﻿audible in the Telephone. 



291 



produce the standard sound is found to be 7*4 x 10~ 8 c.G.s., 

 or 7*4 x 10~ 7 amperes, for telephone T a . 



The results obtained by the method of the revolving magnet 

 are collected into the accompanying table. The " wooden 

 coil " is of smaller dimensions than the " ebonite coil/'' the 

 mean radius being only 3*5 centim. The number of convolu- 

 tions is 370. 



Frequency = 307. Ebonite coil. 



Telephone. 

 T I 



R in ohms. 



84100 Plumbago. 

 8100 Box. 

 4100 Box. 



500 Box. 



200 Box. 



Frequency : 



84100 Plumbago. 

 10100 Box. 

 1600 Box. 

 350 Box. 



Frequency 

 3100 Box. 



Current in 

 amperes. 



3-8 x 10-7 

 7-4x10-7 

 5-2x10-7 

 1-2 x 10-5 

 1-0x10-5 



Sound. 



Below standard. 

 Standard. 



307. Wooden coil. 



I 3-6x10-7 Sta: 



3-7x10-7 



5-4x10-7 

 I 1-1 x 10- 5 



192. Ebonite coil. 

 I 2 5xl0- 6 I Standard. 



The method of the revolving magnet seemed to be quite 

 satisfactory so far as it went, but it was desirable to extend 

 the determinations to frequencies higher than could well be 

 reached in this manner. For this purpose recourse was had 

 to magnetized tuning-forks, vibrating with known amplitudes. 

 If, for the moment, we suppose the magnetic poles to be con- 

 centrated at the extremities of the prongs, a vibrating-fork 

 may be regarded as a simple magnet, fixed in position and 

 direction, but of moment proportional to the instantaneous 

 distance between the poles. Thus, if the magnetic axis pass 

 perpendicularly through the centre of the mean plane of the 

 inductor-coil, the situation is very similar to that obtaining 

 in the case of the revolving magnet. The angle <f> in (2) is 

 no longer variable, but such that sin = 1 throughout. On 

 the other hand m varies harmonically. If I be the mean 

 distance between the poles, 2/3 the extreme arc from rest to 

 rest traversed by each pole during the vibration, m Q the 

 mean magnetic moment, 



m/m = 1 + 2/3// . sin pt } 



