When a wire runs to a distant point from the main operating department
of the telegraph company in a large city, the same electric current
which runs through the key of the operator as he sits at his place,
busily sending messages, does not go out over the wire to that distant
point. It simply goes to the repeater room and operates a repeater,
which sends out another current over the long wire which leads to the
destination of the message. This is necessary because the condition
of the weather affects the lines and the current strength has to be
changed to suit the changing line conditions. The operators haven’t
time to make these adjustments, and so all the repeaters are grouped
together in the repeater room where they are under the watchful eyes
of experts. Here also are the delicate instruments which separate the
messages coming over duplex and quadruplex wires, by responding to
impulses of various strengths. These messages which have been separated
are then transmitted by the duplex or quadruplex repeaters to different
operators in the operating room, who hear their sounders tick out the
message just the same as if it came over a simple Morse wire.]
[Illustration: CABLES ENTERING A CENTRAL OFFICE.
You may not but your father will remember the time when in large cities
there were tall telegraph poles with hundreds of wires on them running
along the main streets, so that the town seemed to be bound with great
spiders’ web. That is all changed now, and the telegraph wires are run
through ducts, placed underground. For this purpose they are made up
in cables, and in the picture you see a number of cables entering a
central office.]
[Illustration: THE MARVEL OF TELEGRAPH INSTRUMENTS