Improvement in Incandescent Electric Lamps.
Year: 1892

page_text: Date of Application, 30th July, 1392-Accented, 3rd Sept., 1892
COMPLETE SPECIFICATION.
Improvement in Incandescent Electric Lamps.
I, ELIHU THOMSON, a citizen of the United States, residing at Swampscott,
County of Essex State of Massachusetts United States of America Electrician 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:
My invention relates to incandescent electric lamps, and its object is to improve
the details of lamps and sockets as hereinafter described.
In the accompanying drawings
Figure 1 is a vertical sectional elevation.
Figure 2 is a top plan view of the lamp.
Figure 3 is a vertical section of the socket taken on a plane at right angles to
Figure 1.
Figure 4 is a vertical section of a modified construction.
The glass bulb A is provided with a screw-threaded neck a, the threads being
formed in a portion of the wall of the exhausted chamber of the lamp. This may
be done by blowing the bulb in a screw-threaded metallic or other mould after
which the tube B, of glass, is inserted into the neck, and the ends of the tube and
neck are sealed together. Or, the tubular portion may be sealed to an unthreaded
bulb, the base of which is then heated, placed in a mould, and blown or pressed
into threads.
The tube B is closed at its inner end, but open at its outer end, thereby forming
a re-entrant pocket in the neck of the lamp. The leading-in wires C pass in through
the inner end of the tube. Their outer ends are each electrically connected with a
terminal, preferably arranged one within the other, as shown. The inner one D may
be a headed pin extending into the tube. The outer one E may be a ring, flanged
if desired, and resting upon or within the mouth of the tube, and preferably less in
diameter than the threaded neck of the bulb.
The space around the pin and beneath the ring is filled with any suitable plastic
substance F capable of withstanding the heat of the lamp, and of affording a firm
support to the terminals or contacts D, E. I prefer to use plaster of Paris and in
case it should be found that the tube B is broken by the expansion of this material
when it sets, a few grains of cork or other inert elastic material may be mixed with
the plaster or a plug of cork G, may be used. The tube B is formed with internal
irregularities b, such as grooves, depressions, knobs, beads, or the like to serve as
anchors for the plaster of Paris. Or it may be made with a narrowed mouth, to
serve the same purpose. The shank of the pin D may also be roughened, serrated,
or grooved, to give the plaster a firm hold upon it.
The socket is composed of a shell H, having one end threaded (preferably by
helical corrugations when the shell is made of sheet metal) to receive the threads
upon the lamp bulb. The body of the shell may be plain, and if preferred it may
be somewhat larger than the threaded portion to give ample room for the switch.
The base of the shell is secured to the cap I, which has the usual tapped opening
to enable the lamp to be fastened to a fixture.
Inside of the cap and the base of the shell is a plate K of insulating material, to
which is secured the switch mechanism. This may be of any suitable design, but it
is preferred to use a flat metallic spring L to bear upon the central contact D:
said spring being attached to the plate K or to a bracket L¹ carrying a binding
screw, by which one of the mains M is electrically connected with the spring L.
The other main M' is connected by a binding screw with a bracket N, fastened to

page_text: the plate K, and having depending ears in which is journalled the stem O. The
ear is slotted vertically to receive the inner journal of the stem, whereby said
stem is permitted to have more or less vertical play.
Mounted loosely on the stem is a block, P, having on each side of the stem a
recess in which plays the end of a pin p driven transversely through the stem, and
by which the block is caused to turn with the stem when the latter is rotated by
the thumb piece O'
the ear n¹.
Secured to the bracket N is a flat spring R, the free end of which presses
against the block P.
A tongue on the end of the spring is guided in the slot in
The parts are so proportioned that when the key is turned into the position shown
in Figure 1, the block P stands vertically, with one end bearing upon the outer
contact E. When the block is turned at right angles to this position, it does not
touch the ring E, and the circuit is broken.
In the modification shown in Figure 4 the lamp bulb is screwed into a sleeve S
which carries at its upper end a plates of insulating material, in the middle of
which is a screw plugs. A curved spring plate is secured to the under side of
the plate and is in electrical connection with the sleeve S.
This sleeve, its plate, the plug and the spring constitute an intermediate socket
or adapter which serves to connect the lamp bulb shown in Figure 1 with sockets
of ordinary construction. The bulb screws into the sleeve S: the central contact D
rests against the plugs and the outer contact E bears against the spring. The
sleeve in turn screws into the threaded shell T of the socket proper.
A shade can be readily attached to this lamp, by means of a nut U, of insulating
material, such as porcelain or hard rubber adapted to screw upon the neck of the
bulb or upon the socket and having an external groove to receive the neck-band of
the shade support V.
The above described construction has many practical advantages. The contacts
in the socket both press against the base of the lamp, holding it firmly in place by
taking up all possible play between the lamp and the socket. The lamp base is
stronger by reason of the screw-thread, and all strain comes directly upon the base
instead of on a part to which the base is secured. The base cannot be severed
without breaking the lamp.
The large surface of the screw-threads give sufficient friction to prevent the lamp
from shaking loose.
The outer shell of the socket is entirely unconnected with and insulated from the
electrical circuit, without special provision therefor. The shell can therefore be
made of any material (insulating or not) capable of withstanding the heat of
the lamp. This feature is of especial value in hasty installations or in those for
architectural effect.
The lamp is smaller, lighter, handsomer, and less expensive to make than any
lamp with which 1 am familiar.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. An incandescent electric lamp having an exhausted chamber formed with
external screw-threads for entering a socket, substantially as described, the lamp
being provided with contacts on its base, which are insulated by the material of the
lamp from the enclosing shell of the socket and are adapted to connect with
corresponding contacts in the said socket.
2. An incandescent lamp having its exhausted chamber provided with external
screw-threads adapted to enter the lamp socket, and a shade or shade holder having
a threaded opening adapted to engage with external screw-threads on the lamp
socket.
3. An adapter for incandescent lamps, consisting of a screw-threaded shell
adapted to receive and hold the neck of the lamp and provided with contacts

page_text: adapted to complete the circuit between corresponding contacts on the lamp and
the socket.
4. The method of making an incandescent lamp which consists in sealing within
the neck of the bulb a tube closed at its inner end, placing the neck in a screw-
threaded mould and blowing the glass into the neck of the mould, whereby screw
threads are formed upon the neck portion of the bulb.
Dated this 30th day of July 1892.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.