On the Suppression of Induction Clamour in Telephones. 279 
have numerous convolutions and are closely juxtaposed, so that 
the secondary current generated in S may be as powerful as the 
Fig. 1. 
secondary current produced by the whole line, to the length of 
which the number of convolutions in S must bear some relation. 
Electro-magnets, « a and b Db’, are inserted for retarding the 
effect on the neutralizing currents generated in Pand 8S. Ido 
not know the date of Wilson’s patent, but it must be prior to 
1878, as it is described in Prescott’s work of that date ; it was 
as stated, devised for use in quadruplex telegraphy. 
In February, 1878, Mr. Edison took out a patent for a similar 
object, applied to the suppression of induction clamour in tele- 
phones. One method proposed was as follows :—An induction 
coil, connected with the telephonic circuit, is so arranged that the 
disturbing line induces within the coil an equal, but opposite 
current to that giving rise to the disturbance, thus neutralizing its 
action. Fig. 2 shows the arrangement. Cand C’ are the induction 
coils in the telephone circuit ; k and I’ iron cores, which can be 
made to approach the electro-magnets f and f’, until the current 
induced in the coils ¢ c' is equal to the induced current from the 
disturbing line No.1. Each disturbing line has a similar arrange- 
ment, each electro-magnet being placed at a distance from the 
iron core corresponding to the strength of the disturbance. 
