IMPROVEMENTS IN ELECTRIC LAMPS AND MECHANISM FOR ELECTRIC LIGHTING
Year: 1879

page_text: LETTERS PATENT to Herbert John Haddan, of the Firm of Herbert and
Company, Solicitors of Patents, of 67,. Strand, in the City of Westminster,
Civil Engineer, for the Invention of "IMPROVEMENTS IN ELECTRIC LAMPS
AND MECHANISM FOR ELECTRIC LIGHTING." A communication from abroad
by Charles F. Brush, of Cleveland, Ohio, United States of America.
PROVISIONAL SPECIFICATION left by the said Herbert John Haddan at
the Office of the Commissioners of Patents on the 18th September 1879.
HERBERT JOHN HADDAN, of the Firm of Herbert and Company, Solicitors of
Patents, of 67, Strand, in the City of Westminster, Civil Engineer." "IMPROVEMENTS
IN ELECTRIC LAMPS AND MECHANISM FOR ELECTRIC LIGHTING." A communication
from abroad by Charles F. Brush, of Cleveland, Ohio, United States of America.
This Invention relates to electric lamps and it consists, first, in an electric lamp
having two or more sets of carbons adapted by any suitable means to burn succes-
sively (that is, one set after another); second, in a lamp having two or more sets of
carbons, each set adapted to move independently in burning and feeding; third, in
an electric lamp having two or more sets of carbons, adapted each to have inde-
pendent movements, and each operated and influenced by the same electric current,
to wit, the general current operating the lamp; fourth, in a lamp having two or
more sets of carbons, said carbons by any suitable means being adapted to be
separated dissimultaneously, whereby the voltaic arc between but a single set of
carbons is produced; fifth, in the combination with one of the carbons or carbon
holders of a lamp employing two or more sets of carbons, as above mentioned, of
a suitable collar tube or extended support of any kind, within or upon which the
carbon (or carbon holder) to which it is applied shall rest and be supported; sixth,
in the combination with the mechanism operating the carbons of any voltaic arc
type of electric lamps of an automatic shunt or cut off, and a resistance so con-
structed, combined, and electrically connected that if for any reason the said shunt
or cut off shall have operated to extinguish the lamp when it was in a normally

page_text: operative condition, the light shall be automatically re-established upon a reunion
of the electrodes, as, for instance, if a carbon stick should break and thus destroy
the arc, in such a case the retistance in the lamps being infinite the cut off would
operate to shunt said lamps out of the circuit by establishing a path of low
resistance for the current outside of the electrodes and the mechanism operating
them. But whenever for any such accidental cause the cut off mechanism is called
into action it is not desirable that the lamp should be permanently extinguished,
for the reason that the lamp proper is not at fault and is still in a perfectly operative
condition. The design therefore in this particular Invention is that upon the
reunion of the electrodes the cut off or shunting mechanism shall cease to operate,
and that the current shall be properly re-established in the lamp and its light
continued.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Herbert John Haddan in the Great Seal Patent Office on
the 17th March 1880.
HERBERT JOHN HADDAN, of the Firm of Herbert and Company, Solicitors of
Patents, of 67, Strand, in the City of Westminster, Civil Engineer. "IMPROVEMENTS
IN ELECTRIC LAMPS AND MECHANISM FOR ELECTRIC LIGHTING." A communication
from abroad by Charles F. Brush, of Cleveland, Ohio, United States of America.
The Invention relates to electric lamps and it consists, first, in an electric lamp
having two or more sets of carbons adapted by any suitable means to burn succes-
sively (that is, one set after another); second, in a lamp having two or more sets
of carbons, each set adapted to move independently in burning and feeding; third,
in an electric lamp having two or more sets of carbons adapted each to have inde-
pendent movements, and each operated and influenced by the same electric current
to wit the general current operating the lamp; fourth, in a lamp having two or
more sets of carbons, said carbons by any suitable means being adapted to be
separated dissimultaneously, whereby the voltaic are between but a single set of
carbons is produced; fifth, in the combination with one of the carbons or carbon
holders of a lamp employing two or more sets of carbons, as above mentioned, of a
suitable collar, tube, or extended support of any kind within or upon which the
carbon (or carbon holder) to which it is applied shall rest and be supported; sixth,
in the combination with the mechanism operating the carbons of any voltaic arc
type of electric lamps of an automatic shunt or cut off, and a resistance so con-
structed, combined, and electrically connected that if for any reason the said shunt
or cut off shall have operated to extinguish the lamp, when it was in a normally
operative condition the light shall be automatically re-established upon a reunion of
the electrodes, as, for instance, if a carbon stick should break and thus destroy the
arc, in such a case the resistance in the lamps being infinite the cut off would
operate to shunt said lamp out of the circuit by establishing a path of low resistance
for the current outside of the electrodes and the mechanism operating them.
But whenever for any such accidental cause the cut off mechanism is called into
action it is not desirable that the lamp should be permanently extinguished for
the reason that the lamp proper is not at fault and is still in a perfectly operative
condition. The inventor's design therefore in this particular Invention is that
upon the reunion of the electrodes the cut off or shunting mechanism shall cease to
operate, and that the current shall be properly re-established in the lamp and its
light continued.
In the Drawings Figure 1 is an isometric view of a lamp embodying the Inven-
tion, the said lamp operating two sets of carbons. Accompanying Fig. 1 is a
diminished view of the lamp, showing its general appearance and proportions.
Fig. 2 is a detached view of the parts operating to lift the carbon rods and thus to
dissimultaneously separate the carbons of the two sets there shown; Fig. 3 is-a
detached view showing a supporting device (here appearing as a tube surrounding
a carbon holder, although it might be a rod or any other device) between the
carbon lifting or separating apparatus and one of the lifted carbons; Fig. 4 is a
vertical sectional view of device shown in Fig. 1; Fig. 5 is a view in longitudinal
section of a carbon holder in the shape of a tube, which tube constitutes the body
or cylinder of a dash pot and which also constitutes the moving element at the
dash pot, the piston or plunger being stationary; Fig. 6 are detachéd plan views
of the plunger and valve of the dashpot, shown in Fig 5; and Fig. 7 is a view
more fully illustrating the combination of cut off mechanism and a resistance above
referred to as the sixth division of the present Invention.
The Inventor desires to state at the outstart that this Invention is not limited in
its application to any specific form of lamp. It may be used in any form of voltaic
arc light regulators, and would need but a mere modification in mechanical form to
be adaptable to an indefinite variety of the present known forms of electric lamp.

page_text: The Invention comprehends broadly any electric lamp or electric light regulator
where more than one set of carbons are employed, where (say in a lamp having
two sets of carbons) one set will separate before the other.
For the purpose merely of showing and explaining the principles of operation
and use of this Invention it shall be described in the form of a lamp wherein the
moveable carbon is operated by a ring or annular clamp, or any friction clutch
surrounding the carbon holder, said clamp actuated and controlled in its move-
ments through the direct influence of magnetism generated by the current operating
the lamp.
The leading feature of this type of regulator is that the carbon holder has a rod
or tube which slides through or past a friction clutch, which clutch is operated
upon to grasp and move said carbon rod or holder, and thus to separate the carbons
and produce the voltaic are light, and it shall be referred to such a lamp in the
following description:-A represents one set of carbons; A¹, another set; each
carbon baving an independent holder B, B¹. The carbon holders B, B¹, may either
be in the form of a rod or tube, and each of them is made to pass through a
clamping and lifting device C, C¹, respectively. These clamps and lifters C, C₁, are
shewn in the present instance in the shape of rings surrounding their respective
carbon holders B, B¹. This form, while the inventor has found it for general
purposes the best, is not necessarily the only form of clamp that may be used in
carrying out the present Invention. Each ring clamp C, C¹, is adapted to be lifted
from a single point, thus lifting it and causing it to grasp and lift its inclosed carbon
holder. This tilting and lifting movement is imparted to the clamps C, C', by any
suitable lifter D, and this lifter may have its movement imparted either by magnetic
attraction due to the current operating the lamp, or by the expansive action of heat
upon any suitable apparatus connected with the lamp, said heat generated by the
electric current operating the lamp.
The inventor does not in any degree limit himself to any specific method or
mechanism for lifting, moving, or separating the carbon points or their holders so
long as the peculiar functions and results hereinafter to be specified shall be
accomplished.
The lifter D in the present instance is so formed that when it is raised it shall
not operate upon the clamps C, C₁, simultaneously, but shall lift first one and then
the other (preferably the clamp C first and C' second, for reasons which will herein-
after appear)..
This function of dissimultaneous action upon the carbons or their holders, whereby
one set of carbons shall be separated in advance of the other, constitutes the
principal and important feature of the present Invention. In the lamp shown in
the Drawings the lifter D is actuated and controlled through the agency of magnetic
attraction due to the influence of the current operating the lamp, and this is
accomplished as follows:-One, two, or more spools or hollow helices E of insulated
wire are placed in the circuit, within whose cavities freely move cores E¹. The
electric current passing through the helices E operates to strongly draw up within
their cavities their respective cores E¹.
The cores E¹ are rigidly attached to a common bar E2, and the upward and down-
ward movement of this bar, due to the varying attractions of the helices E, is
imparted by a suitable link-and-lever connection E³, E4, to the lifter D. By this
connection the lifter will have an up and down movement in exact concert with
the cores E¹, and it is apparent that this connection between magnet and lifter
may be indefinitely varied without any departure from the Invention, and therefore
while prefering for many purposes the construction just specified the inventor does
not propose to limit himself to its use.
The lifter D may be so constructed and applied as to separate the carbons A
and A' successively or dissimultaneously by being so balanced that any difference,
however slight, between the weights of the carbons A, A', or their holders B, B',
shall result in one being and separated before the other.
In order properly to balance the attractive force of the magnets a coil spring F,

page_text: or its equivalent, may be employed, substantially as shown; and to insure a steady
motion to the magnets and to the carbon points A, A, a dashpot G, or its equivalent,
should be employed, as this prevents any too sudden, abrupt, or excessive move-
ment of parts.
H, H¹, are metallic cables through which the current is conducted from above
the clamps C, C¹, to the carbons A, A¹. By this provision is not only insured a
good connection between the upper carbon points and the mechanism above it but
another important advantage is obtained, and that is the prevention of sparks due
to any interruption of the current between the carbon holder B, B', and its clamp
or bearings. This spark if occurring too frequently is liable to burn and roughen
the rods B, B¹, or their bearings, or clamps, and thereby render their operation
uncertain, because it is important that a free movement to any degree however
ninute may be allowed the carbon holder.
These cables H, H2, while operating as just specified are sufficiently flexible and
yielding not to interfere with any movement of their respective carbons or carbon
holders. The operation of the device as thus far specified is as follows:-
When the current is not passing through the lamp the positive and negative
carbons of each set A, A¹, are in actual contact.
When now a current is passed through the lamp the magnetic attraction of the
helices E will operate to raise the lifter D; this lifter D operating upon the clamps
C and C¹ tilts them and causes them to clamp and lift the carbon holders B, B',
and thus separate the carbons and produce the voltaic arc light. But it will be
especially noticed that the lifting and separation of these carbons is not simul-
taneous, one pair is separated before the other, it matters not how little nor how
short a time before. This separation breaks the circuit at that point, and the entire
current is now passing through the unseparated pair of carbons A', and now when
the lifter continues to rise separates these points the voltaic arc will be established
between them and the light thus produced.
It will be apparent by the foregoing that it is impossible that both pairs of
carbons A, A', should burn at once for any inequality of weight or balance between
them would result in one pair being separated before the other, and the voltaic arc
would appear between the last separated pair.
This function of embodying two or more sets or pairs of carbons so far as the
inventor is aware thas never been accomplished or attempted by any previous
Invention, and by thus being able to burn independently and one at a time two
or more carbons in a single lamp it is evident that a light may be constantly main-
tained for a prolonged period without replacing the carbons and without any
manual interference.
In the form of lamp shown in the Drawings one can with twelve inch carbons
maintain a steady and reliable light without any manual interference whatever for
a period varying from fourteen to twenty hours.
It is for some reasons desirable that one set of carbons (say the set A) should be
consumed before the other set commences to burn, although it is not essential in
carrying out the Invention that the carbons should be consumed in this manner,
inasmuch as if desirable they may be arranged to burn alternately instead of
successively.
It is apparent, however, if one set of carbons can be made to entirely consume
before another set begins to burn that there will be less interruption of the light
than if the different pairs were allowed to consume in frequent alternation. The
inventor has therefore shown in the present Invention one method of securing a
consumption of one set of carbons before another shall begin to burn. This is
accomplished through my suitable support K and in such a construction of the
lifter D that it shall be positive in its function of separating one set of carbons
before the other, or in case where more than two sets of carbons are employed to
separate said sets successively,
In the lamp, as shown in the Drawings, the support K is in the form of a tube
surrounding the carbon holder B, and this support K is made of such a length that

page_text: when the carbons A¹ shall have been sufficiently consumed a head upon the carbon
holder B will rest upon the top of the support K, whereby the weight of the carbon
holder B and its support K shall at all times and under any circumstances be sup-
ported by the lifter D.
Besides the carbon holder B with its carbon and the support K, the lifter D
(when the lamp is in operation) should also be made to carry the carbon holder B¹
and its carbon.
The lamp is primarily adjusted so that the magnets through the lifter D. shall
always carry a definite load, to wit (in the lamp shown), the carbon holders B and
B and support K. The desirability of this construction and arrangement may be
explained as follows:-
-
Supposing (as is designed in the present instance) the carbons A are first con-
sumed. During that time of course the magnets are lifting both carbon holders
B, B¹. Now when the carbons A are consumed if no provision were made to the
contrary the carbon holder B would not be lifted during the consumption of the
carbons A', and this diminishment of the weight carried by the magnets would be
liable to materially disturb the adjustment of the lamp and impair its operation
accordingly. To obviate this difficulty the inventor has provided the support K
by which provision the magnets shall always be made to carry both carbon holders
B, B', and the support K.
The difference in weight owing to the consumption of the carbons is a practically
unimportant matter, and does not materially interfere with the operation of the
lamp.
In the case of a lamp where the carbon holders B, B', are very light, and where
the weight of one might be relieved from the magnet (or other moving agent)
without material disturbance, the support K might be dispensed with. Said support
K might also be omitted, if desired, in a lamp where the lifter is actuated through
the agency of the expansion of a metal wire or bar by the action of heat generated
by the current operating the lamp, inasmuch as the force due to said expansion
being practically irresistable it would not be so necessary to obtain a balance
between various parts as is the case with a lamp, as shown in the Drawings.
Thus far have been mentioned but two ways of imparting dissimultaneous motion
to the carbons of an electric lamp, viz., through magnetic attraction and through
the expansive action of heat. This function of the device may be accomplished by
clock work, or equivalent mechanical contrivances, and in this respect, as before
stated, the inventor does not limit himself.
L, L', are metallic hoods or protectors for inclosing and shielding the upper
projecting ends of the carbon holders B, B'.
The poles of the lamp shown in the Drawings are constructed in the form of
suspending hooks or loops from which the lamp is suspended and the corresponding
hooks or loops with which they engage in the ceiling (or other locality where the
lamps are used) are the positive and negative poles of the current-generating
apparatus.
Thus by the simple act of suspension the lamp is placed in circuit ready for use.
Another feature of the improved lamp consists in the provision whereby the
protecting globe surrounding the light can be raised and lowered for convenience in
renewing carbons and handling the lamp. This is accomplished by making the
platform or gallery O upon which the globe rests vertically adjustable upon a rod
O' attached to the lamp frame in any convenient manner. A set screw should be
provided whereby the globe can be adjusted to any desired position.
By this arrangement the work of renewing carbons and the reliable adjustment
of the globe in relation to the voltaic arc are materially assisted.
In order to accommodate long sticks of carbons the platform or gallery O should
be perforated to allow passage down through it of said carbon stick. The inventor
prefers making the gallery Ŏ of metal, and of such shape that globules of molten
copper from the coverings of the carbons in dropping away shall not escape to do
damage

page_text: It will be particularly observed that in the form of dash pot employed, which is
shewn in Fig. 5 of the Drawings, the cylinder is the moveable and the piston or
plunger the stationary element.
This construction implies more than a mere reversal of the usual make and
operation of the dash pot, for by making the cylinder the moveable element the
general construction of a lamp can very often be materially simplified as in the
present instance, and its operation be made correspondingly more certain.
If desired the carbon holder may be either attached to or in reality form a part
of a dash pot, and Fig. 5 illustrates a case wherein the carbon holder is itself a
tube which constitutes the cylinder or body of a dash-pot and the moving element
thereof.
The piston or plunger of the dash-pot is shown stationary. Fig. 6 in plan view
illustrates the valvular construction of the plunger. It will be seen that the
plunger is itself a hollow cylinder perforated at its top, and upon this perforated
top rests a sliding disk which slides upon the plunger rod. Thus it will be seen
that in its upward movement (or the downward movement of the body or tube) it
will be retarded and will move slowly, while a positive movement can be accom-
plished with more ease and rapidity owing to the lifting of the valve and the escape
of fluid through the top of the piston or plunger.
The upper portion of the dash pot tube shown in Fig. 5 has an enlarged diameter
forming a reservoir which is designed to prevent overflow of the liquid contents of
the dash pot.
I will now proceed to a specific description of the 6th division of the Invention
as before set forth, wherein the functions alluded to may be automatically
performed.
Fig. 1 of the Drawings partially illustrates, and Fig. 7 more particularly shows
that which I shall now describe.
P is a bar or slab of wood, or any suitable electro non-conducting substance; Q
is an iron rod attached at its upper end to the slab P, and at its lower end to an
iron cross piece R; S is another rod of any material mechanically connecting the
parts R, P; and T is a holder for a carbon A¹. The parts A¹, T, R, Q, are electri-
cally connected with each other.
B is a vertically sliding rod or tube of brass, or other suitable electro non-con-
ducting material, ending below in a holder for. retaining a carbon A.
The separation of the electrodes A, A', is accomplished by moving the rod B in
the manner here specified, or in any other manner.
This portion of the present Invention is equally applicable to all forms of arc
lamps, that is, lamps wherein light is obtained by the passage of the electric
current through separated electrodes.
U is an electro magnet core of soft iron; it is surrounded by two helices V, VI,
and is attached to the slab P. The helix V is of coarse wire, and of corres-
pondingly low resistance. The helix V₁ is of fine wire, and it offers a higher
resistance to the current. This helix V is always in closed circuit with the
current operating the lamp. so that said current divides itself between the helix V¹,
and the lamp's electrodes in proportion to the relative resistances offered in these
two paths ir manner and effect hereinafter more fully to appear.
The coarse wire helix V connects with the pole W at one end and W¹, after
describing a sufficient number of convolutions about the core U, terminates blindly,
as shown at V2, thus forming no part of a closed circuit while the armature M2 is
separated from it as shown in the Drawings. The armature M² while being
insulated from the lamp frame is pivotally attached thereto. Its drop and con-
sequent distance in separation from the core U is determined by any suitable
adjustable stop M³. As the armature M2 is held closer to or farther from the core U,
a proportionally weaker or stronger current through the fino wire helix V' will be
required to lift said armature into contact with the blind end V2 of the coarse wire
helix V.

page_text: M is a resistance electrically connecting the armature M², and the pole W¹ of the
lamp. The lamp casing X is electrically connected with the rod B.
Having now specified one of a variety of means for carrying out this portion of
the Invention, I will now describe its principal operation.
While the lamp is in normal operation the various parts are in substantially the
relation shown in the Drawings, and the current is, say from the pole W₁ through
frame X, and rod B, to the carbon A. Thence through the carbon A, its holder T,
the cross piece R, and rod Q, to the opposite pole W.
Here is the path for the major portion of the current, but as already said there
are two paths between which the current divides itself, according to their respective
and relative resistances. One is that already traced out, the other is, say, from the
pole W through the wire V, fine wire helix V¹, coarse wire V, to the opposite
pole W¹. Now when the resistance of the lamp proper is normal the armature is
in its open circuit position, i.e., dropped down and separated from the blind end V2
of the coarse wire helix V.
But if, for any reason, the resistance in the lamp (say at the electric arc) is
abnormally great, then the current will be greatly increased through the fine wire
helix V¹ until the core becomes sufficiently magnetic to draw up its armature M²
into contact with the blind end V2 of the course wire helix. As soon as this con-
nection is made the electrodec are practically cut out of the circuit, for now the
path of the current is from pole W through the wire V, resistance M, armature M²,
and helix X, to the opposite pole W₁. So long as the current takes this course the
coarse-wire helix V forms a part of a closed ciecuit, and strongly magnetises the
core U.
We now find the electrodes A, A¹, and the mechanism separating them released
from the control of the operating current, therefore the carbons by force of gravity
will fall into contact, into the position of closed circuit. At this time, if the lamp
is in a normally operative condition it is desirable that the cut off or shunting
mechanism cease its operation, and that the current be again established through
the electrodes so as to produce the arc light. And this will be accomplished; for
now the carbons being united they will offer a passage to the current, having a
resistance so much lower than offered by the resistance M, that the current through
the coarse wire helix V will be so weakened that the core U will not be sufficiently
magnetic to sustain its armature M², which will drop, and thus break the circuit at
that point and reestablish the normal flow through the electrodes A, A¹. But if
the lamp is in such inoperative condition as to continue its abnormal resistance to
the passage of the current then the armature M² will not be released, but will be
maintained in its closed-circuit position, and the lamp will be permanently
extinguished. It will thus be seen that any accidental or immaterial cause, while
it may call into action for a time the shunting mechanism, will not result in the
continued extinguishment of the lamp.
The great utility of this automatic shunt will easily be recognized when it is
employed with lamps, several of which are burning in a single circuit; for in such
a case the putting out of one lamp would extinguish all the rest, unless the current
be provided a passage, as it were, around and outside of the faulty lamp.
The Inventor has found by repeated experiment and practical use, that in a
system according to this Invention where a number of lights are burning in a
single circuit, that the extinguishment and relighting of any lamp as heretofore
specified is certainly effected, and without any interruption of the remaining lights
on the circuit, the only influence being an augmentation of the arc proportionate
to the small increase of current passing through said remaining lamps.
The inventor does not limit himself to any definite number arrangement or con-
struction of parts in any device for carrying out his Invention. The form shown
in the Drawings is merely given to exhibit one embodiment of said Invention, and
to assist in explaining the same. Any form or construction of mechanism may be
adopted which shall operate, 1st., to automatically shunt the current from the lamp,
when for any cause it shall offer an abnormally great resistance, and 2nd., to

page_text: Te-establish the
normal operation of the extinguished lamp upon a reunion of its electrodes.
CLAIMS.
1. In an electric lamp two or more pairs or sets of carbons in combination with
mechanism constructed to separate said pairs dissimultaneously or successively,
substantially as and for the purposes specified.
2. In an electric lamp two or more pairs or sets of carbons in combination with
mechanism constructed to separate said pairs dissimultaneously or successively,
and establish the electric light between the numbers of but one pair (to wit the
pair last separated), while the members of the remaining pair or pairs are maintained
in a separated relation, substantially as shown.
3. In an electric lamp having more than one pair or set of carbons, the com-
bination with said carbon sets or pairs of mechanism, constructed to impart to them
independent and dissimultaneous separating and feeding movements, whereby the
electric light will be established between the numbers of but one of said pairs or
sets at a time, while the members of the remaining pair or pairs are maintained in
a separated relation, substantially as shown.
4. In a single electric lamp two or more pairs or sets of carbons all placed in
circuit, so that when their members are in contact the current may pass freely
through all said pairs alike in combination with mechanism constructed to separate
said pairs dissimultaneously or successively, as and for the purpose shown.
5. In an electric lamp wherein more than one set or pair of carbons are employed
the lifter D or its equivalent, moved by any suitable means, and constructed to act
upon said carbons (or carbon holders) dissimultaneously or successively, sub-
stantially as and for the purpose shown.
6. In an electric lamp wherein more than one pair or set of carbons are employed,
a clamp C or its equivalent for each said pair or set, said clamps C adapted to
grasp and move said carbons (or carbon holders) dissimultaneously or successively,
substantially as and for the purpose shown.
7. In an electric lamp the combination with a carbon holder, and the mechanism
moving said carbon holder of a lifter or support K, or its equivalent constructed to
operate in compelling the said moving mechanism to sustain the weight of the
carbon holder after its carbon is sufficiently consumed or removed, substantially as
and for the purpose described.
8. The resistance M or its equivalent in combination with any contrivance
adapted to shunt the current from an electric lamp, when, for any reason said
lamp shall offer an abnormally great resistance to the passage of the current
operating it, substantially as and for the purpose shown.
9. The combination with the electrodes A of an electric lamp and the mechanism
separating and governing said electrodes of a suitable shunt or cut off, and a re-
sistance M or its equivalent, said shunt or cut off adapted automatically to afford a
sufficiently free passage for the current independent of the lamp, when from any
cause said lamp shall offer an abnormally great resistance to the passage of said
current; and said resistance adapted on the union of said electrodes to weaken or
break the circuit through said shunt, and thus to re-establish the normal flow of
current through the electrodes and reproduce the light, substantially as shown.
In witness whereof, I, the said Herbert John Haddan, have hereunto set
my hand and seal, this Third day of February, A.D. 1880.