AN IMPROVED MÓDE OF AND APPARATUS FOR ASCERTAINING THE ACTINIC POWER OF LIGHT
Year: 1868

page_text: LETTERS PATENT to Louis Bing, of Bishop's Stortford, in the County
of Hertford, Gentleman, for the Invention of "AN IMPROVED MÓDE
OF AND APPARATUS FOR ASCERTAINING THE ACTINIC POWER OF LIGHT,"
Sealed the 17th October 1868, and dated the 21st April 1868.
PROVISIONAL SPECIFICATION left by the said Louis Bing at the
Office of the Commissioners of Patents, with his Petition, on the
21st April 1868.
I, LOUIS BING, of Bishop's Stortford, in the County of Hertford,
Gentleman, do hereby declare the nature of the said Invention for
"AN IMPROVED MODE OF AND APPARATUS FOR ASCERTAINING THE ACTINIC POWER
OF LIGHT," to be as follows:-
My Invention of "An Improved Mode of and Apparatus for Ascer-
taining the Actinic Power of Light." has for its obiect to enable

page_text: photographers and others to determine with precision at any given
time the actinic power of light, and to apply that knowledge to practical
use. To this end I provide a surface on which the light shall fall in
such a manner as to produce a graduated series of shades ranging from
full light to any desired degree of obscurity, and for identifying and
defining the shades thus produced I apply thereto a graduated figured
scale. To the surface thus lighted I apply a sheet or strip of sensitive
or photogenic standard paper, and obtain thereon by exposure for a
determinate time a graduated representation of the progressive change
of tone from light to darkness. With such a scale for measuring the
actinic power of the rays of light the photographer is enabled to decide
with precision the length of exposure required for the time being for
his plate or printing paper in order to obtain certain determinate results.
The scientific investigator is moreover enabled to measure with precision
the degrees of the actinic power of the light for any given fraction
of time.
The instrument for the purpose of producing the graduated shades
of light may be constructed of various forms. Thus it may consist of
a single tube or a series of tubes of various lengths, or of hollow or solid
bodies in the shape of the parabola, ellipse, hyperbola, or sphere, or in any
other shape, whereby determinate graduations of shades may be pro-
duced. Thus for various photographic and scientific purposes I use
either a hollow body in the shape of half a parabola, to one side of which
I apply a strip of sensitized standard paper, and I apply to such strip a
scale made of metal, glass, or any other material, the unit being the first
division of such scale at the rim of the instrument; or I use a single
tube, to one side of the interior of which I apply a scale and a strip
of standard paper in the manner described with the parabola. A series
of tubes of varying lengths may also be employed to admit light
(according to their capacity) to a strip of standard sensitized paper
which will darken in a given time in proportion to the amount of light
admitted to various parts of its surface. The unit of the scale is formed
by the shortest tube, as that will admit the light most freely to the
sensitized paper. As a modification a series of tubes varying in
diameter may be employed for transmitting light to the sensitized
paper. In this case the tube of largest diameter forms the unit.
A series of parabolas, ellipses, or hyperbolas, or any other curved shapes

page_text: may also be employed to receive the rays of light in the manner already
explained.
SPECIFICATION in pursuance of the conditions of the Letters Patent
filed by the said Louis Bing in the Great Seal Patent Office on
the 21st October 1868.
•
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, LOUIS
BING, of Bishop's Stortford, in the County of Hertford, Gentleman,
send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Twenty-first day of April, in the year of
our Lord One thousand eight hundred and sixty-eight, in the thirty-
first year of Her reign, did, for Herself, Her heirs and successors, give
and grant unto me, the said Louis Bing, Her special licence that I,
the said Louis Bing, my executors, administrators, and assigns, or
such others as I, the said Louis Bing, 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 "AN IMPROVED MODE OF AND APPARATUS FOR
ASCERTAINING THE ACTINIC POWER OF LIGHT," upon the condition (amongst
others) that I, the said Louis Bing, 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 Letters
Patent.
NOW KNOW YE, that I, the said Louis Bing, do hereby declare
the nature of my said Invention, and in what manner the same is
to be performed, to be particularly described and ascertained in and by
the following statement :-
My Invention of "An Improved Mode of and Apparatus for
Ascertaining the Actinic Power of Light," has for its object to enable

page_text: photographers and others to determine with precision at any given
time the actinic power of light and to apply that knowledge to
practical use. To this end I provide a surface on which the light
shall fall in such a manner as to produce a graduated series of shades
ranging from full light to any desired degree of obscurity, and for
identifying and defining the shades thus produced I apply thereto a
graduated figured scale. To the surface thus lighted I apply a sheet
or strip of sensitive or photogenic standard paper, and obtain thereon
by exposure for a determinate time a graduated representation of the
progressive change of tone from light to darkness. With such a scale
for measuring the actinic power of the rays of light the photographer
is enabled to decide with precision the length of exposure required
for the time being for his plate or printing paper in order to obtain
certain determinate results. The scientific investigator moreover is
enabled to measure with precision the degrees of the actinic power of
the light for any given fraction of time.
The instrument for the purpose of producing the graduated shades of
light may be constructed of various forms. Thus it may consist of a
single tube or a series of tubes of various lengths or of hollow or solid
bodies of the form of the parabola, ellipse, hyperbola, or sphere, or of any
other suitable form whereby determinate graduations of shades may be
produced. Thus for various photographic and scientific purposes I use
either a hollow body in the shape of half a parabola, to one side of
which I apply a strip of sensitized standard paper, and I apply to such
strip a scale made of metal, glass, or any other material, the unit
being the first division of such scale at the rim of the instrument
or I use a single tube, to one side of the interior of which I apply
a scale and a strip of standard paper in the manner described with
regard to the parabola. A series of tubes of various lengths may
also be employed to admit light (according to their capacity to a
strip of standard sensitized paper which will darken in a given time
in proportion to the amount of light admitted to various parts of its
surface. The unit of the scale is formed by the shortest tube, as that
will admit the light most freely to the sensitized paper. As a modifi-
cation a series of tubes varying in diameter may be employed for
transmitting light to the sensitized paper, in this case the tube of
largest diameter forms the unit. A series of parabolas, ellipses, or

page_text: hyperbolas, or any other curved forms, may also be employed to receive
the rays of light in the manner already explained.
;
The details of the form of instrument I prefer to adopt are
these, namely, in a dark box I mount a cylinder, on the surface of
which I secure a sheet of sensitized paper by springs or otherwise;
on one side (which is moveable) of the dark box, I cut a slit in
which I fit a glass or other tube of square or other section having
three sides of yellow glass or of an opaque substance, and the fourth
side of glass or transparent material with the scale referred to above
marked thereon. The scale can also be produced upon a narrow piece
or rod of metal or opaque substance, and the paper which is to be
open to the light will then be affected quite freely. The scale is to
be marked with an opaque pigment or suitable substance, and this
pigment I prefer to have of a standard tint, or the scale may be marked
or made in any suitable manner. The moveable side is secured in
its position b springs which keep it pressed against the cylinder,
the top of the tube is supplied with a slide for shutting off and admitting
the light as required. When the light is admitted to the tube it acts
on that portion of the sensitized paper which bears against the trans-
parent side of the tube. When the exposed portion of the paper has
been acted upon sufficiently the cylinder can be slightly turned so as
to remove the exposed paper and bring a fresh portion opposite the
scale to be acted upon. When it is desired to compare the exposures
the cylinder can be moved back again so as to bring one half of each
exposure to view. The instrument when required to register the
actinic power of light during successive periods of a day can be
actuated by clockwork applied to communicate motion to the cylinder.
The form of the instrument can be modified to suit different cir-
cumstances, as will be evident to the practical man.
The following is a method for obtaining the graduated scale :-Draw
a rectangle in size equal to the longitudinal section of the tube, let
one of the lines representing the length also represent the surface on
which the scale should be drawn, and at right angles to and at one end
(the bottom of the tube) of this side draw a line one-half the length
of the tube, divide this line into any number of equal parts (say, ten).:
Produce the side opposite the surface side and from the end of the line.

page_text: drawn at right angles to the surface line draw a line passing through
the top of the surface line and intersecting the opposite line, and join
this point of intersection with the point dividing the line drawn
at right angles to the surface line, and where these lines cut the surface
line mark the divisions of the scale. The size of the tube, as also the
divisions of the scale, are optional, and may be varied to suit different
purposes.
In order that the nature of my said Invention, and the manner in
which the same can be performed or carried out in practice, may be more
readily understood, a Sheet of illustrative Drawings accompanying these
Presents which I will now proceed to describe.
Fig. 1, section of instrument constructed according to my Invention;
Fig. 2, plan of the same; Fig. 3, front elevation showing tube and
scale; Fig. 4, diagram to illustrate the method of obtaining the scale.
a, a, dark box; b, b, cylinder; c, c, springs for securing paper on
cylinder; d, d, moveable side of the dark box; e, e, tube; f, f, side of
tube with scale marked thereon; 9, 9, springs for securing moveable
side in its position; h, slide at top of tube for shutting off and admitting
light. These letters refer to Figs. 1, 2, 3.
1
2
In Fig. 4 let A, B, D, F, represent the tube and let A, B, be the side
on which the scale is to be drawn at right angles to A, B, and from
the point B draw a line B, C, one-half the length of A, B, divide B, C,
into ten equal parts, from C draw a line through A, and from the point E
where it intersects F, D, which should be produced, draw lines to the 2
points of division in B, C, and where these lines cut A, B, mark the
scale 1, 2, 3, 4, 5, and so on.
Having now particularly described the nature of the said Invention,
and in what manner the same is to be performed, I hereby declare
that I claim the herein described Invention of "An Improved Mode of 3
and Apparatus for Ascertaining the Actinic Power of Light," it being
understood that I do not claim the constituent parts of the instrument,

page_text: per se, and apart from the objects of the said Invention, as herein-before
set forth.
In witness whereof, I, the said Louis Bing, have hereunto set my
hand and seal, this Seventeenth day of October, in the year of
our Lord One thousand eight hundred and sixty-eight.
L. BING. (L.S.)
Witness,
ALEX. P. WRIGHT,
Secretary to the Inventors' Patent Right Association Limited,
21, Cockspur Street,
Charing Cross.