' Pepreper to mention, that experiments of a similar 
madre, an with similar results, were performed on the 
~ ¥adiation of cold by Count Rumford, They are such 
peony establish the facts, and might be esteemed 
_ valuable, were they not, for the most part, superseded 
_ by those of Professor Leslie, Phil. Trans. 1804, p. 170. 
, *. The general conclusions that may be deduced 
_ the experiments of Pictet, Rumford, and Leslie, are, 
_ that bodies possess a power which generates cold, or 
reduces actual temperature ; and t this power is 
emitted in right lines, and may be reflected, condensed, 
or intercepted in its passage from one body to another, 
__ like the rays of radiant heat. It also follows the same 
laws with respect to the action of surfaces upon it, and 
_ bears the same relation to their reflecting property. 
Certainly the most obvious inference would be, that 
cold, like heat, depends upon the presence of a real 
material agent, capable of being transferred from one 
body to another, and subject to similar laws of radia- 
tion and reflection ; but this supposition is so strongly 
opposed by many other considerations, which seem to 
~ prove, in the most Pee manner, that cold is merely 
| a negative property, and signifies nothing more than the 
abstraction of heat, that we are compelled to look out 
for the explanation of the phenomena upon other princi- 
: these we shall afterwards endeavour to elucidate. 
~ We have very few remarks to make respecting the 
ngi- two other mechanical rties of heat, its Feflexibility 
t. and its refrangibility. e reflection of heat has been 
abundantly goes by the numerous facts that we have 
stated, in which the concave mirrors were employed, 
as well as in all those where the nature of the surface 
absorbing the rays of heat affected this property ; for 
it has been shewn, that in as much as the surfaces 
were unfavourable for absorption, they were, in the 
proportion, favourable for the reflection of heat. 
refraction of heat, as distinct from light, was clear- 
iy exhibited in Herschel’s experiments ; by its 
gh the prism, it was diverted from its straig) t 
course like light, only in a greater degree, as thie calorific 
rays are found to be dispersed over a larger than 
the spectrum formed by the visible rays. i he rays 
proceeding from a candle, or from burning fuel, were 
also found to be capable of refraction, like of solar 
heat. We may conclude that the solar heat consists of 
trays of different degrees of refrangibility, although no 
other ditference has been detected in their nature, as is 
the case with the differently coloured rays of light. 
This conclusion foilows from the fact, that the space 
occupied by the rays after they have passed ge 
the prism is greater than before they entered it. 
Arpenprx to this article. 
xity of Before we conclude our account of what we have sty- 
led the mechanical properties of heat, we shall offer a 
very few remarks upon the velocity with which it moves. 
That the velocity must be very , is a point of 
which there can be no reasonable doubt ; yet it will be 
found: ie difficult to assign the actual velocity. It is 
thaps the most probable conjecture, that heat, when 
radiating from a body, moves at the same rate with 
ok yet we know of no decisive arguments from 
which this can be inferred, as more than a conjecture. 
Pictet made some experiments upon this subject; but 
they only prove that no tible interval elapses in 
the of heat through about 70 feet, a space much 
too small to prove any thing important. 
emical “The second class of properties, which we announced 
as belonging to heat, are its chemical properties, or 
those that tend directly to produce a chemical change 
; 4 
HEAT, 
_in bodies. rereelll powevet, yestane tes consider. Properties 
ation of these to a futare part 
shall then be better prepared to determine, what 
perties ought to be as chemical, after we have 
made ourselves acquainted with the effects of heat, as 
well as with the other p that have not yet been 
considered, which we have styled specific. we 
shall now proceed to examine, 
The ific properties of heat may be classed under 3. Specitic 
two heads : its tendency to diffuse itself equally among porate of 
bodies, or its mode of communication from one body to "+ 
another; and the peculiar manner in which it passes 
through bodies, Whatever be our opinion respecting 
the real nature of heat, it is almost impossible to en« 
ter into any investigation concerning it, without usi 
fanguage the pec to imply, that it ares 3 
from oh cee age the ial cause. HS there: 
fore, we into these forms of expression, it must 
be ascribed, not to our decidedly adopting this h 
sis of the nature of caloric, but to the extreme 
of avoiding them, although they must be admitted to 
be incorrect. With this preliminary caution, we may * 
be allowed to say, that heat differs from other bodies, 
in its. tendency to diffuse or distribute itself uniformly 
through all kinds of matter. When any substance pos- dis. 
sesses a different portion of free caloric from the sub- tribution of 
stances in its vicinity, either in immediate contact, or heat. 
connected with it by the intervention of a third sub 
stance, the superabundant portion of heat will have a - 
tendency to pass from the first to the second, and the 
one will: give and the other receive heat, until they ar« 
rive at a common temperature. This is one of the most 
familiar occurrences, and one of which we eee 
avail ourselves in the arts of life. If we wish to impart 
heat to a body, we bring it near a substance that is 
hotter than itself, when it moe cpm ra, to receive 
heat, and continues to acquire it, as long as it remains 
in its new situation, or until it shall have experienced 
some change, which renders it incapable of the farther 
reception of heat. When, on the con , we wish to 
cool a body, we remove it into the neighbourhood of 
one which is cooler than itself, when an ion the 
reverse of the former will enste ; the cold body will ab- 
stract heat from the warmer, until the common tempe- 
rature be gained. 
The cause of this tendency in heat to fly off from Repulsive 
bodies, or to pass from one to the other, and thus to pone ot 
diffuse itself among them, is attributed to its i 
an inherent repulsive power. The particles of all ki 
of ponderable matter are necessarily attracted to each 
other, and consequently, under all circumstances, they 
have a tendency to be drawn and held together, unless 
some counteracting cause prevents their union. This 
is equally exemplified in the attraction which prevails 
between Jarge masses of matter, by which the planets 
are kept in their orbits, called the attraction of = 
tatior?, and the attraction which exists between the in- 
dividual particles of matter, and influences many of the 
minute operations of nature, under the denomination 
of chemical attraction. The repulsive power, which 
appears to be an inherent quality of heat, may be re 
garded in general as the cause of its diffusion among 
bodies ; but the manner in which it is distributed, or 
the particular law which it follows in passing off from 
ably; and attaching itself to others, seems to de- 
pend upon a different principle, or at least to be modi- 
fied in a way that cannot be referred to repulsion. It 
has been conceived, that the phenomena might be ex- 
plained upon the ided, that there is a combination of 
