422 



KENNELLY, TAYLOR— PROPERTIES OF 



resonant frequency f^. In the case of test No. 3, the load, a small 

 copper disk, about i cm. in diameter, was intentionally placed on 

 the diaphragm excentrically, i. e., at a distance of i cm. ofif center. 

 It will be seen from the table that as the resonant frequency /q was 

 lowered, and with it /'_, the magnitude of ^1° was considerably re- 

 duced but 1^2° was, if anything, slightly increased. The sum /^i" + 

 yS„° between /o = 680'~' and /o=958'-~' has increased from about 

 ^2° to 83° ; while ^1" has increased from 20° to 37°. 



The inference to be drawn from this series of tests is that ^^^ 

 and /32° are, in general, unequal. The angle jB-^^ increases with the 

 frequency, but ^^2° is apparently more nearly constant. A reason 

 which suggests itself for this relation is that the lag jB^, between flux 

 and current, is due not only to hysteresis but also to the eddy cur- 

 rents of skin effect. Owing to hysteresis and skin effect in the 

 steel cores of the telephone electromagnet, the resultant flux lags 

 behind the exciting current to an extent ji^^ which depends upon the 

 impressed frequency and may rise theoretically to 45° at relatively 

 high frequencies, owing to skin effect alone. In the case of ^0°, 

 however, this is a lag between vibrational velocity of the diaphragm 

 and the C.E.M.F. thereby produced. An oscillatory change in 

 length of air-gap may set up hysteretic and eddy-current retardation 

 in the flux oscillation thereby generated, but the skin efifect should 

 perhaps be less than when the flux oscillation is generated from an 

 external magnetizing coil. 



In order to ascertain the effect of an increased air-gap on the 

 angles /?i° and ^o^, ring washers of pasteboard, of successively in- 

 creasing thickness, were inserted under the diaphragm, between it 

 and the clamping surface of the receiver. Starting with a clearance 

 between poles and diaphragm, of 0.32 mm. this was increased up to 

 about I mm. with the results as shown in the following table, the 



TABLE IL 

 Effect of Increasing Air-Gap on ^1 and /S^. 



