IMPROVEMENTS IN REFLECTORS
Year: 1881

page_text: LETTERS PATENT to Jasper Wetter, of New Wandsworth, Surrey, for an
Invention of "IMPROVEMENTS IN REFLECTORS." . A communication from
abroad by William Wheeler, of the State of Massachusetts, United States of
Amanian
PROVISIONAL SPECIFICATION left by the said Jasper Wetter at the Office
of the Commissioners of Patents on the 9th September 1881.
JASPER WETTER, of New Wandsworth, Surrey. "IMPROVEMENTS IN REFLECTORS."
A communication from abroad by William Wheeler, of the State of Massachusetts,
United States of America.
The Invention is particularly designed to provide improved forms of reflectors
of simple construction to be used in combination with any suitable light source,
but especially the electric arc, for the purpose of effecting a uniform and
economical lighting of a street or place, and in general to so direct and disperse
the light emanating from any suitable source that its full illuminating power may
be utilized in or about in the direction and within the prescribed limits of the space
to be lighted.
The Invention consists in a reflector having a continuous reflecting surface, such
as would be generated by the partial revolution of a conic-sectional curve on its
latus rectum, and by the partial revolution of such curve on its prolate axis at one
or each terminus of the partial revolution of the latus rectum, the axes of revolution
intersecting each other in the focus of the curve.
Also in a reflector having a continuous reflecting surface, such as would be
generated by the revolution of a conic-sectional curve about its axis and latus
rectum successively, the length of said curve being varied during different parts of
its revolution.
Also in a reflector consisting of two opposite parts, of which the reflecting
surfaces are such as would be generated respectively by the revolution of two
different conic sections having a common focus about their common axis.
Also in a reflector of two parts having reflecting surfaces of such forms as
would be generated respectively by the revolution of two different conic sections,
10

page_text: each about two or more axes of revolution successively, said axes being common to
both curves and intersecting each other in the common focus thereof.
Also in a reflector of two parts having reflecting surfaces of such forms as would
be generated respectively by the revolution of two different conic sections having
a common latus rectum.
Also in a reflector having a reflecting surface of such form as would be described
by the partial revolution about a common axis of two equal curves having a common
focus.
Also in a reflector having a reflecting surface such as would be generated by
the revolution of a conic-sectional curve about a line in the plane of said curve,
and meeting the axis of the curve perpendicularly in some point other than the
focus.
Also in a reflector having a reflecting surface such as would be generated by
the revolution of a conic sectional curve about two or more axes of revolution
successively, said axes intersecting each other in some point of the principal axis,
or the said axis produced other than the focus.
Also in a reflector having a reflecting surface generated by the revolution or
movement of a conic sectional curve about one or more lines intersecting its axis
or axes produced at right angles, the said curve revolving or moving in the aggrogate
360° about the said lino or lines.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Jasper Wetter in the Great Seal Patent Office on the 8th March
1882.
JASPER WETTER, of New Wandsworth, Surrey. "IMPROVEMENTS IN REFLECTORS."
A communication from abroad by William Wheeler, of the State of Massachusetts,
United States of America.
This Invention is particularly designed to provide improved forms of reflectors
of simple construction to be used in combination with any suitable light source.
but especially the electric arc, for the purpose of effecting a uniform and
economical lighting of a street or place, and in general to so direct and dispense
the light emanating from any suitable source that its full illuminating power may
be utilized in or about in the direction and within the prescribed limits of the space
to be lighted.
It is evident that when a reflector is not used a large proportion of the light
from a common street lamp (radiating as it does equally in all directions) passes
upward into space, while another almost equally large part is intercepted by the
top and bottom of the inclosing lantern without producing any valuable result.
Of the available remainder the greater part is spent in illuminating to a
disproportional excess the bed and sides of the street in the immediate vicinity of
the lamp, leaving to be applied to the general thoroughfare up and down the street
in the two directions in which the light is almost exclusively required only a small
fraction of the total lighting power expended.
In the case of the electric light now coming into use for such purposes, and
which from its excessive brilliancy and the greater space lighted thereby is usually
placed at a much greater elevation; only an extremely small per centage of its
light is utilized for achieving the purpose intended. Not less than fifty per cent.
of the light emitted is often totally lost, since all rays radiating upwards into spaco
above the horizontal plane of the are rather than in the direction in which they
are required must for that requirement be assumed to have no existence, while of
the other fifty per cent. at least one half is consumed in illuminating to a
disproportionate excess the sides of the street in the immediate vicinity of the
lamp within a distance up and down the street often times not exceeding its width,
thus leaving for the general lighting of the thoroughfare in both directions beyond
the above limits less than one fourth of the total lighting power expended.
The simple parabolic reflector concentrates into a beam of great intensity the
rays emanating from any light at its focus, but the concentration is too complete,
there is too little dispersion allowed, the path of illumination is made too narrow
for street lighting, the inner crossing of the rays in different directions is
insufficient, and there is not a sufficient adaptability of the form of the beams or
pencils and their relative intensities to the form and extent of the spaces to be
illumined thereby. For these and other reasons the simple parabolic and other
similar and substitute concentrators of light are poorly adapted for the genera!
purposes of street lighting.
The same objections apply to the combination of two simple reflectors having
the rear part of each removed, the said reflectors being placed back to back so as
to have a common focus. The combination of a simple focal reflector placed above or
below the light source with secondary reflectors used to again reflect the light in the
desired direction horizontally involves a complication and multiplicity of parts and
a waste of light due to two reflectors, and is capable of obviating only in a limited
degree the objections noted in the preceding paragraphs.

page_text: This Invention consists primarily in a reflector having a continuous reflecting
surface generated by the entire or partial revolution of a conic-section curve about
au ordinate of said curve, or about such, and also about the axis of the curve, or in
other words, by the revolution of a single curve about an ordinate of it, and
successively about two different axes which pass through the focus of the said
curve, such focus thereby becoming the common focus of the several parts of the
reflecting surface so generated.
This Invention consists secondarily in a reflector having its upper and lower or
two opposite reflecting surfaces, such as would be generated either as above
described or by the revolution of two different and unlike conic sectional curves
or combinations of such curves about a common axis, all as is here-
after fully described. Fig. 1 represents a reflector produced by the successive
revolution of the curve a, b, about the axis d, c, through an are of 180°, and about
the ordinate a, g, also through an are of 180°. In Figure 2 the line a, b, a¹
represents an elliptic curve, of which the line d, d', denotes that part of the major
axis included between the foci of the said curve at d and d', the line b, f, the minor
axis, and the lines a, g, and a', g'. the double ordinates through the foci. By the
revolution of the said curve a, b, a', successively about the axis d, e, or d, d', and
the double ordinate a, g, in the saine order of sequence, and through the same arcs,
as in the case represented by Figure 1, and omitting from the surface thus
generated the parts generated by the revolution of the lines f, g, and m, a", about
the double ordinate a, g, we obtain another form of reflector continuous throughout
covered by this Invention, in which the parts A and C extend in wing like
projections to a greater distance from the focus than as the parts B and D, all
being as represented by the full lines in said Figure 2. It is to be understood that
the outer limits 6' and a' of the generating curves a, b, and a, b, a¹, may be varied
in their distance from the focus a, both relating to each other and to the axis b, f,
as circumstances may render desirable.
The reflectors shown in Figures 1 and 2 may be placed in any desired and
suitable position, that is to say, so that either the latus rectum a, g, or the axis d, h,
shall be vertical. In the former case, for which the form represented in Figure 1
is well adapted, the light is supposed to be placed at the side of the street or
thoroughfare to be lighted thereby in the usual manner of street lamps with the
axis c, i, parallel thereto, and the mouth or aperture of the reflector facing across
and longitudinally up and down said street or thoroughfare. In this position the
parts A-and-C-intercept-and-reflect up and down the street-that-large-part-of-the-
whole light that would otherwise be spent in lighting to a disproportionate excess
a short length of houses or land immediately behind said light, while the parts
B and D render useful the light that would otherwise he spent in an excessive
illumination of the ground immediately below or in front of the light, and in
useless radiation upward into space respectively. Figure 5 represents a horizontal
section of the reflector shown in Figure 1, Figure 6 a front elevation, and
Figure 7 a side elevation of the same, the broken lines in said Figures repre-
senting the course of the rays as radiated from the light source and reflected
from the above described surfaces in accordance with the well known property of
surfaces generated by the revolution of conic sectional curves.
In certain cases the length of the generating curve during the partial revolu-
tion by which the side parts B and D would be described may be reduced even
In other words, the said parts B and D may be omitted, in which
we have the form shown at A, A, C, C¹, in Figure 3 and hereinafter
- described.-
to zero.
case
When the axis d, h, is made vertical, for which position the form of reflector
represented in Figure 2 is especially adapted, the light is supposed to be placed
high above the middle of the street or thoroughfare to be lighted thereby with
the axis c, i, parallel thereto, and the mouth or aperture of the reflector facing
directly downward and up and down said thoroughfare. In this position the
additional wings A' and C' intercept and reflect downward at different angles

page_text: into the street those rays that otherwise would pass out and upward through large
semicircular apertures at the sides or ends of the reflector to be lost in space, while
the said parts B and D) now prevent the light from passing out laterally over
and against the houses and lands immediately adjoining, and throw it down into
the street where it is required. Figure 8 represents a vertical section of the
reflector shown in Figure 2 in the position just described. Figure 9 an elevation
or plan as seen from below, and Figure 10 an end elevation of the same, the
broken and dotted lines in said Figures representing the course of the rays as
radiated from the light source and reflected from the above described surfaces in
accordance with the well known property of conic sectional curves.
Figure 3 represents in a double form a reflector having the upper parts A, A',.
and C, C¹, the same as the corresponding parts shewn and described in and in
reference to Figure 2, and the opposite or lower parts E and F hyperbolical
reflectors of 180°, having with said upper parts their common focus in d, and their
common axis in c, i. The said parts E and F intercept that light radiating
downward at more than a certain angle measured from the axis c, i, and cause
it to pass out a lesser angles with said axis in line radiating from the secondary
foci d and d", whereby said light is made effective at a greater distance from
the source, but always below the horizontal plane of the said source.
By means of this combination of the upper ellipsoidal reflector and the shorter
hyperbolical reflector below two valuable results are secured. First, the rays that
would otherwise be expanded in lighting to a disproportionate excess the
immediate vicinity below and beside the lamp, are distributed as desired and made
available at a greater distance; and, second, the rays that would otherwise be lost
in space above are reflected downward at different angles through the secondary
foci d and , and that part intercepted by the projecting wings A and C
utilized in imparting a moderate and normal degree of illumination to that space
immediately below and beside the lamp from which the direct rays are cut off as
described by the reflectors E and F. Figure 11 is a plan view of the reflector.
shown in Figure 3 as seen from below, and Figure 12 represents a vertical section
of the same, the broken and dotted lines in the said Figures exhibiting the course
of the light rays so radiated from the light source and reflected from the surfaces
of the said combination of reflectors.
It is to be understood that between the two quadrantal parts of both the
ellipsoidal reflecting surface c, c', and the hyperbolical surface E generated by the
revolution of their respective curves about their common axis d, d", may be inserted
sectors of surfaces generated by the revolution of said curves through any suitable
angle about their common vertical ordinates p, q, produced through the focus d
whereby the width of the aperture of said reflectors may be increased, substantially
as described in reference to and shown in Figure 1. Thus the form and
character of the pencil of rays emanating from a reflector formed by the revolution
of variously combined curves about variously combined axes of revolution, as
herein described, may be adapted to the form and extent of the place to be
illumined.
Figure 4 represents a reflector in two parts, the upper one of which has a
reflecting surface, such as would be generated by the revolution of the elliptic
curve a, b, a', about the ordinate a, d, while the lower one has such a reflecting
surface as would be generated by the revolution of the hyperbolic curve o, f, about
the ordinate o, d, the said curves having the focus d and the axis d, d', in common.
At the said focus d the light source is maintained.
By means of this special combination equal illumination is effected in directions
laterally. All or any desired part of the light radiated upward is reflected down-
ward in directions in which it will be most effective, that part intercepted by the
outer part of the upper reflector when sufficiently extended being so reflected as to
impart a normal degree of illumination to the space immediately below the lamp
from which the direct rays are cut off by the lower reflector in a manner similar
to that already described with reference to Figure 3.

page_text: Figure 13 represents a vertical section of the reflector, shown in Figure 4, with
a side elevation of the electric lamp shown in combination therewith, the broken
lines showing the course of the light rays as radiated from their source and reflected
from the surface generated as above explained.
Among the superior advantages of the ellipsoidal reflectors described above is
the noticeable fact that every part of the space illuminated receives its portion of
light from and through at least two different foci of such reflector, while with the
combination of the ellipsoidal with the hyperbolical forms nearly every illuminated
part of the field is lighted from and through three different foci of the reflector,
whereby is effected the result due to a group or chandelier of lights at and around
each lamp. The intercrossing of rays as from a multiplied number of sources thus
effected is productive of the brilliant, uniform, diffusive and tempered light most
to be desired in artificial illumination.
A simple method of manufacturing reflectors having surfaces such as would be
generated by the revolution of a curve upon two or more different axes succesively,
as in the cases represented by Figures 1 and 2, or by the revolution of two different
curves about the same axis as in the case shewn in Figures 3 and 4, is described as
follows:
=;
:
The form shown in Figure 1 consists of four parts, comprising two pairs of the
corresponding parts A, C, and B, D, respectively. To form the like parts A and C
a sheet of suitable material is shaped by spinning, stamping, hammering, moulding,
or otherwise into a paraboloid similar to an ordinary parabolic reflector, and its
ends cut in vertical planes intersecting the axis at the focus and aperture. It is
next to be cut into two halves by a plane passing through the axis, whereby we
obtain the two like parts A and C. The parts B and are similarly made from
one piece of suitable material formed into a suitable shape, with a cross section
corresponding to the two curves b, a, and a, m, in the position shown. It is next
cut into two halves in a plane passing through the latus-rectum of the generating
curve, whereby we have formed the two like parts B and D. Said parts A, C, B,
and D are next to be joined together in the positions shown, whereby a continuous
surface throughout will be formed. They may be of metal polished on the inside,
or the metal form may constitute a case to be lined with small plane pieces of
silvered glass suitably arranged in regular series, or the reflector may be of glass
silvered on the back side and the silver coating duly protected by varnish and a
thin metal covering. The reflector, shown in Figure 2, may be formed in like
manner as has been described-above,-the-additional-parts-A1-and--being
duplications of the parts A and C, and joined thereto in the positions shown.
The various parts of the combination represented in Figure 3 may be similarly
formed and joined. It is evident however that the junction of the upper and lower
parts (said parts being constructed upon entirely different curves) does not give a
continuous surface between the two. Hence they are joined by suitable connections
at the points of contact b, f, k, and m, and by other proper devices.
In the combination shewn in Fig. 4 the upper and lower parts of the reflector,
being separated from each other, are to be joined by the rods a', f, etc., as shewn,
or by any other suitable devices.
Again, the simple form of reflector represented in Fig. 1 may be formed of
sheet metal entire by spinning, using suitable cores and models for the guidance
of the metal plate and forming tool, as in the turning lathe for irregular forms.
Any of the reflectors above described may be used in combination with suitable
lantern bodies or otherwise.
In the remaining Figures of the Drawings I have represented other forms or
combirations of this Invention relating to reflectors.
The improvements shewn in the said Figures, No. 14 to 16 inclusive, consist in
a reflector having a linear focus and a reflecting surface generated by the revolution
or movement of a conic-sectional curve, about one or more lines intersecting its
axis or axes produced at right angles; the said curve revolving or moving in the
aggregate 360° about the said line or lines: The line or path described by the

page_text: focus of the said curve may therefore be circular, polygonal, elliptical, or even a
right line, which latter is an extreme modification of the ellipse.
parts
Fig. 14 is an isometric projection of a double reflector, the upper and lower
of which are constructed upon different curvaturos, in which the reflecting surface
of each part is such as would be described by the revolution of the curve of a conic
section about a line outside of such section and lying in the plane thereof, such
line intersecting the axis produced, whereby the focus of the generating curve
describes the circumference of a circle coincident with or constituting the
curvelinear focus of the reflecting surface thus described.
Fig. 15 shews a vertical section of the aforesaid reflector together with au
elevation of an electric lamp designed to produce and maintain therewith several
electric arcs in the said curvelinear focus.
In some cases the conic section may be reversed about a line at right angles to
the axis of the curve, and situated between the focus and the vortex of the curve,
in which case the line would be inside of the curve.
In said Figs. 14 and 15 A denotes the upper reflector, the reflecting surface of
which is of such form as would be described by the revolution of the elliptic
curve a, b, c, d, through an angular space of 360° about the line m, n, which lies
outside of the curve but in the plane of said curve produced, and intersects
perpendicularly in the point i the produced axis i, j, of the curve.
By the
revolution of the focus o of said curve about the said line m, n, the circum-
ference o, p, q, r, is described constituting a curvelinear or circular focus of the
reflecting surface A, in which the lights generated between the several carbon
pencils and l, 8 and t, uand v, etc., are maintained. In like manuer the reflecting
surface of the lower reflector C would be described by the revolution about the
line m, n, of the conic or hyperbolic curve e, f, g, having the focus o common to
both the upper and lower parts A and C.
It is evident that the upper and lower parts of the double reflector A, C, may be
made continuous with each other at their vertices and e, either by adapting
generating curves of different conic sections having a common vertex and focus, or
by using throughout a curve of the same conic section.
When the horizontal angular space to be lighted by the use of a reflector of this
description is less than 360° the revolution of the generating curve upon which
such reflector is formed about the line m, n, should be limited to the required
angular extent, and each of the reflectors so defined is to be formed by the
revolution of the said generating curve about its principal axis i, j, through an
arc 180°, whereby the width of the aperture of the reflector may be limited or
varied. In other words this Invention includes the formation of a reflector having
a continuous reflecting surface such as would be generated by the revolution of a
conic sectional curve, in mauuer substantially as described, about two or more axes
of revolution successively, the said axes intersecting each other in any point or
points of the principal axis or axes produced of said curve.
The orifice or opening through the reflectors A, C, formed within the circle
described by the vertex a of the generating curve may be occupied by the
standard E of the lamp shown in combination therewith, or by the shaft of a
column or tower upon which the cluster of lights is to be maintained, or it may be
used as a man-hole, all depending upon the size of the reflector, the manner in
which it is mounted, and the uses to which it is applied.
Figure 16 is an isometric projection of a reflector in which the reflecting surface
is such as would be generated by the successive semi-revolutions of a conic-section
curve about its latus-rectum, and by intermediate and intermittent movements
of the whole of said curve equally in opposite directions, whereby the focus of
the said curve describes a straight line which contains the foci of all the surfaces
thus described.
In said Figure 16 A and B denote the reflecting surface, such as would be
described by the two semi-revolutions and two intermediate rectilinear movements
of the elliptic curve b, c, that is to say, the elliptic curve is first to be moved

page_text: around the latus-rectum through an arc of 180°, next it is to be moved laterally or
rectilinearly a suitable distance o, q, next it is to be revolved on its latus-rectum
another half a revolution, after which it is to bo moved rectilinearly and laterally
back to its starting position. This form of reflectors is especially intended for use
with single lamps in which two sets of carbon pencils are employed, the second set
to be automatically put into the electric circuit only when the others are con-
sumed, thereby extending the effective duration of the light. The same form of
lamps are particularly well adapted for use in the reflector shown in Figs. 14
and 15.
It has been noticed that the focal path or orbit of the generating curve under
the form of revolution first described and shown in Figure 14 is circular. If we
conceive the radius of revolution or the distance from the axis of revolution to the
focus of the generating curve to be constantly variable, the said focal path or orbit
may be elliptical or be of some other curvelinear figure, while if the radius be
made zero and infinity successively, the focal path will be a straight line or a
succession of straight lines, as already shown in Figure 3, and hence may be
polygonal also.
Hence, if an extra amount of light is required in any direction, the reflector may
be so formed as to present at right angles to such direction a greater length of its
linear focus. An elliptical focus, for instant, should present its broadest side
toward the field or space to be most fully lighted.
Having thus described this Invention, what I claim as such, as hereinbefore
explained and represented in Figures 1 to 13 of the Drawings, is as follows, viz. :-
1. A reflector having a continuous reflecting surface, such as would be generated
by the partial revolution of a conic-sectional curve on its latus rectum, and hy
the partial revolution.of such curve on its prolato axis at one or each terminus of
the partial revolution of the latus rectum, the axes of revolution intersecting each
other in the focus of the curve, and all being substantially as set forth.
2. A reflector having a continuous reflecting surface, such as would be generated
by the revolution of a conic sectional curve about its axis and latus rectum
successively the length of said curve, being varied during different parts of its
revolution, substantially as set forth.
3. A reflector consisting of two opposite parts, of which the reflecting surfaces
are such as would be generated respectively by the revolution of two different
conic sections having a common focus about their common axis, substantially as
set forth.
4. A reflector_of_two_parts,-having-reflecting-surfaces-of-such forms as would
be generated respectively by the revolution of two different conic sections, each
about two or more axes of revolution successively, said axes being common to
both curves and intersecting each other in the common focus thereof, substantially
as set forth.
5. A reflector of two parts, having reflecting surfaces of such forms as would be
generated respectively by the revolution of two different conic sections having a
common lutus rectum, substantially as set forth.
6. A reflector having a reflecting surface, of such form as would be described by
the partial revolution about a common axis of two equal curves having a common
focus, substantially as set forth.
Furthermore what I claim, as herein before described with reference to Figures 14,
15, and 16, is as follows:-
1. A reflector having a reflecting surface, such as would be generated by the
revolution of a conic sectional curve about a line in the plane of said curve, and
meeting the axis or the axes produced of the curve perpendicularly in some point
other than the focus, substantially as set forth:
2. A reflector having a reflecting surface, such as would be generated by
the revolution of a conic-sectional-curve about two or more axes of revolution
successively, said axes intersecting each other in some point of the principal axis
or the said axes produced other than the focus, substantially as set forth.

page_text: 3. A reflector having a reflecting surface, generated by the revolution or move-
ment of a conic sectional curve about one or more lines, intersecting its axis or axes
produced at right angles, the said curve revolving or moving in the aggregate 360°
about the said line or lines, substantially as set forth.
In witness whereof, I the said Jasper Wetter, have hereunto set my hand
and seal, this 8th day of March, A.D. 1882.
J. WETTER. (L.S.)