HEAT OR CALORIC. H9 



If we suppose that the entrance of heat continues to expel light 

 from a body for an indefinite time, this difficulty is perhaps removed 

 by adverting to the fact, already suggested, that at the temperature 

 of ignition, the light enters the body along with the heat, and that both 

 bodies thus find a transit through it. This however does not ac- 

 count for the indefinite ignition produced by friction ; even allowing 

 that it is indefinite, which has not yet been proved, there is no great- 

 er difficulty than attends the indefinite emission of heat under the 

 same circumstances. 



Perhaps it would not be useful, in a concise text book, to intro- 

 duce the speculations of the learned and able philosophers who would 

 make heat, and perhaps light, to depend upon the internal motions 

 of the particles of bodies ; one kind of effect depending upon sup- 

 posed vibratory, or expansive, or retrocessive, and another upon gy- 

 ratory motions of uncognizable particles.* We might quote the 

 great names of Newton, Boyle, Hooke, Rumford, Davy, Leslie, 

 and others. The question can perhaps never be decided ; but in dis- 

 cussing the nature of light and heat, the statements of facts and the 

 reasonings can be exhibited most conveniently upon the supposition 

 that these agents are material, and that they are different from each 

 other. This course may therefore be pursued provisionally, until 

 other views shall be conclusively established, f 



VII. CAPACITY;); FOR HEAT, AND SPECIFIC HEAT. 



(a.) The capacity of a body for heat, is its power of containing a 

 given quantity of heat at a given temperature. $ The comparative 

 estimate between different bodies is usually made, by taking them 

 hi equal weights ; but it may be made also upon bodies in equal 

 volumes ; the numerical results will of course be different, but are 

 capable of being intelligibly compared. 



(6.) The specific heat of a body, is the particular quantity of that 

 power which it contains at a given temperature. 



* See Davy's Chemistry. 



t See Dr. Hare's paper on the materiality of heat, Am. Jour. Vol. IV. p. 142, 

 and the ingenious discussions between him and Professor Olmsted, in the same Jour- 

 nal, Yols. XI, XII, XIII. Dr. Hare has shewn that the phenomena of heat are 

 inconsistent with the opinion that they depend upon corpuscular motion. There 

 seems then to be no other alternative than that there must be a material cause of 

 heat, although that cause is too subtle to be recognized by us in any other way than 

 by its effects. 



t The term is evidently figurative, and alludes to the capacity of a containing 

 vessel. The use of the word, in relation to heat, implies merely a power, without 

 deciding on the mode. 



For a description of that elegant intrument, the Calorimeter of Lavoisier, see 

 his elements, and most of the larger chemical works. The quantity of water ob- 

 tained by the fusion of ice, during certain changes in bodies surrounded by that 

 substance, was made the criterion of the quantity of heat ; but there were some, 

 perhaps inherent, sources of error, and the instrument is now very little, if at all 

 used. 



