KENXELLY AND UPSON— HUMMING TELEPHONE. 



347 



TUBE LENGTH - CENTIMETERS. 



Fig. 10. Comparative Behavior of Three Regular Standard Transmitters 



with Reduced Tube-lengths. 



The test indicates, therefore, that different standard transmitters 

 in normal adjustment do not alter the mean-frequency tube-lengths ; 

 but that variations in breaking lengths may be expected within cer- 

 tain limits. 



A further test was made of the effect of modifying the trans- 

 mitter, by selecting for experiment a particular Western Electric 

 Co.'s standard type of transmitter which had been used in the labora- 

 tory for some years, and was not in the best adjustment. A test 

 was made with this instrument (using the same receiver, coil, battery 

 and connections as in preceding tests), first without any extra load 

 on its diaphragm, second with a load, and third with the load re- 

 moved. The load consisted of a small brass disk 1.5 cm. (0.59 in^ 

 in diameter, and 0.2 cm. (0.079 ^^O tliick, clainped at its center 

 between the two small nuts at the center of the external surface of 

 the diaphragm. This added a mass of 2.7 gm. to the vibrating 

 system of the transmitter. The results are seen in Fig. 11. Curves 

 I and 3 represent the behavior of the system unloaded, before and 

 after loading respectively, the tube-length being steadily diminished 



