IMPROVEMENTS IN ELECTRIC LAMPS
Year: 1882

page_text: PROVISIONAL SPECIFICATION left by Charles Scott Snell at the Office of
the Commissioners of Patents on the 24th August 1882.
CHARLES SCOTT SNELL of No. 46 Tudor Road Hackney in the County of
Middlesex "IMPROVEMENTS IN ELECTRIC LAMPS
"
According to the present invention a rod carrying the upper carbon of an electric
lamp passes through two coils one of which is of thick wire and carries the main
current while the other is a potential or shunt circuit of fine wire, these coils being
so arranged relatively to each other and to a piece or pieces of soft iron, that the
magnetism of the latter tends to move the rod either by attraction or repulsion, in
opposite directions, the combined effect being such as to keep the rod in equilibrium
so long as the carbons remain at the distance which gives a maximum intensity of
light, while the increase of the current in the potential circuit consequent on the
burning away of the carbons causes the rod to be moved downwards, bringing
the carbons nearer together. Should the light become extinguished, the potential
circuit would cause the rod to descend until the carbons came in contact, and the
current then increasing in the main coil and diminishing in the potential coil, would
cause the rod and its carbon to be raised until the before mentioned position of
equilibrium had been again attained.
Various arrangements may be employed for carrying out the above described
mode of operating; thus according to one arrangement the main current coil is
arranged above the potential coil, each coil being in two parts that are wound in
opposite directions and the one part of each coil has a soft iron lining or sleeve
through which the before mentioned rod passes. The sleeve of the main current
coil is magnetised by the part of the coil surrounding it, while the contiguous part
of the rod beyond the sleeve, being surrounded by the other part of the main coil
wound in the contrary direction, will consequently be magnetised oppositely to the
sleeve, thus causing poles of like sign respectively on the upper end of the sleeve
and on the rod to face each other, whereby the rod will be repelled by the sleeve,
which will tend to make it rise. In the same manner the sleeve of the potential
coil being magnetised in the contrary direction to the part of the rod situated in
the other part of this coil, the sleeve will repel the rod in the contrary direction to
the action of the main coil, tending to move the rod downwards. The coils are so

page_text: adjusted that when the carbons are at the normal distance apart, the upward repelling
force of the main coil sleeve will exactly balance the downward repelling force of
the potential coil sleeve acting in combination with the weight of the rod and
carbon, while any increase in the distance of the carbons will produce an increased
repelling force of the potential coil and a decrease of that of the main coil, causing
a downward motion of the rod and carbon as before stated. The contrary action
will take place when an excess of current passes through the main coil. This
relative action of the two coils will consequently be resolved into a steady forward
motion of the carbon as the lamp burns, preventing all flickering due to fluctuating
supply.
The rod is by preference constructed of a number of thin sheet iron discs
insulated from each other and tied together by a brass rod passing through them
and secured at the ends by screws; by this means only the portions of the rod
within the coils will become magnetic. A plain soft iron rod may however also
be used.
According to a modification of this arrangement, only the main coil is divided
and provided with magnetic sleeve as described, the potential coil being made to
act directly on the rod so as to induce magnetism therein in such manner as to
produce the before described repelling force of the main coil sleeve.
According to another modification, instead of making each coil of two parts
wound in contrary directions as described, and containing a soft iron sleeve, I
provide at the end of each coil one or more electromagnets the coils of which form
continuations respectively of the main and potential coils, while their cores are so
magnetised and placed as to present poles towards the rod that are of like sign
with the poles formed on the contiguous part of the rod within the main and
potential coils. Thus the electromagnets of the main coil tend to repel the rod
in one direction while those of the potential coil repel it in the contrary direction
as before described. In this case the potential coil would be arranged above the
main coil. This arrangement may also be modified by employing electromagnets
only in connection with the main coil, the potential coil being made to act directly
on the rod.
According to another modification a single thick disc of soft iron is placed between
the two coils, and being magnetised thereby will tend to move the rod in one
direction or the other according as the parts of the rod within the respective coils
have their magnetism increased or diminished owing to an increase or decrease of
the main or potential current.
Or, according to another modification a disc of soft iron is placed at the outer
end of each of the coils, which being magnetised, tend to attract the rod in contrary
directions.
When the rod is built up of insulated iron discs as described, these are so arranged
as to be farther apart in the upper part of the rod, than in the lower part, so that
the magnetic force will be decreased as the rod descends, thus compensating for the
decrease of the weight on the rod due to the consumption of the carbon.
When a
solid or tubular iron rod is employed its mass may be decreased towards the upper
end for the same purpose. The rod may be slightly held between springs to prevent
excessive sensitiveness in its motion.
When the arrangement with the magnetised sleeves first described is employed
these sleeves are by preference not made cylindrical but with their inner ends of
enlarged diameter so as to be farther removed from the rod than the outer ends
which alone exercise the repelling power.