﻿and some Applications to Physical Measurements. 483 

 inductance L and capacity C, is given very approximately by 



71 = 1/(2^01). 



Changes in n can thus be brought about by changes in 

 ( ! or L. In the experiments to be described below, the 

 changes in n were brought about by variations in L, and in 

 this case, with C constant, a small variation, dh, in the 

 inductance produces a corresponding change, tin, in the 

 frequency given bv 



dn/n=--idL/L (i.) 



The experimental part thus reduces itself to a determination 

 of dn. This is accomplished by obtaining beats between the 

 heterodyne note and a note o£ constant pitch, and then 

 counting the change in the number of beats per second 

 caused by the change in inductance. A considerable amount 

 of practice in listening is required in order readily to be able 

 to adjust the heterodyne note to the pitch of the constant 

 note. This note can be very conveniently obtained by means 

 of a third set, some distance away from the other sets, 

 oscillating with audible frequency, in the plate circuit of 

 which a telephone is placed. The intensity of the note 

 heard can be altered by adjusting the filament current, and 

 in this respect the note is very much more convenient than 

 that obtained from a tuning-fork. For it was found that 

 the heterodyne note could be more easily brought to tune 

 with the standard note, and false beats more readily recognized 

 when this latter could be altered so that both notes had 

 approximately the same intensity. 



In some of the experiments * it was found impossible to 

 obtain a beat note of convenient audible frequency when the 

 fundamental frequencies of the oscillations were approxi- 

 mately the same. It was observed that, as the capacity of 

 one of the sets was altered, only very shrill notes could he 

 heard on either side of the very large region of silence. 

 This synchronization effect appears to depend on several 

 factors, but chiefly on the coupling between the circuits. 

 On account of the limited size of the box containing the 

 coils, the coupling could not be reduced beyond a certain 

 lower limit, and reducing the strengths of the oscillatory 

 currents merely reduced the intensity of the limited note. 

 In all these cases it was possible to obtain the heterodyne 

 note between the fundamental of Set 2 and the first overtone 

 of Set 1, which was quite steady and possessed the normal 

 region of silence. Since the changes in n were produced by 



* Those in which the determinations of the magnetic susceptibilities 

 of certain salts were made, see below. 



2 I 2 



