CALORIC. 



tays possess a mean degree of refrangi- 

 bility. Hence the rays in the middle of 

 the spectrum have the greatest illuminat- 

 ing 1 power; those beyond the red end 

 the greatest heating power; and those be- 

 yond the violet end the greatest deoxi- 

 dizing power : and the heating power on 

 the one hand, and the deoxidizing pow- 

 er on the other, gradually increase, as 

 we approach that end of the spectrum 

 where the maximum of each is concen- 

 trated. These different bodies resemble 

 each other in so many particulars, that 

 the same reasoning respecting refrangi- 

 bility, re flexibility, &c. may 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 unmeaning 

 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 surfaces of bodies ; and that when 

 thus radiated, it moves with a very con- 

 siderable velocity. Like light, too, it is 

 liable to be absorbed when it impinges 

 against the surfaces of bodies. When it 

 has thus entered, it is capable of making 

 its way through all bodies ; but its mo- 

 tion in this case is comparatively slow. 

 Heat then moves at two very different 

 rates. 1. It escapes from 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 tempera- 

 ture of the surrounding atmosphere. 

 That different substances, when placed in 

 this situation, cool down with very dif- 

 ferent degrees of rapidity, could not 

 have escaped the most careless observer; 

 but the influence of the surface of the 

 hot body in accelerating or retarding the 

 cooling process, was not suspected till 

 lately. For this curious and important 

 part of the doctrine of heat, we are in- 

 debted 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 

 pervious to it. Through solids, then, it 

 must pass in a different manner. In ge- 

 neral, its passage through them is re- 



in arkably slow. Thus, if we put the end 

 of a bar of iron, 20 inches long, into a 

 common fire, while a thermometer is at- 

 tached to the other extremity, four mi- 

 nutes elapse before the thermometer be- 

 gins to ascend, and 15 minutes 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 be conducted through bodies. It 

 is in this manner alone that it passes 

 through non-elastic bodies ; and though 

 it often moves by radiation through elas- 

 tic media, yet we shall find that it is ca- 

 pable 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 parti- 

 cles of the conducting body, and conse- 

 quently must be attracted by them. 

 Hence it follows, that there is an affinity 

 or attraction between caloric and every 

 conductor. It is in consequence of tins 

 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 in- 

 definitely with additional doses ot 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. The process consists in an 

 almost infinite number of repeated com- 

 positions and decompositions. We see, 

 too, that when heat is applied to one ex- 

 tremity of a body, the temperature of 

 the strata of that body must diminish 

 equably, according to their distance from 

 the source of heat. Every person must 

 have observed that this is always the case. 

 If, for instance, we pass our hand along* 

 an iron rod, one end of which is held in 

 the fire, we shall perceive its tempera-, 

 ture gradually diminishing from the end 

 in the fire, which is hottest, to the other 

 extremity, which is coldest. Hence the. 

 measure of the heat transmitted must al- 

 ways be proportional to the excess of 

 temperature communicated to that side 

 of the conductor which is nearest the . 

 source of heat. The passage of caloric 

 through a body by its conducting power 

 must have a limit ; and that limit depends 

 upon the number of doses of caloric,with 

 which the stratum of the body nearest 

 the source of heat is capable of combin- 

 ing. If the length of a body be so great, 

 that the strata of which it is composed 

 exceed ths mjmber of doses of caloric; 



