IMPROVEMENTS IN TELEPHONIC APPARATUS AND ELECTRIC CALL. BELLS
Year: 1882

page_text: PROVISIONAL SPECIFICATION left by Henry George Ellery and John
Thomas Gent at the Office of the Commissioners of Patents on the 27th October
1882.
HENRY GEORGE ELLERY, trading as John, T. Gent & Co. of Faraday Works,
Leicester and JOHN THOMAS GENT of 63 Hinckley Road, Leicester, in the county
of Leicester, Electricians "IMPROVEMENTS IN TELEPHONIC APPARATUS AND
ELECTRIC CALL. BELLS
"
This invention relates first to improvements in telephone receivers. In carrying
out this part of our invention instead of a diaphragm of metal capable of being
acted upon by undulatory magnetic currents and itself capable of producing induced
currents by its vibrations when in proximity to a magnet, the said diaphragm
being usually an iron disc placed at right angles to the length of the magnet and
resting so far as its circumference is concerned upon the wooden cases and firmly
secured by the cap or cover; we propose to substitute a thin bar of iron or steel
slightly curved and of sufficient length to rest with its ends in cavities provided in
the sides of the cases containing the magnet, in these cavities are inserted small
pieces of metal upon which the ends of the bar rest and which allow them to move
freely when set in motion by the vibratory currents of the magnet, the grooved
cavities must be of sufficient depth that when the cover securing the tympan is
fastened to the case the curved bar is free to lengthen outwards when brought
nearer the straight line by the action of the magnet near to the face of which it
rests but not in contact therewith. The length of the bar will depend upon the
form of the case in which it is to be mounted and bears no relation to the size and
shape of the tympan placed immediately over it and which may be of ebonite,
mica, wood, cork, brass or other non-magnetic substance. The said tympan may
also be of any shape, (round or square) and secured in the most convenient manner
so as to press lightly against the metal bar and be capable of moving with it, so
that when pulsatory currents are sent through the magnet producing vibrations of
the curved bar-the same is transmitted with the tympan reproducing sound waves
corresponding to those by which the undulatory currents in the magnet were
originated.
The width of the plate or bar which we have found to give good results is a
little less than the diameter or width of the pole of the magnet against which it

page_text: vibrates, thus if the pole of the magnet is three eighths of an inch in diameter the
plates ould he one thirty second of an inch less than three eighths of an inch.
We have found that if two of these instruments be coupled together they will
not produ e when spoken to sufficient magnetic action in the helix of the magnet
to transmit and reprod ce the vibrations at each end and cannot be used inter-
changeably, these improved instruments are therefore to be used as receivers only
and inrst receive the impulses from a transmitter having microphone arrangements
in connection with a secondary coil; a modification of the form invented by
Professor Hughes in which carbon points are placed in loose contact is found to
give good results.
It wou'd appear that when the tympan and har are attempted to be usel as a
transmitter the nature of tho material admits of its yielding to the impact of the
sound waves the bar also not being rigid does not auswer to the vibrations of the
tympan and so when spoken to no currents are set up in the helix surrounding the
magnet.
In the centre of the curved bar above described a small-projecting button is
placed so that the centre of the tympan only may come in contact with the centre
of the bar, this provision together with the metal plates on which the ends of the
bar move give a greater and easier motion to the tympan and bar when the
undulatory currents are produced in the magnet, emitting a clear and loud volume
of sound considerably louder than can be given by a tympan bound round its edges
and being capable of being magnetized. The bar described must not touch either
of the poles of the magnet or be secured in any way other than by the slight
pressure of the tympan against the projecting button.
Our invention also relates to an improvement in the transmitting apparatus for
which Letters Patent were granted to John Thomas Gent and Henry George Ellery
dated the twenty fourth day of May one thousand eight hundred and eighty one,
N° 2265.
In the specification of the said Lotters Patent the various parts therein described
are secured to a sounding board attached to the door of the case, but according to
our present improvements we remove the series of metal arms therein described
from the door altogether and mount them upon two bars of wood placed across the
caso containing the other parts of the apparatus; to one bar of wood wo attach
brackets carrying the metal arms and to the other bar of wood we attach the
carbon plates on which rest the pieces of carbon carried by the arms, by this
improvement the sound waves fall direct upon the metal arms without the inter-
vention of any sounding board or diaphragin and may be used when the door
stands open or the door may have a large opening cut in it and covered with a
piece of perforated zinc or gauze made to open, so as to protect the interior parts
from injury, all connections and other arrangements are as described in the above
named specification.
Our invention also relates to an improved construction of electric call bell to be
used in conjunction with the before described apparatus or for other signalling
purposes the object of the improvements being to obtain more effective results in a
simpler manner and at less cost than by any other construction of signal bell with
which we are acquainted. Usually these bells or signalling apparatus consist of an
armature or keeper carrying a hammer for striking the bell, the armature being
attached by one end to springs or working on pivots or bearings and standing
lengthwise to the ends of the poles of the magnet making and breaking contact
with thyment to and fro in front of the said magnet's poles. By our improve-
ments instead of the ordinary electro-magnet whose poles terminate at the end of
the spools or plates provided to keep the wire wound around them in its proper
place we allow the ends of the cores of the magnet to project sufficiently for the
armature to play on the top or bottom of the projection and we file the projection
at an angle and suspend the armature so as to move to and from the face of the
Bame; by this means we obtain a greater magnetic surface and by suspending the
armature over it its face is at equal distance in all opposite points, presenting a

page_text: large magnetic surface and exerting a greater influence upon the armature whenever
a current of electricity is sent through the helix surrounding the cores.
The armature as usually constructed, does not stand at equal distance from the
poles of the magnet at all points, unless it be pivotted or work in bearings when a
great loss of power is experienced in giving the necessary motion to the hammer
which strikes the bell.
By our improvements the armature is suspended by means of a metallic spring,
the same being part of the case upon which the magnet and bell are secured, but
bent round in such a manner that the armature when at rest is held by it at the
desired distance under or over (as may be preferred) the projecting ends of the
magnet, a projecting end of the spring being in contact with an adjustable screw
and platinum points so arranged that on passing a current through the helix, the
usual wake and break action is imparted to the points of contact and a to and fro
movement given to the arinature and hammer operating upon the bell. The best
mode of attaching the spring is by screws passing into the base plate at one end
and into the armature or an elongation of it at the other end. By this method of
suspending the armature in face of an extension of the poles of a magnet, coils of
about one half the size and quantity of wire are required to produce au equal force.
upon the armature as compared with those of an ordinary bell.