IMPROVEMENTS IN ELECTRIC LAMPS
Year: 1879

page_text: LETTERS PATENT to John Hopkinson, of 4, Westminster Chambers, London,
for the Invention of "IMPROVEMENTS IN ELECTRIC LAMPS."
PROVISIONAL SPECIFICATION left by the said John Hopkinson at the Office
of the Commissioners of Patents on the 16th May 1879.
JOHN HOPKINSON, of 4, Westminster Chambers, London.
ELECTRIC LAMPS.”·
"IMPROVEMENTS IN
My improvement relates to that class of electric lamp in which the electric arc is
used, and in which the current passing is kept constant by means of an electro-
magnet through which the current passes on its way to the electric arc. Such
lamps, as ordinarily constructed, cannot be burned with two or more arranged in
series, and my improvement consists in modifying or adding to them that this end
may be attained.
I connect points of the main circuit on opposite sides of the electric arc by a fine
wire forming a solenoid or electromagnet. The current in this fine wire is
necessarily proportional to the difference of electric potential on the two sides of
the lamp. When the carbons are so far parted that this difference is greater than
the proper amount the solenoid or electromagnet of fine wire actuates a connection,
whereby the electromagnet of the lamp itself is short circuited and is caused to
permit the carbons to approach. The result of this arrangement is that the lamp
maintains the difference of electric potential on the two sides of the arc constant
instead of maintaining the quantity of the current constant, as is the case when.
my improvement is not used.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said John Hopkinson in the Great Seal Patent Office on the 13th November
1879.
JOHN HOPKINSON, of 4, Westminster Chambers, London.
ELECTRIC LAMPS"
"
IMPROVEMENTS IN

page_text: i
electro-magnet through which the current passes on its way to the electric arc.
Such lamps, as ordinarily constructed, cannot be burned with two or more arranged
in series, and my improvement consists in modifying or adding to them that this
end may be attained.
I connect points of the main circuit on opposite sides of the electric arc by a fine
wire forming a solenoid or electro-magnet. The current in this fine wire is
proportional to the difference of electric potential on the two sides of the lamp.
When the carbons are so far parted that this difference is greater than the proper
amount the solenoid or electro-magnet of fine wire actuates a connection, whereby
the electro-magnet of the lamp itself is short circuited and is caused to permit the
carbons to approach. The result of this arrangement is that the lamp maintains
the difference of electric potential on the two sides of the arc constant instead of
maintaining the quantity of the current constant, as is the case when my improve-
ment is not used.
My Invention may be applied to any lamp which is constructed to maintain the
current passing through the electric are invariable, and which operates by an
electro-magnet or solenoid through which the main current passes; it is therefore
unnecessary to describe any such lamp, many forms being well known. The form
of the automatic key, which short circuits the electro-magnet or solenoid of the
lamp, may be varied. I prefer the form shewn in the Drawing, which Drawing
will also serve to indicate the electrical connections which have to be made. A.
represents the ordinary electro-magnet of an electric lamp through which the
current passes on its way to the carbons B, C. This electro-magnet may, as is well
known, be mechanically connected to the carbons in a variety of ways, so that
when the current is less than it should be the electro-magnet will operate through
its armature to permit the carbons to approach. D is the key which, when my
Invention is employed, short circuits the electro-magnet A. It consists of an
electro-magnet or solenoid of high resistance E which is connected to points on
opposite sides of the electric arc. If the current in this electro-magnet exceeds a
certain amount it draws down the armature F, which is preferably carried on a
spring, so as to make contact at G and short circuit the electro-magnet A, thereby
causing the carbons to approach. In addition to the electro-magnet E the main
circuit may be arranged to act on the short circuiting key D either in opposition to
or in the same direction with the electro-magnet E.
I make no general claim to the use of an electro-magnet or solenoid of high
resistance connected to points on opposite sides of the arc, such an electro-magnet
having been previously used to effect the motions of the carbons directly; but I
claim the use of such an electro-magnet or solenoid in combination with a key for
short circuiting the electro-magnet or solenoid of the lamp itself, substantially as
herein described.
In witness whereof, I, the said John Hopkinson, have heretofore set my hand
and seal this Thirteenth day of November 1879.
JOHN HOPKINSON. (L.S.)