Improvements in Aro Lamps, and in Stands therefor.
Year: 1895

page_text: Date of Application, 19th Sept., 1895
Complete Specification Left, 19th June, 1896-Accepted, 22nd Aug., 1896
PROVISIONAL SPECIFICATION.
Improvements in Aro Lamps, and in Stands therefor.
I, BENJAMIN JOSEPH BARNARD MILLS, of 23 Southampton Buildings, in the
County of London, Patent Agent, do hereby declare the nature of this invention,
(a communication to me from Edward Powell Hopkins, of the City, County and
State of New York, in the United States of America) to be as follows:-
The object of the invention is to produce a small compact and light focussing
electric arc lamp especially adapted for lantern projections, photography and like
purposes, which will give an absolutely steady light, can be used in any position,
and the light of which may be increased or decreased at will without changing
the regulation of the lamp itself, enabling the projection of dissolving effects with
the stereopticon and adapting the lamp for stage lighting and similar purposes; a
further object is to produce a stand for supporting such an arc lamp which will
provide in a simple and effective manner for the ready adjustment of the lamp
vertically and horizontally.
The carbon-holders of the improved lamp are geared together so as to have the
proper relative movement in approaching each other, and this gearing forms part
of a spring-driven clock-train, the driving spring of which is placed under an
initial tension and acts to move the carbon-holders together with a positive move-
ment independent of the position of the lamp. This clock-train is mounted in a
stationary frame and terminates in an escapement which is locked by the armature
of an electro-magnet located in a constantly closed shunt circuit around the arc.
The armature of the shunt magnet locks the train in its retracted position and
releases it when attracted. The carbons are given an initial separation to form or
strike the arc by another electro-magnet, which is located in series with the arc
itself and acts to move one of the carbon-holders independently of the feeding
mechanism. This is accomplished by pivotting the carbon-holder upon the sliding
plate which carries it and mounting the magnet upon the same plate in relation to
act upon the pivotted carbon-holder.
In use the lamp is preferably operated from a constant potential circuit, being
connected with such circuit through a regulating adjustable resistance. The
principle of regulation is based upon the fact observed from numerous experiments
that the quantity of current or amperes flowing through the arc may be varied
between quite wide limits without varying substantially the difference of potential
at the arc itself, i.e., the difference of potential at the arc is independent of the
quantity of current, or substantially so. If the arc acted like an ordinary
resistance, the voltage would have to be increased in direct proportion to the
amperes, according to Ohm's law, and if a difference of potential of 45 volts were
required to produce a flow of 10 amperes, to increase the current to 20 amperes
would require 9 volts, assuming that the resistance remained the same. The
apparent resistance however does not remain the same, but decreases with the
increased current flow, and in some cases it has been found that by increasing
the current, the difference of potential at the carbons is actually lessened.
The phenomenon is explainable on the theory that with a small current,
a greater percentage of the heat produced at the arc is conducted away
by the carbons themselves than with a larger current, thus permitting with
the greater current the formation of a proportionately larger amount of the
conducting carbon vapor which exists in the arc. The shunt magnet of the lamp
being adjusted to maintain a definite difference of potential at the arc, the flow of

page_text: current to the lamp is increased or decreased by the adjustment of the regulating
resistance which is connected in circuit with the lamp. The effect of varying the
current in the lamp is to vary the length of the arc, a shorter are being pro luced
for a small current. And this is an exceedingly desirable feature of the lamp,
since it enables the light to be varied for the production of dissolving effects for
the stereopticon and for stage lighting and like purposes, by simply adjusting the
resistance external to the lamp.
The holder for the improved arc lamp consists of a U shaped frame acting as a
base upon which the lamp stands. At the centre of the closed end of the frame
rises a post upon which is a tube closed at its upper end and provided with a set
screw turning through that end and setting against the head of the post. The
case of the lamp is provided with a split clamping sleeve embracing the tube and
having a thumb nut for locking it in position. A rough vertical adjustment is
secured by moving the clamping sleeve, while a finer adjustment is secured by
turning the set screw which sets upon the head of the supporting post. The lamp
is free to turn upon the supporting post, and to regulate and adjust that turning
movement, the sides of the U shaped frame are provided, one with a plate spring
which rises from the frame and projects inwardly against the box of the lamp,
and the other with a post through which a set screw turns bearing against the
other side of the lamp box. By turning this set screw forward, the lamp box will
be swung against the pressure of the spring on the other side, while by turning the
set screw backwards, the spring will force the box against the set screw and cause
it to swing in the other direction.
Dated this 19th day of September 1895.
HARRIS & MILLS,
23. Southampton Buildings, London, W.C., Agents.
I, BENJAMIN JOSEPH BARNARD MILLS, of 23 Southampton Buildings, in the
County of London, Patent Agent, do hereby declare the nature of this invention,
(a communication to me from Edward Powell Hopkins, of the City, County and
State of New York, United States of America,) and in what manner the same is to
be performed, to be particularly described and ascertained in and by the following
statement:
The object of the invention is to produce a small, compact and light focussing
electric arc lamp especially adapted for lantern projections, photography and like
purposes, which will give an absolutely steady light, can be used in any position,
and the light of which may be increased or decreased at will without changing the
regulation of the lamp itself, enabling the projection of dissolving effects with the
stereopticon and adapting the lamp for stage lighting and similar purposes; a further
object is to produce a stand for supporting such an arc lamp which will provide in
a simple and effective manner for the ready adjustment of the lamp vertically and
horizontally.
The carbon-holders of the improved lamp are geared together so as to have the
proper relative movement in approaching each other, and this gearing forms part
of a spring-driven clock-train, the driving spring of which placed under an initial
tension and acts to move the carbon-holders together with a positive movement
independent of the position of the lamp. This clock-train is mounted in a
stationary frame and terminates in an escapement, which is locked by the armature
of an electro-magnet located in a constantly closed shunt circuit around the arc.
The armature of the shunt magnet locks the train in its retracted position and
releases it when attracted. The carbons are given an initial separation to form or

page_text: strike the arc by another electro-magnet which is located in series with the arc
itself and acts to move one of the carbon-holders independently of the feeding
mechanism. This is accomplished by pivoting the carbon-holder upon the sliding
plate which carries it, and mounting the magnet upon the same plate in position to
act upon the pivoted carbon-holder.
In use the lamp is preferably operated from a constant potential circuit, being
connected with such circuit through a regulating adjustable resistance." The
principle of regulation is based upon the fact observed from numerous experiments
that the quantity of current or amperes flowing through the arc may be varied
between quite wide limits without varying substantially the difference of potential
at the arc itself, ie., the difference of potential at the arc is independent of the
quantity of current, or substantially so. If the arc acted like an ordinary
resistance, the voltage would have to be increased in direct proportion to the
amperes, according to Ohm's law, and if a difference of potential of 45 volts were
required to produce a flow of 10 amperes, to increase the current to 20 amperes
would require 90 volts, assuming that the resistance remained the same.
The
apparent resistance however does not remain the same, but decreases with the
increased current flow, and in some cases it has been found that by increasing
the current, the difference of potential at the carbons is actually lessened. The
phenomenon is explainable on the theory that with a small current a greater per-
centage of the heat produced at the arc is conducted away by the carbons
themselves than with a larger current, thus permitting, with the greater current,
the formation of a proportionately larger amount of the conducting carbon vapour
which exists in the arc. The shunt magnet of the lamp being adjusted to maintain
a definite difference of potential at the arc, the flow of current to the lamp is
increased or decreased by the adjustment of the regulating resistance which is
connected in circuit with the lamp. The effect of varying the current in the lamp
is to vary the length of the arc, a shorter are being produced for small current.
And this is an exceedingly desirable feature of the lamp, since it enables the light
to be varied for the production of dissolving effects for the stereopticon and for stage
lighting and like purposes, by simply adjusting the resistance external to the lamp.
The holder for the improved are lamp consists of a U shaped frame acting as a
base upon which the lamp stands. At the centre of the closed end of the frame
rises a post, upon which is a tube closed at its upper end and provided with a set-
screw turning through that end and setting against the head of the post. The
case of the lamp is provided with a split clamping sleeve embracing the tube and
having a thumb-nut for locking it in position. A rough vertical adjustment is
secured by moving the clamping sleeve, while a finer adjustinent is secured by
turning the set-screw which sets upon the head of the supporting post. The lamp
is free to turn upon the supporting post, and to regulate and adjust that turning
movement, the sides of the U shaped frame are provided, one with a plate spring
which rises from the frame and projects inwardly against the box of the lamp, and
the other with a post through which a set-screw turns, bearing against the other
side of the lamp box. By turning this set-screw forward, the lamp box will be
swung against the pressure of the spring on the other side, while by turning the
set-screw backwards, the spring will force the box against the set-screw and cause
it to swing in the other direction.
In the accompanying drawings forming a part hereof,
Fig. 1 is a side view of the lamp, with the side plates of its enclosing case
removed.
Fig. 2 is a similar view from the other side of the lamp, the light shield being in
section.
Fig. 3 is a side view of the lamp on a smaller scale, with the side plate of the
enclosing case in position.
Fig. 4 is a top view of the lamp on the same scale as Fig. 3.
Fig. 5 is a vertical section through the parts mounted on the main-shaft of the
driving clockwork, with the other wheels of the train in elevation.

page_text: Fig. 6 is a vertical section on the line 6-6 in Fig. 5.
Figs. 7 and 8 are sections showing the method of insulating the carbon-holders
from their supports, and
Fig. 9 is a diagram illustrating the circuit connections of the lamp.
The operative parts of the lamp are enclosed within, or mounted upon, a
quadrangular box A of metal, composed of a quadrangular frame and two side
plates secured thereto by screws. For projection purposes, for which the lamp is
especially designed, the box A is adjustably mounted upon a U shaped stand B.
For this purpose, to the rear of the box A is secured, by a substantial foot, a split
clamping sleeve a, having on opposite sides of the split, lugs a' through which
passes a screw 6 for operating the clamp by means of a suitable thumb-piece. The
clamping sleeve a slides upon a tube c, which is mounted on a post d rising from
the stand B. The upper end of the tube c is screw-threaded, and receives a
screw c', which bears against the upper end of the post d. These parts give
a vertical adjustment to the lamp, the clamp a being for the purpose of giving a
proximate and quick vertical adjustment by moving the clamp up and down on the
rod d, while the screw c¹ enables an exact adjustment to be secured. The lamp,
being carried by the tube c, turns freely upon the post d to obtain a lateral
adjustment, which lateral adjustment is produced by a screw e passing through
a post e rising from one side of the U shaped stand and bearing against one side
plate of the box, while from the other side of the U shaped stand rises a leaf-spring e
which presses inwardly against the face plate on that side of the box. By turning
the screw e forward, the box is pushed sideways against the pressure of the spring,
while by turning the screw backward, the spring causes the box to follow the screw.
The carbons in the improved lamp are fed together positively, without regard to the
position of the lamp, by a spring motor having a fixed position and operated by a
clock spring having considerable initial tension. The clock movement is carried
by two plates C C, which are enclosed within the box and supported from its top.
The clock movement comprises a main shaft D, which projects beyond the
plate C, and has a squared end, on which is mounted a winding wheel E, located
outside of the box and having a hub extending through the face plate of the box
for engaging with the main shaft. Upon this main shaft is secured the inner end
of the driving spring F, the outer end of this spring being attached to the
stationary stud f. Upon the other end of the shaft D, on opposite sides of the
plate C, are secured two pinions G G¹, engaging with racks H H' for feeding
the carbons. The pinion G, which feeds the positive. carbon, is larger than the
pinion G which feeds the negative carbon, the difference in size being pro-
portional to the difference in the burning rate of the positive and negative carbons,
i.e., 166 to 1. This proportion is secured by making the pinion G, one with
twenty teeth, and the pinion G¹, one with twelve teeth. The pinions G G¹ being
fixed to the shaft D, the turning of that shaft by the winding wheel E to wind up
the spring, will also turn the pinions G G and will move the racks H H¹ in the
direction of separating the carbon-holders. The reverse movement of the shaft D,
under the effect of the spring F, will move the racks H H' in the direction of
feeding the carbons together. To retard the feeding movement, the shaft D is
connected by wheels and pinions, with an escapement g, which is operated as the
shaft D is turned by the unwinding of the spring F, but is not operated by the
reverse movement of the shaft. To accomplish this, there is mounted loosely on
the shaft D, a gear wheel gl engaging with a pinion on the shaft g², which shaft
is provided with a gear wheel engaging with a pinion on the shaft g, which latter
shaft carries the scape wheel. A ratchet wheel fixed to the shaft D, is engaged
by a spring pawl carried by the gear wheel g¹. The pawl and ratchet permit
the turning of the shaft D to wind up the spring F and move the racks H H' for
separating the carbon-holders without operating the escapement. The rack bar H
is supported at its ends by guide collars i sliding on a round rod I, which extends
from the bottom of the box through and above the top of the box. The collar i
engages with the rod I within the box, and the collar with the upper portion of

page_text: the rod I above the box. The positive carbon-holder J is connected by an L shaped
arm with the collar ", the parts being insulated, preferably with mica, as
illustrated in Fig. 7. The rack bar H is guided not only by the rod I, but also
by the opening through the top of the box A, with which it makes an accurate
fit. The rack H', by means of which the negative carbon is fed, passes through
and accurately fits a hole in the top of the box A. At its upper end it is rigidly
connected by a cross-piece k with a vertical slide k¹, which is guided upon the
face of a supporting plate K mounted upon studs and thimbles secured to the
front of the box A, but separated therefrom by an air space. The slide ' carries
at its lower end the negative carbon-holder L, which is mounted upon an L shaped
projection depending from the armature m of the series wound striking magnet M,
and insulated therefrom as illustrated in Fig. 8. This magnet is preferably one
having a winding only upon one leg of the magnet, and having the armature m
pivoted upon the other leg of the magnet by means of a piece n of spring brass,
the play of the armature being regulated by a screw n¹ which passes through a
slot in the armature and enters the other pole piece, the head of the screw limiting
the backward movement of the armature. To regulate and control the feeding
movement of the carbons, there is provided, within the box, an electro magnet N
having a high resistance winding, whose armature o is pivoted upon one leg of the
magnet and is retracted by a spring o', whose tension is adjusted by a spring p
engaging with a screw pl projecting through the rear of the box and having a
milled head outside of the box for turning it. The forward movement of the
armature o is regulated by a screw of passing through the armature and
striking the pole of the magnet, while the retraction of the armature is
limited by a stop p secured by a screw to the plate C. The armature o carries
a catch arm q, which engages, when the armature is retracted, with the tail q' of
the escapement verge g, arresting the movement of the escapement and locking the
train. When the armature o is attracted by the magnet N, the escapement is
released and the train of wheels is run by the spring F, feeding the carbons
together. Upon the plate K is mounted the light shield O, separated therefrom
by an air space, and provided with a forwardly projecting tubular shield, which is
slotted at the top and at the bottom to permit the movement of the carbons and
carbon-holders. Within the shield O and projecting horizontally forward from its
back plate below the centre of the shield, and hence below the arc, is an iron or
steel plate P, which is cut out so as to partially encircle the negative carbon,
which plate performs the double function of intercepting the passage of light
downwardly through the slotted bottom of the shield and, by the magnetizing
effect of the electric current, draws the arc inwardly and prevents it from flaming
up on the face of the positive carbon. It also prevents the rising current of air
from blowing directly on the arc. Flexible cords Q and R extend from the
binding posts S and T through the top and front of the box, and are connected
with the positive and negative carbon-holders for conveying the electric current to
them and through the coils of the striking magnet M. The magnet N is located
in another circuit between the binding posts S and T, which circuit includes
preferably an additional resistance U which may, however, be omitted if the
magnet N is made large enough and wound with a sufficient length of wire to give
the amount of resistance required to prevent an excessive flow of current through
the magnet coils and a consequent burning out of such coils.
In general the operation of the improved lamp is effected by the initial separation
of the carbons by the series magnet M, (which separation causes the formation or
striking of the arc), and by the subsequent feeding of the carbons together by the
shunt magnet N. The negative carbon-holder projects somewhat beyond the
positive carbon-holder, so that the axis of the negative carbon is somewhat in
advance of that of the positive carbon. The effect of this is to cause the formation
of the crater of the arc in an oblique position on the forward side of the positive
carbon aud facing to the front, so that the light will be largely projected forward,
and this effect is aided by arranging the carbons in an inclined position as

page_text: illustrated. The negative carbon-holder, being mounted upon a pivot, is moved
by the striking magnet in an arc of a circle, and the point of the negative carbon
is therefore moved laterally and downwardly away from the positive carbon,
following the lateral course which the are takes in passing from one carbon to the
other. The front of the lamp is effectively protected from the heat of the arc,
first by the light shield O and, second, by the front plate K. Since both of the
racks enter the movement box at the top and pass through openings which they
fit closely, that box is made largely dust-proof, and is also made more convenient
for the mounting of the lamp. Many advantages arise from the details of
construction of the improved lamp which it is not necessary to call attention to in
.detail.
In operating the improved lamp it is preferably connected with a constant
potential circuit 1, 2, through an adjustable resistance W, as illustrated in Fig. 9.
Assuming the voltage of the circuit 1, 2, to be one hundred and twenty volts, and
the magnet N to be adjusted to maintain approximately forty-five volts at the arc,
my communicator has found that by adjusting the resistance W the current passing
through the arc can be increased or decreased without changing the difference of
potential at the arc itself, or requiring any adjustment of the regulating magnet N.
The amount of current flowing through the lamp has been found to be almost
exactly that which would be produced under Ohm's law by dividing the voltage
found by deducting the constant voltage of the arc from the entire voltage, by
the number of ohms of the resistance W at the time in circuit. In other words,
if the magnet N is adjusted to maintain an arc of forty-five volts, and considering
the voltage of the circuit 1, 2, to be one hundred and twenty volts, the difference
between the two voltages will be seventy-five volts, and the current flowing
through the arc will be equal in amperes to seventy-five volts divided by the
number of ohms of the resistance W which are in circuit. In Fig. 9 is given the
resistance in ohms of the several sections of the resistance W above that resistance
in the figure, and below the resistance the number of amperes are marked at the
several contact points. Thus, if the arm of the rheostat is thrown to the first
contact at the left of the resistance, there will be three ohms in circuit, and the
current will be twenty-five amperes; if moved one point to the right, the resistance
of W in the circuit will be 3-4 ohms, and the current flowing through the arc will
be 22 amperes, and so on. The effect of varying the current in the lamp is to
vary the length of the arc, a shorter arc being produced for a smaller current.
And this is an exceedingly desirable feature of the improved lamp since it enables
the brilliancy of the light to be varied for the production of dissolving effects for
the stereopticon and for stage lighting and like purposes by simply adjusting the
resistance W.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what
I claim is :-
.
1. An improved focussing electric arc lamp constructed and operating
substantially as herein described.
2. The herein described method of regulating the brilliancy of an electric arc
lamp, whereby the lamp is adapted for lantern projections, photography, and the
projection of dissolving effects with a stereopticon, for stage lighting, and similar
purposes.
3. In an electric are lamp of the character herein described, the employment, in
combination with positive and negative carbons and the slotted light-shield O, of
the plate P projecting forward from the back plate of the shield above its lower
slots and partially encircling the negative carbon, substantially as and for the
purpose set forth.
4. In an electric arc lamp of the character herein described, the employment, in
combination with the casing A and the carbon-holders, of the light-shield O and
front plate K for protecting the lamp movement from the heat of the arc by

page_text: means of the two air spaces located respectively between the movement and the
plate K, and between said plate and the light-shiell O, substantially as set forth.
5. In an electric arc lamp of the character herein described, the combination
with the casing A, the feeding motor and controlling magnet enclosed thereby, of
the racks H and H' passing through the top of the casing, the carbon-holders J
and L connected with said racks H and H₁ respectively, the guide rod I, and the-
guide plate K, substantially as and for the purpose set forth.
6. In an electric arc lamp of the character herein described, the combination
with the casing A enclosing and supporting the mechanism of the lamp, othe
tubular clamp a, the tube c, the screw c', and the post d for supporting the lamp
and providing for its vertical adjustment, substantially as set forth.
7. In an electric arc lamp of the character herein described, the combination
with the casing A enclosing and supporting the mechanism of the lamp and
mounted upon a vertically adjustable pivoted support, of the screw e and spring e³:
for adjusting the lamp laterally, substantially as set forth.
Anno 10 ARD UC Sa
1000.
HARRIS & MILLS,
23 Southampton Buildings, London, W.C., Agents.
HARRIS & MILLS,
23 Southampton Buildings, London, W.C., Agents.