HEAT. 
277 
HEAT,/, [lie.!?, hae?, Sax. heete, Dan.] The fen¬ 
fation cau.fcd by the approach or touch of’ fire.— Heat is 
a very brific agitation of the infenfible parts of the ob'- 
jeCt, which- produces in us that fenfation from whence 
we denominate the objeCt hot ; fo what in our fenfation 
is heat, in the objeCt is nothing but motion. Locke. —The 
word heat.ls ufed to fignify the fenfation we have when 
we are near the fire, as well as the caufe of that fenfa¬ 
tion, which is in the fire itfelf; and thence we conclude, 
that there is a fort of heat in the fire refembling our own 
fenfation : whereas in the fire there is nothing but little 
particles of matter, of fuch particular lhapesas are fitted 
to imprefs fuch motions on our flefli as excite the fenfe 
of heat. Watts. —The caufe of the fenfation of burning.— 
The fword which is made fiery doth not only cut by 
reafon of the Iharpnefs which fimply it hath, but alfo 
burns by means of that heat which it hath from fire. 
Hooker. —Hot weather : 
Mark well the flow’ring almonds in the wood; 
The glebe will anfwer to the fylvan reign ; 
Great heats will follow, and large-crops of grain. Dryd. 
State of anybody under the a&ion-of the fire.—The 
heats ffmiths take of their iron are a blood-red heat, a white 
flame heat, and a fparkling or welding heat. Moxon. —Fer¬ 
mentation ; effervefcence.—One violent adlion uninter¬ 
mitted.—The continual agitations of the fpirits mud 
needs be a weakening of any Conftitution, efpecially in 
age : and many cattles are required for refrelhment be¬ 
twixt the heats. Dryclen. —The fiate of being once hot ; 
a Angle effort: 
I’ll ftrike my fortune with him at a heat, 
And give him not the leifure to forget. Dryden. 
They the turn’d lines on golden anvils beat. 
Which look as if they ftruck them at a heat. Tate. 
A courfeata race, between each of which courfes there 
is an intermiflion : 
Feign’d zeal, you faw, fet out the fpeedier pace ; 
.But the laft heat plain dealing won the race. Dryden. 
Pimples in the face; flnfh.—It has raifed animofities in 
their hearts, and heats in their faces, and broke out in 
their ribbans. Addifon. —Agitation of hidden or violent 
paflion ; vehemence of aCfion.—It might have pleafed 
in the heat and hurry of his rage, but mud have dif- 
pleafed in cool fedate reflection. South. 
The friend hath loft his friend ; 
And the beft quarrels, in the heat are curft. 
By thofe that feel their Iharpnefs. Shakfpeare. 
Faction ; conteft; party rage.—I was forry to hear with 
what partiality and popular heat elections were carried. 
King Charles. 
What can more gratify the Phrygian foe 
Than thofe diftemper’d heats? Dryden. 
Ardour of thought or elocution : 
Plead it to her 
With all the ftrength and heat of eloquence 
Fraternal love and friendfhip can infpire. Addifon. 
To HEAT, v. a. To make hot ; to endue with the 
power of burning.—He commanded that they Ihould 
heat the furnace one feven times more than it was wont 
to be heated. Dan. iii. 19.—To caufe to ferment.—Hops 
lying undried heats them, and changes their colour. Mor¬ 
timer.— -To make "the conftitution feverifli.—Whatever 
increafeth the denfity of the blood, even without in- 
creafing its celerity, heats, becaufe a denfer body is hot¬ 
ter than a rarer. Arbuthnot. 
Thou art going to lord Timon’s feaft. 
—Ay, to lee meat fill knaves, and wine heat fools, Shakefp. 
To warm with vehemence of paflion or defire : 
Vol. IX. No. 584, 
A noble emulation heats your breaft, 
And your own fame now robs you of your reft. Dryden. 
To agitate the blood and fpirits with aCtion.—When he 
was well heated, the younger champion could not ftand 
before him; and we find the - elder contended not for 
the gift, but for the honour. Dryden. 
The inveftigation of the properties of heat, or caloric, 
and the importance of its agency in the grand laboratory 
of Nature, are objeCts of confiderable intereft to the phi- 
lofophical world. It has been laid down as a law, that 
the principal agent employed to balance the power of 
attraction or cohefion, is fire. By the natural effeCt of 
attraction, we Ihould poflefs none but foLid and compaCl 
bodies; but .the caloric, unequally difperfed in bodies, 
tends to deltroy this adhefion of particles. Hence the 
various Jubilances that compofe this globe are fubjedl, 
on the one hand, to a general law which tends to bring 
them together ; and on the other, to a powerful agent 
which tends to remove them from each other: and upon 
the refpedtive energy of thefe two forces, the confid¬ 
ence of all bodies _depends. When the attradiion pre¬ 
vails, they are in a folid (fate ; when the caloric is moft 
powerful, they are in a Hate of gas ; and the liquid form 
appears to be the point of equilibrium between thele 
two powers. The term heat, in common language, has 
a double Tignification : it is ufed indiferiminately to ex- 
prefs a fenfation of the mind ; and an unknown princi¬ 
ple, which is the exciting caufe of that fenfation. Phi- 
lofophers and chemifts ufe it in the latter fenfe. See 
tlve article Caloric, vol. iii. p. 634. The effedts of 
heat are known and meafured, firft, by the peculiar 
fenfations which it excites in animals ; and, when confi- 
dered as exciting thofe fenfations, it is called fenfible he at. 
Secondly, heat is known by the effedt it produces on the 
thermometer. This is called the temperature of heat in 
bodibs. It is found by experiment that, in bodies of 
different kinds, the quantities of abfolute heat may be un¬ 
equal, though the temperatures and weights be the fame. 
Heat has a conftant tendency to diffufe itfelf over all 
bodies, animate and inanimate, till they are brought to 
the fame temperature. Thus it is found, by the ther¬ 
mometer, that if two bodies, of different temperatures, 
are mixed together, or placed contiguous, the heat 
pafles from one to the other till their temperatures be¬ 
come equal ; and that all inanimate bodies, when heated, 
and placed in a cold medium, continually lofe heat, 
till they are brought to the ftate of the furrounding me¬ 
dium.—See this fubjeCt moft amply difeuffed and ex¬ 
plained under the heads Fire, Light, and Caloric, 
in the article Chemistry, vol. iv. p. 179-189. 
But though heat or caloric has a conftant tendency 
to diffufe itfelf over all bodies ; yet it does not permeate 
all bodies alike. This has been lately proved in a very 
fatisfactory manner, by the interefting and curious ex¬ 
periments of Mr. Leflie, as given in his Enquiry into the 
Nature and Propagation of Heat, publilhed in 1804. 
This ingenious philofopher provided himfelf with a pe¬ 
culiar apparatus, confining of reflectors or Jpecula, and 
of tubes containing hot water, formed on purpofe to fa¬ 
cilitate this enquiry. Thefe reflectors were hammered 
out of block-tin, and highly finifhed, exhibiting great 
brightnefs, fmoothnefs, and regularity of furface. When 
expofed to the direCt light of the fun, they collected 
the rays into a diftinCt focus, which was fo powerful, 
that bits of wood or cloth, held in the focus, were burnt 
through, or fet on fire, in a few ffeconds. The part of 
the apparatus intended to contain hot water, confided 
of hollow tin ciibes or canifters, formed exaCtly, and 
hammered to a fmooth and bright furface. Thefe ca¬ 
nifters had an orifice at the middle of the upper fide, 
from half an inch to an inch in diameter, and* the fame 
in height, fitted to receive a cap through which was in¬ 
fected a thermometer, whole bulb might-reach nearly 
to the centre of the.water. The cubes were of different 
lizes; of three, four, fix, and ten, inches.’ In two of 
4 3 them, 
