connected with the Telephone. 287 



2. By screening the wire from the influence of induction. 



3. By neutralizing the effects of induction. 



1. Mr. Edison in America has partially succeeded in effect- 

 ing the first cure ; but his results, though promising, have not 

 yet reached a practical point. 



2. I have overcome the second difficulty in a way that will 

 now be described. 



Let 1, fig. 3, be a wire used for telephonic purposes, and 2 



m 



& 



be an ordinary telegraphic wire contiguous to it. Let us re- 

 gard 1 and 2 as symmetrical and contiguous particles of the 

 two wires. If a current flow through 2 it will affect 1 induc- 

 tively both statically and magnetically. Let us regard the 

 static effect first. If the current flow away from us, then we 

 may consider the particle 2 as charged positively ; lines of 

 electric force will radiate all around it, and that line which 

 passes through 1 will inductively charge that particle negatively, 

 This influence being felt all along the wire, a current in the 

 reverse direction to that in 2 will flow through 1. The reverse 

 would occur if we assumed the primary current to flow in the 

 other direction. Hence, an induced current will flow through 

 1, whenever the current in 2 commences and whenever it 

 ceases. Now, if we place between 1 and 2 a screen of metal, 

 or other conducting matter, in connexion with the earth, then 

 the line of electric force, instead of passing through 1, will 

 terminate at the screen. Hence, if we surround the wire 2 

 with a covering or sheath of metal, or if we submerge it in 



