thermometer 
into which :uiy desired part of the mercury can be drawn 
off. This device enables the thermometer to be used over 
a wide range of temperature, and the scale to be gradu- 
ated to small fractions of a degree, without increasing the 
length of the stem. For each different state of the instru- 
ment, the temperature corresponding to some part of the 
scale must be determined by comparison with a standard 
thermometer. Methyl-butyrate thermometer, one 
in which the thermometric substance ia methyl butyrate. 
Sir William Thomson, Encyc. Brit., XI. 569. Minimum 
thermometer, a thermometer that registers the mini- 
mum temperature to which it is exposed. The alcohol 
minimum, devised by Rutherford in 1794, is now univer- 
sally used. The registration is effected by a light steel or 
glass index enlarged and rounded at the end, and wholly 
immersed in the column of alcohol. When the tempera- 
ture falls, the index is carried toward the bulb by the sur- 
face-tension at the end of the contracting liquid column, 
and when the temperature rises the alcohol flows around 
and past the index, leaving it to mark the lowest temper- 
ature. Optical thermometer, a thermometer proposed 
by Conm for the study of high temperatures, based on the 
principle that in certain crystals the amount of the rota- 
tion of the plane of polarization depends on the tempera- 
ture. As quartz can be submitted to a wide range of tem- 
perature, it is considered to be specially adapted for the 
application of this method in determining high tempera- 
tures. Overflowing or mercurial-weight thermom- 
eter 1 , a mercury-thermometer consisting of a bulb with a 
short piece of tine stem perfectly filled with mercury at 
C. Any higher temperature is determined by weigh- 
ing the quantity of mercury expelled, instead of by mea- 
suring it volumetrically, as in the ordinary mercurial stem- 
thermometer. Radiation thermometer. See terres- 
trial-radiation thermometer and solar-radiation thertnom- 
eter. Reaumur thermometer. See del. 1. Regis- 
tering thermometer, a self-registering thermometer; 
a maximum or minimum thermometer. Six's ther- 
mometer, a self-registering thermometer, invented by 
J. Six in 1781, combining in one instrument the registra- 
tion of maximum and minimum temperatures : for many 
years very widely used, but now generally superseded by 
separate maximum and minimum instruments. Sling- 
thermometer, a thermometer with which the tempera- 
ture of the air is obtained by whirling the instrument in 
the free air. The resulting rapid convection brings the tem- 
perature of the thermometer into close accordance with 
the temperature of the air. Solar-radiation thermom- 
eter, a thermometer for measuring the intensity of solar 
radiation. A form frequently adopted for this purpose is 
the blade-bulb thermometer in vacuo, first suggested by Sir 
John Herschel. It consists of a sensitive mercurial ther- 
mometer having the bulb and about an inch of the stem 
covered with lampblack. The whole is inclosed in a glass 
tube, of which one end is blown into a large bulb in the 
center of which is fixed the bulb of the thermometer, and 
the tube is then exhausted of air. The thermometer-bulb 
thus prepared absorbs all the solar heat that falls upon 
it, and loses none by convection. With the black-bulb 
thermometer there is frequently used a bright-bulb ther- 
mometer similarly incased. This has its bulb covered 
with polished silver, or some equivalent coating, which re- 
flects most of the radiation that falls upon it. The differ- 
ence between the readings of these two instruments is as- 
sumed to measure the intensity of solar radiation. Sub- 
marine thermometer. Same as deep-sea thermometer. 
Terrestrial-radiation thermometer, a minimum ther- 
mometer used to register the cooling of the earth's surface 
below the temperature of the air by nocturnal radiation. 
The bulb of the thermometer is generally shaped with 
special regard to obtaining a high degree of sensitiveness. 
Also called nocturnal-radiation thermometer. Upsetting 
thermometer, a form of mercurial thermometer devised 
by Negretti and Zambra for registering the temperature 
at any desired time. The registration is effected by in- 
verting the instrument, after which it remains unaltered 
until it is reset. By means of clockwork, the upset may 
be made to occur automatically at any desired time, and 
a series of such thermometers constitutes a method for 
obtaining hourly temperatures. The instrument finds its 
principal use as a deep-sea thermometer. See above. 
Water-steam thermometer, a proposed form of ther- 
mometer in which the thermometric substance is satu- 
rated water-vapor, and in which the temperature is given 
from the pressure of the vapor as measured by the height 
of the water-column it can support. Wet-bulb ther- 
mometer. See psychrometer. 
thermometric (ther-mo-met'rik), a. [= F. 
thermometrique ; as thermometer + -ic.] 1. Of 
or pertaining to a thermometer : as, the thermo- 
metric scale or tube. 2. Made by means of a 
thermometer: as, thermometric observations. 
Thermometric steam-gage, a form of steam-gage which 
shows the amount of pressure in a boiler by the degree of 
expansion of a fluid at the temperature produced by the 
pressure. E. 11. Knight. 
thermometrical (ther-mo-met'ri-kal), a. [< 
thermometric + -al.] Same as thermometric. 
Boyle, Works, II. 466. 
thermometrically (ther-mo-met'ri-kal-i), adv. 
In a thermometrical manner; by means of a 
thermometer. 
thermometrQgraph (ther-mo-met'ro-graf), . 
[= F. thermometrographe, < 6r. Sippi, heat, + 
titrpov, measure, + ypaijietv, write.] Aself-regis- 
tering thermometer, especially one which reg- 
isters the maximum or minimum temperature 
during long periods. Also thermetrograph. 
thermometry (ther-mom'e-tri), n. [< Gr. dip/it/, 
heat, + -perpia, < perpov, measure.] The art of 
measuring temperature. A numerical unit of tem- 
perature difference is derived from the measurable physi- 
cal effects produced in bodies by heat for example, linear 
expansion, volumetric expansion, change of gaseous elas- 
;lc pressure, and change in electric resistance. In the 
customary use of the thermometer, changes in tempera- 
ture are assumed to be directly proportional to the ob- 
6284 
served changes in the thermometric material, and tempera- 
ture units are denned in terms of the particular material 
and phenomenon adopted. The thermometric unit at pres- 
ent (1891) adopted by the International Bureau of Weights 
and Measures is one centigrade degree, or the hundredth 
part of the fractional increase of pressure of a volume of 
pure dry gas originally at a pressure of one standard at- 
mosphere, and heated from the standard freezing-point 
to the standard boiling-point of water. With this unit, in- 
crements of temperature are closely proportional to in- 
crements of heat, and the air- (or gas-)thermometer of con- 
stant volume is the adopted instrumental standard. The 
air-thermometer, however, is not adapted to ordinary uses, 
and it is the object of thermometry to obtain comparable 
temperatures with convenient and portable instruments. 
The expansion of liquids is closely proportional to succes- 
sive increments of heat, and is taken as the basis of the 
usual secondary thermometric standards. It should be 
observed, however, that in general the subject of measure- 
ment is not the simple expansion of the liquid, but the 
differential expansion of the liquid and the glass bulb in 
which it is contained ; and from the standpoint of pre- 
cise thermometry it is in this uncertain, irregular, and 
varying behavior of the glass that the principal residual 
discrepancies of normal mercurial thermometers lie. The 
most important of these sources of error in mercurial 
thermometers is a change in the zero-point with time and 
with the temperatures to which the thermometers are ex- 
posed. This change depends upon the nature of the glass. 
Glass of special composition is now used in the construc- 
tion of thermometers, which will practically eliminate 
this source of error. The method of graduating ther- 
mometers between two fiducial points, instead of by vol- 
ume, was an advance in construction adopted by Fahren- 
heit that first made possible the construction of compara- 
ble thermometers. The adoption later of the freezing- 
point and the boiling-point of water for these two standard 
temperatures brought different kinds of thermometers 
into substantial agreement. In the recent progress of 
precise thermometry, residual sources of error have been 
discovered, and outstanding discrepancies have been in- 
vestigated, so as to render possible the reduction of all 
observed temperatures to the thermodynamic scale. 
thermomotive (ther-mo-mo'tiv), a. [< Gr. Gipjat, 
heat, + E. motive.] Broadly, pertaining to or 
derived from molar motion produced by heat, 
as in any heat-engine, but more particularly 
used with reference to heat-engines in which 
motion is derived from air or other gas expanded 
by heat: as, thermomotive i power; thermomotive 
effect ; thermomotive efficiency. 
thermomotor (ther-mo-mo'tpr), n. [< Gr. Oepfir/, 
heat, + LL. motor, a mover.") A heat-engine, 
particularly a so-called caloric engine, or an air- 
engine driven by the expansive force of heated 
air. Compare gas-engine, heat-engine, and ca- 
lorie engine (under caloric). 
thermomultiplier (ther-mo-mul'ti-pli-er), n. 
[< Gr. Kpuri, neat, + E. multiplier.] Same as 
thermopile. See the quotation. 
The discoveries of Oersted and Seebeck led to the con- 
struction of an instrument for measuring temperature in- 
comparably more delicate than any previously known. To 
distinguish it from the ordinary thermometer, this instru- 
ment is called the thermomultiplier. 
W. R. Grove, Con. of Physical Forces, iii. 
thermonatrite (ther-mo-na'trit), . [< Gr. 
Otpfiri, heat, + E. natron + -ite'*.] Hydrous 
sodium carbonate (Na2CO 3 + H 2 O), occurring 
chiefly as an efflorescence in connection with 
saline lakes. 
thermo-pair (ther'ino-par), . [< Gr. Bepfiri, 
heat, + E.jKM'r 1 .] A thermo-electric element 
or couple. See thermo-electricity. 
thermopalpation (ther"mo-pal-pa'shon), n. [< 
Gr. Bepfi-r/, heat, + L. palpatio(n-), a stroking: 
see palpation.] Palpation of the surface of the 
body to determine temperature, especially to 
determine topographical differences of temper- 
ature with a view to determine the position and 
condition of internal organs. 
thermophone (ther'mp-fon), . [< Gr. 0fftui?, 
heat, -f 0ov#, a sound.] An electrical instru- 
ment in which sounds are produced by the 
changes in the circuit due to variations of tem- 
perature. 
thermopile (ther'mo-pll), n. [< Gr. etp/tr/, heat, 
+ E. pile 2 .'] A thermo-electric battery, espe- 
cially as arranged for the measurement of small 
quantities of radiant heat. See thermo-electri- 
city. 
thermoregulator (ther-mo-reg'u-la-tor), . [< 
Gr. IKpiiTi, heat, + E. regulator.] A device for 
regulating the temperature of a heating-appa- 
ratus. 
thermoscope (ther'mo-skop), n. [= F. thermo- 
scope = Sp. It. termoscopio, < Gr. fffp/Jt, heat, + 
aKo-xeiv, view, examine.] An instrument or a 
device for indicating variations in temperature 
without measuring their amount. The name was 
first applied by Count Rumford to an instrument in- 
vented by him, resembling the differential thermometer 
of Leslie. Out of an indefinite number of thermoscopes, 
a class of chromatic thermoscopes may be mentioned in 
which changes in temperature are indicated by changes 
in the shade or the color of a substance coated with cer- 
tain chemical preparations. These have been used to 
some extent for indicating a rise in temperature caused 
thermotelephone 
by the heating of a journal in machinery. Thermoscopes 
consisting of a tube containing air or mercury, and hav- 
ing an adjustable scale, or a scale limited to a few de- 
grees, are used in machines for testing lubricants, in ap- 
pliances for physical research, as in Osborne's esthermo- 
scope, and in diagnosis, as in Dr. Seguin's thermoscope 
for detecting minute variations in the temperature of the 
body. 
thermoscopic (ther-mo-skop'ik), a. [< thermo- 
scope + -ic.] Pertaining to the thermoscope ; 
made by means of the thermoscope : as, ther- 
moscopic observations. Grove. 
thermoscopical (ther-mo-skop'i-kal), a. [< 
thermoscopic + -a/.] Same as thermoscopic. 
thermosiphon (ther-mo-si'fon), n. [< Gr. 6ep/ai, 
heat, + aitfuv, siphon.] An arrangement of si- 
phon-tubes serving to induce circulation of 
water in a heating apparatus. 
thermostat (ther'mo-stat), n. [< Gr. Qeppi, 
heat, + oraTof, verbal adj. of unavai, stand: see 
static.] An automatic instrument or apparatus 
forregulatingtemperature. It is essentially a mod- 
ideation of the thermometer, so arranged that, in place 
of indicating thermal variations, it controls the source of 
heat or of ventilation, and thus indirectly regulates the 
temperature. One of the earliest forms of thermostat 
was that devised by Dr. Ure. It consisted of a bar com- 
posed of two metals, say steel and copper, having differ- 
ent degrees of expansion under the same temperature. 
This bar, when fixed in position, was made by simple me- 
chanical means to open a furnace-door, move a damper, 
or open a window, by means of the bending of the bar 
under the influence of an increase in heat, other forms 
of this thermostat have since been used to make or break 
a, base; b, involute expansion-strip, composed of two metalshaviny 
different coefficients of expansion, as brass and steel : f, adjustment- 
screw, forming part of an electric circuit whenever b is expanded by 
heat so as to touch the point of the screw ; </, </, conducting wires. 
an electric current, and thus move an armature that con- 
trols a damper, steam-valve, or other heat-regulating 
mechanism. Another form consists of a balanced ther- 
mometer that, under the movements of the mercury in a 
tube pivoted in the center in a horizontal position, would 
rise or fall, and thus control a damper or flre-door. An- 
other form consists of a thermometer resembling a thermo- 
electric alarm (see thermo-electric), except that the closing 
of the circuit by the rise of the mercury in the tube oper- 
ates a fire-door or damper in place of sounding an alarm. 
Where a thermostat is merely used to ring a bell, it is 
called a thermostatic alarm. A very simple and yet deli- 
cately responsive form is a slender bar of gutta-percha, 
fixed at one end, and attached at the other to a lever, which 
is caused to act by the expansion or contraction of the 
bar. Another form of thermostat consists of a bent tube 
partly filled with mercury. The heat expands the air in 
the larger end of the tube and displaces the mercury, and 
this in turn moves a piston controlling, by means of some 
mechanical device, a steam-valve or damper. Another 
form, used with steam-heating fumaces, consists of an 
elastic diaphragm in a cylinder, the pressure of the steam 
against the diaphragm serving to move a piston that con- 
trols the damper of the furnace. Such appliances are 
also called heat-reffulators. More recently, the name has 
been given to fusible plugs used to control automatic 
sprinklers, a rise in the temperature causing the plug to 
melt and release the water. This, however, is only a trade 
use of the word. 
thermostatic (ther-mo-stat'ik), a. [< thermo- 
stat + -ic.] Pertaining to the thermostat; 
characterized by the presence of a thermostat ; 
involving the principle of the thermostat. 
thermostatically (ther-mo-stat'i-kal-i) , adv. By 
means of a thermostat: as, a thermostatically 
adjusted radiator. 
thermostatics (ther-mo-stat'iks), n. [PI. of 
thermostatic (see -ics).] The theory of the equi- 
librium of heat. See the quotation under tl/er- 
mokinematics. 
thermotaxic (ther-mo-tak'sik), a. [Prop. *ther- 
motactic; (. thermotaxis (-tact-) + -ic.] Lnphys- 
iol., pertaining to regulation of the tempera- 
ture of the body, or the adjustment of thermo- 
genesis and thermolysis so as to produce a 
certain temperature. 
thermotaxis (ther-mo-tak'sis), . [NL., < Gr. 
6fppr], heat, + ragif, order, arrangement.] The 
regulation of the bodily temperature, or the 
adjustment of thermogenesis and thermolysis 
so as to secure a certain temperature. 
thermotelephone (ther-mo-tel'f-fon), n. [< Gr. 
8ep/iti, heat, + E. telephone.] 1. A telephone 
receiver in which the changes of length, due to 
