TELEPHONE DIAPHRAGMS. 



457 



be seen that the vakie of A remained but Httle changed throughout 

 the series, diminishing from 0.575 to 0.51 megadyne per absampere. 

 The mechanical resistance r of the diaphragm changes, however, 

 largely, diminishing from about 600 to 200 dynes per kine. 



Fig. 20. 



Mkthub of Am Gai- Measurement. 



At first sight, it seems difficult to explain why the change in imposed 

 screwing-on torque should affect the mechanical resistance so mark- 

 edly. It was found, however, that a noticeable effect of screwing 

 on the cap tightly, was to increase the air-gap between diaphragm 

 and poles. This is a reasonable effect, if it is remembered that the 

 magnet poles bow the dia- 

 phragm down towards them, 

 when the diaphragm is laid 

 on the clamping ring, and 

 that the application of cap 

 pressure, under the influence 

 of screwing torque, to the 

 upper clamping ring, tends 

 to lessen this bowing. 



The increase in air-gap 

 accompanying increase in 

 torque was measured by the 

 device shown in Figure 20, 

 where the micrometer-head 

 depth gauge is applied to the 

 upper surface of the dia- 

 phragm, from a temporary 

 brass frame attached to the io 20 30 



shell Fie-iire '>! shows the CAP DEFLECTION, DEGREES 



snen. j^igure -i snows me khj. 21. _ cukve showing Kelai ion 



magnitudes of the deduced between Air-Gap in Keceiver 



air-gaps, as ordinates, against B and the Cap Adjustment. 



