Improvements in or relating to Magnetically Affecting the Counter Electro-motive-force of the Voltaic Arc of an Electric Arc Lamp.
Year: 1896

page_text: Date of Application, 19th May, 1896-Accepted, 27th June, 1896
Improvements in or relating to Magnetically Affecting the Counter
Electro-motive-force of the Voltaic Arc of an Electric Arc Lamp.
A communication by CHARLES LEWIS COFFIN, of 980, Jefferson Avenue, Detroit,
in the County of Wayne and State of Michigan, United States of America,
Chemist.
1, WILLIAM PHILLIPS THOMPSON, F.C.S., M.I.M.E., of The Agency for
Foreign Patent Solicitors, 6, Lord Street, Liverpool, and 6, Bank Street,
Manchester, both in the County of Lancaster, 118 New Street, Birmingham, in
the County of Warwick, and 322 High Holborn, in the County of Middlesex,
Civil 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 :-
This invention consists in an improvement in apparatus for magnetically affecting
the counter electro-motive-force of the voltaic arc of an electric arc lamp, herein-
after fully described and claimed.
It is well known that when a current of electricity is caused to flow across a gap
between two electrodes, an effect of great heat and light is produced, which we
call a voltaic arc, and that the production of this arc is attended with considerable
resistance to the flow of said current. It is believed that this resistance is not due
solely to the imperfect conductivity of that part of the circuit in which the arc is
formed, but that the voltaic arc itself exerts a distinct, positive and powerful
influence or counter E.M.F. against the flow of the current which produces the
arc, and that if means can be found for wholly or partially neutralizing this
counter E.M.F., the size of the voltaic arc produced by a given current can be
considerably increased.
The inventor has discovered that if a magnet be placed in such relation to a
voltaic are that the lines of its field of force are parallel with, and in the same
direction as, the current producing the arc, that is, if the positive carbon of an
electric lamp be encircled by a magnet whose north pole is nearest the end of said
carbon, the effect of said magnet will be to increase the size of the arc formed
between said carbon and the negative carbon, with a given current.
To illustrate this invention, a single carbon lamp, Figure 1 has been shown being
an elevation of said lamp, and Figures 2 and 3 being elevations of part of the two
carbons.
F represents the frame of the lamp, C and C¹ the positive and negative carbons,
respectively, and A an electro-magnet having a core B shown in this case as a
hollow core, large enough to allow carbon C to pass through it, and supported by
a yoke on the two uprights of the frame F. The lamp circuit is the same as in the
well known "Brush" lamp, or in any other electric arc lamp, and magnet A is
connected in shunt with the arc by the conductors y . and y represent the
line wires.
In Figure 2, A represents a hollow permanent magnet embracing positive
A solenoid or coil of
carbon C. N represents the north pole of the magnet A.
conductor through which current passes may be used for the purposes of this
invention.
In Figure 3 the magnet is shown arranged with relation to the negative electrode,
being still with the lines of its field of force parallel with and in the same direction

page_text: as the current producing the arc, the south pole in this case being nearer the arc
and the north pole further removed from the arc.
This arrangement performs the same function as the arrangement in Figures 1
and 2, but it is not so good where the arc is to be used merely for its light
producing effect, as the presence of the magnet below the are would give rise to
shadows.
With this arrangement the lines of the field of force in core B, Figures 1 and 3,
or in magnet A, Figure 2, will be parallel with and in the same direction as the
current passing through the positive carbon C, and the said magnet will to a large
extent neutralize the counter E.M. F. of the voltaic arc between carbons C and C¹,
and materially increase the length of the arc.
The inventor has found that with a current which, without the magnet, will only
maintain an arc of of an inch in length, he can, with the magnet arranged as
shown, maintain an arc of of an inch in length, and has maintained it nearly, if
not quite, of an inch in length.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, as communicated to me by
my foreign correspondent, I declare that what I claim is :-
1. The herein described mode of magnetically affecting an electric arc lamp
consisting in subjecting the arc to the influence of a magnet in which the lines of
the field of force are substantially parallel with, and in the same direction as, the
current producing said are, for the purpose of reducing the counter electro-motive
force of the arc.
2. The combination with a positive electrode of an electric arc lamp of a magnet
having the lines of its field of force substantially parallel with, and in the same
direction as, the current passing through said positive electrode, and having its
north pole presented to the arc, the arrangement being such as to reduce the
counter electro-motive-force of the arc.
3. The combination with an electrode of an electric arc lamp of a magnet having
the lines of its field of force substantially parallel with and in the same direction
as, the current passing through said electrode, and having its polar extremity
presented to the arc, whereby the counter electro-motive force of the arc is reduced,
substantially as shown and described.
4. The combination with the two carbon electrodes of an electric arc lamp and
means for maintaining a voltaic arc between them, of a magnet having its lines of
force substantially parallel with, and in the same direction as the arc producing
current, the arrangement being such as to reduce the counter electro-motive force
of the arc, substantially as and for the purposes set forth.
5. The combination with the negative electrode in a mechanism for maintaining
a voltaic arc, of a magnet having the lines of its field of force substantially parallel
with and in the same direction as the current passing through said negative
electrode, and having its south pole presented to the arc, whereby the counter
electro motive-force of the arc is reduced.
2000
W. P. THOMPSON & Co.,
Agents.