ACOUSTIC TELEGRAPHY. 
47 
without an interrupter. The line and the receiver of the distant 
station are connected with the secondary wire of the coil, the 
other end of which communicates with the receiver of the 
station and with the earth. It follows from this arrangement 
that the line currents are currents induced by the variations of 
intensity in the current which passes through the primary wire 
of the coil. The effect of this arrangement is to transform into 
tension currents the vibratory currents of the transmitter, and 
to make them less sensitive to the variations of the line resist¬ 
ance. It also renders the fittings of the apparatus more simple, 
and dispenses with a portion of the commutators, the manipu¬ 
lation of which might cause errors. 
The receiver is a Phelps telephone, similar to the Bell tele¬ 
phone, but with its magnet bent into the form of a ring, so that 
it is very easily handled. 
In the position of rest, or of waiting, the telephone is sus¬ 
pended on its hook, and in this position it causes a piece to 
turn, forming a commutator, which cuts off all the telephonic 
part of the circuit, and puts the electric bell into the circuit. 
Everything is then ready for a call. 
In taking up the telephone by the hand, the piece by again 
turning automatically resets all the connections with the 
telephone. 
The telephones of the clerks of the central station, trans¬ 
mitting and receiving, are similar to those of the subscribers ; 
but in order to facilitate the manipulation of these apparatus, 
the transmitter and the receiver are mounted on the same 
support, which is a little curved, so that it may be used as a 
handle, as shown in Fig. 15, while at the same time it forms 
the magnet of the receiver. 
We are now able to follow the whole series of the operations. 
Let us suppose that the subscriber No. 411, whom we may 
call Brown, wishes to correspond with No. 131, whose name, 
say, is Jones. Brown begins by several times pressing a small 
stud placed at the right-hand side of his desk. 
While the telephone is hanging, the result is that the cur¬ 
rent of Brown’s battery traverses the line and a small electro¬ 
magnet at the central station. This electro-magnet when thus 
excited allows a little door to open, and the slight noise it 
makes in doing so suffices to attract the attention of the 
