The telegraph manual: a complete history and description of the semaphoric, electric and magnetic telegraphs of Europe, Asia, Africa, and America, ancient and modern.

486 TELEGRAPH ELECTRIC CIRCUITS.
represented by fig. 3. Suppose, for example, the line is 300
miles, and the stations are thus arranged.
A d e f g B h i k 1 C
300 miles.
Stations A, B, and c, have main batteries and stations; d c f g
h i k and 1 are local. The current traverses the whole line
from A to c, passing through the coils or spools of the electromagnets throughout the whole line. If A transmits a message
to B, or c, all the other stations can receive the same. Every
magnet attracts and lets go its armature, every local circuit is
opened and closed, and every pen lever is put in motion. If A
wishes to send a message to all the stations, he transmits a
signal, which indicates that fact, and in proper time every
operator puts in motion the clock-work of his apparatus, and
the dispatch is indented upon the ribbon paper.
If the line be 600 miles long, and the battery arrangements
fail to charge it sufficient for telegraphing, it is the practice to
operate it by " compound circuits," and the application of an
apparatus called a repeater.
To thus arrange a line, it is necessary to sever the circuit at
the half-way station B, as represented by the following diagram.
The line is divided at B. The section between A and B is 300
A d e f g B h i- k 1 C
0oo 300 miles. ooo ooo 300 miles. ooo
miles long, and at A and B are earth wires and main batteries.
The section between B and c is the same as the former. At B,
there are two batteries and an apparatus that opens and closes
the next circuit in succession, from the station manipulating.
Thus, when A transmits to c, the circuit between A and B is
opened and closed by the operator at A, which, by the aid of
magnets, opens and closes the circuit between B and c. If c
wishes to respond, he opens his circuit and manipulates with
his key, which action is immediately perceived by the operator
at A. In the same manner d and 1, or any other of the stations,
can communicate one with the other. In general practice, it
is the custom for the lesser intermediate stations to transmit
their dispatches for places on other circuits, to the end station
of the section on which the local or intermediate station is
situated.