IMPROVEMENTS IN ELECTRO-TELEGRAPHIC APPARATUS
Year: 1881

page_text: PROVISIONAL SPECIFICATION left by Jocelyn Home Thomson at the Office
of the Commissioners of Patents on the 3rd May 1881.
JOCELYN HOME THOMSON, of Shoeburyness, in the County of Essex, Lieutenant
Royal Artillery. "IMPROVEMENTS IN ELECTRO-TELEGRAPHIC APPARATUS."
My Invention relates to improvements in step by step electric telegraphs, and it
has for its principal object to enable the needles or pointers to be rotated in either
direction. The Invention is more particularly applicable to indicators and similar
instruments which have a comparatively slow motion, but it may also be applied
to telegraphic purposes generally.
The transmitter consists of a serrated wheel rotated in unison with or in a certain
definite ratio to the index of the transmitter, and whose teeth by the movement of
the wheel in either direction cause electrical contacts to be made in such manner
as to put the one pole of the battery to earth and the other to line, or vice versa,
according to the direction in which the wheel is rotated.
A convenient arrangement consists of a V piece of ivory mounted on a centre
in such position. as to be oscillated by the teeth of the wheel. Two springs
respectively connected with the poles of the battery press against the base of the
V piece and hold it in its normal position, and at same time respectively make
electrical contact with two spring pallets insulated from one another, and mounted
the one above and the other below the V piece in such a position as to be struck
by the teeth of the wheel and make momentary contact therewith at the instant
the V piece escapes from the tooth. In the normal position of the V piece between
two teeth of the wheel, the first mentioned springs are held just off two contacts,
both in connection with the same line wire, but on the V piece being oscillated by
a tooth of the wheel the one spring is allowed to fall onto its contact (at same time
that contact is broken between said spring and the corresponding spring pallet on the
V piece) thus putting the one pole of the battery to line, whilst the contact of the
other spring with the corresponding spring pallet of the V piece remains unbroken,
and the other pole of the battery is put to earth by the contact of this spring pallet
with the tooth of the wheel. A momentary current is thus sent through the line
wire and it will be evident that if the direction of rotation of the wheel be
reversed the action above described, and consequently the current, will also be
reversed.

page_text: The receiver consists of a wheel rotated in either direction by a propelment
capable of being adjusted to move the receiver as small a portion of a revolution
at each step as may be desired, so that its rotation shall be in unison with or in
any given ratio to that of the toothed wheel of the transmitter. The wheel of the
receiver has a smooth or roughened periphery, and its propelment consists of a
nipping lever pivoted to the extremity of a radius arm or arms pivoted on the
axis of the wheel and held in position by a spring.
The nipping lever is magnetised, and it is pivoted by one of its ends close to
the periphery of the wheel, so as when oscillated in either direction it will bind
against the wheel and carry it round, and the other end or pole of the lever is
situated between the dissimilar poles of two electro magnets in the circuit of the
line wire. When a current passes the lever is attracted by one or other electro
magnet and moves the wheel, and when the current ceases it is returned to a
position midway between the electro magnets by its attraction for a piece of iron
fixed opposite this point, the wheel being prevented from returning with it by
friction. By adjusting the distance between the electro magnets the distance
moved at each step can be made as small as desired, the rate of revolution of the
toothed wheel of the transmitter being increased in proportion by multiplying gear
introduced between the said wheel and the needle of the instrument, so as to make
the needles of the two instruments synchronous.