VIBRATING TELEPHONE DIAPHRAGMS. 423 



load attached to the center of the diaphragm being 0.73 gm. in each 

 case. 



It appears from this table that the increase in air-gap greatly 

 diminished the force-factor A and the amplitude of vibration, which 

 is proportional to the diameter D of the impedance circle. The 

 equivalent mass and the elastic constant are both increased. It 

 appears that ^0° has undergone but little change ; whereas /J^" has 

 distinctly increased. 



The inference to be drawn from Table I. and Table II. col- 

 lectively, is that ySo" seems to be nearly constant for a given receiver ; 

 but that /?i° is affected both by the air-gap length and the impressed 

 frequency. Thus there seems to be no close connection between jSi° 

 and yffo"- I" the first five cases of Table I., and in all the cases of 

 Table II., the angle ^^2° exceeds jS^"; but this is not necessarily true 

 in all cases. In test 6 of Table I., p^P is considerably less than (i^^. 

 This case refers to another receiver and diaphragm. In the par- 

 ticular instrument investigated by Kennelly and Pierce® in 191 2, 

 the angles ^^^ and ySo° happened to be nearly equal. 



A number of tests were made with a series of different thick- 

 nesses of diaphragm in one and the same receiver. The results 

 showed that the angles ^^^ and ^0° were different with different 

 diaphragms ; but the quantitative relations have not yet been ascer- 

 tained. 



2. Investigation of REiJNTRANT and Distorted Circle Diagrams. 



The engineering research department of the Western Electric 

 Co., when examining some motional-impedance diagrams in 191 3, 

 seem first to have discovered cases of distorted and reentrant 

 circles. Such cases presented themselves in the course of the M. 

 I. T. researches in 1915.' Distorted diagrams of this type appear 

 in Figs. 5 to 9 and 11 to 17 of this paper. 



These distorted circle diagrams presented themselves at first in 

 a small percentage of the cases of telephone receivers tested in the 

 M. I. T. researches. When first encountered in these, they were 

 regarded as curiosities of unknown origin, and were set aside. At 



8 Bibliography, 7. 



