CERTAIN IMPROVEMENTS IN SIGNAL LAMPS
Year: 1872

page_text: LETTERS PATENT to Enoch Bassett Keeling, of No. 1, Verulam
Buildings, Gray's Inn, in the County of Middlesex, Architect, for
the Invention of "CERTAIN IMPROVEMENTS IN SIGNAL LAMPS.”
PROVISIONAL SPECIFICATION left by the said Enoch Bassett Keeling
at the Office of the Commissioners of Patents, with his Petition,
on the 18th January 1872.
I, ENOCH BASSETT KEELING, of No. 1, Verulam Buildings, Gray's
Inn, in the County of Middlesex, Architect, do hereby declare the nature
of the said Invention for "CERTAIN IMPROVEMENTS IN SIGNAL LAMPS," to be
as follows:-
-
My Invention is especially applicable to colored lights for maritime
uses and in connection with railways.
In the case of colored lights I propose to obtain the color required by
the use of glass of two or more colors other than the color required, my
object being to cause the emission of a greater amount of light of the

page_text: required color (by passing light separately through sheets of glass of the
two or more colors which will produce it) than if the light were passed
through sheets or a sheet of glass of the color required; in other words,
I produce the emission of light of the required color by mixing light of
the two or more colors which will produce the color required, instead of
mixing the color in the glass, or passing light directly through the glass
of the required color, or directly through two or more sheets of glass of
different colors. Thus a light seen through green glass (and especially
of the shade or tone known as signal green) can be seen with less
distinctness (that is to say, the light seen through glass of that color is
less brilliant) than if seen through blue glass or yellow glass of such
shades or tones of color as will in combination produce the same shade
or tone of green as that than which they are each more brilliant. The
inference being that green glass absorbs more, will emit less, and
obstructs light more than blue or yellow glass, I take a sheet of blue
glass and a sheet of yellow glass which placed together produce a green
of the required tone or shade, and placing a light behind each separately
mix the rays of blue and yellow light inside a lantern, so as to cause the
light seen from the outside through a colorless lens to be green of the
same shade as that produced by looking at onc light through the two
sheets (of blue and vellow) placed together (face to face, that is to say,

page_text: of one or of two or more colors in varying shapes and proportions, as
circumstances may require. From these reflectors and through these
surfaces of colored glass the light from the two or more lamps or
sources of light and color is thrown into and against a series of reflectors
of such shape, form, and arrangement, as to present such variety of
surfaces at such varieties of angles to the bodies of colored light as to
cause the general body of reflected light seen through outer lens to be of
the color seen by looking at a single source of light through sheets of
glass of the two or more colors used if placed together. These reflectors
form the top, bottom, back, and partly the sides of a light box or
chamber, of which the outer lens and the surfaces of colored glass (in
front of the lights) form the front and the remaining portion of the
sides, so that with the exception of the surface through which the light
of the compound color is emitted, and surfaces through which the com-
ponent colors and light are transmitted, the light box or chamber is
composed of reflecting surfaces designed to mix and blend the rays of
light of the component colors, and by the absence of all dark or
absorbing surfaces and the multiplication of light by reflectors acting on
cach other, to cause the greatest body of colored light of the compound
color to be seen through the outside colorless lens which can be procured
from any given power of light behind the surfaces of colored
glass.
I prefer to use for the light box or chamber a combination of plain
semi-spherical reflectors to form the top and bottom, and a prismatic
reflector of special curves for the back and part of the sides of the light
box or chamber; the special curves being formed on plan at top and
bottom by arcs struck from the same centre as the semi-spherical reflec-
tors forming the top and bottom of the light box or chamber, the centre
curve being struck to meet the same points from a centre in advance, or
nearer the reflector than that from which the top and bottom are struck,
thus allowing the top, bottom, and centre of the sides of such reflector
to be on the same vertical line. I may corrugate this reflector so as to
form zig-zags on plan of varying section. I propose to use this con-
struction of reflector not only in signal lamps comprising one or more of
my improvements, but also in signal lamps generally.
In addition to the objects of mixing the component colors to produce
the compound color, and the increase of light by reflection, the position
of the lights and of the surfaces of colored glass is intended to secure

page_text: an even texture of color, and an even intensity of light being presented
on the outside of the lens, and the absence of any visible centre of
light.
As to the amount of light obtainable from a given power in the sources
of light, there is a great advantage secured by the products of com-
bustion being confined to the small inner lanterns by the glass surfaces
forming the medium of color, and being thus shut out from all contact
with the surfaces of the reflectors forming the light box or chamber
immediately behind the outer lens, so that in cases where color is not
required there are the advantages of evenness of texture and intensity to 1
be secured from this mode of construction by the substitution of sheets
or lenses of colorless glass in the place of the colored glass; and in other
cases, where the front or outer lens is the medium of color, the con-
struction of lanterns in this manner admits of the production of improved
tone of color by the use of slightly tinted glass of similar or other colors 1
in front of the lights, and thus partially tinting the light before it passes
through the lens.
It will be evident from the preceding that all the clements of
my Invention are only necessary where the object is to produce a
light of a color capable of production by the use of two or more a
separate colors different to that required, such as a green light
produced by the combination of blue and yellow, or as a purple light
produced by the combination of red and blue.
That certain elements of my Invention are nevertheless applicable to
all colored lights where the required color is produced by the use of glass
of the color required, without the use of glass of two or more colors to
produce it, namely, the construction of the lamp, the form, shape, and
arrangement of the reflectors, the position and arrangement of the lights,
and the position and arrangement of the glass used to impart the
required color as seen from the outside of the lantern.
That in some cases the required color may be produced by the
position and arrangement of sheets of colored glass inside the lantern
quite independent of any color in the outside lens, through which the
light is seen from the outside.
That in some cases the required color may be produced by the position
and arrangement of sheets of colored glass inside the lantern of the same

page_text: or a different color to that required, in combination with a colored
outside lens of the same or a different color to that required.
That certain elements of my Invention are moreover applicable to
signal lamps where no color is required, namely, the construction of the
lamp, the position and arrangement of the lights, and the form, shape,
and arrangement of the reflectors, with or without the use of sheets of
glass inside the lantern, other than or in addition to the outside lens
through which the light is seen from the outside.
Also that certain elements of my Invention are applicable to colored
lights where the required color is produced entirely by the use of color in
the outside lens through which the light is seen from the outside, with
or without the use of sheets of colorless glass in the inside of the
lantern, namely, the construction of the lantern, the form, shape, and
arrangement of the reflectors, and the position and arrangement of the
lights.
I would further observe that it might in some cases be desirable to
use but a single source of light, invisible when looking through the
outer lens or glass from which the light is seen from the outside of the
lamp, as for instance where the dimensions of the lamp might be thus
reduced to meet some particular requirement.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Enoch Bassett Keeling in the Great Seal Patent
Office on the 17th July 1872.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ENOCH
BASSETT KEELING, of No. 1, Verulam Buildings, Gray's Inn, in the
County of Middlesex, Architect, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Eighteenth day of January, in the
year of our Lord One thousand eight hundred and seventy-two, in the
thirty-fifth year of Her reign, did, for Herself, Her heirs and suc-
cessors, give and grant unto me, the said Enoch Bassett Keeling,
Her special licence that I, the said Enoch Bassett Keeling, my
executors, administrators, and assigns, or such others as I, the said

page_text: Enoch Bassett Keeling, my executors, administrators, and assigns,
should at any time agree with, and no others, from time to time
and at all times thereafter during the term therein expressed,
should and lawfully might make, use, exercise, and vend, within the
United Kingdom of Great Britain and Ireland, the Channel Islands,
and Isle of Man, an Invention for "CERTAIN IMPROVEMENTS IN SIGNAL
LAMPS," upon the condition (amongst others) that I, the said Enoch
Bassett Keeling, my executors or administrators, by an instrument in
writing under my, or their, or one of their hands and seals, should
particularly describe and ascertain the nature of the said Invention,
and in what manner the same was to be performed, and cause
the same to be filed in the Great Seal Patent Office within six
calendar months next and immediately after the date of the said

page_text: more than blue or yellow glass, I take a sheet or sheets of blue glass and
a sheet or sheets of yellow glass, which placed together produce a green
of the required tone or shade (the proportion of blue and yellow placed
in front of cach source of light cannot be fixed, as it will be dependent
upon the tone of green required and upon the quality of the shades of
color used to produce it), and mix the rays of blue and yellow light inside
a lantern, so as to cause the light seen from the outside through a color-
less lens to be green of the same shade as that produced by looking at
one light through the two sheets (of blue and yellow) placed together
face to face, that is to say, one behind the other).
To produce the mixing of the two or more colored lights so as to
produce a light of the color seen by placing the two or more sheets of
colored glass together in front of one source of light, I place the two or
more lamps, candles, or source of light in such positions inside the
lantern as for the lights themselves not to be visible from any position
by looking through the outer glass or lens, through which the colored
light produced by the two or more separate colors is seen. In front of
these lamps, candles, or sources of light I place glass (whether sheets or
lenses) of the two or more colors used in producing the required color,
but so as for no portion of the surface of the sheets or lenses to be visible
from any position by looking through the outer and colorless lens,
through which the light of the required color is emitted. Behind these
lights I place reflectors of such form and shape as to transmit the
greatest amount of light at the greatest number and variety of angles
through the colored glass (whether sheets or lenses) in front of the
lights. The surfaces of color in front of each light may consist wholly
of one or of two or more colors, in varying shapes and proportions, as
circumstances may require. From these reflectors and through these
surfaces of colored glass the light from the two or more lamps or sources
of light and color is thrown into and against a series of reflectors of such
shape, form, and arrangement as to present such variety of surfaces at
such varieties of angles to the bodies of colored light as to cause the
general body of reflected light seen through outer lens to be of the color
seen by looking at a single source of light through sheets of glass of the
two or more colors used, if placed together. These reflectors form the
top, bottom, back, and partly the sides of a light box or chamber, of
which the outer lens and the surfaces of colored glass (in front of the
lights) form the front and the remaining portion of the sides; so that

page_text: with the exception of the surface through which the light of the com-
pound color is emitted, and surfaces through which the component colors
and light are transmitted, the light box or chamber is composed of
reflecting surfaces designed to mix and blend the rays of light of the
component colors, and by the absence of all dark or absorbing surfaces,
and the multiplication of light by reflectors acting on each other to
cause the greatest body of colored light of the compound color to be
seen through the outside colorless lens, which can be produced from
any given power of light behind the surfaces of colored glass.
I prefer to use for the light box or chamber a combination of plain
semi-spherical reflectors to form the top and bottom, and a prismatic
reflector of special curves for the back and part of the sides of the light
box or chamber, the special curves being formed on plan at top and
bottom by arcs struck from a centre on the same vertical line as the
semi-spherical reflectors forming the top and bottom of the light box or
chamber, the centre curve being struck to meet the same points from a
centre in advance or nearer the reflector than that from which the top
and bottom are struck, thus allowing the top, bottom, and centre of the
sides or edges of such reflector to be on the same vertical line. I may
corrugate this reflector so as to form zig-zags on plan of varying section,
or I may use a reflector formed of the curves stated with a plain surface,
that is to say, without a corrugation. I propose to use this construction
of reflector not only in signal lamps comprising one or more of my
improvements, but also in signal lamps generally.
On the accompanying Sheet of Drawing Fig. 1 represents a sectional
elevation through the body of a lamp embodying my Invention as
indicated by the line A, B, on plan; Fig. 2 is a sectional plan of the
above through the line C, D, showing the relative positions of lights,
reflectors, and glass lens.
A is the case or body of the lamp; B, B, are the two lights, which
may be candles or of any kind of lamp or other source of light, and in
front of which are sheets of glass U, C; D is a corrugated reflector to
which is attached the top reflector E, but may be detached if found
convenient; F is the bottom reflector; G is a glass lens; H, chimney
or flue.
The light passing through the glasses C, C, is mixed and blended

page_text: in the centre of reflector D, from whence it is reflected through the
lens G.
As above stated the glasses C, C, may be of two or more colors, the
blending of which will produce the color required to be reflected through
5 lens G, or they may be of one color only, and the lens G will be colorless
or otherwise, according to the light required.
It will be seen that an arc struck from the centre a of top reflector E
will meet the line c of reflector D, and another from the centre of E will
meet the line f, but that to meet the centre d of reflector D an arc must
Obe struck from 6, by which novel method of construction I obtain the
top, bottom, and centre of the sides on the same vertical line; the
curvation to the centre d concentrates the rays of light in front of the
lens G, but an equal distribution of light along its whole centre is
secured. The top and bottom reflectors E, F, may be joined to the
5 reflector D, or separate therefrom, as may be desired.
may be set in sliding frames or fitted in any suitable manner.
The glasses C, C,
I would also observe that to suit the shape of the lamp to certain
exceptional situations and where no mixing of colored light is needed
only one source of light B may be used.
In addition to the objects of mixing the component colors to produce
the compound color and the increase of light by reflection, the position
of the lights and of the surfaces of colored glass is intended to secure an
even texture of color, and an even intensity of light being presented on
the outside of the lens, and the absence of any visible centre of light.
As to the amount of light obtainable from a given power in the sources
of light there is a great advantage secured by the products of combustion
being confined to the small inner lanterns by the glass surfaces forming
the medium of color, and being thus shut out from all contact with the
surfaces of the reflectors forming the light box or chamber immediately
behind the outer lens, so that in cases where color is not required there
are the advantages of evenness of texture and intensity to be secured
from this mode of construction, by the substitution of sheets or lenses of
colorless glass in the place of the colored glass, as also by the isolation
the front lens is kept cool, and is consequently not liable to "fly" or
crack from the contact of the sea spray, and in other cases where the

page_text: front or outer lens is the medium of color the construction of lanterns
in this manner admits of the production of improved tone of color by the
use of slightly tinted glass, of similar or other colors, in front of the
lights, and thus partially tinting the light before it passes through
the lens.
It will be evident from the preceding that all the elements of my
Invention are only necessary when the object is to produce a light of a
color capable of production by the use of two or more separate colors
different to that required, such as a green light produced by the com-
bination of blue and yellow, or as a purple light produced by the
combination of red and blue.
That certain elements of my Invention are nevertheless applicable to
all colored lights where the required color is produced by the use of glass
of the color required without the use of glass of two or more colors to
produce it, namely, the construction of the lamp, the form, shape, and
arrangement of the reflectors, the position and arrangement of the lights,
and the position and arrangement of the glass used to impart the required
color as seen from the outside of the lantern.
That in some cases the required color may be produced by the position
and arrangement of sheets of colored glass inside the lantern, quite
independent of any color in the outside lens, through which the light is
seen from the outside.
That in some cases the required color may be produced by the position
and arrangement of sheets of colored glass inside the lantern of the same
or a different color to that required in combination with a colored outside
lens of the same or a different color to that required.
That certain elements of my Invention are moreover applicable to
signal lamps where no color is required; namely, the construction of the
lamp, the position and arrangement of the lights, and the form, shape,
and arrangement of the reflectors, with or without the use of sheets of
glass inside the lantern other than or in addition to the outside lens
through which the light is seen from the outside.
Also that certain elements of my Invention are applicable to colored
lights where the required color is produced entirely by the use of color
in the outside lens through which the light is seen from the outside, with
or without the use of sheets of colorless glass in the inside of the lantern,

page_text: Lastly. The use of sheets of plain or colored glass as at C, C, for the
purpose of isolating or shutting off the sources of light, and consequently
the products of combustion, from the main body of the lamp and the
autan lana
In witness whereof, I, the said Enoch Bassett Keeling, have here- 5
unto set my hand and seal, this day of July, in the year of
our Lord One thousand eight hundred and seventy-two.