IMPROVEMENTS IN PRODUCING THE ELECTRIC LIGHT, AND IN LAMPS APPLICABLE TO THAT AND OTHER SOURCES OF ILLUMINATION."
Year: 1878

page_text: LETTERS PATENT to John Toby Sprague, of Bordesley Green, Birmingham,
in the County of Warwick, Electrician, for the Invention of "IMPROVEMENTS
IN PRODUCING THE ELECTRIC LIGHT, AND IN LAMPS APPLICABLE TO THAT
AND OTHER SOURCES OF ILLUMINATION."
PROVISIONAL SPECIFICATION left by the said John Toby Sprague at the
Office of the Commissioners of Patents on the 16th November 1878.
JOHN TOBY SPRAGUE, of Bordesley Green, Birmingham, in the County of
Warwick, Electrician. "IMPROVEMENTS IN PRODUCING THE ELECTRIC LIGHT, AND
IN LAMPS APPLICABLE TO THAT AND OTHER SOURCES OF ILLUMINATION."
My improvements in producing the electric light consist in substituting for the
ordinary electric arc, consisting of conductors with a variable space between them,
a closed circuit, consisting of a conducting substance capable of carrying the current
united with a substance capable of becoming incandescent and luminous.
For the purpose of maintaining the conductivity and conveying the current I
employ any conducting substance, such as carbon, or any suitable metals, either as
fine wires or rods, or in a finely divided state, using only so much as is necessary
to carry the desired current and to cause the developement of great heat. For the
luminous agent or incandescent substance I use any of the substances known to
possess that property, such as the various oxides, carbonates, sulphates, and silicates
of the earthy metals, such as calcium, barium, aluminum, and such like. These
latter substances I form into a pasty consistence intermingled with finely divided
carbon or metals; or I add to such paste any suitable metallic salt, which I reduce
to the metallic state by either an ordinary chemical agency or by heat, as may be
suitable, my improvements relating not to the particular substances used, but to
the intermingling them, so as to combine in one body the properties of conduction,
heating, and incandesence. This compound substance I form into rods or plates,
which are then dried, and in some cases heated; or in similar rods or plates of the

page_text: incandescent body I insert fine wires of metal or rods of carbon, so that these shall
conduct the current and generate the heat, while the incandescent body surrounding
them prevents their dissipation in consequence of this heat. I insert these com-
pound rods or plates between two supporting conductors connected to a source of
electricity. In some cases I use several such rods or plates for one light, and then
I construct one of the supporting sides in sections distinct from each other. Each
such section is provided with a conducting wire connected to a commutator, which
enables the current to be passed into one or more of the rods to increase or diminish
the light; or such commutator may be controlled by an electro-magnet actuated by
the current. This may be effected among other means by causing the armature to
press upon mercury contained in a vessel closed with an elastic membrane, or by
causing a rod of iron magnetized by the current to descend into a chamber in a
coil of wire containing a similar reservoir of mercury.
This action causes the
mercury to rise in a tube connected with the reservoir, and so make contact with
the ends of the several wires properly arranged in the tube.
My improvements in lamps for use with this or other lights aim at distributing
the light of the source evenly over the space to be illuminated instead of allowing
it to follow the natural law of diminution. I effect this by two reflectors, the
lower one of which I make of translucent material polished on the upper surface
to transmit only a portion of the light in the neighbourhood of the source, and to
reflect the rest of it upwards. This reflector I make in the form of a circular
trough or of a dish, rising in the centre and at the circumference in such curves as
to throw the reflected light against the upper reflector in such directions as will
allow this again to reflect it, as necessary; or the rise in the middle may be so
arranged as to send the rays against the outer edge, to be thence sent upwards.
The upper reflector I form as a curve, commencing in the light, and spreading
outwards to a suitable height and then again descending so far as to intercept as
much as possible the upward rays of the light, and to reflect them towards the
more distant portions of the space to be illuminated. The curves of both reflectors
will vary according to the distance to which the rays are intended to be sent.
The lower reflector may be opaque in some cases, and the upper reflector may be
either a bright metallic surface, or be of a white material to soften the light, and
produce the effect known as white-cloud illumination.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said John Toby Sprague in the Great Seal Patent Office on the
16th May 1879.
JOHN TOBY SPRAGUE, of Bordesley Green, Birmingham, in the County of
Warwick, Electrician. "IMPROVEMENTS IN PRODUCING THE ELECTRIC LIGHT, AND
IN LAMPS APPLICABLE TO THAT AND OTHER SOURCES OF ILLUMINATION."
My improvements in producing the electric light consist in substituting for the
ordinary electric-arc a closed circuit consisting of a conducting substance capable
of carrying the current united with a substance capable of becoming incandescent
and luminous.
For the purpose of maintaining the conductivity and conveying the current I
employ any conducting substance, such as carbon, or any suitable metals, either as
fine wires or rods or in a finely divided state, using only so much as is necessary
to convey the requisite current, while presenting resistance sufficient for the
developement of the requisite heat.
For the luminous agent I employ any of the substances known to possess the
property of becoming incandescent, such as various oxides, sulphates, carbonates,
and silicates of the earthy metals, calcium, barium, magnesium, aluminium, and
such like. These materials I unite together either by forming them into a pasty
consistence with water or by powerful pressure in the nearly dry state, so as to
form them into thin plates or rods. I do not limit myself to the use of the various
incandescent substances singly, as it is advantageous to use two or more together.
Thus by using finely divided asbestos or powdered steatite together with magnesia
or zirconia a stronger substance and a more effective lighting material is obtained
than either would produce alone. These earthy materials I intermingle thoroughly
with finely divided carbon or platinum; or in some cases I may make the substance
in layers coated with the conducting material; or I may add to the earthy material
salts, which may be afterwards reduced either by ordinary chemical agency or by
heat, as may be suitable, my improvements relating not to the particular substances
used, but to the using them so intermingled as to combine in one body the pro-
perties of conductivity, heating, and incandescence. The proportions to be used
will vary according to the conditions aimed at. When the source of electricity has
a high electro-motive force the material may be prepared so as to offer considerable
resistance; while if the force is low but large currents are to be used, the substance
may be made with a larger proportion of conducting material; or I use fine wires
of highly infusible metals or thin rods of carbon, and imbed them in the incan-
descent material, the extremities of the bars in this case being sheathed or fitted
with conducting plates connected to the conducting rods, the whole being so formed
as to prevent the dissipation of the conductor, while the heat generated shall
render the mass incandescent.
The rods or plates of the compound material I place between two supporting
conductors connected to a source of electricity. In some cases I use several such
rods or plates for one light, and then I construct one of the supporting sides in
sections electrically insulated from each other, and each connected to a commutator,
by which the current may be passed into so many of the rods as may be desired.
Such a commutator may be controlled by an electro magnet controlled by the
current in various ways, among others, by causing the armature to press upon
mercury contained in a vessel closed with an elastic membrane or by causing an
iron rod to descend into a tube containing mercury, and enclosed within a coil of
wire conveying the current. The mercury being pressed up into a tube connected
with the reservoir makes electrical contacts with wires properly adjusted in the
tube.
My improvements in lamps for use with the kind of light herein before described,
or other lights, aim at distributing the light of the source evenly over the space to

page_text: be illuminated instead of allowing it to follow the natural law of diminution by
distance. I effect this by reflectors so formed as to collect the light and distribute
it as required. I employ a reflector beneath the light formed of translucent
material, such as ground or opal glass, with a smooth upper surface; or in some
cases ordinary glass may be used coated with a thin film of silver or platinum,
such as is employed for mirrors, and which yet permits part of the light to pass.
This reflector diminishes the intensity of the light in the neighbourhood, and
reflects a portion to a distance. In order to produce this latter effect I make this
reflector in the form of a circular trough of such a section in the line A, B, in the
diagram accompanying this Specification, the form of which is designed to direct
the reflected rays upwards in a suitable manner. The curve in this reflector,
as in the others to be described, will vary according to the space intended to be
illuminated. Instead of reflecting the rays upwards this reflector may be formed
of the section shown in line C, D, so as to throw the rays outwards at once. A
small conical reflector of metal (E) is used to take up the downward rays, which
would be absorbed in the supports, and this reflector forms the end of a polished
metal tube surrounding the lower carbon of an electric regulator, or the support of
any kind of light, as shewn in F, A, and G, C, according to the construction of the
lower reflector. The upper reflector I form as a curve, which may be considered
as commencing in the light, but the commencement of this curve is modified, as
shown at H, J, in order to collect the upward rays. This curve rises at first, and
then descends to a point below the level of the light, so as to intercept the upward
rays, and direct them, as shown, into the space I, B, which may be filled with
ground glass, through which they pass to the more distant parts of the area to be
illuminated. The upper reflector may be formed of any suitable material, such as
polished metal, or of a white material to soften the light, and produce the effect
known as white cloud illumination. K, L, is part of a glass hemisphere, which
may be employed to enclose the light when the lower reflector is of the form C, D.
The form and construction of lamp will vary according to the requirements of each
case; the diagram therefore only illustrates the principles involved.
Having now particularly described and ascertained the nature and object of the
said Invention, and in what manner the same is to be performed or put in
practice, I hereby declare that I claim,―
1st. The use in a closed circuit of the compound incandescent conductors for
purposes of electric lighting, substantially as herein before set forth and described.
2nd. The construction of lamps for electric and other lights fitted with a trans-
lucent reflector below the light, and opaque reflector above, substantially as herein
set forth and described.
3rd. The use in upper reflectors of a curve of the nature shown in the accom-
panying Drawing, which after rising descends towards or below the level of the
light, substantially as herein set forth and described.
In witness whereof, I, the said John Toby Sprague, have hereunto set my
hand and seal, this Fourteenth day of May, in the year of our Lord One
thousand eight hundred and seventy-nine.