530 On the Tranfmijlfion of Caloric and 



pofe to examine. But it will be proper, in the firft place, in order to prevent verbal dif- 

 putes, to explain what I mean by Ae conduEfine ^ower of bodies. Count Rumford has 

 negledled to do this.; and I am not abfolutely certain that he affixes the fame meaning to 

 the phrafc that I do. 



Dr. Hcrfchel appears to me to have demonftrated, that caloric is emitted from the fun 

 in rays, and that it moves with the fame velocity as light, or at the rate of nearly 200,000 

 miles in a fecond. It follows, from his experiments, and from thofe of Scheelc and 

 Piftet, that caloric moves through air without any fen.fible diminution of its velocity. It 

 has been demonftrated, too, that it is capable of moving' through glafs of a certain tem- 

 perature, without any fenfible diminution of its celerity. Now, whenever caloric paffes 

 through a body with undiminiflied celerity, we may fay that it is tranfmitted through the 

 body. Air^ thjsn, and gh/s^ have the property of tranfmitting cjkloric through them. 

 When caloric is tranfmitted through a body, as its velocity is too great to be meafured, 

 it appears to pafs through the body inftantanec^lly. Thus M. Pi£let found that caloric 

 moved inftantaneoufly through 69 feet of air. 



When the end of an iron rod, 20 inches long,'is put into the fire, while a thermometer 

 is applied to the other extremity, it is four minutes before the thermometer begins to 

 rife, and it takes 15 minutes before it rifes 10". Caloric, then, does not pafs through a rod 

 of iron inftantaneoufly ; confequently, it is not tranfmitted through the iron, but moves 

 through it in a different manner. Its veloqity is prodigioufly diminiflied, fince inftead of 

 moving at the rate of 200,000 miles in a fecond, it moves only at the rate of 20 inches in 

 4'. Now, whenever caloric pafles in this manner through bodies, with its velocity pro* 

 djgioufly diminiflied, it is faid to to be conduced through them. It appears, then, that 

 caloric is tranfmitted through bodies, and conduSled through them, in quite a different 

 manner. 



If we take an iron rod, and another of baked clay, of preclfely the fame fize and fliape, 

 and, putting one end of each into the fire, apply thermometers to the other extremity, wc 

 (hall find that the thermometer applied to the iron rod rifes fooner than that applied to thq 

 clay rod. Caloric is then conducted with more rapidity through iron than through baked 

 clay. Confequently, iron is a letter conduBor of caloric than baked clay. When a body 

 does not allow caloric to pafs. through it at all, it is called 3 non-conduElor. 



It is not difficult to form fome notion of the manner in which caloric is Qondufled 

 through bodies. As its motion is prodigioufly ret^ded, it is clear that it does not move 

 without reftraint. It muft be detained for fome time by the particles of the condu£l;iijg 

 body, and, confequently, muft be attra(aed by them : hence it, follows, that there is an 

 attraElion or ajinity between caloric and every condi^ftpr of caloric. Now it is in con- 

 fequencc of this affinity that the caloric is conduded through the body. 



Let 



