HEAT. 



Count Rumford considered it to be 

 equal to that of nine wax candles, each 

 three- quarters of an inch in diameter, 

 burning the same length of time. 



In searching for the source of heat in 

 this experiment, it could not be found 

 in any change of capacity, as the borings 

 continued of the same capacity as the 

 metal from which they were abraded. 

 The air of the atmosphere having been 

 excluded in the process, no part of the 

 heat could be ascribed to its agency ; 

 the water used underwent no chemical 

 change, and could not, therefore, have 

 contributed any portion of the heat, nor 

 could any part of the heat have been 

 derived from surrounding bodies, as 

 they rather received heat from the mat- 

 ter exposed to friction. 



The Count considered it proved by 

 these experiments that heat may be ob- 

 tained, without limitation, by subjecting 

 metal to friction ; and concluded that 

 what can be obtained from insulated 

 bodies without limitation cannot be ma- 

 terial, and believed it impossible to 

 account for such phenomena upon any 

 other hypothesis than that of motion 

 among the particles of bodies. 



It had been before proved by Boyle 

 that friction in vacuo produces heat,*he 

 having obtained this result by making 

 two pieces of brass rub against each 

 other in the exhausted receiver of an 

 air-pump. The same fact was proved 

 by Pictet, who found that the intro- 

 duction of a soft substance, such as 

 cotton, between the rubbing surfaces, 

 increased the heat. He conjectured 

 that electricity is concerned in the pro- 

 duction of heat by friction. 



Sir H. Davy made various experi- 

 ments illustrative of this subject. He 

 insulated an apparatus for occasion- 

 ing friction, by placing it on ice in 

 vacuo, in which situation heat was pro- 

 duced. Two pieces of ice, similarly 

 circumstanced, being made to rub 

 against each other, heat enough was 

 produced to melt them. The heat 

 produced in this experiment could not 

 arise from any diminution of capacity, 

 as the water 'resulting from the melt- 

 ing of the ice has the greater capacity 

 for heat. It seemed to be satisfactorily 

 shown also, that it could not be derived 

 from air, and the same conclusion was 

 drawn from these experiments that 

 Count Rumford drew from his, namely, 

 that heat is produced by motion among 

 the particles of bodies. 



Having thus detailed the most re- 

 markable experiments favourable to 

 both of the prevailing hypotheses as to 

 the cause of heat, and having stated 

 the conclusions drawn from them, it 

 may be useful to quote the opinions 

 of two philosophers who think diffe- 

 rently on the subject, and place them 

 in opposition to each other. 



Dr. Murray, (System of Chemistry, 

 third edition, vol. i. page 468,) after 

 describing the hypothesis upon which 

 heat is supposed to be material, proceeds 

 to speak of the other in the following 

 words: "The opposite opinion, that 

 caloric is motion, placing it on the same 

 ground, or considering it as an hypo- 

 thesis, does not afford an explanation of 

 those phenomena equally satisfactory. 

 The most general effect arising from the 

 operation of caloric, is expansion ; but 

 if caloric is mere motion, or vibration of 

 the particles of the heated body, how is 

 this effect produced ? Vibration is the 

 alternate approximation and retroces- 

 sion of the particles ; but from this state 

 it is evident that no permanent and 

 uniform increase of volume can take 

 place. Still less can this cause account 

 for the augmentation of volume which 

 accompanies fluidity and vaporisation. 

 When water is converted into vapour, 

 it occupies 1800 times the space which 

 it did while in the liquid form. Suppose 

 vibration increased to any intensity, it 

 cannot be shown how it can permanently 

 separate the particles of a body to such 

 distances. The deficiencies of this opinion 

 are likewise evident in its application to 

 other phenomena. The laws of its pro- 

 pagation through bodies are different 

 from the established laws of motion. 

 Were they the same, the propagation of 

 caloric ought to be momentary ^through 

 elastic bodies, and should be more or 

 less rapid through others, according to 

 their elasticity, which is far from being 

 the case. Neither is any cause pointed 

 out why it should be so slowly trans- 

 mitted through liquids or airs. We are 

 equally unable to account for its distri- 

 bution in bodies, and the quantities of 

 it required to produce given tempera- 

 tures in different substances, or the 

 portions of it absorbed when bodies 

 change their forms, on any laws it could 

 observe, supposing it to be any species 

 of motion." 



Dr. Young (in his Lectures on Natu- 

 ral Philosophy, vol. i. page 653,) pro- 

 ceeds thus with the discussion of the 



