IMPROVEMENTS IN ELECTRIC LAMPS
Year: 1882

page_text: PROVISIONAL SPECIFICATION left by John Henry Johnson at the Office
of the Commissioners of Patents on the 30th June 1882. Communicated
to him from abroad by Louis Bardon of Paris in the Republic of France.
JOHN HENRY JOHNSON of 47 Lincolns Inn Fields in the County of Middlesex
Gentleman. "IMPROVEMENTS IN ELECTRIC LAMPS." A cominunication to me
from abroad by Louis Bardon of Paris in the Republic of France.
•
The improvements forming the subject of this Invention are applicable to all
descriptions of Electric Lamps in which the light is produced by the Voltaic arc.
The said improvements render the light extremely steady and constant and consist
in causing the upper carbon to descend very slowly when the arc is lengthened in
lieu of descending suddenly as in the case of a great number of electric lamps
heretofore employed.
A distinguishing feature of this Invention consists in the employment for
supporting the upper carbon of a rod provided with a helix or quick screw thread
and pressed or acted upon by a lever of peculiar form whose function is to maintain
the rod in position by acting in combination with a solenoid or electro-magnet in a
shunt from the main wire.
In carrying out this Invention the upper carbon is held in a socket at the lower
extremity of a rod as in ordinary lamps and the lower carbon is or may be
supported in the usual manner. The rod to which the upper carbon is attached is
provided with a helical groove or quick screw thread and passes through guides
the lower guide being provided with an internal helix or female screw and acting
as a nut to the rod whilst the other guide serves simply to steady the rod and is
attached to a bracket or support common to both guides. This support is connected
with a solenoid or electro-magnet composed of fine wire arranged as a shunt
offering a resistance equal to or greater than the normal resistance of the arc.
the under side of the nut or threaded guide is pivotted a bent lever the short arm
of which bears against the side of the rod whilst the long arm of the same lever
bears against the lower extremity of the armature of the solenoid the said armature
being suspended by a spring or arm attached to the support. The extremity of the
short arm of the lever is of a concave form corresponding with the side of the
To

page_text: threaded rod and is covered with india-rubber or felt or the like to increase the
friction.
During the normal working of the lamp the short arm of the lever bears against
the side of the upper carbon holder and retains it in position, but when in
consequence of the consumption of the carbons the resistance at the arc becomes
excessive, a portion of the current is diverted into the solenoid or electro-magnet of
the shunt and causes it to operate the armature to release the upper carbon holder
so that it is free to slip down but is prevented from descending with a jerk by the
action of the screw-thread or helix herein before described. The upper carbon
holder thus descends gradually until the normal length of arc is reestablished
whereupon the normal working of the lamp is resumed, until the arc is again
lengthened when the same operations are repeated and so on in succession.