Improvement relating to Electric Arc Lamps.
Year: 1899

page_text: PROVISIONAL SPECIFICATION.
Improvement relating to Electric Arc Lamps.
I, THOMAS JOSEPH DIGBY, Electrical Engineer, of 32, Shaftesbury Avenue, in
the County of London, do hereby declare the nature of this invention to be as
follows:-
This invention relates more particularly to the means for regulating the quantity
or intensity of light thrown by arc lamps on a theatre stage, but is applicable
also to arc lamps for other localities.
Hitherto it has been usual, to regulate the light of an arc lamp by means of a
variable resistance inserted into the lighting circuit, but this involves the risk
of extinguishing the arc, when the light is reduced below a moderate limit.
To avoid this drawback, I vary the distribution or emission of light by shifting
the lower carbon at a right angle to the line of feed, in other words, I regulate
the distance between the axes of the two electrodes.
If, as is usual in theatre stage lamps, the stage is illuminated through a lens
situated in front of the carbon points, the maximum of light is thrown on the
stage, when the lower carbon is approximately in line with the upper carbon. If
now the lower carbon is shifted parallel to itself, so as to recede from the lens,
a portion of the light emitted by the lower carbon will be intercepted by the upper
carbon, and the light passing through the lens will be reduced.
Various means may be adopted for regulating the position of the lower carbon
holder at a right angle to the feed motion, according to requirements.
The lower carbon holder may, for instance, be mounted on a pair of short hori-
zontal rods guided in suitable bearings and provided at their rear ends with a
suitable handle. One of the horizontal guide-rods may be provided with a screw-
thread and set in motion by turning a screw-nut. Or a rack and pinion or a
worm-gear may be employed.
Instead of being vertical, the electrodes may be inclined at any convenient
angle, and instead of the lower carbon, the upper carbon may be rendered laterally
adjustable, according to the direction in which the electric current passes through
the lamp.
As usual, the lamp may be enclosed in a suitable box, provided in front with
a projecting lens.
The feed motion of the carbon may be produced or regulated by hand or auto-
matically, as in other arc lamps, provided that one of the carbons is rendered
moveable sideways independently of the ordinary carbon feed.
Dated this 13th day of December 1899.
FAIRFAX & WETTER,
Agents for the Applicant.

page_text: I, THOMAS JOSEPH DIGBY, of 32, Shaftesbury Avenue, in the County of London,
Electrical 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:-
Inis invention relates more particularly to the means for regulating the quantity
or intensity of light thrown by electric arc lamps on a theatre stage, but is appli-
cable also to arc lamps for other localities.
Hitherto it has been usual to regulate the light of an arc lamp by means of a
variable resistance inserted into the lighting circuit, but this involves the risk
of extinguishing the are when the light is reduced below a moderate limit.
To avoid this drawback, I vary the distribution or emission of light by shifting
the lower carbon at a right angle to the line of feed, or, in other words, i regulate
the distance between the axes of the two electrodes.
If, as is usual in theatre stage lamps, the stage is illuminated through a lens
or by a reflector situated in front or centrally of the carbon points, the maximum
of light is thrown on the stage when the lower carbon is approximately in axial
line with the upper carbon. If, however, the lower carbon is displaced or shifted
parallel to itself so as to recede from the lens or reflector, a portion of light emitted
by the lower carbon, will be intercepted by the upper carbon, and the light
reflected, or passing through the lens will be reduced.
In the further description of this invention reference is made to the accompany-
ing drawings, in which Fig. 1 is a side elevation, showing the principal parts
of an arc lamp adapted to carry out the object of my invention. Fig. 2 is a
transverse sectional plan of a sliding device, arranged and operating to displace
the axial line of the lower carbon in relation to the axial line of the upper carbon.
In these drawings a is the upper carbon, secured in a clamping device b, b,
the clamping screw being denoted by 5. A suitable terminal 62 is electrically
connected to the clamping device b, and the whole of the device is suitably
insulated and connected to an upper sliding cross-head c through which three holes
have been bored.
A similar clamping device d, d, having a clamping screw d', and terminal d²,
is also combined with the lower carbon e, the parts being also connected to a lower
sliding crosshead f by means of two parallel rods f¹ sliding in corresponding holes
in a flange f forming a part of the lower crosshead, and guides f³ also secured
thereto. One of the guides has a set screw and milled head f, for securing the
sliding crosshead carrying the lower carbon e at any particular point required,
and by means of a transverse bar or handle f, secured to the back end of the two
parallel sliding rods f₁, the lower clamping device d, together with the lower
carbon e, can be shifted backwards and forwards at right angles to the axial line
of the carbon e and of the line of feed, as indicated by the dotted line and reverse
arrow heads; thus regulating the distance between the axes and points of the
two carbons, and therefore varying the distribution or emission of light from the
arc formed at the points of the electrode.
The upper and lower crossheads, c and f, each having three corresponding holes
bored therein, are fitted to slide upon two turned and parallel guides, g, g, which
pass through the outer holes. The central hole in each crosshead is tapped, one
with a right hand thread, the other with a left hand thread; and a central screw
spindle h, having a corresponding right and left hand thread cut thereon, is fitted
into the tapped holes of the two crossheads c and f, and the upper ends of the

page_text: guides are secured to a top frame or cross bar g', while their lower ends are secured
to a base frame g². The screw spindle h is fitted into the cross bar g' at the top,
and the base frame g³ at the bottom, so as to be capable of turning therein, which
turning action produces a to and fro motion of the sliding crossheads c and f,
together win their respective clamping devices b and d, and with them the carbon
electrodes a and e. A bevel wheel his secured to the bottom end of the screw
spindle h, where it projects through the base frame g³, and the wheel h¹ engaging
with a pinion h2, carried on a shaft h³, working in a bearing bored in the base
frame g, and actuated by the ebonite hand wheel h', enables an operator to bring
the carbons together and cause them to recede in striking the arc, to maintain
the feed, and generally to work the lamp. In addition to this, the operator is
enabled by means of the transverse handle fo to slide the lower clamping device d
backwards or forwards, and with it the carbon e, so as to regulate the emission of
light, as before mentioned, and to secure it in any desired position by means of
the set screw f. A reflector i may be secured on one of the guides g, as shown
in Fig. 1, and the whole is mounted upon a convenient base j, or fitted into a
suitable box having a projecting lens, as desired.
It will be understood that other means than those shown for regulating the
axial or lateral position of the carbons in relation to each other may be adopted,
without departing from the nature of my invention; and that automatic means
for feeding the carbons, such as are common to many arc lamps, may be used
instead of the hand feed shown in the drawings, provided that one of the carbons
is rendered moveable sideways or transversely, independently of the ordinary
carbon feed.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed, I declare that what
I claim is:
The herein described improvement in electric arc lamps, consisting of a cross
or transverse regulating motion of one electrode in relation to the other, com-
bined with and at right angles to the ordinary axial feed or regulating motion
of the said electrodes, substantially as and for the purpose specified, and shown
by the drawings.
Toted thin 12th day of Santambar 1000
FAIRFAX & WETTER,
37 & 39, Essex Street, Strand, London, W.C.