286 PHILOSOPHICAL TRANSACTIONS. [ANNO 1798. 



without interruption or intermission, and without any signs of diminution, or 

 exhaustion. Then whence came the heat which was continually given off in this 

 manner, in the foregoing experiments ? Was it furnished by the small particles of 

 metal, detached from the larger solid masses, on their being rubbed together ? 

 This, as we have already seen, could not possibly have been the case. Was it 

 furnished by the air ? This could not have been the case; for in 3 of the experi- 

 ments the machinery being kept immersed in water, the access of the air of the 

 atmosphere was completely prevented. 



Was it furnished by the water which surrounded the machinery ? That this 

 could not have been the case is evident; first, because this water was continually 

 receiving heat from the machinery, and could not, at the same time, be giving 

 to, and receiving heat from, the same body; and 2dly, because there was no 

 chemical decomposition of any part of this water. Had any such decomposition 

 taken place, one of its component elastic fluids, most probably inflammable air, 

 must, at the same time, have been set at liberty, and, in making its escape into 

 the atmosphere, would have been detected; but though I frequently examined the 

 water, to see if any air bubbles rose up through it, and had even made prepara- 

 tions for catching them, in order to examine them, if any should appear, I could 

 perceive none; nor was there any sign of decomposition of any kind whatever, or 

 other chemical process, going on in the water. 



Is it possible that the heat could have been supplied by means of the iron bar to 

 the end of which the blunt steel borer was fixed? or by the small neck of gun-metal 

 by which the hollow cylinder was united to the cannon? These suppositions ap- 

 pear more improbable even than either of those before-mentioned; for heat was 

 continually going off*, or out of the machinery, by both these passages, during the 

 whole time the experiment lasted. And, in reasoning on this subject, we must not 

 forget to consider that most remarkable circumstance, that the source of the heat 

 generated by friction, in these experiments, appeared evidently to be inexhaustible. 

 It is hardly necessary to add, that any thing which any insulated body, or system 

 of bodies, can continue to furnish without limitation, cannot possibly be a material 

 substance: and it appears to me to be extremely difficult, if not quite impossible, 

 to form any distinct idea of any thing, capable of being excited, and communicated, 

 in the manner the heat was excited and communicated in these experiments, except 

 it be motion. 



I am very far from pretending to know how, or by what means, or mechanical 

 contrivance, that particular kind of motion in bodies, which has been supposed to 

 constitute heat, is excited, continued, and propagated, and I shall not presume to 

 trouble the Society with mere conjectures ; particularly on a subject which, during 

 so many thousand years, the most enlightened philosophers have endeavoured, but 

 in vain, to comprehend. But, though the mechanism of heat should, in fact, bf 

 one of those mysteries of nature which are beyond the reach of human intelligence, 

 this ought by no means to discourage us, or even lessen our ardour, in our at- 



