1826.] Mr, Graham on the Heat of Friction, 261 



a state similar to our ordinary conceptions of the electric fluid. 

 As a fluid, powerfully repelling its own particles, and attracting 

 those of other matter, spread equally over the surfaces of all 

 bodies, independently of their composition or temperature, with- 

 out combining with these bodies, diff'used (to borrow an illus- 

 tration from chemistry) like a drop of oil upon the surface of 

 water, without being in combination with it. To the matter of 

 heat in this quiescent state, we shall, for the sake of conve- 

 nience, give the name superficial heat, from its covering the 

 superficies or surfaces of bodies. It is merely heat to which 

 there has not been imparted that original velocity, upon which 

 the characteristic properties of sensible heat depend. Superfi- 

 cial heat, it is evident, must be insensible. But project it with 

 the necessary velocity, and you render it sensible. This might 

 result from extraordinary accumulation of our idio-repulsive 

 body, or its concentration upon a particular spot. Dissipation, 

 by means of radiation, appears to be a natural effect of the 

 repulsion between the particles of superficial heat, aggravated 

 to a great degree. 



Now in friction, circumstances are favourable to the conver- 

 sion of superficial into sensible heat, in this manner. The 

 surfaces of the bodies rubbed together are brought rapidly into 

 exceedingly close contact, so that as surfaces they virtually 

 cease to exist. From the violent approximation, the idio- 

 repulsive power of the superficial heat investing both the 

 surfaces, is powerfully exerted ; so that a portion of the superfi- 

 cial heat is expelled as radiant heat, and impinges upon the 

 rubbing surfaces. But more superficial heat is suppUed from 

 the earth ; and as long as the friction is continued, superficial 

 heat is converted into sensible, and the bodies become hotter 

 and hotter. Hence the heat attending friction ; and the reason 

 why more heat is elicited, when the surfaces are smooth than 

 when they are rough, their approach in the former case being 

 more close, and the investing superficial heat more condensed. 



In a course of experiments upon the heat produced in friction, 

 M. Haldat attempted to insulate his apparatus for that purpose, 

 by means of non-conductors of electricity. Upon reference, 

 however, to his paper,* it will be found, that notwithstanding 

 the body of the apparatus was electrically insulated with great 

 care, yet the insulation of the machine and contrivance by which 

 motion was conveyed to the rubbing surfaces, was overlooked. 

 The result of this imperfect insulation was a diminution of one- 

 third in the amount of heat evolved. New experiments upon 

 this subject are very desirable. 



The theory which we have appHed to friction admits of very 

 great extension. We may suggest that the pheenomena of elec^ 



• Nicholson's Journal, vol. xxvi. p. 30. 



