ane eat 
On the Suppression of Induction Clamour in Telephones. 283 
clamour without interfering in any way with neighbouring 
lines. 
Here, of course, the differential coil is useless, as whatever 
destroys the effect of induction will, in like manner, destroy the 
effect of Telephonic currents. Equal and opposite motions being 
simultaneously imparted to the iron diaphragm it remains motion- 
less and silent. 
But the question arises, is it not possible to eliminate the dis- 
turbing induced currents from the Telephonic currents by the 
differences in electrical character that exist between them? Here 
no second wire, nor any access to the disturbing line, is necessary, 
There are three methods by which this may possibly be accom- 
plished :— 
1. By increasing the intensity of the telephone currents 
that they overpower the effects produced by induction disturb- 
ance, 
This is done in the Edison carbon telephone, by which I have 
been enabled to carry on conversation over lines when the in- 
duction clamour was so loud that no articulation whatever could 
be heard when a magneto-transmitter was used. 
2, By diminishing the sensitiveness of the receiving apparatus 
so that it shall not respond to induction currents, though 
sensitive to telephonic currents. This either involves the use of 
more powerful telephonic currents, as in No. 1, or some electric 
or mechanical contrivance, which, while preserving the sensitive- 
ness to telephonic currents, shall lessen the sensitiveness to in- 
duced currents. Efforts have been made in two directions to 
accomplish this: (a.) By inserting artificial resistances in the 
circuit, whereby the induced currents may be largely destroyed, 
but the telephonic currents are thereby so much weakened that 
not much is gained. (b.) By damping the vibration of the diaph- 
ragm, either by loading it with a weight, or pressing on it gently 
with the finger; this lessens induction disturbance, but, necessarily, 
enfeebles the articulation: something, however, is gained. 
3. By sifting out the induced currents through their difference 
in character from the telephonic currents. There is here also a 
threefold difference :— 
(a.) The induced currents are alternating, the currents from the 
telephone may be in one direction only. At the moment of clos- 
