332 



KENNELLY AND UPSON— HUMMING TELEPHONE. 



[July lo, 



internal diameter of 4.8 cm. (1.9 in.), and also by the application 

 of a pair of rubber-tipped flat metal springs to areas between the 

 center and edge. The resistance of the microphone varied between 

 the approximate limits of 20 ohms when quiescent, and no ohms 

 when in powerful vibration. 



The Receivers. — The receivers used in most of the measurements 

 were of the standard bipolar Western Electric Co.'s type, known as 

 No. 122, having poles 1.4X0.2 cm. (0.55X0.08 in.), separated 

 by 0.82 cm. (0.325 in.). They had a resistance of 210 ohms, and 

 an inductance of 0.025 henry, at a frequency of 1,000—'. With 

 steady currents, their resistance, at 15° C, was about 70 ohms. The 

 diaphragm of varnished ferrotype iron had an external diameter of 

 5.5 cm. (2.17 in.), a clamping diameter of 4.95 cm. (1.95 in.) and 

 a thickness, over varnish, of 0.292 mm. (0.0115 in.). Its weight 

 was 4.0 grammes. 



The Induction Coil. — The induction coil used was of the standard 

 Western Electric Co.'s type, known as No. 13. Its resistances and 

 inductances were taken as follows :* 



Table I. 



The principal dimensions of the coil were : Length over all 8.2 

 cm. (3.16 in.). Interflange 6.3 cm. (2.5 in.). Diameter over out- 

 side cover 2.5 cm. (i in.). Internal diameter of core tube 0.75 cm. 

 (0.296 in.). Diameter of iron wires in core 0.0356 cm. (0.014 in.). 

 Total number of iron wires in core about 75. 



Observation Series No i. Effect of Shortening the Tube. — 

 Commencing with the connections of Fig. i, a battery of 8.6 volts, 

 and a tube length of 267 cm., as indicated in Fig. 2 on the scale of 

 abscissas, a loud steady note between G"# and A" (850 '—') was sus- 

 tained in the telephone. The pitch of this note is shown at P on the 



*The data for the coil at 1,000 ~' were kindly supplied by the engineering 

 department of the Western Electric Co. 



