refpeilhig Heat and Caloric. 73 



the general law — drive all the water out of it, that is, con- 

 vert it into glafe, and it then obeys the general law. 



We (hall fin't attend a little to the operation of the fore- 

 going laws in fome given cafes; and afterwards examine 

 the doctrines which have been eftabliflicd from the pheno- 

 mena obfervcd to accompany them: 



If two bodies of the fame nature, unequally heated, be 

 brought into contact, the heat will diffufe itfelf equally- 

 through them, and the quantities in each will bear the 

 fame proportion to each other as the mafies thcmfelves; but, 

 if the bodies differ in kind, though equilibrium take place, 

 and each indicate the fame temperature, yet the proportions 

 of heat in each will not be as the maffes, but vary according 

 as the bodies differ. 



(E) This property of bodies to hold different quantities of 

 heat, even when that fluid is in a ftate of equilibrium, Dr. 

 Black calls the capacity of a body for heat ; the quantity itfelf 

 he calls fpeeific heat. The diitinetion is perfectly philofo- 

 phical, nor need the terms be objected to; but they mould be 

 accurately defined, that they may never be employed to convey 

 ideas different from the fa6ts that gave rife to their adoption, j 



That the fenfe in which we underhand and ufe the terms 

 may be clearly conceived, we mall fubttitute another fub- 

 ftance for heat, all other circumftances being as before. If 

 two fubftances of the fame kind (two pieces of chalk), un- 

 equally wetted with water, be brought into contact, the one 

 will give off water to the other (or the one will ablorb water 

 from the other) till the quantity in each be as their maffes. 

 If two bodies different in kind (chalk and wood) be thrown 

 into water, the quantity thev will each take in will be as 

 their capacities : this will alfo be the cafe if, inftead of 

 throwing them into water, we fu'pcnd both in the fame 

 damp atmofpherc; and the quantity in each, whether re- 

 ceived by imtnerfion in water or in the atmofpherc, is fpe- 

 eific. The latter term mult be thus confiderecl, otherwife 

 we {hall lead nurfelvcs into error; fur there is at leall a* 

 great a difference between the extremes of t he general tem- 

 perature in fummcr and in winter as there is between a 

 lnosft, and a comparatively dry (but yet moift) atmofpherc. 



Vol. VIII. L Some 



