HEAT. 
was actually brought to the boiling heat. Here a v 
& Gpiderable quantity of heat was liberated, and the 
only mechanical change effected upon the materials was, 
that a quantity of brass turnings were formed ; but nei- 
ther these, nor the cylinder itself, appeared to have ex- 
perienced any menses except a slight degree of com- 
ion. Rumford found by experiment, that the ca- 
pacity of these turnings would not be affected by the 
operation ; and the effect of the compression, which the 
metal had experienced, must have very inconsi- 
derable. Yet the power of the substance to extricate 
y unlimited ; for there: is no reason 
ced, or that the apparatus would not have continued to 
ve heat, until its texture had been destroyed, by 
brass being all reduced into small fragments: (Es- 
ys, Vol. ii.” p. 469; et seq.) Upon this experiment we 
offer some remarks in the next Section, where we 
treat upon the nature of heat. 
. The heat excited by the electric or galvanic shock 
Chong nwa tien poibe  coocidanchle diverdepel one 
u is point, a consi é diversity of opi- 
nions bene ed. he effect, however, is w: pau 
to be very powerful, perhaps even more so than that 
uced by the convex lens ; but it is still more con- 
fined as to the extent of its operation. Ifthe two wires, 
in the interrupted galvanic circuit, be brought nearly 
into contact, and any substance, in very minute quan- 
tity, be placed upon them, it may be subjected to a 
temperature more intense than can be produced in any 
ether manner; and by this means bodies have been 
burned or fused that had been before completely in- 
tractable. Whether in this operation the heat is, as it 
were, merely forced out of the wire by the commotion 
which its particles experience from the passage. of the 
galvanic influence ; or whether, as has been supposed, 
under certain circumstances, heat and electricity can 
be converted into each other, or may be separated by a 
kind of decomposition, are intricate questions of theory, 
upon which it seems at present beyond our power to 
decide, and which must depend very much upon the 
inion that we entertain respecting the nature of heat. 
The simple facts, however, independent of hypothesis, 
seem to indicate, that heat and electricity are distinct 
from each other, whether they are to be regarded as 
species of subtile fluids, or only as properties of mat- 
ter. 
heat was a 
iipeen thes ome thing like exhaustion was produ-) 
SECT. IV. 
On the Nature of Heat. 
_ Arter having made ourselves acquainted with the 
P ies that are usually ascribed to heat, with the 
effects which it produces, and with the sources whence 
it is derived, we shall be more competent to enter upon 
the investigation of its nature. This has been a-sub-. 
ject of discussion from the earliest period of philosophi- 
cal inquiry, and is yet far from being determined ; for 
although the most generally received: opinion is in fa~ 
vour of its being a substance, capable of a separate ex- 
istence, and possessed of a material, although very sub- 
tile nature; yet there are, on the contrary, many emi- 
nent men who regard it as merely. a property, necessa- 
rily attached to other matter, and, arising from some 
peculiar modification or affection of it, 
The illustrious Bacon adopted this latter: hypothesis, 
and conceived that heat depended upon a vibration of: 
VOL. X. PART Ik 
by Dr Black’s 
689 
the particles of matter ; an hypothesis which he endea- ee 
voured to substantiate by showing, that whatever exci- 
ted temperature, tended to produce a motion in the 
particles of the heated body. His description of this 
peculiar action is, that “ heat is an expansive motion, 
restrained and resisting in the minute parts ;” a phrase 
which, if expressed in modern language, weal pro- 
bably signify a reaction between the expansive power 
of heat, and the attractive force of the particles of mat- 
ter towards each other. The idea of Bacon, that heat 
depends upon a vibratory motion among the particles 
of matter, received the powerful sanction of Boyle and’ 
Newton, As, however, observations on the phenomena 
of nature were multiplied, and especially as chemical 
science advanced, the hypothesis which considered heat 
as merely consisting in motion of the particles of mat- 
ter, appeared less easy to reconcile with the new disco- 
veries, and) consequently a different doctrine was ad- 
vanced, in which the effects of heat were attributed to: 
a species of subtile fluid, of a proper material nature, 
although differing, in many important particulars, fromr 
any other kind of matter. The first writer who dis- 
tinctly maintained this doctrine, and applied.it in a phi- 
losophical manner to the explanation of facts, waa Boer= 
haave ; and it was, for the most part, embraced 
French. The general impression that was p 
to imagine, how a mere property can be so exactly mea- 
sured, and can be enapictcd from one body to pe ne 
at one time rendered latent, and again coming into ac- 
tion, without its quantity being either increased or di-+ 
minished., The successive discoveries of Crawford and: 
Irvine, together with the whole fabric of the Lavoiserian 
chemistry, strongly favour the same opinion ; so that, 
in the present day, it must be regarded as the h e~ 
sis which is by far the most generally received. It has, 
however, been zealously opposed by Rumford; and the Ruroford’s 
experiments on the heat excited by friction, of which opinion. 
we have given an account, were brought forward as’ 
an unanswerable objection against it. Our limits will 
not permit us to take a very full view of all the argu« 
ments that have been urged on both sides of the ques- 
tion ; but we must endeavour to give a sketch of some 
of the principal points that have been adduced by the 
advocates of pains the opinions. It will scarcely be 
denied, that if we admit the existence of a subtile elas- 
tic fluid, the particles of which are endowed with a re- 
pulsive power, which tends to unite itself to all kinds 
of matter, to insinuate itself into their pores, to produce 
their expansion, and, if added in sufficient quantity, to 
impart to them its own elastic nature, we are in 
sion of an agent, which very conveniently explains a 
t variety of phenomena ; for excepting the experi- 
ments of Rumford on friction, and others of a similar 
nature, we do not know of any facts which are adverse 
to the supposition, or which are not better explained on 
this than on any other that has been adduced. It must, 
however, be admitted, that it is merely an hypothesis ; 
and as there is no direct experiment which proves the 
existence of this subtile elastic fluid, it must be aban- 
doned, if there be any sing 
solutely irreconcilable to it. 
this to be the case, in the present instance, it- is neces- 
sary to shew, that our acquaintance with the phenome- 
non in question is complete ; that we thoroughly under- 
stand all its relations, and are com 
the connexion which it‘has with all: the other actions 
4s 
the Boer- 
uced haave’s. 
iscovery, was much in favour of the plack’s 
materiality of heat ; and indeed it seems very difficult doctrine. 
le phenomenon which is ab- Heat ex- 
ut before we can allow cited by 
ent to decide upon lity. 
