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X. On the Accumulation of Heat ly Friction. 



To Mr. Tilloch. 



SfPv, — J. HE principal arguments that have been advanced 

 against the existence of a material fluid of heat, are those de- 

 rived from the experiments on the generation of heat bv friction: 

 from those experiments it is inferred, that the quantity of heat 

 «X)ntained in a given piece of metal is inexhaustible. No di- 

 rect experiment, however, has been made in support of this 

 opinion ; but because a piece of metal connected with and sur- 

 rounded by conductors, continued to give out heat as long as 

 friction was applied, the author of the experiments concludes, 

 " that any thing which any insulated body, or system of bodies, 

 can continue to furnish without limitation, cannot possibly be a 

 material mi h stance." 



If heat be a material fluid, the effect of force on a body con- 

 taining it would be similar to the effect of force on a body con- 

 taining any other fluid diffused through its pores in a similar 

 manner. Water being a fluid which in many instances produce? 

 effects similar to those produced by heat, it appears best adapted 

 to illustrate the generation of heat by friction. 



I procured a piece of light and porous wood, three inches in 

 length, two in width, and one in tliickness ; and having im- 

 mersed it in water till it was saturated, I fixed it firmly over a 

 vessel filled with water, the lower end being about half an inch 

 below the surface of the water, and then moved a piece of hard 

 wood backwards and forwards on the upper end, with a consi- 

 derable degree of pressure. I thus found that water could be 

 raised througii the pores of wood by friction. The process is 

 casilv luiderstood : the rubber, or piece of hard wood, as it is 

 jnoved along, presses the water out of the pores, and closes 

 them, driving the water which is pressed out before it ; but 

 when the rubber has passed over those pores, the water from 

 below rusiies into them to restore the e()uilibrium. 



The action of the blunt borer in Count Rumford's experiments 

 appears to have produced a similar kind of effect; the heat 

 having been forced out of the pores of the metal by the borer, 

 its place would be supplied by the heat from the adjacent parts. 

 Gun-metal being a good conductor, the neck which connected 

 the cylinder with the cannon would be capable of giving passage 

 to all the heat that was accumulated from the cannon, and the 

 other conductors with which it was connected. 



Count Rumford considered it improbable that the heat could 

 have been supplied by means of the small neck of metal, be- 

 cause heat was given out by it during the whole of the experi- 

 ment ; 



