Year: 1893

page_text: Figure 3, a side view: and
Figure 4, a horizontal section.
This apparatus' consists of a metal basin or cistern a, hinged on a plate b,
arranged so as to rest against the masonry of the furnace, the temperature of which
is to be measured.
This arrangement has for its object to allow of the apparatus being withdrawn
when it is not in operation, and more particularly during the lighting of the fire in
order to avoid the introduction of dust and especially of steam (which is then
produced in abundance) which, without this precaution, would be condensed on the
interior surfaces of the apparatus, which surfaces should always remain dry.
The basin or cistern a encloses two thermometers t and t', which may be replaced,
if desired, by a differential thermometer, and is kept full of water which the waste
heat of the furnace suffices to maintain constantly at the boiling temperature. A
tube n is also provided for indicating the water level.
The principal thermometer or thermometer for observation t, is arranged in a
water tight receptacle / opposite a circular opening o made in the lower part of the
cistern, which opening corresponds to an opening formed in the masonry. This
opening allows the rays of heat coming from the interior of the furnace to impinge
on the surface of the thermometer, which, as well as the internal walls of the
apparatus, is covered with blacking.
In order, as may be necessary in some cases, to retard the rate of cooling, one
or more concentric tubes of blackened brass may be arranged round the ther-
mometer t, separating the layers of air by which the cooling is effected.
The second thermometer, or thermometer for comparison t', is immersed directly
in the water of the basin or cistern, and allows the boiling temperature to be
ascertained. This temperature, which varies with the atmospheric pressure, I take
as approximately the beginning of my scale for the principal thermometer t. The
zero of the scale of the actinometric pyrometer thus corresponds to the 100 point
of the centigrade scale.

page_text: This first fixed point is most important, owing to the necessity of conveniently
obtaining an initial temperature which is almost unvarying, and also because the
centigrade scale is in practice only continued beyond this point by an extension
which, though at first not inconvenient, soon becomes troublesome. Ordinary
temperatures directly measureable by the centigrade thermometer may be said to
end at this point, at least nominally.
For the second fixed point of my scale, I have chosen a temperature characterised
by a very common phenomenon, namely, the appearance or disappearance of
luminous or visible radiation which indicates, also nominally, the commencement of
high temperatures. In fact, it is usual to include under this class only such
temperatures as commence at faint red. This temperature is, it is true, under
ordinary conditions, somewhat difficult to determine, and this difficulty is due
principally to variations in the sensibility of the eye; but it will be understood
that it is only a question here of producing the maximum sensibility of the eye by
a previous prolonged continuance in obscurity.
In order to determine the above temperature for this second fixed point, I
proceed in the following manner with a single instrument which is afterwards
preserved as a standard from which to graduate all other instruments :-
I place the actinometric pyrometer in front of a heated brick coated with lamp
black, the temperature of which brick I can vary at will, and I adjust the
thermometer't, which has simply a centigrade scale, in such a position relatively to
the opening o that it indicates when the temperature of the brick has been reduced
to the point at which visible radiation disappears precisely 100 degrees above the
temperature of the boiling point of water, say 200 degrees centigrade. I thus obtain
the first hundred degrees of the actinometric scale by having the opening o fully
uncovered and taking the actinometric angle at a maximum.
In conducting the above experiment, the brick is placed in a muffle, the door of
which is provided with two circular openings, one of which allows the calorific rays
to impinge upon the thermometer t of the instrument, whilst the other admits of
optical examination, and an inert gas, such as azote or carbonic acid, is introduced
into the muffle during the experiment to prevent the destruction of the lamp black
on the brick. The water in the basin a is kept at boiling point during the
experiment by a jet of steam, as the heat radiated from the furnace walls in this
case is insufficient for that purpose.
By regulating the admission of air to feed the combustion, the brick is heated
slowly until luminous or visible radiations appear, which are observed from behind
a blackened screen, all other light being excluded. The furnace is then allowed to
cool, the air supply being stopped, and the brick watched attentively whilst cooling
until the visible radiations completely disappear. Without losing an instant, the
degree indicated by the thermometer is now exactly noted, and is taken as the
100 point for the actinometric scale, as explained.
In order to measure higher temperatures commencing from incandescence, it will
suffice to diminish the actinometric angle by a quantity proportionate to the energy
of the radiation, by removing the thermometer t to a suitable distance from the
opening o, or by reducing or covering the latter with a diaphragm.
But let us suppose in this case that the diameter of the opening is constant, and
the thermometer t is alone drawn back, causing it to slide in its bearings parallel
to the axis of the rays in such a way that it does not receive more than the tenth
part of these latter, that is to say, in such a way that it does not indicate more
than 10 degrees above the temperature of boiling water, say 110 degrees centigrade,
at the temperature the intensity of which I have just defined by the number 100,
the calorific effect is thus reduced to the tenth of its normal value, and it follows
therefrom that the same thermometer may in this position be submitted to a
radiation ten times more intense, without, however, ceasing to work between the
limits of temperature for which it was constructed. It is only necessary to
multiply by 10 the number of degrees indicated in this new position of the ther-
mometer t in order to give such indication the value which it had lost by the

page_text: diminution of the actinometric angle.
One hundred degrees indicated are thus
equal to one thousand actinometric degrees.
Finally, in a third position still more distant than the preceding one, the starting
angle being further diminished to such an extent that the same thermometer, at the
same temperature which I have above defined as of the intensity of 100, only
indicates 1 degree above the temperature of the boiling point of water, that is to
say, the hundredth part of the normal calorific effect, it will be necessary, in this
case, to multiply the results by 100. One hundred degrees shown in this third
position of the thermometer t will, consequently, make ten thousand actinometric
degrees.
It is in order to simplify these explanations that I have made the position of the
thermometer t to vary in several instances; it is preferable, in practice, to leave.
the thermometer in a fixed position, and to regulate the diameter of the opening o
according to the rise in the temperature which is to be measured, which diameter
will naturally be smaller in proportion as the temperature in question becomes
higher. The regulation may further be always modified by means of internal.
diaphragms.
It will be seen that my invention does not consist of the ordinary arrangements
which consist in placing the pyrometer in the centre of the incandescent furnace in
order to measure the temperature, in which case it is consequently impossible to find
a sufficiently resistant material for the measuring instrument, but really of an
entirely new method simply based on the rational use of the ordinary thermometer;.
the instrument being arranged outside the destructive medium in order to measure
at a distance the increase or decrease of the heat, the instrument being transformed
for the purpose into an actual optical instrument.
The ordinary disadvantages, as well as their cause, of pyrometers inserted directly
into the medium at a high temperature, are thus avoided; these are permanent
deformations, molecular alterations, and generally any modification of the original
condition of the instrument which might prevent it returning of itself to the zero.
of the scale when the influence of the temperature to which it was exposed has
ceased. From this it is right to conclude that several exactly similar instruments.
will, when tested on the same temperature, always yield identical indications; this.
is confirmed by experience, which I have verified by the following process:-
In order to obtain as constant and homogeneous a temperature as possible, a plate
of fireclay is raised vertically, so as form a sort of isolated partition inside a thick.
muffle, which is intended to protect it from the direct action of the fire. In front
of this plate, three similar actinometric pyrometers in accordance with my invention
are arranged and are adjusted to the same angle facing various points of its surface
The
by means of as many openings made in the door which closes the muffle.
furnace having been lighted, the three instruments are carefully observed, and I
have ascertained that, so long as the fire burns quite regularly and the combustion.
is equal on both sides of the muffle, they act perfectly in unison, indicating very
exactly the same degree and the same fraction of a degree simultaneously as if
moved by a common spring, and this at any temperature, whether the latter is
rising or falling, or whether it remains stationary. When a difference, however
small, arises between the indications of the two outermost instruments, the centre
instrument shows an intermediate temperature, from which I conclude that the
variations ascertained in the indications of the different instruments are indeed the
certain effect of corresponding variations which are produced in the temperature of
the different points of the plate. In fact, in this latter case, it is sufficient to open
the door of the furnace to ascertain the unequal distribution of the combustible
round the muffle. The latter being heated more strongly on one side than on the
other, it is evident that the effect will not be long before it re-acts on the internal
plate itself.
If then I install a series of my actinometric pyrometers, not, as before stated,
behind an internal protected plate, but directly facing various points of the external
surface of the muffle, the agreement between them no longer exists. The fact is

page_text: there are no two points of this surface which are exactly at the same temperature,
and the difference in the indications in this case only confirms the extreme sensitive-
ness of the method.
Finally, it is scarcely necessary to add that, if, during the course of the operation,
I modify, in any way, the actinometric angle by advancing or withdrawing the
thermometer, a corresponding modification is instantaneously produced in the
indication of the degree, the exact actinometric value of which is invariably
determined by the opening of this angle.
This experience shows that, where the best trained eye can only distinguish a
uniform tint, which is also very inconvenient to appreciate and to classify in the
optical scale, the thermometer marks the most delicate gradations of heat and
translates them into clear and intelligible indications. Hence, the exceptional
qualities of this new pyrometer, the excellent results of which, when compared with
the crude approximations of the processes at present employed, render this
apparatus the simplest, most precise, and most convenient indicator of temperatures,
and one capable of responding to all industrial requirements.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
1. An actinometric pyrometer consisting of a metal basin or cistern a arranged
preferably against the wall of a furnace, or the like, the temperature of which
it is desired to ascertain, said cistern containing water or other suitable liquid,
which is maintained at a practically constant temperature; and a thermometer t
coated with blacking, arranged in a tight chamber in front of an opening o formed
in the side of the cistern a; also a second thermometer t indicating the tem-
perature of the liquid in the cistern; and of two graduated scales, one giving the
temperature of the liquid in cistern a, and the other the actinometric degrees,
substantially as and for the purposes hereinbefore described.
2. For the measurement of temperatures, the use of a thermometer covered with
blacking placed in a medium of a practically constant temperature, and receiving
a given portion of calorific rays emanating from a furnace or other industrial
apparatus the degree of heat of which it is desired to ascertain, the temperature of
the enclosure or medium which contains the thermometer being further indicated at
each moment by another thermometer, substantially as described.
Dated this 4th day of October 1893
WM. P. THOMPSON & Co.,
Of 6, Lord Street, Liverpool, Agents for the Applicant.