

 motional-impedance diameters will indicate what correction should 

 be applied to the measured amplitudes. 



In conclusion, the authors desire to express their acknowledg- 

 ments to Professor C. A. Adams and Mr. A. A. Prior, for their 

 collaboration in the analysis of an oscillograph ; also to Dr. G. A. 

 Campbell for valuable criticisms and suggestions on the MSS. 



APPENDIX I. 



Outline Theory of the Bifilar Oscillograph and Duddell 

 Vibration Galvanometer.^^ 



It is assumed that the apparatus consists of a bifilar vertical sus- 

 pension, of adjustable tension, part of which suspension vibrates in 

 a fairly uniform magnetic field. The two vertical wires of the 



11 This theory is substantially the same as that developed in the Kennelly 

 and Affel paper (Bibliography, 10), with respect to vibrating diaphragms, 

 replacing translatory forces by corresponding couples. 



