AN IMPROVEMENT IN PHOTOMETERS
Year: 1884

page_text: We, WILLIAM HENRY PREECE of Wimbledon in the county of Surrey, Civil
Engineer, and ALEXANDER PELHAM TROTTER of Furnivals Inn in the county of
Middlesex, Electrical Engineer do hereby declare the nature of our invention for
AN IMPROVEMENT IN PHOTOMETERS" to be as follows:-
66
In comparing lights by means of Photometers, it is necessary to ascertain the
distance at which the light acts and then to estimate the power of the light by
computing the inverse square of the distance. Our invention relates to apparatus
applicable to a photometer, whereby equal degrees on a graduated scale are made to
correspond with the inverse squares of the distance at which the light acts, without
requiring arithmetical computation. The accompanying drawing is a vertical
section illustrating one form of photometer to which our invention is applied.
Within a box A, an electric or other lamp or candle B is fitted to slide nearer to or
farther from the semi-transparent screen C, such as is employed in what is known
as a Bunsen photometer. From the slide of the lamp, a bar D extends upwards to
a nut fitting a screw E, this bar being pressed by a spring F against a cam guide G.
This guide G is so shaped that a series of movements or distances of the lamp B
from the screen C being taken such that their inverse squares are in arithmetical
progression, the corresponding distances moved by the nut along the screw E are
also in arithmetical progression. An equally graduated scale being placed by the
side of the screw E, or the wheel H, by which the screw is turned, being graduated
in equal divisions, the power of the light can at once be read off without
computation. For facility of inspecting the screen C on both sides, mirrors K K
may be placed as shewn, on each side of it.
Instead of employing a straight bar D. pressed against a stationary cam guide, the
bar D itself might be made to present an edge of proper cam shape bearing against
a straight guide or against a circular guide or roller.
11001
ABEL & IMRAY,
Agents for the Applicants,
28, Southampton Buildings,
London, W.C.

page_text: We, WILLIAM HENRY PREECE' of Wimbledon in the county of Surrey, Civil
Engineer, and ALEXANDER PELHAM TROTTER of Furnivals Inn in the county of
Middlesex, Electrical Engineer do hereby declare the nature of our invention for
"AN IMPROVEMENT IN PHOTOMETERS" and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement:
In comparing lights by means of Photometers, it is necessary to ascertain the
distance at which the light acts and then to estimate the power of the light by
computing the inverse square of the distance. Our invention relates to apparatus
applicable to a photometer, whereby equal degrees on a graduated scale are made
to correspond with the inverse squares of the distance at which the light acts,
without requiring arithmetical computation. The accompanying drawing is a
vertical section illustrating one form of photometer to which our invention is
applied. Within a box A, an electric or other lamp or candle B is fitted to slide
nearer to or farther from the semi-transparent screen C, such as employed in what
is known as a Bunsen photometer. From the slide of the lamp, a bar D extends
upwards to a nut fitting a screw E, this bar being pressed by a spring-F-against a
cam guide G. This guide G is so shaped that a series of movements or distances
of the lamp B from the screen C being taken such that their inverse squares are in
arithmetical progression, the corresponding distances moved by the nut along the
screw E are also in arithmetical progression. An equally graduated scale being
placed by the side of the screw E, or the wheel H, by which the screw is turned,
being graduated in equal divisions, the power of the light can at once be read off
without computation. For facility of inspecting the screen C on both sides,
mirrors K K may be placed as shewn, on each side of it.
Instead of employing a straight bar D pressed against a stationary cam guide,
the bar Ditself might be made to present an edge of proper cam shape bearing
against a straight guide or against a circular guide or roller.
Having now particularly described and ascertained the nature of our said
invention, and in what manner the same is to be performed, we declare that what
we claim is :-
The construction of photometer substantially as herein described and illustrated
by the accompanying drawing.