KENNELLY AND PIERCE. — TELEPHONE RECEIVERS. 



141 



2 and multiplying the reciprocal by F, which gives a circle of diameter 

 F/r symmetrically disposed with reference to the axis of reals. 



The use of this circle is as follows. For a given value of co find the 

 angle a by ecjuation (9) and lay off this angle negatively at 0; then 



F 



the length of the chord OP of the circle gives the amplitude j^, of x, 



O 



P 



Figure 14. Left straight line graph of z. Right, circular graph of F Iz. 



for the given w, and the angle is the angle of lag of x behind the 

 impressed force. As w changes from zero to infinity, the point P 

 moves negatively once around the circle from 0, through A', back to 0. 

 Magnetic Flux as Dependent on Current and Mechanical 

 Displacement. — • In the proljlem under consideration, the pull / act- 

 ing on the diaphragm is determined by the magnetic flux through the 

 air gap, or air gaps, of the receiver. If ^ is the mean flux through 

 the active part of the magnetic circuit, we have, for a bipolar receiver, 

 approximately 



5 Jo + 47r iV-i 



= - = 



^0 + 



2 (/ - X) 

 S 



= Si' S maxwells (10) 



and for a monopolar receiver, approximately 



^0 + 47r Ni 



G^ 



"^ ^ ¥x^ 



?T 



+ 



l-X 



S 



maxwells (11) 



in which 



^ = the total m. m. f. due to the permanent magnet and to the 

 current i in the coils (gilberts), 



^0 — ni. m. f. due to permanent magnet alone (gilberts), 



