38 ON THE HEAT PRODUCED BY FRICTION, 



which is greater than that of copper, gave but an equal 

 quantity of heat, while zinc, which is less dense than either, 

 gave a greater quantity. 

 Influence of The influence of pressure is shown by the 5th and 6th ex- 

 prcssure, periments, and as its effect on compressible bodies is neces- 



sarily to crush and condense them, does it not seem to indi- 

 cate the approach of the particles as the cause of the extri- 

 cation of heat ? Yet as this condensation must be the greater, 

 in proportion as the same pressure is exerted on a small num- 

 ber of points at a time, and is employed to detach particles, 

 that cannot be separated till they have experienced a consi- 

 derable approximation of their' parts, the 7th experiment/in 

 which the steel file-cut rubber detached a considerable quan- 

 tity of particles of copper, should have produced a propor- 

 tionate quantity of heat: yet it gave less by half than the 

 friction with a smooth rubber, 

 and of conden- The influence of condensation on the production of heat 

 sanon. j § ren( ] ere( ] s tm more uncertain by the 10th experiment, in 



which the iron wire, compressed and flattened by strokes of 

 a hammer, ought to have set free a quantity of heat so much 

 greater, in proportion as the force employed to effect the 

 compression was more powerful. In vain would it be ob- 

 jected, that there was no condensation, the specific gravity 

 of the wire not appearing to be changed: the electricity and 

 fragility it had acquired, certain signs of compression, leave 

 no doubt of the reality of this condensation, though it was 

 too little to affect the hydrostatic balance. The condensa- 

 tion was greater than that produced by simple pressure, yet 

 the quantity of heat extricated was less. These facts, the 

 reverse of what might have been expected, render the expla- 

 nation of the calorific phenomena produced by friction very 

 difficult. They would seem to favour the opinion of count 

 Rumford ; but the materiality of heat is confirmed by so 

 many arguments, that we ought not to relinquish a theory 

 so fertile in useful explanations, before fresh experiments 

 have completely elucidated this important point. 

 Difficulties in In admitting, that the calorific phenomena, produced by 

 the hypothesis f,.j c ti on depend on the extrication of caloric, expelled from 



of maleiial ca- £''••, P • 



loric, the pores of substances by forcing the particles nearer toge- 



ther, how is it that the particles, in resuming their former si- 



tuatiqn, 



