118 



KENNELLY AND VELAXDER— POTENTIOMETER 



Receiving-End Impedance of a Cable with a Variable- 

 Inductance Load. 



The a.-c. potentiometer lends itself advantageously to the experi- 

 mental study of a.-c. artificial lines in the laboratory. An example 

 of such an application appears in Fig. 12. The plan of connections 

 shows an artificial telephone cable ten miles (16.1 km.) in length, in 

 /-sections of two miles each, or less. The lumpiness correction for 

 this cable, at 1200-—', was found to be negligible. The constants of 

 the cable are r" = 88 ohms per loop mile (54.7 ohms per loop km.) 

 and c" = o.o6 microfarad per loop mile (0.0373 fii. per loop km.). 

 The total conductor resistance was thus 880 ohms, and the total 

 distributed loop capacitance 0.6 microfarad. 



Fig. 12. Vector current circular locus at receving end of an artificial 

 telephone cable with variable inductance load, under constant impressed 

 e.m.f. at sending end and at a steady frequency of 1,208 cycles per second. 



At the sending end A of the artificial cable, a pliotron oscillator 

 impressed a steady e.m.f., reduced to i.o volt at reference phase 

 and of frequency 1208-^. At the receiving end B', an adjustable 



