TELEPHONE DIAPHRAGMS. 



433 



of the voltaic cell E. Readings of the advance of the point P, could be 

 made on the micrometer head to 10"^ inch (25 fj.) and could be well 

 estimated to 10~* inch (2.5 fx). Impressed forces were used in suc- 

 cession up to about 100 grams wt. (10^ dynes). 



Fig. 8. — Apparatus for Diaphragm Elasticity Measurement. 



Figure 9 shows the results obtained, with ordinates deflections in 

 microns, and abscissas impressed central force in dynes. The different 

 curves refer to diaphragms of different thickness. In every case the 

 clamping circle of the diaphragm in the receiver had a diameter of 

 5.0 cms. The dotted curves show the deflections with the permanent 

 magnet of the telephone removed. The full curves show the corre- 

 ponding deflections with the permanent magnet present. 



It will be seen that the deflections obtained with varying impressed 

 forces, follow substantially straight-line laws, up to say 50 microns, 

 a range of deflection considerably in excess of what the telephone dia- 

 pl ragm has ordinarily to undergo in practice. There is, however, a 

 considerable difference between the deflection produced by a given 

 impressed force when the permanent magnets were present, and when 

 they were removed. This difference is accentuated in the cases of the 

 thinnest diaphragms. The presence of the permanent magnet causes 

 the diaphragm to be bowed from the plane of the clamping circle, 

 and subsequent deflections, due to impressed forces, occur from this 

 distorted position of equilibrium. 



