IMPROVEMENTS IN ELECTRIC TELEGRAPHS
Year: 1859

page_text: PROVISIONAL SPECIFICATION left by William Andrews at the Office of
the Commissioners of Patents, with his Petition, on the 25th January
1859.
I, WILLIAM ANDREWS, of 30, Cornhill, in the City of London, Engineer of
the Submarine Telegraph Company, do hereby declare the nature of the
Invention for "IMPROVEMENTS IN ELECTRIC TELEGRAPHS," to be as follows:-
This Invention has for its object improvements in electric telegraphs. In
telegraphing through long lengths of telegraphic lines, it is sometimes
desirable to employ a relay instrument at a place intermediate of the two
terminals, so that the relay instrument may receive the currents transmitted
to it from one terminal, and be actuated by them in such manner as to
forward to the other terminal, from a battery in connection with the relay
instrument, other currents corresponding with those which the relay instrument
receives. Now, if the line wires between the relay and the terminals be
submarine or subterranean, its action is much interfered with by the return
or induced currents which enter the relay instrument. To overcome this
difficulty is the principal object of my Invention.
The relay instrument which I employ consists of two magnetic bars, each
balanced on a knife-edge or otherwise, and having an electro-magnet or
electro-magnets under each of their poles. The coils of the electro-magnets
are connected with the line wires in either direction, so that the electro-
magnets which act on one magnetic bar receive all the currents entering the
instrument by one line wire, and the electro-magnets of the other bar all the
currents by the other line wire. The receiving instruments employed at the

page_text: two terminals are of such a description, that the currents which actuate them
may always be passed in one direction. When a current is sent from one of
the terminal stations to the relay, it passes by an insulated arm and wire
attached to the magnetic bar of one set through the coils of the other set of
electro-magnets to the earth, there being a permanent connection between
these coils and the earth. The electro-magnets of this set being thus mag-
netised, act on their magnetic bar, the one attracting and the other repelling
it, and both tending to cause it to move. The effect of the motion is to make
a connection between the relay battery and the line wire to the other terminal
station, and also to break the connection between this line wire and the
electro-magnet coils of the other set, otherwise the battery current would pass
through those coils to the earth. Immediately the original current ceases,
the magnetic bar displaced by it is drawn back by a spring to its former
position, and the relay battery circuit is broken, the return or induced current
of the relay battery now comes back by the line wire to the relay instrument,
and passes (by the connection now re-made) to its electro-magnet coils, and
thence to earth. But this induced current, although it magnetises the
electro-magnets, does not move the magnetic bar, for it is of an opposite
polarity to the telegraphic currents from the terminal stations, and so only
tends to assist the spring which holds the magnetic bar in its position of rest:
Thus the induced current immediately it is produced is drawn out of the line
wire, and prevented from interfering with the action of the telegraph. As the
induced currents, in passing through the coils of the electro-magnets, have a
tendency to maintain a magnetism of opposite polarity to that produced by
the telegraphic currents, I arrange permanent magnets, the ends of which
may be approximated to the electro-magnets, so as to induce magnetism into
them to any desired extent to assist the telegraphic currents. The same
maguets may also be employed to moderate the action of the telegraphic
currents, should they be too powerful.
A portion of the instrument above described, that is to say, one of the
magnetic bars with its electro-magnets and other adjuncts, may be employed
to complete the circuit of a local battery, as is required to work a Morse's o
other similar instrument.