IMPROVEMENTS IN MEDIA MAD Trax
Year: 1881

page_text: LETTERS PATENT to Ferdinard Hurter, Ph.D., of Widnes, in the County of
Lancaster, Alkali Manufacturer, for an Invention of "IMPROVEMENTS IN
MEDIA
MAD
Trax">
PROVISIONAL SPECIFICATION left by the said Ferdinand Hunter at the
Office of the Commissioners of Patents on the 23rd April 1881.
FERDINAND HURTER, Ph.D., of Widnes, in the County of Lancaster, Alkali
Manufacturer. "IMPROVEMENTS IN ACTINOMETERS OR PHOTOMETERS, OR INSTRUMENTS
FOR MEASURING LIGHT."
My Invention relates to improvements in instruments for measuring the
intensity of light from any source, but more particularly diffused day light, and
direct sunlight.
According to one mode of carrying out my Invention I cause rays of different
refrangibility of the light to be absorbed by the two bulbs of a differential air
thermometer, which are so arranged as to absorb or reflect wholly or partially the
respective rays. A. difference of temperature is thus produced, which is measured
in the ordinary manner upon a syphon gauge or other pressure gauge, and which is
a measure also of the intensity of the light, the absorption of which causes a rise of
temperature.
In order to cause the bulbs to absorb rays of different refrangibility I either coat
them outside with substances of different colors, but which should be equal
absorbents of radient heat, that is to say, rays of lower refrangibility than
luminous rays.
Or in lieu of coating the bulbs with different colored substances I place such
substances inside the bulbs, as (for example), I may employ strips of colored papers,
placed one color in one bulb, another in the other. Or I coat both the bulbs inside
or outside with lamp black, and cause rays of light to fall upon them, after having
passed through colored glass or colored liquids, or other colored transparent media.
The one bulb receiving the light which passed through the glass of one colour, whilst
the other bulb is illuminated by the light which has passed through glass of
another colour. Or in lieu of filling the bulbs with air I fill them with a colored

page_text: .
vapour, such, for example, as nitrogen, dioxide, or bromine, and cause the light to
fall upon the bulbs, after having passed through different colored transparent
substances, such, for example, as different colored glasses.
The choice of the colors depend upon the purpose for which the instrument is
used, and the kind of rays which are to be measured. For photographic and
photo printing purposes I use red and white substances, or red and colourless
substances and liquids; for general photometric purposes I prefer lamp black and a
white substance, such, for example, as white lead.
Extreme care should be taken to guard against differences in the heat absorbing
power of the two bulbs and the colored glasses and substances used. I place the
bulbs in a box made of wood or other imperfect conductor of heat, and coat it
outside with polished metal or other imperfect radiator. The side of the box
through which the light enters is covered with thick plate glass or with a vessel of
glass filled with water or a solution of various salts capable of almost completely
absorbing heat rays.
In lieu of using differential air thermometers I may employ thermometers filled
with other gases and vapours; or I may use ordinary thermometers of extreme
sensitiveness; or I may use a thermopile and galvanometer as an indicator of the
difference of temperature, and consequent upon the absorption of rays of different
refrangibility by the two sensitive sides of the pole.
I also use reflectors and condensers in order to concentrate as much light as
possible upon the sensitive parts of the apparatus. Such condensers and reflectors
may again be of different colours and materials, but they also should be chosen so
that radiant heat shall pass equally through them, or be reflected equally by them,
otherwise the indications of the instruments will not be due to light rays only, and
become absolutely useless.
For the purpose of illuminating the bulbs or sensitive surfaces of piles with rays
of different refrangibility I may also use the dispersive power of prisms, placing,
for instance, one bulb in one part of the spectrum while the other is placed in
another part:

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Ferdinand Hurter in the Great Seal Patent Office on the
19th October 1881.
FERDINAND HURTER, Ph.D., of Widnes, in the County of Lancaster, Alkali
Manufacturer. "IMPROVEMENTS IN ACTINOMETERS OR PHOTOMETERS, OR INSTRUMENTS
FOR MEASURING LIGHT."
My said Invention relates to improvements in instruments for measuring the
intensity of light from any source, but more particularly diffused daylight and
direct sunlight.
According to one mode of carrying out my said Invention I cause rays of
different refrangibility of the light. to be absorbed by the two bulbs of a differential
air thermometer which are so arranged as to absorb or reflect wholly or partially
the respective rays. A difference of temperature is thus produced which is
measured in the ordinary manner upon a syphon gauge or other pressure gauge,
and which is a measure also of the intensity of the light, the absorption of which
causes a rise of temperature. The differential thermometer used may be of the
type of that known as Leslie's, or a differential thermometer of any other suitable
description.
In order to cause the bulbs to absorb rays of different refrangibility I either
coat them outside with substances of different colours, but which should be equal
absorbents of radient heat, that is to say, rays of lower refrangibility than luminous
rays; or in lieu of coating the bulbs with different coloured substances I place
such substances inside the bulbs, as (for example), I may employ strips of coloured
papers placed one colour in one bulb, another in the other; or I coat both the
bulbs inside or outside with lamp black, and cause rays of light to fall upon them
after having passed through coloured glass or coloured liquids, or other coloured
transparent media, one bulb receiving the light which passed through the glass of
one colour, whilst the other bulb is illuminated by the light which has passed
through glass of another colour. Or in lieu of filling the bulbs with air I fill them
with a coloured vapour, such, for example, as nitrogen dioxide or bromine, and
cause the light to fall upon the bulbs after having passed through different coloured.
transparent substances, such, for example, as different coloured glasses.
The choice of the colours depends upon the purpose for which the instrument is
used, and the kind of rays which are to be measured. For photographic and
photo-printing purposes use red and white substances, or red and colourless
substances and liquids; for general photometric purposes I prefer lamp black and
a white substance, such, for example, as white lead.
Extreme care should be taken to guard against differences in the heat absorbing
power of the two bulbs and the coloured glasses and substances used. I place the
bulbs in a box made of wood or other imperfect conductor of heat, and coat it
outside with polished metal or other imperfect radiator. The side of the box
through which the light enters is covered with thick plate glass or with a vessel
of glass filled with water, or a solution of various salts capable of almost completely
absorbing heat rays.
In lieu of using differential air thermometers I may employ thermometers filled
with other gases and vapours. Or I may use ordinary thermometers of extreme
sensitiveness. Or I may use an electric differential thermometer, that is to say, a
thermopile and galvanometer an indicator of the difference of temperature and
consequent upon the absorption of rays of different refrangibility by the two
sensitive sides of the pile.
I also use reflectors and condensers in order to concentrate as much light as

page_text: possible upon the sensitive parts of the apparatus. Such condensers and reflectors
may again be of different colours and materials, but they also should be chosen so
that radiant heat shall pass equally through them or be reflected equally by them,
otherwise the indications of the instruments will not be due to light rays only, and
become absolutely useless.
For the purpose of illuminating the bulbs or sensitive surfaces of piles with rays
of different refrangibility I may also use the dispersive power of prisms, placing,
for instance, one bulb in one part of the spectrum while the other is placed in
another part.
The method of carrying my said Invention into effect which I have found most
satisfactory is the following
I construct entirely of glass, without any cemented, or indiarubber joints, a
differential thermometer represented on the annexed Drawing in front elevation,
and elevation, and plan in Figures. 1, 2, and 3 respectively. A, A¹, are
two glass cylinders ending in small tubes, made altogether of as thin glass as
possible. To these two cylinders which form the sensitive parts of the thermometer
is fused on. a. capillary syphon gauge B1, B2, B3, B4, bent exactly as shown in the
Figure. At the bend between B and B a small nozzle H is drawn out which
serves to introduce into the syphon the coloured liquid C.
While the small tubes in which the cylinders A, A!, terminate are still open I
insert into them coils of Berlin wool D wrapped loosely upon fine capillary glass
tubes serving as supports. The wool for tube A is red coloured, that for A¹ is pure
white. Both these coils of wool should be perfectly dry, and in order to ensure
the more perfect absence of all moisture I draw through the apparatus a current of
air absolutely dry, and I place in each of the tubes a few small lumps of fused
chloride of calcium, as shewn at a. When the coils have been placed in the
tubes A and A¹ I introduce the liquid into the syphon through the nozzle H by
placing this liquid first into a wide test tube, and then lowering the syphon into
the liquid. When the syphon has thus been filled to about half its length in
both B & B³ I rapidly withdraw the syphon and incline it so as to cause the
liquid to flow into the bends B1, B2 taking care that none of the liquid flows into
the cylinder A.
The nozzle H is then fused up, and when cool the liquid is again caused to flow
into the bend B2, B³. The whole apparatus is then immersed in cold water to
such an extent only that no water flows into the cylinders. When the whole has
cooled to a uniform temperature the ends of the cylinders A and A' which are still
open are fused up also.
The differential thermometer so prepared is then placed in a wooden box lined
with polished metal inside and outside. This box is shewn in plan and elevation,
Figures 4 and 5. G, G, is the box. The front of the box is made of a glass
plate F, F. The large cylinders A, A¹, are in the centre of the box; the syphon B¹,
B2, B3, B4, is outside at the back of the box. Suitable openings or slits are provided
to allow the connecting tubes to pass through the wood.
Behind the cylinders are placed two parabolical reflectors E¹, E², and E2, E³,
made of sheet lead silvered on one side, in order that they may reflect the light
coming through the glass plate F, F, and concentrate it upon the coils D of wool in
the centre of the tubes A, A. It is necessary that the centres of these tubes be
exactly in the focus of the parabolic reflectors.
Behind the syphon between it and the wood I place a sliding scale I in order to
admit of conveniently reading the change of level of the liquid which takes place
when the apparatus is exposed to diffuse daylight. The scale is divided into
arbitrary degrees. The intensity of the light is proportional to the number of
degrees registered. This however is only the case when the apparatus is very
carefully constructed, and when a liquid is used for filling the syphon which has a
very small vapour tension. The most satisfactory liquid I have yet found is oil of
turpentine coloured with alkanet root.
In order to be good the apparatus should stand the following tests:-1, when.

page_text: placed in water of different temperatures in the dark the level of the liquid should
not change as the temperature of the water is altered. This is only the case when
all moisture is completely removed; 2, when placed opposite a dark source of heat,
such as a stove the level of the liquid should not alter.
Should it alter it is a proof that the cylinders are not affected equally by
radiant heat. I then cover that side of the glass F, F, which is opposite the
cylinder most easily heated with transparent colourless varnish, such, for example,
as negative varnish, or I screen both cylinders A and A' with a larger glass
cylinder, and by adjusting the length of these screening tubes I can make the
apparatus almost insensitive to heat.
These extreme precautions however are only necessary for instruments which
are intended to measure low degrees of light for the ordinary work of the photo-
grapher; the apparatus does not need the extremely fine adjustment for radiant
heat, and the changes of level caused by alteration of temperature are so small
as to interfere very little with the measurement of light, and can be taken into
account if necessary.
Having now described and particularly ascertained the nature of my said
Invention and the manner in which the same is or may be used or carried into
effect, I would observe in conclusion that what I consider to be novel and original,
and therefore claim as the Invention secured to me by the hereinbefore in part
recited Letters Patent is,-
Measuring the intensity of light by causing rays of different refrangibility to
be received by or pass through different colors, and to be absorbed by the two
sensitive parts of a differential thermometer, and measuring the difference of
temperature thus produced whence the intensity of the light may be ascertained,
substantially as herein before described.
In witness whereof, I, the said Ferdinand Hurter, have to this my Specifi-
cation set my hand and seal, this Fourteenth day of October, One thousand
eight hundred and eighty one.
FERDINAND HURTER. (L.S.)