CALORIC. 
parate from each other with inconceivable 
rapidity. This property necessarily sup- 
poses the existence of a mutual repulsion 
between tlie particles of caloric. Thus it 
appears that caloric and light resemble 
each other in a great number of properties. 
Both are emitted from the sun in rays, with 
the velocity of 200,000 miles in a second ; 
both of them are refracted by transparent 
bodies, and reflected by polished surfaces ; 
both of them consist of particles which 
mutually repel each other, and which pro- 
duced no sensible effect upon the weight 
of otlier bodies. They differ, however, in 
this particular: light produces in us the 
sensation of vision j caloric, on the con- 
trary, the sensation of heat. Upon the 
whole, we are authorized by the above 
statement of facts, to conclude, tliat the 
solar light is composed of three distinct 
substances, in some measure separable by 
the prism, on account of the difference of 
their refrangibility. The calorific rays are 
the least refrangible, the deoxidizing rays 
are most refrangible, and the colorific rays 
possess a mean degree of refrangibility. 
Hence the rays in the middle of the spec- 
trum have the greatest illuminating power ; 
those beyond the red end the greatest 
heating power, and those beyond the 
violet end the greatest deoxidizing pow- 
er; and the heating power on the one 
hand, and the deoxidizing power on the 
other, gradually increase as we approach 
that end of the specti-um where the 
maximum of each is concentrated. These 
different bodies resemble each other in so 
many particulars, that the same reasoning 
respecting refrangibility, reflexibility, &c. 
fnay be applied to all ; but they produce 
different effects upon those bodies on which 
they act. Little progress has yet been 
made in the investigation of these effects ; 
but we may look forward to this subject as 
likely to correct many vague and unmean- 
ing opinions, which are at present in vogue 
among chemists. 
From this account of the nature of ca- 
loric, we learn that it is capable, like light, 
of radiating in all directions from the sur- 
faces of bodies; and that when thus ra- 
diated, it moves with a very considerable 
velocity. Like light, too, it is liable to be 
absorbed when it impinges against the sur- 
faces 0 ^ bodies. When it has thus entered, 
it is capable of making its way through all 
bodies ; but its motion in this case is com- 
paratively slow. Heat then moves at two 
vfery different rates. 1. It escapes from 
VOL. II. 
the surfaces of bodies. 2. It is conducted, 
or passes through bodies. 
When bodies artificially heated are ex- 
posed to the open air, they immediately 
begin to emit heat, and continue to do so 
till they become nearly of the temperature 
of the surrounding atmosphere. That dif- 
ferent substances when placed in this situa- 
tion, cool down with very different degrees 
of rapidity, could not have escaped the 
most careless obsei-ver ; but the influence 
of the surface of the hot body in accele- 
rating or retarding the cooling process, was 
not suspected till lately. For this curious 
and important part of the doctrine of heat, 
we are indebted to the sagacity of Mr. 
Leslie, who has already brought it to a 
great degree of perfection. To whose work 
we refer the philosophical reader, for much 
useful and highly interesting matter. 
Although caloric is incapable of moving 
in rays through solid bodies ; yet it is well 
known that all bodies whatever are' per- 
vious to it. Through solids, then, it must 
pass in a different manner. In general its 
passage through them is remarkably slow. 
Thus if we put the end of a bar of iron, 
20 inches long, into a common fire, while 
a thermometer is attached to the other ex- 
tremity; four minutes elapse before the 
thermometer begins to ascend, and 15 mi- 
nutes by the time it has risen 15“. In this 
case, the caloric takes four minutes to pass 
through a bar of iron 20 inches in length. 
“When caloric passes in this slow manner, it is 
said to he conducted through bodies. It is 
in this manner alone that it passes through 
non-elastic bodies; and though it often 
moves by radiation through elastic media, 
yet we shall find that it is capable of being 
conducted through them likewise. As the 
velocity of caloric, when it is conducted 
through bodies is greatly retarded, it is 
clear that it does not move through them 
without restraint. It must be detained for 
some time by the particles of the conduct- 
ing body, and consequently must be at- 
tracted by them. Hence it follows, that 
there is an affinity or attraction between 
caloric and every conductor. It is in con- 
sequence of this affinity that it is conducted 
through the body. 
Bodies then conduct caloric in conse- 
quence of their affinity for it, and the pro- 
perty which they have of combining inde- 
finitely with additional doses of it. Hence 
the reason of the slowness of the process, 
or, which is the same thing, of the long time 
necessary to heat or to cool a body. Th® 
E 
