ting circuit
because the transmitter would produce fluctuations in the steady
current flowing in the line and thus be able to affect the distant
station. The transmitter, therefore, has a direct action on the
currents flowing in the line by the variation in resistance which it
produces in the line circuit. There is, however, a subsidiary action
in this circuit. Obviously, there is a drop of potential across the
transmitter terminals due to the flow of steady current. This means
that the upper terminal of the condenser will be charged to the same
potential as the upper terminal of the transmitter, while the lower
terminal of the condenser will be of the same potential as the lower
terminal of the transmitter. When, now, the transmitter varies its
resistance, a variation in the potential across its terminals will
occur; and as a result, a variation in potential across the terminals
of the condenser will occur, and this means that alternating currents
will flow through the primary winding of the induction coil. The
transmitter, therefore, by its action, causes alternating currents to
flow through the primary of this induction coil and it causes, by
direct action on the circuit of the line, fluctuations in the steady
current flowing in the line. The alternating currents flowing in the
primary of the coil induce currents in the secondary of the coil which
supplement and augment the fluctuations produced by the direct action
of the transmitter. This circuit may be looked at, therefore, in the
light of combining the direct action which the transmitter produces in
the current in the line with the action which the transmitter produces
in the local circuit containing the primary of the induction coil,
this action being repeated in the line circuit through the secondary
of the induction coil.

The receiver in this circuit is placed in the local circuit, and is
thus not traversed by the steady currents flowing in the line. There
is thus no necessity for poling it. This circuit is very efficient,
but is subject to the objection of producing a heavy side tone in the
receiver of the transmitting station. By "side tone" is meant the
noises which are produced in the receiver at a station by virtue of
the action of the transmitter at that station. Side tone is
objectionable for several reasons: first, it is sometimes annoying to
the subscriber; second, and of more importance, the subscriber who is
talking, hearing a very loud noise in h