ice currents is great.
They act as though they were not connected differentially, so far as
voice currents are concerned.

Because of the condensers serially in the telephone line, voice currents
can pass through it, but direct currents can not. Impulses due to
discharges of cores, coils, and capacities in the Morse circuit _could_
make sounds in the telephones, but these are choked out, or led to earth
by the 30-ohm impedance coils and the heavy Morse condensers.

=Ringing.= Ringing over simplex circuits is done in the way usual where
no telegraph service is added. Both telegraphy and telephony over
simplex circuits follow their usual practice in the way of calling and
conversing. In composite working, however, ringing by usual methods
either is impossible because of heavy grounds and shunts, or if it is
possible to get ringing signals through at all, the relays of the Morse
apparatus will chatter, interfering with the proper use of the telegraph
portion of the service.

It is customary, therefore, either to equip composite circuits with
special signaling devices by which high-frequency currents pass over the
telephone circuits, operating relays which in turn operate local ringing
signals; or to refrain from ringing on composite circuits and to
transmit orders for connections by telegraph. The latter is wholly
satisfactory over composite lines between points having heavy telegraph
traffic, and it is between such points as these that composite practice
is most general.

=Phantoms from Simplex and Composite Circuits.= Phantom and simplex
principles are identical, and by adding the composite principle, two
simplex circuits may have a phantom superadded, as in Fig. 469.
Similarly, as in Fig. 470, two composite circuits can be phantomed. This
case gives seven distinct services over four wires: three telephone
loops--two physical and one phantom--and four Morse lines.

[Illustration: Fig. 469. Phantom of Two Simplex Circuits]

[Illustration: Fig. 470. Phantom of Two Composite Circuits]

=Railway Composite.= The foregoing are problems of making telegraphy a
by-product of telephony. With so many telegraph wires on poles over the
country, it has seemed a pity not to turn the thing around and provide
for telephony as a by-product of telegraphy. This has been accomplished,
and the result is called a railway composite system. For the reason that
the telegraph circuits are not in pairs, accurately matched one wire
against a