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iS77*J Recent Advances in Telegraphy . 
much that the local relay no longer avails, and recourse 
must be had to another device. This consists in adding a 
derived or loop circuit to the bridge wire, consisting of a 
condenser, c, eledtro-magnet, m, and adjustive resistance, r. 
The eledtro-magnet is set so as to add upon the other end of 
the tongue of the neutral relay, as shown. In this way, 
when a change of current takes place, the discharge from 
the condenser through m serves to keep the tongue in its 
place until the critical time is past ; r is merely for adjust- 
ment. By these ingenious contrivances Messrs. Prescott 
and Edison have rendered their quadruplex system a prac- 
tical success. Within the last few years other systems, 
more or less similar, have been devised, but as yet theirs is 
the only one of note. 
Telephonic Telegraphy. 
a. The Tone Telephone . 
The last five years have seen the practical development 
of this interesting branch of telegraphy. For many years 
back attempts have been made to transmit musical tones 
or articulate sounds to a distance by means of electricity, 
but the results were at best only hopeful until, in i860, Herr 
Phillip Reis, of Homburg, profiting by the researches of 
Wertheim, Marian, and Henry, invented the first telephone. 
In Reis’s telephone a stretched membrane is set into vibra- 
tion in unison with the sound to be transmitted, and, by a 
little contadt-piece which it carries, this vibrating membrane 
is caused to interrupt the eledtric current circulating in the 
line. The current so interrupted is utilised at the distant 
station to produce a sound similar to the original sound at 
the near or sending station. To produce such a sound Reis 
made use of Page’s discovery, that an audible “ click ” ac- 
companies the demagnetisation of a bar of iron inserted in 
an eledtro-magnetic helix. He surrounded an iron wire 
with a helix, and caused the interrupted current from the 
sending station to pass through the helix to earth. At every 
interruption a distindt sound was given out by the iron core, 
and the joint effedt of these reproduced a note of the same 
pitch as that sounded at the sending station. 
In telegraphy, however, the telephone only acquires spe- 
cial importance when it is regarded as a means of multiplex 
transmission. A single message by telephone can have 
small advantage over the ordinary methods ; so Reis’s 
telephone was negledted as a kind of scientific curiosity, 
a c 2 
