350 KENNELLY AND UPSON -HUMMING TELEPHONE. [July 20, 



left circular, D^ and D^ had symmetrical sectors cut from opposite 

 sides, reducing their width to 4 cm. (1.57 in.) and 3 cm. (1.18 in.) 

 respectively. In clamping these strip diaphragms in front of the 

 bipolar magnet of the standard receiver, their angular position did 

 not appear to affect the system appreciably. 



The results obtained with these three diaphragms are indicated 

 in Fig. 12, for tube-lengths diminished steadily from 270 to 80 cm. 

 It will be seen that the receiver diaphragm influences the hum pro- 

 foundly. Thus, the circular diaphragm D^ developed a mean- 

 frequency of 1,100 '—^ or c"'S, judging by the points of minimum 

 primary current, and its pitch zig-zag formed ascending intersections 

 with this line at 95, 125, 155, 185, 215 and 245 cm., approximately, 

 in conformity with the series 5 -|- 30m cm. The sectored diaphragm 

 r>2 developed a mean-frequency of A"S, at 920 r^, with ascending 

 intersections nearly in conformity with the series 36;;* cm. The 

 narrowest diaphragm D^ developed a mean-frequency of F", at 

 705 .—', and ascending intersections in substantial conformity with 

 the series 33 -|- 47m cm. 



It will be observed that there are double breaks in pitch on zig- 

 zag D-^. This tendency was found to follow irregularity in the dia- 

 phragm, or in its mounting. Thus, the ordinary standard diaphragm 

 used in all the preceding tests was observed to develop similar double 

 breaks when the* clamping screw-cover was slackened, so as to leave 

 the diaphragm somewhat loosely clamped. 



The pitch zig-zag of D^ shows gaps. These gaps seemed to be 

 due to the enfeebled condition of the electromagnetic vibrating sys- 

 tem in the receiver when used with the experimental diaphragm 

 D^. A very marked case of such gaps is presented in Fig. 13, which 

 indicates the frequencies and currents obtained with a particular 

 single-pole telephone receiver, the remainder of the apparatus being 

 unchanged, and the tube-length being steadily reduced from 165 to 

 80 cm. The line of mean-frequency is at 1,025 /—', and the ascend- 

 ing intersections with this line are formed at points conforming 

 with the series 28 + 327^ cm. Only short pieces of the zig-zag 

 were, however, obtainable, and these only with the aid of a condenser 

 in the secondary circuit. The dotted segments RS and TV were 

 obtained with the receiver terminals reversed, and correspond ap- 



