Improvements in Photometers.
Year: 1890

page_text: Date of Application, 25th Mar., 1890
Complete Specification Left, 29th Dec., 1890--Accepted, 25th Mar., 1891
We, WILLIAM
PROVISIONAL SPECIFICATION.
Improvements in Photometers.
FRIESE GREENE, of 92, Piccadilly, Photographer, and
FREDERICK HENRY VARLEY, of 82, Newington Green Road, Civil Engineer,
in the County of London, do hereby declare the nature of this invention to be as
follows:-
Our invention consists in employing two rotatory discs or shutters pierced with
two semi-circular apertures placed one before the other and driving them at such a
speed that the said apertures produce a circular luminous band when light is passing
through and in an appliance for opening and closing the apertures whilst the discs
are rotating and thereby determining the amount of light by the angular values of
the opening.
Dated this 24th day of March 1890.
WILLIAM FRIESE GREENE.
FREDERICK H. VARLEY.
COMPLETE SPECIFICATION.
Improvements in Photometers.
We, WILLIAM FRIESE GREENE, of 92, Piccadilly, in the County of London,
Photographer, and FREDERICK HENRY VARLEY, of 82, Newington Green Road,
in the County of London, Civil Engineer, 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:-
This invention relates to an improved photometer, wherein both the standard
light and the light to be measured are placed at the same distance from the screen
on which they are to be balanced, and are simultaneously projected through
separate variable apertures made in opposite rotating discs which can be adjusted
during rotation until the amount of light from the one source passing to the screen
through one of such apertures balances that from the other source passing thereto
through the other of such apertures, the comparison being made by the respective
lights reaching the screen, or by shadows cast by such lights thereon, such lights
or shadows (in consequence of the standard light and the light to be measured
being placed at the same distance from the screen) being of equal size, so that the
luminosity or density thereof respectively when balanced is the same for equal
areas; and wherein, when the lights are thus balanced on the screen, the angular
values of the respective apertures determine the respective values of the lights and
are respectively directly indicated and can be directly read off.
In the improved photometer, two opposite rotary discs or shutters are used, one
of which is, or both of which may be, peripherally graduated, and each of which is
formed with separate apertures at different radial distances from its axis of rotation,
such apertures preferably being two in number, each semicircular in extent and
arranged with their diameters at right angles to each other. The discs are mounted
side by side, but not in contact, on separate shafts with their axes of rotation
coincident, and their respective apertures in opposite or coincident pairs as regards
their radial distances from said axis, but so arranged as that one of such coincident
pairs of apertures is open to its full angular extent (say, a semicircle, as aforesaid)
at such time as the other of such coincident pair of apertures is completely closed.
The aforesaid dises are combined with a pair of collimators, funnels or other
suitable means of projecting the lights to be measured on to the screen upon which
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page_text: they are to be balanced, such devices being so arranged relatively to the said dises
as to project the lights respectively through the said different coincident pairs of
apertures on to the screen.
'
The aforesaid discs are also combined with means for rotating them at differential
speeds, or at the same speed at the will of the operator, in the former case for the
purpose of causing one of such discs to advance on the other an equal amount at
cach revolution, whereby both such opposite or coincident pairs of apertures are
caused simultaneously to have constantly varying angular openings admitting the
passage of the respective lights alternating with constantly varying closed
segments preventing the passage of such lights, the one of such angular openings
increasing or decreasing in the ratio of the decrease or increase respectively of the
other thereof, while the following dark or closed segments respectively correspond-
ingly decrease and increase or increase and decrease in the like ratio.
The discs are driven at such a speed as to cause the said angular openings of
their said apertures to appear (owing to the phenomenon of the persistence of
vision) when light is passing therethrough, as concentric luminous bands, the
relative luminosity of which is dependent upon the amount of light passing through
the respective openings, which amount is dependent upon the relative angular
extents of such openings and of the following closed segments, so that, when the
apparatus is driven at such speed by the aforesaid differential gearing, such bands
will appear of constantly differing relative luminosity due to the constantly varying
amounts of the angular openings of said apertures and of the following closed
segments-thus, the amounts of light projected, as aforesaid, from the said sources
of light through the said collimators, funnels or other equivalent apparatus, which
pass through the said apertures to the screen, will be directly proportional as the
angular extent of one of said openings is to that of the other.
The apparatus is continued in motion until the lights or shadows projected upon
the screen are balanced, when the differential gearing is disconnected from the
discs, and the motion of the apparatus is stopped the angular openings of the said
apertures, at such time, are directly indicated by the said peripheral graduation of
one or other or of both of the discs and indicate the relative intensities of the lights,
and can be read off in the form of a simple fraction, say, for example, 100 +
indicating that the one light is four times more intense than the other.
=====
When the differential gearing is disconnected from the discs, the motion of the
latter may then (if required) be continued at the same speed, without altering the
relative angular openings of their said apertures for continued comparison of the said
lights or shadows projected upon the screen.
Such being the nature and object of the said invention we will now proceed to
describe more in detail the manner in which the same is to be or may be performed
or carried into practical effect, and in order that the invention may be completely
understood we have annexed hereunto a sheet of drawings illustrative of such a
photometer as aforesaid and have marked the same with figures of reference corre-
sponding with those in the following explanation thereof.
On the accompanying drawings
Fig. 1 represents a front elevation of the improved apparatus;
Fig. 2, represents a side elevation thereof;
Fig. represents a plan view thereof, partly in section:
Fig. +, represents a sectional elevation thereof through the plane indicated by the
line ab, Fig. 3, looking in the direction of the arrow c.
Fig. 5, represents a sectional elevation thereof through the plane indicated by
the line de, Fig. 3, looking in the direction of the arrow, 7.
Figs. 6, represent sectional views of collimators such as hereinafter referred to.
7, represents a suitable stand to which is screwed or otherwise suitably secured a
casting 8, forined with front and rear standards 9, 10, into which are screwed
bearings 11, suitable for supporting the spindle 12, upon which there is mounted
fast one, 13, of the said discs, a toothed or frictional pinion 14, and a pulley 15,
which is driven by a band 16, from a manually actuated driving pulley 17, which

page_text: is supported by an adjustable stud 18, working in a slot 19, made in a depending
extension 20, of the standard 9, and secured by a set nut 21, the pulley 17, being
secured on the stud by a thumb mut 22. The other disc 23, is mounted fast on a
tubular spindle 24, which surrounds the spindle 12, and is fast with a toothed or
friction pinion 25, similar to the pinion 14, and such disc, when not in gear with the
differential gearing hereinafter described is driven at the same speed as the disc 13,
by the frictional contact between the bosses of the pinions 14, 25, and of the
discs 13, 23.
Each disc is formed with apertures 26, 27, at different radial distances
from its axis, such apertures being preferably but not necessarily of the formation
and relative position represented on the accompanying drawings most clearly
in Fig. 4, wherein the coincident (as regards their radial distance from their
common axis of rotation) apertures 26, are also coincident in position, and fully
opened so as to admit light through their whole angular extent, and wherein the
other coincident (as regards their radial distance from their common axis of
rotation) apertures 27, are, at such time, respectively on opposite sides of the axis
of motion and so do not, at such time, admit of the passage of any light. The
periphery of the apertured side of each disc is preferably strengthened and balanced
so as to avoid any undesirable vibration by projecting parts 28. The periphery of
the disc 13, is graduated, for a semicircle or to any other required extent, and
with any suitable equal subdivisions, say for example, 2000 to the semicircle, which
may be further subdivided by a vernier and such graduations are
spondingly numbered from both ends towards the right and left respectively,
and the periphery of the disc 23, is cut away as at 29, to exhibit such sub-
divided half-circle, the ends of such recessed periphery 29, acting as indicators
on the doubly numbered graduated scale of the other disc, and thus indicating
the respective angular values of the openings of the apertures 26, 27, vide Fig. 1.
30, 31, represent a suitable modification of the aforesaid differential gearing
which may be toothed or frictional. The gearing represented is toothed.
and consists of two wheels 30, 31, fast together, the one (the driven or driving
one) having a tooth more than the other, so that, as such wheels respec-
tively engage with the pinions 14, 25, which are of an equal diameter or have
an equal number of teeth, from one of which (the pinion 14,) the wheel 13,
receives the motion, and to the other of which (the pinion 25,) the connected
wheel 31, imparts the motion received, but differentially, the discs 13, 23, are
respectively advanced in the proportions of the wheels 30, 31. In the modification
represented, two such arrangements of differential gearing are used, in the one of
which the driven wheel 30, and in the other of which the driving wheel 31, has one
more tooth than the other connected wheel the use of two such arrangements being
of advantage in permitting of either of the said dises being caused to advance on
the other one as may be desired.
corre-
Such arrangement or arrangements of differential gearing is or are mounted in
brackets 32, and an adjustable carrier 33, which latter is held with a sufficient
frictional contact against the standard 9, to prevent its shifting out of its desired
position, by springs 34, which are located by screws 35, which also act as guides to
the carrier 33, the position of which can be raised or lowered so as to bring one or
other of the said arrangements of differential gearing into engagement with the
pinions 14, 25, or can be set so that both of such arrangements of differential
gearing will be out of gear with such pinions, by a hand-lever 36, centred at 37,
to the standard 9, and linked as at 38, to the carrier 33, the position of the hand-
lever being determined by a stopping plate 39, with recesses 40, in which there
engages a projection 41, on a spring plate 42, carried by the handle 36.
The carrier 33, is slotted at 43, where the spindle 12, passes through, to permit
of its adjustment, and the standard 9, is slotted at 44, to permit of the convenient
placement of the spindle 12.
45, represents convenient standards, which are supported by the stand 7, and are
adapted to receive funnels 46, at the mouths of which the lights to be tested are
situated, suitable provision being made to prevent the one light from interfering

page_text: with the other. Or, in lieu of such funnels, two equal collimating tubes 47, 47*,
ride Figs. 6, may be used, and applied to such standards 45, the one 47, of such
tubes projecting an annular disc of light around a black centre, and the other 47×,
projecting a luminous disc corresponding in size to the said black centre. While one
or other of the lights passing through the said apertures preponderates, the said centre
and annular parts of the light reaching the screen will be of different luminosity;
to balance such lights, the apparatus is set in motion until an uniformly luminous
disc is projected. Or the lights may be caused to project shadows on the screen,
in which event a T-shaped screen pierced with holes in alignment with the said
lights and apertures respectively is placed so as to prevent the lights from interfering
with each other, and the apparatus is rotated and the said apertures adjusted until
the projected shadows are balanced.
Having now particularly described and ascertained the nature of the said
invention, and in what manner the same is to be performed, we declare that what
we claim is :-
1. In a photometer, the employment of rotating discs or shutters formed,
combined and co-acting in the manner hereinbefore described.
2. In
a photometer, the employment, in combination, of such dises, with
collimators, funnels or other means of projecting the lights to be compared from
positions equally distant from the screen on which they are to be balanced, through
the different variable apertures of such discs on to the screen.
3. In a photometer, the employment, in combination, of such discs, with means for
differentially rotating the same so as to cause the through openings of the different
apertures in such discs to assume different angular values.
4. In a photometer, the employment, in combination, of such discs, means for
projecting the lights therethrough and means for differentially rotating the same.
5. The improved photometer hereinbefore particularly described with reference
to the accompanying drawings.
6. Effecting the comparison of different lights by projecting the same through
different opposite or coincident pairs of apertures made in the same opposite pair of
rotating dises which are differentially driven so as to vary the angular values of
the different through openings of such apertures until the projected lights are
balanced.
Dated this 29th day of December 1890.
DAY, DAVIES & HUNT,
321, High Holborn, London, W.C., Agents for the Applicants.