IMPROVEMENTS IN ELECTRIC LIGHTING APPARATUS
Year: 1880

page_text: LETTERS PATENT to William Robert Lake, of the Firm of Haseltine, Lake,
& Co., Patent Agents, Southampton Buildings, London, for an Invention of
"IMPROVEMENTS IN ELECTRIC LIGHTING APPARATUS." A communication
from abroad by Hiram Stevens Maxim, of Brooklyn, New York, United
States of America
PROVISIONAL SPECIFICATION left by the said William Robert Luke at the
Office of the Commissioners of Patents on the 27th October 1880.
IN
WILLIAM ROBERT LAKE, of the Firm of Haseltine, Lake, & Co., Patent Agents,
Southampton Buildings, London. " IMPROVEMENTS ELECTRIC LIGHTING
APPARATUS." [A communication from abroad by Hiram Stevens Maxim, of
Brooklyn, New York, United States of America.]
This Invention relates to the class of lamps or lighting apparatus known as
incandescent lamps, in which light is produced by the incandescence of a con-
tinuous strip or conductor of low conductivity, forming a part of the electrical
circuit of the lamp.
It has been found that carbon is the best material of which to construct the
light-giving or incandescent part of such lamps, on account both of its high
resistance and of its infusibility, but as carbon readily oxidizes at high tem-
peratures it is essential that it should be protected while highly heated from all
access of oxygen. For this purpose the carbon conductor has usually been enclosed
in a glass globe from which the air has been more or less perfectly exhausted or
excluded, and various means have been devised for making perfectly tight joints
about the conducting wires, such as stoppers of wood or other material sealed
with gum or wax, mercurial seals, and fusing the glass of the globe directly
upon conducting wires of platinum. Where the glass is sealed directly to or upon
the conducting wires, the carbon conductor must necessarily be made of quite high
resistance, as only small conducting wires can be used in lamps so constructed, on
account of the liability of the glass to crack if sealed to wires of any considerable
size. Other constructions have not provided so secure a joint, and none of the

page_text: constructions heretofore used have provided a perfectly secure joint about the
conducting wires so as to prevent all leakage of air into the globe, and at the same
time admitted of the ready and convenient removal and replacement of the carbon
conductor.
Perfectly secure joints are essential, and it is desirable under some circumstances
to use a conductor of low resistance, while it is also desirable that means should be
provided for the convenient replacement of the carbon. Even under the most
favorable circumstances the carbon conductor is of limited duration, and as its cost
is a very small fraction of that of the whole lamp, it is obvious that suitable means
should be provided for readily replacing it when it is worn out or destroyed.
It is the object of the present Invention to so construct the globe and the other
parts of the lamp that a conductor of any desired resistance may be used, and
that the lamp may be readily taken apart for the insertion of a new carbon, while
all the joints are perfectly tight and secure against any influx of air when the
globe is closed.
In carrying the said Invention into practice the carbon conductor or light-giving
part of the lamp is enclosed in the glass globe and clamped to the conducting
wires. The globe has a neck, which is made wide enough to permit of the free
passage of the carbon and its connections through it. I provide a hollow glass
stopper ground into the mouth of the neck of the globe so as to form as perfect a
joint as possible with it, and there is an opening for exhausting the air from the
globe. The inner end of the aforesaid stopper is constructed with two tubular
extensions which are sealed directly to the conducting wires, but when it is desired
to make the incandescent or light-giving part of the lamp of low resistance, each
of the conducting wires is divided into a greater or less number of branches
where it passes through the glass. The branches are all securely joined above and
below to the main parts of their conductors. I prefer to make the branches of
platinum and the main parts of the conductors of copper. By means of this device
I am enabled to use a current of much greater quantity, without danger of
fracturing the glass about the connections, than it has heretofore been practicable
to use in lamps having the globe sealed to the conducting wires. As is well known
only very small conducting wires can be used when the glass is sealed directly to
them on account of the liability of the glass to crack from the unequal expansion
and contraction of the parts, and as platinum is the metal which has been found
most available for conducting wires when sealed in this manner, and its con-
ductivity is comparatively low, it has been found necessary to make the conductor
of very high resistance, and to use a current of small quantity and high potential
in such lamps as they have heretofore been constructed.
Lamps of high resistance cannot well be used in any considerable number in
series on account of the immense electromotive force required for passing a current
through their combined resistances, and it is one of the objects of this Invention to
provide an incandescent lamp adapted to be used in series and capable of giving a
large amount of light.
By means of the device which I have described above I am enabled to decrease
the resistance of the carbon conductor and increase the quantity of the current by
increasing the number of the branches into which the conducting wires are divided
where they pass through the glass. Any number of branches may be used without
increasing the danger of fracturing the glass, provided the size of each branch is
made sufficiently small. Clamps by which the carbon is joined to the conducting
wires are made preferably of platinum, and the carbon is made broader and
thicker at the points of attachment to prevent danger of fusing the clamps; a cross-
piece of glass or other insulating material is clamped to the conducting wires to
hold them in position.
In order to prevent all possibility of leakage of air into the globe about the
stopper or the conducting wires, the neck of the globe above the stopper, and also
the stopper itself, are filled with wax or gum copal, melted and poured in. This
forms a supplemental seal, and if there should be any slight imperfections in the

page_text: joints about the stopper, all air will be effectually excluded, and the wax or gum
will keep its place, even if it is melted by the heat of the globe.
Instead of leaving a vacuum in the globe a rarefied atmosphere of hydrocarbon
vapor or gas may be introduced after the air is removed and before the globe is
sealed. It is evident that the pressure of the air will keep the stopper securely
seated, and as the globe and the stopper are of the same material, they expand and
contract equally upon heating and cooling, and the joint between them remains
tight. If there should be any inequality of expansion and contraction, the tapering
form of the stopper and the pressure of the outside air would keep the joint closed.
When it is desired to renew the carbon the tip at the opening is broken off, the
stopper is drawn out, and a now carbon is secured to the clamps. The stopper is
then replaced and the air is exhausted and the globe scaled as before.
Instead of sealing the opening a device may be used in which a glass cap is fitted
to the end of a tube with a ground joint. The said cap has a tubular branch on
the side for attachment to the air pump, and the opening in this branch corresponds
with an opening in the side of the stopper, so that as the cap is turned around
it acts as a faucet or valve. To make the joints entirely secure the opening in the
branch and the space in the cap above the joint may be filled with gum or wax in
the same manner as with the spaces about the stopper.
This improved lamp is especially adapted to be worked in series, as the resistance
of the carbon may be made as low as desired, and the lamp may be made of
sufficient size to give as much light as an ordinary voltaic are lamp. The same
construction may however be used for lamps of high resistance, adapted to bo
worked in multiple are as follows, that is to say:-The conductor is in this case made
longer, and of less diameter, so as to interpose much greater resistance, and as a
current of high electromotive force is used, the division of the conducting wires into
branches is not essential. The stopper has a rim or lip turned up about the edge
of the neck of the globe, and the neck is joined to this lip with a ground joint.
The lip flares out slightly above the joint, so as to form a trough for the reception
of gum or other sealing material, and is recurved, so that the material used will not
run out when the lamp is inverted. This latter formation of the parts about the
base is especially adapted to lamps in which the globe stands above the neck, and
the former construction to lamps in which the globe is suspended. The position of
the lamp is not material.
It is obvious that the stopper may be made in whole or in part of other material
than glass, provided the co-efficient of expansion of such material is approximately
the same as that of the glass of the globe. It is essential however that the part of
the stopper adjacent to the conducting wires should be made of metal which will
forn a tight joint with the metal of such conductors.
It is obvious that the division of the conducting wires into branches is
applicable to globes constructed in a single piece, as the advantages of such division
are not dependent upon the particular form or construction of the globe above
described.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said William Robert Lake in the Great Seal Patent Office on the 27th
April 1881.
WILLIAM ROBERT LAKE, of the Firm of Haseltine, Lake, and Co., Patent Agents,
Southampton Buildings, London. "IMPROVEMENTS IN ELECTRIC LIGHTING
APPARATUS." A communication from abroad by Hiram Stevens Maxim, of
Brooklyn, New York, United States of America.
"
This Invention relates to that class of lamps known as incandescent lamps, in
which light is produced by the incandescence of a continuous strip or conductor of
low conductivity, forming a part of the electrical circuit of the lamp.
It has been found that carbon is the best material of which to construct the
light-giving or incandescent part of such lamps, on account both of its high
resistance and of its infusibility, but as carbon readily oxidizes at high
temperatures it is essential that it should be protected while highly heated from
all access of oxygen. For this purpose the carbon conductor has usually been
enclosed in a glass globe from which the air has been more or less perfectly
exhausted or excluded, and various means have been devised for making perfectly
tight joints about the conducting wires, such as stoppers of wood or other material
sealed with gum or wax, mercurial seals, and fusing the glass of the globe directly
upon conducting wires of platinum. Where the glass is scaled directly to the
conducting wires the carbon conductor must necessarily be made of quite high
resistance, as only small conducting wires can be used in lamps so constructed, on
account of the liability of the glass to crack if sealed to wires of any considerable
size. Other constructions have not provided so secure a joint, and none of the
constructions heretofore used have provided a perfectly secure joint about the
conducting wires so as to prevent all leakage of air into the globe, and at the same
time admit of the ready and convenient removal and replacement of the carbon
conductor.
Perfectly secure joints are essential to the efficiency of the lamp, and it is
desirable under some circumstances to use a conductor of low resistance, while it is
also desirable that means should be provided for the convenient replacement of the
carbon. Even under the most favorable circumstances the efficiency of the carbon
conductor is of limited duration, and as its cost is a very small fraction of that of
the whole lamp it is obvious that suitable means should be provided for readily
replacing it when it is worn out or destroyed.
It is the object of the present Invention to so construct the globe and the other
parts of the lamp that a conductor of any desired resistance may be used, and that
the lamp may be readily taken apart for the insertion of a new carbon, while all
the joints are perfectly tight and secure against any influx of air when the globe is
closed.
In the Drawing,-
Figure 1 is a central vertical section of a lamp constructed in accordance with
the present Invention, with several transverse sections of the same taken at
different points.
Figure 2 is a detached view of the carbon conductor, shewing one of the clamps.
Figure 3 is a sectional view of a valve to be applied to the exhausting tube of
the globe of the said lamp.
Figure 4 is a side elevation of a modified form of the said lamp.
Figure 5 is a central vertical section of the same with transverse sections taken
at different points.
Figure 6 is a plan or top view of the same, and
Figure 7 is a transverso section taken on the line x, x, Figure 5.
Similar letters of reference indicate corresponding parts throughout the
Drawing

page_text: A is the carbon conductor or light-giving part of the lamp. It is enclosed in
the, preferably transparent, glass globe B, and clamped to the conducting wires C, C¹.
The globe has a neck D, which is made wide enough to permit of the free passage
of the carbon and its connections through it. E is a hollow glass stopper ground
into the mouth of the neck of the globe, so as to form as perfect a joint as possible
with it. At F is an opening for exhausting the air from the globe. The inner
end of the said stopper E is constructed with two tubular extensions G, G¹, which
are sealed directly to the conducting wires, but when it is desired to make the
incandescent or light-giving part of the lanp of low resistance each of the con-
ducting wires is divided into a greater or less number of branches where it passes
through the glass. This is best shewn in Figure 1, where C, C¹, are the main parts
of the conducting wires, and c, c, are the branches sealed into the glass. These
branches are all securely joined above and below to the main parts of their
conductors. I prefer to make the branches of platinum and the main parts of the
conductors of copper. By means of this device I am enabled to use a current of
much greater quantity without danger of fracturing the glass about the connections
than it has heretofore been practicable to use in lamps having the globe sealed to
the conducting wires. It is well known that only very small conducting wires can
be used when the glass is sealed directly to then on account of the liability of the
glass to crack from the unequal expansion and contraction of the parts, and as
platinum is the metal which has been found most available for conducting wires
when sealed in this manner, and its conductivity is comparatively low, it has been
found necessary to make the conductor of very high resistance, and to use a current
of small quantity and high potential in such lamps as they have been heretofore
constructed.
Lamps of high resistance caunot well be used in any considerable number in
series on account of the immense electromotive force required for passing a current
through their combined resistances, and it is one of the objects of this Invention
to provide an incandescent lamp adapted to be used in series, and capable of giving
a large amount of light.
By means of the device which I have described above I am enabled to decrease
the resistance of the carbon conductor and increase the quantity of the current by
increasing the number of the branches into which the conducting wires are divided
where they pass through the glass. Any number of branches may be used without
increasing the danger of fracturing the glass, provided the size of each branch is
made sufficiently small. The clamps H, H', by which the carbon is joined to the
conducting wires are made preferably of platinum, and the carbon is made broader
and thicker at the points of attachment to prevent danger of fusing the clamps.
J is a cross-piece of glass or other insulating material clamped to the conducting
wires to hold them in position.
In order to prevent any possibility of leakage of air into the globe, the stopper,
or the conducting wires, the neck of the said globe above the stopper, and also the
stopper itself, are filled with wax or gum copal melted and poured in, as shewn at
L, L, in Figure 1. This forms a supplemental seal, and if there should be any
slight imperfections in the joints about the stopper all air will be effectually
excluded, and the wax or gum will keep in its place, even if it is melted by the
heat of the globe.
The stopper, with the conducting wires and the carbon, being placed in position,
as shewn in Figure 1, the air is carefully exhausted from the globe as perfectly as
practicable through the opening F by means of a mercury air pump or other suitable
means, and the opening F is then hermetically sealed.
Instead of leaving a vacuum in the globe a rarefied atmosphere of hydrocarbon
vapor or gas may be introduced after the air is removed and before the globe is
sealed.
It is evident that the pressure of the air will keep the stopper securely seated,
and as the globe and the stopper are of the same material they expand and contract

page_text: equally upon beating and cooling, and the joint between them remains tight. If
there should be any inequality of expansion and contraction the tapering form of
the stopper and the pressure of the outside air would keep the joint closed. When
it is desired to renew the carbon the tip of F is broken off, the stopper E is drawn
out, and a new carbon is secured to the clamps. The stopper is then replaced and
the air is exhausted, and the globe sealed as before.
Instead of hermetically sealing the opening F the device shewn in Figure 3 may
be used, in which a glass cap M is fitted to the end of a tube with a ground joint.
The said cap has a tubular branch N on its side for attachment to the air pump,
and the opening in this branch N corresponds with an opening O in the side of F,
so that as the cap is turned around it acts as a faucet or valve. To make the joints
entirely secure the opening in the branch N and the space in the cap above the
joint may be filled with gun or wax in the same manner as the spaces about the
stopper.
This improved lamp is especially adapted to be worked in series, as the resistance
of the carbon may be made as low as desired, and the lamp may be made of
sufficient size to give as much light as an ordinary voltaic arc lamp. The same
construction may however be used for lamps of high resistance adapted to be
worked in multiple arc. In Figures 4, 5, 6, and 7 I have shewn my Invention as
applied to such a lamp. The conductor A is in this case made longer and of less
diameter so as to interpose a much greater resistance, and as a current of high
electromotive force is used the division of the conducting wires into branches is
not essential. The stopper has a rim or lip e turned up about the edge of the neck
of the globe, and the neck is joined to this lip by means of a ground joint. The
lip flares out slightly above the joint so as to form a trough for the reception of
gum or other sealing material, and is recurved, as shewn, so that the material used
will not run out when the lamp is inverted. This latter formation of the parts
about the base is especially adapted to lamps in which the globe stands above the
neck, and the former construction to lamps in which the globe is suspended. The
position of the lamp is not material.
In the form of lamp shewn in Figures 4 and 5 the cap or valve M is made in the
form of a stopper, as shewn, and the form of the parts is somewhat changed, but
their operation is substantially the same as that above described.
It is obvious that the stopper E may be made in whole or in part of other
material than glass, provided the co-efficient of expansion of such material is
approximately the same as that of the glass of the globe. It is essential however
that the part of the stopper adjacent to the conducting wires should be made of
metal, which will form a tight joint with the metal of such conductors.
It is obvious also that the division of the conducting wires into branches is
applicable to globes constructed in a single piece, as the advantages of such division
are not dependent upon the particular form or construction of the globe above
described.
Having thus fully described the said Invention as communicated to me by iny
foreign correspondent, and the manner of performing the same, I wish it understood
that I claim,-
First. In an electric lamp the combination of a transparent globe enclosing the
light giving part of the laup in a vacuum, with a stopper fitted to the mouth of
the said globe with a ground joint, and carrying the conducting wires scaled
directly into the material of which the said stopper is composed.
Second. In an electric lamp a transparent globe enclosing the light-giving part
of the lamp in a vacuum, in combination with a stopper fitted to the mouth of the
said globe, with a ground joint, and with gum or wax applied as a supplemental
seal outside of and above the said joint, substantially as above described and for the
purposes specified.
Third. In an electric lamp a globe enclosing the light giving part of the lamp in
a vacuum, in combination with a tapering stopper fitted to the mouth of the said

page_text: globe with a ground joint, conducting wires sealed into the material of the said
stopper, and a supplemental seal applied outside of and above the said joint,
substantially as above described and for the purposes specified.
Fourth. In an electric lamp a continuous incandescent conductor enclosed in a
transparent vacuum globe, in combination with conducting wires leading to the
said conductor, each of which is divided into two or more branches where it passes
into the said globe, substantially as above described and for the purpose
specified.
Fifth. In an electric lamp a transparent vacuum globe enclosing the light giving
part of the lamp, in combination with an exhausting tube and a valve fitted with
ground points, and a supplemental scal applied outside of and above such joints,
substantially as abovo described and for the purpose specified.
In witness whereof, I, the said William Robert Lake, have hereunto set my
hand and seal, this Twenty seventh day of April, in the year of our Lord
One thousand eight hundred and eighty one.