Ther′mo-scope.
An instrument for indicating relative differences of temperature.
The term was applied by
Count Rumford to an instrument invented
[
2550]
by him, and similar in principle to the differential thermometer of
Professor Leslie.
See differential thermometer. See also
Fig. 6360.
Any instrument which shows variations of temperature, whether or not it indicates the actual differences, is sometimes called by this name, including the thermometer.
Such were those of Galileo, who in 1593 constructed thermoscopes, which were dependent concurrently on changes of temperature and on variations in the pressure of the external air. These were probably similar to the aerometers of the
Spanish Saracens.
See Aerometer.
As early as 1641 observations of temperature were made at regular intervals with spirit-thermometers similar to our own.
Barker and
Mayer's thermoscope, August 26, 1873, is designed to indicate in a manner to be readily discernible to the eye the existence of excessive heat in journal-bearings, etc., and also the proper degree of heat to be employed in various processes in the arts.
For this purpose two compounds are used.
The first is produced by adding a solution of copper sulphate, mixed with sulphurous acid, to a clear solution of hydrargyro-iodide of potassium; the resulting red precipitate is washed, dried, and, by means of suitable varnish or other agent, applied directly or mediately to the object.
It changes color at about 160° Fah., but resumes its natural color when the temperature is reduced.
The second is a bright yellow silver precipitate, produced by adding a solution of silver nitrate to the hydrargyro-iodide solution above.
For many purposes the compounds may be applied to cardboard, leather, or thin metal, and by this means attached to the object.
Marcy's thermoscope consists of a thin copper tube of very small bore, and having a bulb at one end. This is inserted within a glass tube, fixed on the periphery of a wheel to which it corresponds in curvature.
The tube is hermetically sealed at one end, and in it is poured a certain amount of mercury, which assumes the lowest position in the tube.
The axis of the wheel carries a hand which serves as a pointer on a graduated index, and the wheel is balanced on knife-edges.
The instrument is particularly designed for experiments on animal heat: the bulb of the copper tube being applied to any part of the body, the contained air expands, displacing the mercury and causing a movement of the index.
On being applied to a cooler part, or being cooled by water, the index is caused to move in a reverse direction.
 |
|
Stapfer's apparatus for testing lubricants.
(side elevation and partial Section.) |
Figs. 6366,
6367, are
Stapfer's apparatus for testing lubricants by the number of revolutions required to effect a certain elevation in the temperature of parts of the apparatus.
A cylindrical block
a fixed on a spindle revolves between two shells
d e, fitting the cylinder, to which they are pressed by weighted levers
f h. The quality of the lubricant is tested by observation of the heat generated by the friction of the opposing surfaces.
The upper shell
d is held down by the weighted lever
f, which is jointed to the upper end of the standard
g, the lower shell
e being pressed upward by the weighted lever
h that rests upon a fulcrum at
i. The shells are prevented from revolving with the cylinder by pins in the levers engaging in slots formed in lugs on the shells.
A metallic cistern
j containing mercury is attached to the upper shell, and the bulb of a thermometer
k, being immersed therein, indicates the temperature to which it has attained.
A band-wheel
m is mounted on the spindle, and the worm
o formed on the spindle drives a train in the counter
n, which registers the number of revolutions.
The counter is attached to the standard
c by two screws, indicated at
p p.
 |
|
Stapfer's lubricant-tester.
(vertical transverse Section.) |
In another application of the machine, the band-wheel is fitted to revolve loosely on the spindle, and through its engagement with the sliding-clutch
q, imparts motion thereto.
The clutch is changed in and out of gear with the band-wheel by the fork-lever
r, which is mounted on a stud carried by the bracket
s, and is acted upon by a spring
t that tends to throw the clutch out of gear.
The clutch is retained in gear by a catch on one arm of the bell-crank lever
u, where it engages with a projection on the lever
r. The other arm of the bell-crank lever is connected with the armature of an electro magnet
v in such a manner that so long as the armature is not attracted by the magnet, the clutch remains in gear, and the cylinder
a consequently continues to revolve.
A battery is connected with the magnet and with the upper end of a thermometer
x, and the glass tube thereof forms a break in the circuit.
The mercury of the thermometer contained in the metallic cistern
y fixed to the shell
d rises with the increased temperature of the shell, caused by the loss of the lubricating properties of the oil, until it touches the end of the wire
z that projects into the tube.
The mercury then serves to make the circuit, and the armature is attracted, raising the catch from the projection of the lever
r, and the spring
t forcing back the said lever, the clutch is thereby disengaged, and the rotation of the cylinder ceases.
See also thermo-electric alarm.
Fig. 6368 is a thermoscope of peculiar construction, for meteorological purposes, the invention of
J. W. Osborne of
Washington.
The object of this instrument is to give expression to the aggregate of all the climatic influences which tend at any time and place to affect the normal temperature of the body, or to modify the demand on it for the physiological production of animal heat.
As warmblooded animals, we are constantly losing just as much heat as we make, and therefore in estimating weather or climate, we speak of it as cold or hot in proportion as it cools us rapidly or slowly, irrespective of the nature of the several causes which determine that cooling.
The three great factors which affect us thermically are the actual temperature, the moisture of the air, and its motion as wind over our bodies.
The first of these alone is all but universally accepted as indicating relative temperatures affecting animal life.
A little reflection will show that it does not do so in reality, playing often quite a subordinate part in determining the sensible heat or cold which we experience.
A so-called temperate climate, for instance, will, if windy, cool us faster than a cold and frosty one when perfectly still: and a summer temperature of 90° is fresh and pleasant if dry and breezy, while it is almost unendurable if thoroughly moist and free from wind.
[
2551]
This instrument, shown at
Fig. 6368, consists of an upright standard of heavy brass tubing
a, about six feet high, from which several horizontal brackets extend.
One of these
b carries a ring
c, from which hangs a cylinder of “bond,” or bank-note paper
d, 100 millimetres diameter, and 150 long (about 4 × 6 inches). The lower end of this is closed by a very thin brass disk, the paper being attached to it and to the ring above by strong rubber bands, or very thin clamping-rings of brass.
The arm
e with the upright wooden pin is used to steady the cylinder when exposed to the wind, or while moving the instrument.
The bracket
f carries a thermometer, the bulb of which is about the center of the cylinder.
This cylinder is usually full of cold water, but when an observation is to be made, its temperature is raised to blood heat, or higher, if desired, in the following manner: the copper vessel
g, being partly filled with hot water, is then elevated above the cylinder, so that the hot water flows in by pipe
h, and the cold water flows off by the tube
i into the receptacle
j. In this way, by simple displacement, any desired temperature can be reached with facility.
The cylinder is shown in section at
k. To maintain the water at an equable temperature throughout, an agitator, consisting of a spiral ribbon, is made to rotate by means of the horizontal pulley
m, driven by the clock-work
l, while from the disk below three stationary blades rise perpendicularly, which serve to hold the water from revolving, and force a current to descend the sides and rise in the center against the bulb of the thermometer.
The temperature of the water having been raised to blood heat, or any other point fixed upon, the time in seconds which each degree takes to fall is noted by means of the spring-back stop-watches, on the arm
n (which also carries the ordinary wet and dry bulb thermometers). These watches are so connected that the movement required to stop one starts the other: whereby a series of intervals can be measured and recorded, each from zero, with perfect accuracy.
We thus get the rate of cooling of the mass of water (weighing nearly three pounds) for a series of six or eight degrees, from which a single expression can be calculated.
It will be seen that the cylinder is subjected to influences similar to those which act upon the human body.
The paper of which it is made is quite porous, enough to admit of evaporation analogous to that from the skin and lungs.
It is cooled.
by this, and by radiation and convection, as the body is cooled.
The rate at which it cools furnishes therefore an expression of the intensity of the aggregate thermal effect, comparable with that experienced by the human body, and proportional for the same or similar instruments at different times and places.
The very obvious necessity for the information sought when once pointed out, and the difficulty of obtaining it, give to this invention a peculiar interest.
Fig. 6369 is an instrument devised by
Dr. Seguin of New York, to be used in diagnosis.
It is intended to detect variations of temperature of the body and the rate of radiation going on therefrom.
It consists of a glass tube seven terminating at the other in a bulb.
An adjustable scale is attached to the outside of the tube.
To prepare it for use, immerse the bulb in hot water, which rarefies the air inside.
The open end is then plunged into cold water and quickly withdrawn, when a drop or two will he found to have entered the tube.
This forms a
water index, which shoal I become stationary within an inch or two of the bulb.
If it falls into the bulb, or does not approach it sufficiently, too much or too little heat was applied in the first instance, and it will be necessary to jar the water from the tube and try again.
When the index is provided, adjust the scale, bringing its lowest, figure on a level with the top of the column of water in the tube, and it is then ready for use. It may be applied to any part of the surface where disturbance of temperature is suspected.
It is said to give, by contact, indications of the volume of heat escaping by radiation, and the velocity of loss; and by blowing on the bulb, to indicate the degree of combustion that takes place in the lungs.
