IMPROVEMENTS IN PHOTOMETERS
Year: 1875

page_text: LETTERS PATENT to William Morgan-Brown, of the Firm of Brandon
and Morgan-Brown, Engineers and Patent Agents, of 38, South-
ampton Buildings, London, and 18, Rue Gaillon, Paris, for the.
Invention of "IMPROVEMENTS IN PHOTOMETERS."-A communication
from abroad by Otto Shuette, Engineer, of 13, Rue Gaillon, Paris..
PROVISIONAL SPECIFICATION left by the said William Morgan-
Brown at the Office of the Commissioners of Patents, with his
Petition, on the 21st May 1875. .
I, WILLIAM MORGAN-BROWN, of the Firm of Brandon and Morgan-
Brown, Engineers and Patent Agents, of 38, Southampton Buildings,
London, and 13, Rue Gaillon, Paris, do hereby declare the nature of
the said Invention for "IMPROVEMENTS IN PHOTOMETERS," to be as
follows:-

page_text: subsequent calculation, it consists in interposing between the eye and
the light to be measured a series of sheets of partially transparent
matter, such as paper of gradually and regularly increasing thickness,
each sheet being marked with a consecutive figure so as to form an
ascending scale, increasing in the same ratio as the thicknesses of
material interposed. For the highest figure of this scale I take as a
standard either a constant artificial light, or the sun at. midsummer at
its passage on the meridian which will correspond with the greatest
thickness of obturating material through which such figure can be read,
and for the lowest figure darkness or such absence of light that such
figure cannot be read through a material of the thinnest description.
For one form of instrument I make use of circular layers of paper
placed one over the other to the required thickness, the bottom one
being a completo disc, whilst I cut out sections of gradually increasing
surface on each successive sheet, so that the upper one will consist of a
mere angular strip of the same section as the amount cut out of the
second sheet; I call this assemblage of matter a photometric disc. I
mark a consecutive figure on each section, thus forming a photometric
scale, the lowest figure being marked on the bottom single sheet and the
highest figure on the upper section constituting the greatest thickness.
I place this disc in a small instrument provided, if requisite, with a
lens and focussing glass, and so arranged that when the other extremity
is placed to the eye each section on the disc being rotated will be
brought singly and successively to sight.
SPECIFICATION in pursuance of the conditions of the Letters Patent, 2
filed by the said William Morgan-Brown in the Great Seal Patent
Office on the 6th October 1875.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
MORGAN-BROWN, of the Firm of Brandon and Morgan-Brown, Engineers
and Patent Agents, of 38, Southampton Buildings, London, and 13, Rue 3
Gaillon, Paris, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Twenty-first day of May, in the year
of our Lord.One housand eight hundred and seventy-five, in the thirty-.

page_text: eighth year of Her reign, did, for Herself, Her heirs and successors,
give and grant unto me, the said William Morgan-Brown, Her special
license that I, the said William Morgan-Brown, my executors, adminis-
trators, and assigns, or such others as I, the said William Morgan-
Brown, 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 Inven-
tion for "IMPROVEMENTS IN PHOTOMETERS," a communication to me from
abroad by Otto Shuette, Engineer, of 18, Rue Gaillon, Paris, upon the
condition (amongst others) that I, the said William Morgan-Brown,
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 William Morgan-Brown, do hereby
declare the nature of the said Invention, and in what manner the
same is to be performed, to be particularly described and, ascertained
in and by the following statement thereof, that is to say :-
This system of measuring light can be practised by the aid of an
infinity of different arrangements and combinations, I will therefore
limit myself to describe conjointly with the twelve Figures of the
annexed Sheets of Drawings four different systems embodied, each in a
simple, portable, and inexpensive instrument giving accurate indications,
and requiring for their use no special scientific or technical knowledge.
I find convenient for one or the other of these systems to make use of thin
paper as the material for obturating light. I cut this paper into discs
and I superpose these discs, the lower one forming a complete circle
whilst from each successive disc I cut out an angular piece radiating
from the centre according to a constant and uniform progression, that
is to say, from each successive disc I abstract a regular and additional
fraction of paper until the remaining surface of the last disc is merely
equal to the quantity cut off from the second disc. Figure 1 represents
in plan, and Figure 2 in elevation a series of sixty of these discs super-
posed and numbered consecutively from 1 to 60.

page_text: First arrangement of instrument, Figures 3 and 4.-Figure 3 is a longi-
tudinal elevation in section, and Figuro 4 an end view of my first form
of photometer provided with one of my photometric discs a inserted in a
metal box b rotating at 6' centrally on the main body c, and which is
pierced with a series of holes d corresponding with each section of the
disc a; e is the ocular opening, and ƒ a small lens which directs the
visual ray on each section of the disc, whilst such sections are being
brought successively before the lens; instead of marking the numbers in
each disc as aforesaid, an independent disc of transparent or partially
transparent material may for that purpose be applied to the flat end of
the photometric disc; g is a ground glass, covering externally the photo-
metric disc. In this instrument the disc is supposed to consist in 20
superpositions of paper.
Second arrangements of instrument, Figures 5 and 6.-Figure 5 is a
longitudinal elevation in section, and Figure 6 an end view, with the 1
back plate taken off of my second form of photometer, in which I place
the photometric disc a in a rotating box b, which rotates eccentrically
in the mount c, and which is arranged in such a manner that the visual
ray passes directly in the centre of the instrument; f is a lens as in
the photometer, Figures 3 and 4, and i a tube for focussing purposes.
In this case each hole d is covered with a separate piece of glass, or all
the holes by one large sheet of glass . The figures of the photometric
scale are marked on these glasses instead of being marked on a sheet of
partly transparent paper, as in the case of the instrument above
described; g is a glass disc, covering externally the photometric disc a,
which latter in this case consists of 16 layers.
Third arrangement of instrument, Figures 7, 8, 9, and 10.-Figuro 7
is an external longitudinal elevation; Figure 8 a similar elevation in
section; Figure 9, a plan; and Figure 10, a second plan in section
through A, A, Figure 8, of my third form of photometer, in which I
substitute to the photometric dise a photometric ring a composed of
successively superposed layers of thin paper mounted on a tubo m, which
is susceptible of turning on the lower extremity of the tube c, provided
internally with a mirror n set at an angle of 45 degrees; the tube m is
pierced with as many holes as there are layers of paper on the photo-1
metric ring a, and the tube c is pierced with one hole c', before which on
the tube m being rotated each hole is caused to coincide. The visual
ray passes through the centre of this instrument and is projected at

page_text: right angles by its contact with the mirror n towards the centre of the
hole c' pierced in the tube c.
Fourth arrangement of instrument, Figures 11 and 12-Figure 11
is a plan, and Figure 12, a back elevation of a system of binocular
photometer constructed on the same principle as that described under
Figures 3 and 4, each tube being provided with similar photometric
disos, and caused to rotate in the same direction by means of the central
pinion p and gears o, o, as generally used for focussing opera glasses. In
this arrangement of instrument it is not necessary that both photometric
discs be provided with a figured scale. In the example illustrated the
photometric discs are supposed to be composed of 24 thicknesses.
When in use, either of the three first forms of this instrument must
be applied at e to one eye so as to exclude all extraneous light (the
other eye being closed), and directed towards the light to be measured;
the cap containing the photometric disc a is then to be rotated until
there be interposed between the eye and the light to be measured such
a thickness of the obturating material that the corresponding number
'thereon can only just be read. If this number be, 10 for instance, on
a scale graduated from 1.to 20, it will indicate that the light measured
is one half of the standard; if whilst in this position the instrument be
directed to an object less exposed to light, the said number 10 will no
longer be visible, and the cap will have to be turned back in direction
of the sections of lesser thickness, until a number be presented which
can just be read, which number corresponding to a lesser thickness of
material indicates the exact ratio of the light, with respect to the
former observation; if on the contrary it is directed towards an object
better lighted than in the first case, then the Figure 10 will be too
glaring, and the cap will have to be rotated in the contrary direction,
until such a number is presented that can only just be read. The
binocular instrument, Figures 11 and 12, is used in a similar manner,
with the exception that both eyes are employed instead of one. For
greater convenience I mark outside of the tube or mount c, Figures 8,
4, 5, 6, and 11, 12, a scale corresponding to the sections of the diso,
and on the rotating cap an arrow, so that the readings obtained inter-
nally are at the same time recorded or checked externally in my
photometer.
With mofosance to the instrument indiented at Figures 7. 8. 9. and 10.

page_text: .
plate of the mount, and the arrow on the under face of the rotating
ring m.
Having thus explained the nature of my Invention as well as the best
means that I am acquainted with for putting the same into practice, I
claim for my Invention,—
Firstly. The photometric disc a or its equivalent in the shape of a
ring, Figures 8 and 10, with their corresponding numbers marked
thercon, as above described.
Secondly. The different modes of construction and forms of instru-
ments wherein I place this photometric disc or ring with or without a
lens, or a focussing tube, or both, as above described.
Thirdly. The rotating caps or ring, as described, with reference to
Figures 3 and 4, 5 and 6, and 7, 8, 9, 10.
1
In witness whereof, I, the said William Morgan-Brown, have here-
unto set my hand and seal, this Twenty-seventh day of September, 1
in the year of our Lord One thousand eight hundred and seventy-
five.