260 Mt\ Graham on the Heat of Friction. [Oct. 



Article III. 



-a.; 



On the Heat of Friction. By T. Graham, MA. <' 



(To the Editors of the Annals of Philosophy.) 



GENTLEMEN, Edinburgh, Sept. 7, 1826. 



It is generally allowed, that the heat extricated in friction is 

 inexplicable upon the theory of the materiality of heat, as at 

 present entertained. It would be easy to show that this heat 

 does not arrive at the bodies rubbed together, by the ordinary 

 ttnd admissible methods of conduction or radiation, or, that no 

 reduction of bulk takes place, or diminution of capacity for heat. 

 Yet the materiality of heat is involved in the principal doctrines 

 of chemistry, while the simplicity and easy application of the 

 theory render its establishment exceedingly desirable. In these 

 circumstances, an attempt to reconcile the substantial existence 

 of heat with its appearance in friction, may not be unworthy of 

 attention, even although the suppositions on which it is founded 

 should be altogether novel; elucidating, as they do, other 

 departments of science. "''' 



Heat is observed by us, either radiant in motion, and possessetl 

 of great velocity ; or in union with matter, and capable of regain- 

 ing^this velocity. 



Probably this velocity is necessary to its entering into bodies 

 and uniting with them ; at least we never observe heat do so 

 without it. For, when communicated by radiation, this is 

 evident ; and in conduction, which in close contact supplies the 

 place of radiation, it is evident that heat is communicated with 

 a force. Indeed conduction may be reduced with considerable 

 plausibility to an internal radiation. 



It appears that this motive power, which is essential to the 

 communication of heat and our perception of it, is really never 

 annihilated. It disappears when heat passes into a body, but it 

 is merely overpowered for a time, and not altogether lost ; for 

 upon reduction of temperature, the heat emanates from the 

 body, evincing its pristine velocity. We may compare the state of 

 the heat in union with matter to that of a bent spring, or a com- 

 pressed elastic substance, the attraction of the matter for heat 

 being the restraining force. Sensible heat, therefore, we never 

 find destitute of this motive power, nor to lose it — at least heat 

 is never so divested of it as to be incapable of resuming it. 



These observations prepare us for the conception of heat in a 

 different state from that in which it is generally supposed to 

 exist. Let us suppose that the calorific principle is capable, 

 likewise, of existing destitute of this motive power; and yet not 

 in combination with matter, which this motive power seems 

 necessary to effect. We may suppose it capable of existing in 



