280 Scientific Proceedings, Royal Dublin Society. 
Another arrangement given in Edison’s patent was proposed 
when the disturbances arose from the employment of very power- 
ful currents. It is shownin Fig. 3. Coil 3 is in connexion 
with the telephonic circuit, and so wound that the currents in- 
duced in it by the coils 1 and 2 are opposite in direction to those 
induced in the line by the disturbing wires 1 and 2. To augment 
the corrective induction an iron core g passes through all the coils. 
Fig. 3. 
Mr. Edison has also employed condensers to correct static 
induction, and hence this remarkable man may really be said to 
have done what others were subsequently groping after. 
English electricians appear to have been unaware of what had 
been already accomplished in America; for in April, 1878, Mr. 
Preece read an interesting paper before the Physical Society, 
wherein he gave an account of some experiments he had made 
with the object of overcoming this induction disturbance. Mr. 
Preece proposed to surround the Telephone line with an earth- 
connected sheath of iron to neutralize both static and magnetic 
disturbance, anticipating that the lines of both electric and mag- 
netic force would be cut off by this means. But even were this 
idea successful, it would be obviously impracticable under ordi- 
nary circumstances. 
Mr. Preece also proposed to use a return wire, and states that 
Mr. Graham Bell had excellent results from this arrangement. 
When, last autumn (1878), Professor Graham Bell announced this 
double-wire arrangement for overcoming current induction in 
Telephones, Mr. D. Brooks, of Philadelphia, claimed to have 
already patented this invention. Mr. Graham Bell’s or Mr. 
Brook’s plan involves, as we have said, the use of a return wire 
to the Telephone in place of the earth-connexion, as shown in 
Vig. 4. 
