Telegraph, Over-house.
An English term for telegraph lines led over houses and supported on
standards on the roofs.
Telegraph Pole Brackets.
Arms for carrying insulators, which arms are attached to telegraph poles
or other support. They vary in style; sometimes they are straight bars
of wood gained into and bolted or spiked in place; sometimes they are of
iron.
Telegraph, Printing.
Various telegraphs have been invented for printing in the ordinary
alphabet the messages at the receiving end of the line.
Representative instruments of this class are used for transmitting
different market and stock reports to business offices from the
exchanges. The type faces are carried on the periphery of a printing
wheel, which is rotated like the hand of a dial telegraph, and against
whose face a paper riband is pressed whenever the proper letter comes
opposite to it. As each letter is printed the paper moves forward the
space of one letter. Spacing between words is also provided for. In the
recent instruments two lines of letters are printed on the paper one
above the other.
In England, and on the continent of Europe, printing instruments have
received considerable use for ordinary telegraphic work. Hughes' type
printer and Wheatstone's ABC telegraph meet with extensive use there for
ordinary transmission.
Telegraph, Quadruplex.
Duplex telegraphy is the sending of two messages in opposite directions
simultaneously through the same wire. Duplex telegraphy is the sending
of two messages simultaneously in the same direction. The two combined
constitute quadruplex telegraphy. [SIC]
The system was suggested by Stark of Vienna and Bosscha of Leyden in
1855; the successful problem was solved by Edison in 1874.
The principle is based on the two orders of difference in electric
currents; they may vary in strength or in direction. Thus we may have
one instrument which works with change of strength of current only, the
other with change of direction only. The two can be worked together if
the direction of the current can be altered without alteration of
strength, and if strength can be altered without alteration of
direction. Double current and single current working are so combined
that one relay works by one system of currents and another relay by the
other system. A current is constantly maintained through the line. The
relay operated by change in direction is a simple polarized relay which
works by change of direction of current. The relay operated by change in
strength is the ordinary unpolarized relay.