An Improvement in Incandescent Electric Lamps.
Year: 1897

page_text: An Improvement in Incandescent Electric Lamps.
I, THEOPHILUS DAVIES FARRALL, of 82, Judd Street, in the County of London,
Electrician, do hereby declare the nature of this invention to be as follows:-
My invention relates to the production of light by electricity and in particular to
that kind or class of lighting known as incandescent electric lighting.
The object of my invention is to construct an improved incandescent electric
lamp which shall be more efficient than the lamps at present commonly in use.
According to my invention I utilise not only the ordinary resistant property of
a poorly conductive material to the passage of an electric current but also the
magnetic properties developed in the space immediately surrounding a conductor
by the current flowing therein, and for this purpose I so arrange the conductor
that the magnetic field surrounding one portion of the conductor interferes with,
or the lines of magnetic force in said field are cut by, the field or the lines of force
produced by or appertaining to the electric current flowing in the other portion of
the conductor. By this construction the heat imparted to the conductor by the
current passing through the resistant body of which it is made is supplemented by
the interference of the magnetic fields. In place of one continuous conductor I
may provide two or more conductors through which the current passes said con-
ductors being connected either in series or in parallel but being arranged so that
the current passes in the opposite direction in two adjacent conductors whereby
the two magnetic fields interfere as above described.
It is desirable that the adjacent conductors or portions of one conductor if only
one is provided should be located as near together as possible consistent with the
maintenance of insulation between the same, since the magnetic fields are most
intense close to the conductor and the heating effect of their interference increases
with the intensity of the fields. I prefer to place adjacent conductors so near that
when they are rendered incandescent they blend together and appear to form a
single light emitting surface.
In order that the nature of my invention may be more clearly understood I will
proceed to describe by way of example one method of carrying the same into
practice. I provide a single conductor which is of a refractory material having a
high electrical resistance such as carbon for example in the form of a filament or
wire. The filament or wire is wound in a double spiral that is to say wound into a
spiral and then wound backwards so that the current passes in opposite directions
in adjacent spires. The convolutions are made as close as possible without touch-
ing when rendered incandescent, and preferably so close that when hot the entire
spiral glows like a single solid body. In order to prevent oxidation and consequent
waste of the conductor it may be enclosed in an airtight chamber such as a glass
globe exhausted of air, suitable leading in wires being provided for leading the
current to the conductor as in ordinary incandescent electric lamps.
Lamps constructed in accordance with my invention have a higher efficiency
than ordinary electric incandescent lamps the conductor being raised to the

page_text: required temperature with a less current at the same potential difference than
would be required with lamps of the usual construction. A considerable saving in
the cost of supply is thereby effected and at the same time the cost of production
and the life of the lamp is not appreciably altered.
W. P. THOMPSON & Co.,
Patent Agents for the Applicant, 322, High Holborn, London, W.C.
I, THEOPHILUS DAVIES FARRALL, late of 82, Judd Street, now of 2, Ossulston
Street, Euston Road, in the County of London, 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:-
The object of my invention is to construct an electric incandescent lamp, which
shall be more efficient than the lamps of this description at present commonly in
use.
According to my invention I utilize not only the ordinary resistant property of
a poorly conductive material to the passage of an electric current but also the
magnetic properties developed in the space immediately surrounding the conductor
by the current flowing therein, and for this purpose I so arrange the conductor
that the magnetic field surrounding one portion of the conductor interferes with,
or the lines of magnetic force in said field are cut by, the field or the lines of force
produced by or appertaining to the electric current flowing in the other portion of
the conductor. By this construction the heat imparted to the conductor by the
current passing through the resistant body of which it is made is supplemented by
the interference of the magnetic fields. In place of one continuous conductor I
may provide two or more conductors through which the current passes said con-
ductors being connected either in series or in parallel but being arranged so that
the current passes in the opposite direction in two adjacent conductors whereby
the two magnetic fields interfere as above described.
It is desirable that the adjacent conductors or portions of one conductor if only
one is provided should be located as near together as possible consistent with the
maintenance of insulation between the same, since the magnetic fields are most
intense close to the conductor and the heating effect of their interference increases
with the intensity of the field. I prefer to place adjacent conductors so near that
when they are rendered incandescent they blend together, and appear to form a
single light emitting surface.
In order that my invention may be clearly understood, I will proceed to
describe the same with reference to the accompanying drawings in which
Figure 1 is an elevation of an improved lamp constructed according to my
invention.
Figures 2 and 3 are elevations of modified forms of filament.
Figure 4 is a plan and Figure 5 an elevation illustrating a further modifica-
tion and
Figure 6 is an elevation illustrating another shape.
Like letters of reference denote the same parts throughout the drawing.
The filaments are made of refractory material, having a high electrical resistance
such as carbon, for example. I propose to construct the filaments of any suitable
material.

page_text: In Figure 1, A is a glass globe, intended to be exhausted of air, and provided
with leading in wires B, like an ordinary incandescent lamp. The filament is
composed of a single wire or thread C of carbon or other suitable refractory and
ill-conducting material wound in a double spiral, that is to say, the filament is bent
into two continuous parallel branches, and said branches are together wound in
a single spiral. The current then in passing from end to end of the filament passes
in opposite directions in the two branches and therefore in opposite directions in
adjacent spires. The field of force of one spire are thereby caused to interfere with
the fields of force of the adjacent spires on both sides. The convolutions are made
as close as possible consistent with proper insulation, and preferably so close that
when incandescent the entire spiral glows like a single solid body.
Figure 2 shews a filament wound so as to envelop a cone. The bottom point of
the cone is supported, if necessary, from the side or the top of the lamp by a rod D
of any suitable material which will not of course make connection at its upper
end with the electric circuit. One or more such supports may be used when
required with filaments of other shapes.
Figure 3 illustrates a flat doubly wound spiral intended to be supported in the
lamp in a vertical plane, and Figure 4 is the plan of a similar spiral, Figure 5
being the elevation, this latter spiral being intended to be used in a horizontal
plane in the lamp. These flat spirals when brought to incandescence by the
passage of the current appear at a little distance like discs of light, and with
properly manufactured and operated lamps, the separate spires should not be able
to be distinguished when the lamp is lit.
In Figure 6 I shew a filament made of two spirals placed one inside the other,
being so arranged that the current passes in opposite directions in adjacent spires.
It will be obvious that there are a very considerable number of different shapes
of filament, which will fulfil the objects of my invention, and I do not confine
myself to the spiral shapes suggested.
Lamps constructed in accordance with my invention have a higher efficiency
than ordinary electric incandescent lamps the conductor being raised to the
required temperature with a less current at the same potential difference than would
be required with lamps of the usual construction. A considerable saving in the
cost of supply is thereby effected and at the same time the cost of production and
the life of the lamp is not appreciably altered.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the saine is to be performed, I declare that what I claim
is:
-
1. An electric incandescent lamp, the filament of which is so shaped that the
magnetic field set up by the current flowing in one portion of the filament is caused
to interfere with or cut the magnetic field produced by the current flowing in
another adjacent portion of the filament, substantially as described.
2. For an electric incandescent lamp a filament of refractory ill-conducting
material bent into a close doubly wound spiral so that adjacent parallel portions of
the filament have currents flowing through them in opposite directions and with a
supplementary rod for the filament if required, substantially as described.
3. The modification in which the single filament is replaced by two or more
separate spirals connected in series or in parallel but arranged so that the current
passes in the opposite direction in two adjacent conductors.
4. Incandescent electric lamps provided with filaments shaped substantially as
described.
THEOPHILUS D. FARRALL,
W. P. Thompson & Co.,
322, High Holborn, London, W.C., Patent Agents for the Applicant.