﻿Specific Inductive Capacities of Water, Alcohol, fyc. 5(37 



increased. To invoke the inertia of tho plate seems inad- 

 missible, seeing that telephones with diaphragms * fifteen (15) 

 centimetres thick have been made to respond (Breguet). 



I have therefore hazarded a straightforward supposition f, 

 that the interval of silence is to be referred to a molecular 

 inertness of the plate of the telephone very similar in its 

 nature to quiescent friction. The diaphragm at rest seems 

 initially to resist further deformation, and this resistance must 

 first be overcome before the telephone will respond with 

 nicety to fine gradations of the actuating stress. In other 

 words, as soon as the internal friction encountered in moving 

 the diaphragm has passed from the quiescent to the kinetic 

 stage, the instrument is ten or more times more sensitive than 

 it was before the critical stress value had been exceeded. 



Washington, D.C., U.S.A. 



LXVI. Note on the Measurement of the Specific Inductive 

 Capacities of Water, Alcohol, §c. By Reginald A. 

 Fessenden, Professor of Electrical Engineering, Western 

 University of Pennsylvania %. 



IT appears to have been hitherto accepted that the high 

 values for the specific inductive capacities for water, 

 alcohol, and some other similar fluids which have been ob- 

 tained by various experimenters are correct. If this were 

 so, Maxwell's rule for the relation between specific inductive 

 capacity and the index of refraction would not hold in 

 these cases for wave-lengths of visible light, and the phe- 

 nomena of dispersion &c. have been called in to explain this 

 anomaly. It may be well to point out that these high values 

 are not correct, but that the true values are in every one of 

 these substances very nearly equal to that called for by the 

 theory. 



This fact was first noticed by the writer in 1891. A sen- 

 sitive electrometer had been constructed, with two fixed and 

 one movable cylinder, mounted on jewels, and provided with 

 a commutator, so as to act as an electrostatic wattmeter. 

 With a pressure of 1000 volts on the fixed and 50 volts on 

 the movable part, it made 300 revolutions per minute. At 



* Cf. Du Moncel's 'Telephone,' American edition, p. 115, containing 

 an account of experiments due to Breguet and to Boll. 



f References to hysteresis, to inconstancy of the batteries, &c. seem 

 inadmissible. 



| Communicated by the Author. 



