d is thereby retarded in
rising to its full strength. Consequently no sound is heard in a
telephone, T, inserted in the line-circuit. Neither the currents which
start from one end nor those which start from the other will affect
the telephones inserted in the line. And, if these currents do not
affect telephones in the actual line, it is clear that they will not
affect telephones in neighboring lines. Also the telephones so
inserted in the main line might be used for speaking to one another,
though the arrangement of the telephones in the same actual line would
be inconvenient. Accordingly M. Van Rysselberghe has devised a further
modification in which a separate branch taken from the telegraph line
is made available for the telephone service. To understand this
matter, one other fact must be explained. Telephonic conversation can
be carried on, even though the actual metallic communication be
severed by the insertion of a condenser. Indeed, in quite the early
days of the Bell telephone, an operator in the States used a condenser
in the telegraph line to enable him to talk through the wire. If a
telephonic set at T1 (Fig. 2) communicate through the line to a
distant station, T2, through a condenser, C, of a capacity of half a
microfarad, conversation is still perfectly audible, provided the
telephonic system is one that acts by induction currents. And since in
this case the interposition of the condenser prevents any continuous
flow of current through the line, no perceptible weakening will be
felt if a shunt S, of as high a resistance as 500 ohms and of great
electromagnetic rigidity, that is to say, having a high coefficient of
self-induction, be placed across the circuit from line to earth. In
this, as well as in the other figures, the telephones indicated are of
the Bell pattern, and if set up as shown in Fig. 2, without any
battery, would be used both as transmitter and receiver on Bell's
original plan. But as a matter of fact any ordinary telephone might be
used. In practice the Bell telephone is not advantageous as a
transmitter, and has been abandoned except for receiving; the Blake,
Ader, or some other modification of the microphone being used in
conjunction with a separate battery. To avoid complication in the
drawings, however, the simplest case is taken. And it must be
understood that instead of the single instrument shown at T1 or T2, a
complete set of telephonic instruments, including transmitter,
battery,