Improvements in Electrical Contacts.
Year: 1891

page_text: Date of Application, 7th Aug., 1891
Complete Specification Left, 7th June, 1892-Accepted, 9th July, 1892
PROVISIONAL SPECIFICATION.
Improvements in Electrical Contacts.
I, GEORGE FORBES, of 34 Great George Street, Westminster, in the County of
Middlesex, Engineer, do hereby declare the nature of this invention to be as
follows:-
The object of this invention is to provide a safe and convenient contact for
portable electric lamps and other translating devices or to act as a switch.
The two wires from the source of electricity terminate each in a plate of soft
metal as lead and the two wires connected with the translating device terminate
each in one or more needle points of hard metal as steel. To make contact the
needle points are pushed into the soft metal. In some cases more than one pair of
plates may be used.
When used as a single pole switch one plate and one set of needle points suffice.
In the case of switches the force required to tear the needles from the lead is
utilized to prevent arcing when this is an object. In this case, the needle points
come out of the lead with such a jerk that they cannot remain in proximity to the
lead so as to form an arc.
The invention is peculiarly well adapted for lighting a dining table by means of
a portable lamp without making holes in the table cloth while still concealing the
wires. In this and other cases the plates of lead may be held in an insulating
plate forming a flat block. The two sets of needle points may be each fixed in a
brass plate at the base of the lamp. The wires connected to the source of
electricity pass under the table cloth. Flat copper strips may be used under the
cloth in place of wires. The needle points pass through the cloth.
The arrangement. I prefer is as follows:-
I make the base of the lamp more or less bell shape so that it may stand flat on
the table whilst concealing a wooden or other disc within it, but with the table
cloth between, as the disc is placed on the table beneath the cloth.
A piece of lead about the size of a shilling is let into the disc at the centre,
whilst around this and insulated from it a ring of lead is embedded in the disc both
being flush with the upper surface. The rings are electrically insulated the one
from the other and to each at the underside of the disc a flat band of copper is
fixed. These bands are led to the edge of the table and beneath the table top they
are brought together in an insulating clip which is furnished with suitable fastenings
to connect with the electric leads.
Within the bell like base of the lamp and at the centre thereof are three or other
number of steel points, they are fixed to a conductor which supplies current to the
lamp filament or filaments.
set.
The other conductor supplying the filament or filaments is made to terminate in
an insulated metal ring into which also three or other number of steel points are
The whole is so arranged that as the lamp is placed on the table the steel
points within the base penetrate the leaden pieces in the disc upon the table and
so establish the required connections.
With a square base to the lamp it is convenient to use four lead and four brass
With a circular base
plates those at opposite corners being connected in parallel.
the plates are best formed of a central round disc and a concentric ring. The lamp
may have a cap at its base to cover the block under the table cloth.
Dated this 6th day of August 1891.
GEORGE FORBES.

page_text: ⋅
COMPLETE SPECIFICATION.
Improvements in Electrical Contacts.
I, GEORGE FORBES, of 34 Great George Street, Westminster in the County of
Middlesex, Engineer, do hereby declare the nature of this invention and in what
manner the same is to be performed to be particularly described and ascertained
in and by the following statement :--
The object of this invention is to provide a safe and convenient contact for
portable electric lamps and other translating devices or to act as a switch.
The two wires from the source of electricity terminate each in a plate of soft
metal as lead and the two wires connected with the translating device terminate
each in one or more needle points of hard metal as steel. To make contact the
needle points are pushed into the soft metal. In some cases more than one pair of
plates may be used.
When used as a single pole switch one plate and one set of needle points suffice.
In the case of switches the force required to tear the needles from the lead is
utilized to prevent arcing when this is an object. In this case, the needle points
⚫ come out of the lead with such a jerk that they cannot remain in proximity to the
lead so as to form an arc.
The invention is peculiarly well adapted for lighting a dining table by means
of a portable lamp without making holes in the table cloth while still concealing
the wires. In this and other cases the plates of lead may be held in an insulating
plate forming a flat block. The two sets of needle points may be each fixed in a
Brass plate at the base of the lamp. The wires connected to the source of electricity
pass under the table cloth. Flat copper strips may be used under the cloth in place
of wires. The needle points pass through through the cloth.
The arrangement I prefer is as follows:-
:-
I make the base of the lamp more or less bell shape so that it may stand flat on
the table whilst concealing a wooden or other disc within it, but with the table
cloth between, as the disc is placed on the table beneath the cloth.
A piece of lead about the size of a shilling is let into the disc at the centre,
whilst around this and insulated from it a ring of lead is embedded in the disc both
being flush with the upper surface. The rings are electrically insulated the one
from the other and to each at the underside of the disc a flat band of copper is
fixed. These bands are led to the edge of the table and beneath the table top they
are brought together in an insulating clip or connection which is furnished with
suitable fastenings.
Within the bell like base of the lamp and at the centre thereof are three or other
number of steel points, they are fixed to a conductor which supplies current to the
lamp filament or filaments.
set.
The other conductor supplying the filament or filaments is made to terminate in
an insulated metal ring into which also three or other number of steel points are
The whole is so arranged that as the lamp is placed on the table the steel
points within the base penetrate the leaden pieces in the disc upon the table and so
establish the required connections.
With a square base to the lamp it is convenient to use four lead and four brass
plates those at opposite corners being connected in parallel. With a circular base
the plates are best formed of a central round disc and a concentric ring. The lamp
may have a cap at its base to cover the block under the table cloth.
In order that my said invention may be fully understood and readily carried into
effect I will proceed to describe the drawings hereunto annexed.
DESCRIPTION OF THE DRAWINGS.

page_text: Figure 3 is a vertical section and shows the base of an electric table,lamp and in
connection with it a double pole contact maker.
Figure 4 is an underside view and Figure 5 is à section of some of the parts
shown in Figure 3.
Figure 6 shows a table with part of the contact maker upon it and made ready
to receive the electric table lamp.
Figure 7 illustrates a modification.
b
In Figures 1 and 2 a is a lever pivotted at the point & carrying a brass plate e in
which are fixed several needle points.
is a block of soft metal, as lead, held in a framework of harder metal, as brass,
and fixed to the slate or other base e.
g
h.
The lever a has a certain amount of lateral play, turning about the point bas
centre, so that it can take up any position between those indicated by the lines
This is to avoid the needle points always piercing the soft metal plate in the same
place.
The soft metal plate forms one terminal and the bolt the other terminal. When
it is desired to close the circuit, the lever carrying the needle points is moved from
the position shown by dotted lines, which it takes up when the circuit is
open, to
that shown in full lines, the needle points being forced to enter the soft metal plate
and make good electrical contact.
Sometimes it is advisable to place the soft metal block between vertical slides, so
that it can be moved up and down.
This enables the points of contact of the needle points and metal plate to be still
.further altered.
For a double pole switch the parts may be simply duplicated, the levers of the
two being joined by an insulating connecting piece pivotted on each; or one lever
may be used with an insulating cross bar carrying the two sets of needle points,.
provision being made for each set being connected electrically with its own wire.
Or a concentric arrangement may be used.
In Figure 3 A and B are two discs of insulating material as porcelain or slate,
A being fixed within the base X of the lamp C which is hollow or bell like in form,
and B resting on the table. The disc B is connected to the electric lighting circuit
by means of Hexible bare or insulated copper strips, (which may be of gauze) passed
around the edge of the table, as shown in Figure 6. The copper strips are drawn
together underneath by means of straps. The straps S may be sewn to the copper
strips or to pieces soldered thereto and drawn together by a buckle.
The ends of the strips may however be drawn together in any convenient way.
The copper strips are connected up to circuit wires led from any ordinary socket
arrangement in the floor or walls.
The disc A has, sunk below the surface, a ring of soft metal as lead A, and a
brass plate E carrying several needle points A².
These are put in electrical connection with the lamp filaments by means of the
wires F which pass through holes in the disc. In the disc B there is a central disc.
of lead B', and a ring of brass 12 carrying several needle points, both disc and ring
are sunk below the surface, and connected to the copper strips by means of the
short lengths of wire G G which pass through holes in the disc, and also through
the brass plates H H each wire and brass plate being then soldered together. The
copper strips are soldered to the brass plates H H.
The table cloth K K passes over the disc B. When the lamp carrying the
dise A is placed over it, the needle points pierce the cloth and enter the soft metal
plates and so put the lamp filaments in electrical connection with the main circuit:
The cavity over the brass pieces holding the needle points may be filled up, flush
with the surface of the disc, with a waterproof insulating cement. This, together
with the disposition of the needle points and the sinking of the lead pieces, reduces
any possible leakage of current through a damp cloth to a minimum.
The attachment between the copper strips and disc 13 may be made as shewn in
Figures 3, 4 and 5. The disc B has a slot cut across the under side, the section of

page_text: which is shewn in Figure 5. In this the conductors lie. A waterproof insulating
cement is applied all over the slot and conductors and a thin piece of vulcanite or
insulating material M is then slipped in from one end. The ends of the piece M
are bevelled off to allow the conductors a certain amount of play. When the lamp
is put upon the table the hollow base X guides it to its place over the disc B so as
to ensure the needle points encountering the soft metal.
A square base to the lamp is used as is indicated in Figure 7, in this arrangement
there are four corner pieces, two of which may be of lead and the other two carrying
needle points, the opposite corner pieces being connected in parallel.
Other arrangements may be adopted, such as having all the needle points on the
upper disc, and the lead pieces flush with the surface of the other disc, the lead
pieces being electrically connected to two plates of metal screwed to the under side
of the disc to which the copper strip would be joined.
Sometimes the base of the lamp stand has a ring of insulating material along the
edge to obviate danger of short circuiting the conducting strips. The lamp-stand
should be tolerably massive to give stability.
In place of lead any other metal may be used which the needle points are able to
penetrate so as to establish contact not only at their extremities but also at their
sides so that the contact extends from the sharp extremity for some distance along
each needle point.
Any metal which the points can so penetrate 1 term soft metal.
It is not necessary that the upper disc should be fixed to the lamp stand, but it
may be attached by a length of wire, which, with the two discs, would be concealed
under the base of the lamp when placed over them after making contact between
the discs. The lower disc may be sunk in the table.
Having now particularly described and ascertained the nature of my said invention
and in what manner the same is to be performed I declare that what I claim is :-
1. Electric contacts in which needle points on the one part are made to penetrate
into lead or other soft metal on the other part such needle points and soft metal
being connected with the circuit wires and a lever or other suitable mechanical
appliance being provided to force the points to penetrate the soft metal.
2. Electric contacts for lamps or other translating devices in which two conductors
leading from the source of electricity and two other conductors leading to the lanips
or translating devices are arranged to terminate the one pair in needle points, and
the other pair in soft metal, the said terminals being so arranged that the needle
points may be made to penetrate the soft metal or be withdrawn therefrom
according as it may be desired to close or to open the circuit.
3. The combination of parts substantially as described in respect to portable
table lamps consisting of the conductors L L lying beneath the table cloth, the
conductors upon the portable table lamp F F permanently in circuit with the light
emitting filaments; the soft. metal terminals A' B' of two of the said conductors
and the needle points penetrating the table cloth and forming the terminals of the
other pair of conductors.
4. The combination of parts substantially as described in respect to portable
table lamps consisting of the conductors L L in connection with the source of
electricity and terminating in the ring and central disc of the part B; the
conductors F F permanently in circuit with the light emitting filaments and
terminating in the ring and central disc of the part A and points on one terminal of
each pair of conductors penetrating into the other terminal and the hollow or bell
like base of the lamp enclosing the contact parts and serving to guide the lamp
to its proper position as it is placed upon the table.
5. Electrical contacts substantially as herein described and shewn.
CARPMAEL &. Co.,
Agents.