Il6 Experiments on the Heat excited by Fil^uin. 



agreeable when the furfaces rubbed together were wet with water, as when they were In 

 conta6l with air. 



By meditating on the refults of all thefe experiments, we are naturally brought to that 

 great queftion which has fo often been the fubjedt of fpeculation among philofophers, 

 namely, "What is heat? — Is there any fuch thing as an igneous Jluid ? — Is there any thing 

 that can with propriety be called caloric ? 



We have feen that a very confiderable quantity of heat may be excited in the fri£lion of 

 two metallic furfaces, and given off in a conftant ftream or flux in all direHions, without 

 interruption or intermiffion, and without any figns of diminution or exhaultion. 



From whence came the heat which was continually given off in this manner in the fore- 

 going experiments ? Was it furniflied by the fmall particles of metal detached from the 

 larger folld mafies on their being rubbed together I This, as we have already feen, could 

 not polTibly have bean the cafe. 



Was it furr.ifhed by the air ? This could not have been the cafe ; for in three of thefe 

 experiments, the machinery being kept immerfed in water, the accefs of the air of the at- 

 mofphere was completely prevented. 



Was it furniflied by the water which furrounded the machinery ? That this could not 

 have been the cafe is evident ; jf^, becaufe this water was continually receiving heat from 

 the machinery, and could not at tlie fame time be giving to and receiving heat from the 

 fame body ; vciA,fecondly, becaufe there was no chemical decompofition of any part of this 

 water. Had any fuch decompofition taken place (which indeed could not reafonably have 

 been expefled), one of its compound elaftic fluids (mod probably inflammable air) mud 

 at the fame time have been fet at liberty, and, in making its efcape into the atmofphere, 

 would have been detefted ; but though I frequently examined the water to fee if any air 

 bubbles rofe up through it, and had even made preparations for catching them in order to 

 examine them if any fhould appear, I could perceive none; nor was there any fign of de- 

 compofition of any kind whatever, or other chemical procefs going on in the water. 



Is it poffible the heat could have been fupplied by means of the iron bar to the end of 

 which the blunt fteel borer was fixed ? or by the fmall neck of gun-metal by which the^ 

 hollow cylinder was united to the cannon ? Thefe fuppofitions appear more improbable 

 even than either of thofe before mentioned ; for heat -was continually going off or out of 

 the machinery, by both thefe laft paflTages, during the whole time the experiment lafted. 



And, in reafoning on this fubjedt, we muft not forget to confider that mod remarkable 

 circumftance, that the fource of the heat generated by fridion in thefe experiments ap- 

 peared evidently to be inexhauftible. 



It is hardly neceflary to add, that any thing which any infulated body or fyllem of bo- 

 dies can continue to furnilh without limitation, cannot pofFibly be a material fubftance ; and 

 it appears to me to be extremely difficult, if not quite impoflible, to form any diftimSt idea 

 of any thing capable of being excited and communicated in the manner the heat was ex- 

 cited and communicated in thefe experiments, except it be motion. 



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

 ance, that particular kind of motion in bodies which has been fuppofed to conftitute heat 



1 » 



