C FI E M 
Caloric, which are neceflary to raife the temperature of 
equal quantities of thefe bodies the fame number of' de¬ 
grees, provided the bodies do not change their hate or 
form, while, this increafe of temperature takes place. 
Lavoifier and La Place have employed the language of 
ipecific heat, to exprels the lame idea. 
Temperature denotes the hate by which a body pof- 
feffes the power of exciting the undefinable feufations of 
heat or coldnefs ; and it is to be observed, that the words 
temperature and heat are here taken in the moh extend¬ 
ed fenfe. The organs of the human frame are not only 
imperfect when applied to meafure the temperatures of 
bodies, but likewife exceedingly limited in this as well 
as in every other fimilar cale. Temperature is therefore 
uftd to exprefs every degfee of heat or coldnefs, whether 
within the limits of perception or not, and is apprecia¬ 
ted by the oblervation of its effects on bodies. Heat, 
confidered as the caufe of temperature and of other ef¬ 
fects, is for ever fubjeCt to variation. It is therefore an 
objeCt of mathematical inquiry, aspolfeiling quantity ei¬ 
ther abfolutely, or in the fame fenfe as various attributes, 
fuch as ratios or motion, are faid to pofiefs it. But it is 
no part of this inquiry, whether heat be motion or mat¬ 
ter. Perfpicuity requires that thefe objects Ihouid be 
feparately attended to. 
Bodies in contaCt, or communicating with each other, 
do, after a length of time, affume or acquire one com¬ 
mon temperature; but the time of acquiring the com¬ 
mon temperature is different in different bodies. When 
the temperature of a given folid is increafed, there is a 
certain period at which it becomes fluid ; and, as the tem» 
perature is increafed beyond this laft point, the fluid 
takes a rare and elaftic form, with more or lei's rapidity 
forming vapour. Whether an increafe of temperature 
would convert vapour into a fourth ftate, namely, that 
of a permanently elaftic fluid, or air, has not been deci¬ 
ded; but it is probable. The temperatures at. which dif¬ 
ferent bodies affume the fluid of vaporous Hates, are ex¬ 
ceedingly various. Some bodies, as for example, mer¬ 
cury, are not frozen but by extreme cold: others, as 
rock cryftal, cannot be melted, but by the moft vehe¬ 
ment heat modern chemiftry can excite : others again 
cannot be brought into fome of the ftates ; and of thefe 
the rule is inferred from analogy, till future experiments 
may tend to clear up the point. The importance of the 
theory ofheat, however in chemical operations, requires 
a more ItriCt and critical inveftigation of the fubjeCt than 
lias hitherto been given. 
. Axiom i. The quantities of heat in two equal bo¬ 
dies of the fame kind' and temperature are equal. 
Theorem i. The quantities of heat in bodies of the 
fame kind and temperature are as their maffes. 
Theorem 2. Two equal bodies of the fame kind, but 
different temperatures, being brought into contaCt ; the 
hotter will impart half its furplus of heat to the other. 
For they will acquire a common temperature by contact, 
and by that means, the quantities of heat will be made 
equal. This can only be efteCted. by the hotter body im¬ 
parting half its furplus. 
Theorem 3. Two bodies of the fame kind, but dif¬ 
ferent temperatures, being brought into contaCt; the 
furplus of heat, by means of which the one exceeded the 
other m temperature, wall be divided between the two 
bodies in proportion to their maffes. For they will ac¬ 
quire a common temperature, and the whole quantity of 
heat in each will then be in proportion to its mafs. This 
can only be effected by dividing the furplus in the fame 
proportion. 
Corollary 1. The quantities of heat required to be 
added to, or taken from bodies, of the fame kind, to 
bring their temperature to a given ftandard, will be as 
their mafies. 
Corollary 2. Hence a thermometer, with a very 
fmall bulb, may be confidered as poffefiing the tempera¬ 
ture of the body it is in contaCt with, became the com- 
I S T R Y. 183 
mon temperature will not fenfibly differ therefrom when 
the body is or conftderable magnitude. 
The mercurial thermometer nearly meafures the true 
increments of temperature. This is determined by an 
experiment of De Luc : let a thermometer be graduated 
fo as to (how the equal increments of the expanlion of the 
mercury ; and the common temperature of two equal bo¬ 
dies of the fame kind in contaCt (as for example, mea- 
lures of water) will be nearly the arithmetical mean be¬ 
tween the two original temperatures, as ftiown by fuch 
an inftrument. The inftrument therefore gives refults 
nearly agreeing with dedubtions made from the general 
phenomena ofheat, or it nearly meafures the true incre¬ 
ments of temperature. 
Axiom 2. If two equal maffes at different tempera¬ 
tures be brought into contadt, and the common tempe¬ 
rature be either higher or lower than the arithmetical 
mean, the furplus of heat, by means whereof the one 
exceeded the other in temperature, will be unequally di¬ 
vided ; and the difpofition to be heated, or the capacity 
or affinity for heat, is greater in one body than in the 
other. 
Theorem 4, The capacity of equal mafies for heat 
are inverfely, as the changes of temperature they undergo, 
when differently heated and brought into contact: and 
the contrary. For the furplus of heat is divided into 
equal parts-by the thermometer : of thefe parts, the hot¬ 
ter body lofes a certain number by communication to the 
colder, and retains the remainder. The number of de¬ 
grees loft, conftitutes the change of temperature in the 
hotter, and the remainder is the change in the colder. 
But caufes are ever proportional to their effeCts; there¬ 
fore the capacities are as the proportions of heat retain¬ 
ed by each, that is, inverfely as the changes of tempera¬ 
ture. 
Corollary r. Hence if any given body, as for exam¬ 
ple, fluid water, be affirmed as a ftandard, the capacities 
of other bodies being experimentally found, may be 
ranged numerically, fo as to form an ufeful table. 
Corollary 2. The quantities of heat required to be 
added to or taken from bodies of equal mafs, t o bring 
their temperature to a given ftandard, will be as their 
capacities. 
Corollary 3. The quantities of heat required to be 
added to or taken from bodies in general, to bring their 
temperature to a given ftandard, will be as their maffes, 
and their capacities jointly. 
Corollary 4. The capacities, in general, will be di¬ 
rectly as the quantities of heat fo taken, and inverfely 
as the mafles; or they will be in the inverfe ratio of the 
changes of temperature, and the mafles of two bodies 
placed in contadt. This, in the form of a practical rule, 
is, Multiply the weight of each body by the number of 
degrees between its original and the common tempera¬ 
ture, and the capacities of the bodies for heat will be in¬ 
verfely as the produCts. 
Theorem 5. The whole quantities of heat contained 
in the bodies of equal mafs and temperature are as their 
capacities. For if the temperatures of various bodies be 
luppofed gradually and equally to dim ini (h till the abso¬ 
lute privation of heat be obtained, the quality of heat 
given out in any portion of the time wiil be proportional 
m each body to its capacity. And the whole time being 
made up of fuch portions, the refpeCtive (inns of the quan¬ 
tities of heat given out by each body will be in the lame 
ratio. It is the bufinefs of experiment to determine 
whether the ratios of the capacities be the fame in all 
temperatures, cceteris manentibus. 
Scholium. From the foregoing theorem, many wri¬ 
ters have called a tabie of capacities by the name of a ta¬ 
ble of Ipecific heats. Thefe terms, which feem impro¬ 
per, or at lealf unhappy, becaufe applied to quantities 
that continually fluctuate, have certainly rendered the 
theory ofheat lets eafy to beginners. 
As far as experiments have hitherto been made, it is 
• found. 
