168 1ttature'0 /Piracies. 



cables, and this leads us to discuss the phe- 

 nomena of induction. 



Every one who has listened at a telephone 

 has heard a jumble of noises more or less pro- 

 nounced, which is the effect of the working of 

 other wires in proximity to those of tin t !<- 

 phone. If, when a Morse telegraph instrument 

 is in operation on one of a number of wires 

 strung on the same poles, we should insert a 

 telephone in any one of the wires that were 

 strung on the same poles or on another set of 

 poles even across the street, we could hear the 

 working of this Morse wire in the telephone, 

 more or less pronounced, according to the dis- 

 tance the wire is from the Morse circuit. This 

 phenomenon is the result of induction, caused 

 by magnetic ether- waves that are set up wlu-n- 

 ever a circuit is broken and closed, as ex- 

 plained in Chapter VI. 



The telephone is perhaps the most sensitive 

 of all instruments, and will detect electrical 

 disturbances that are too feeble to be felt on 

 almost any other instrument, hence the tele- 

 phone is preyed upon by every other system of 

 electrical transmission, and for this reason has 

 to adopt means of self -protection. It has been 

 found that the surest way to prevent interfer- 

 ence in the telephone from neighboring wires 

 is to use what is called a metallic circuit that 

 is to say, instead of running a single wire from 

 point to point and grounding at each end, as 



