Improvement in Carbon Pencils for the Electric Arc-light.
Year: 1896

page_text: Date of Application, 17th Mar., 1896
Complete Specification Left. 12th Dec.. 1896-Accepted. 27th Feb., 1897
PROVISIONAL SPECIFICATION.
Improvement in Carbon Pencils for the Electric Arc-light.
THOMAS CRADOCK HEPWORTH Lecturer of 10 Lysias Road Balham Hill,
London, S.W. do hereby declare the nature of this invention to be as follows:-
In using the electric arc-light for purposes of projection, such as the optical, or
magic lantern, lamps for theatrical effects, search lights & lighthouses, it is known
that when only an alternating current of electricity is available to feed such arc-lights
the light afforded is very poor compared with that given by a continuous current at
the same pressure. The chief reason for this falling off in the light given may be
explained thus:-When the continuous current is used, the light comes wholly from
the crater formed in one of the carbons. But with the alternating current a less
developed crater is formed in each carbon & the light from one is obstructed by the
other owing to their close proximity. Moreover, just in the place where, in pro-
jection apparatus the greatest luminosity is required-i.e. in a horizontal direction
from the arc, there is an area of comparative darkness marked by a violet coloured
band, which greatly detracts from the efficiency of any projection apparatus with
which the alternating current is employed. Now, I eliminate this band of com-
parative darkness by using carbons of a certain design. Such carbons may be
round, elliptical oval or of any other sectional form & they contain an inner core
of softer material than that composing the body of the carbon pencil. This core
is eccentric to the carbon in which it is formed, & of which it forms part, so
that it is brought much nearer to the face of the apparatus than if it were con-
centric as is usual in carbon pencils.
This arrangement causes the formation of two craters on the front edges of the
carbons instead of in their centres, resulting in a great accession of light power,
& greater regularity in consumption.
Dated this 16th day of March 1896.
Improvement in Carbon Pencils for the Electric Arc-light.
THOMAS CRADOCK HEPWORTH Lecturer 10 Lysias Road, Balham Hill London, S. W.
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 :-
In using the electric arc-light for purposes of projection such as the optical or
magic lantern, lamps for theatrical effects search lights & lighthouses, it is known
that when only an alternating current of electricity is available to feed such arc-
lights, the light afforded is very poor when compared with that given by a continuous
current at the same pressure. The chief reason for this falling off in the light
given may be explained thus:-When the continuous current is used, the light comes
wholly from the crater formed in one of the carbons. But with the alternating
current a less developed crater is formed in each carbon pencil, and the light from
one is obstructed by the other owing to their close proximity. Moreover, just in

page_text: the place where, in projection apparatus the greatest luminosity is required, namely,
in a horizontal direction from the arc, there is an area of comparative darkness
marked by a violet coloured band, which greatly detracts from the efficiency of any
projection apparatus with which the alternating current is employed.
Now, I eliminate this band of comparative darkness by using carbon pencils of
a certain design. Such carbons may be round, elliptical, oval, or of any other
sectional form & they contain each an inner core B of softer material than that
composing the body of the carbon pencil A. This core B is eccentric to the carbon
pencil in which it is formed & of which it forms part, so that it can be brought
much nearer to the front of the apparatus in which it is used than if it were
concentric as is usual in carbon pencils.
Having now particularly described & ascertained the nature of my said
invention & in what manner the same is to be performed, I declare that what
I claim is,
An eccentric core to carbon pencils used in the electric are light, when that
light is fed by an alternating current of electricity.
Dated this Eleventh day of December 1896.
T. C. HEPWORTH.