VOL. LXXXVIII.] PHILOSOPHICAL TRANSACTIONS. 285 



weighed, was found to weigh 4145 grs., or about 8-§- oz. Troy. As this quantity 

 was produced in 24- hours, this gives 824 grs. for the quantity produced in half an 

 hour. In the first experiment, which lasted only half an hour, the quantity pro- 

 duced was 837 grs. In the experiment N° 1, the quantity of heat generated, in 

 half an hour, was found to be equal to that which would be required to heat 5lb. 

 avoirdupois of ice-cold water 180°, or cause it to boil. According to the result of 

 the experiment N° 3, the heat generated in half an hour, would have caused 5.31 lb. 

 of ice-cold water to boil. But in this last-mentioned experiment the heat gene- 

 rated being more effectually confined, less of it was lost ; which accounts for the 

 difference of the results of the two experiments. 



It remains for me to give an account of one experiment more, which was made 

 with this apparatus. I found by the experiment N° 1, how much heat was gene- 

 rated when the air had free access to the metallic surfaces which were rubbed toge- 

 ther. By the experiment N° 2, I found that the quantity of heat generated was 

 not sensibly diminished when the free access of the air was prevented ; and, by the 

 result of N° 3, it appeared that the generation of the heat was not prevented, or 

 retarded, by keeping the apparatus immersed in water. But as, in this last-men- 

 tioned experiment, the water, though it surrounded the hollow metallic cylinder 

 on every side, externally, was not suffered to enter the cavity of its bore, 

 being prevented by the piston, and consequently did not come into contact with 

 the metallic surfaces where the heat was generated; to see what effects would be 

 produced by giving the water free access to these surfaces, I now made the 



Exper. 4. The piston which closed the end of the bore of the cylinder being 

 removed, the blunt borer and the cylinder were once more put together; and the 

 box being fixed in its place, and filled with water, the machinery was again put in 

 motion. There was nothing in the result of this experiment that renders it ne- 

 cessary to be very particular in the account of it. Heat was generated, as in the 

 former experiments, and to all appearance quite as rapidly ; and there is no doubt 

 but the water in the box would have been brought to boil, had the experiment been 

 continued as long as the last. The only circumstance that surprized me was, to find 

 how little difference was occasioned in the noise made by the borer in rubbing 

 against the bottom of the bore of the cylinder, by filling the bore with water. 

 This noise, which was very grating to the ear, and sometimes almost insupportable, 

 was, as nearly as I could judge of it, quite as loud, and as disagreeable, when the 

 surfaces rubbed together were wet with water, as when they were in contact 

 with air. 



By meditating on the results of all these experiments, we are naturally brought 

 to that great question which has so often been the subject of speculation among 

 philosophers ; namely, what is heat ? — Is there any such thing as an igneous 

 fluid ? — Is there any thing that can with propriety be called caloric ? We have 

 seen that a very considerable quantity of heat may be excited in the friction of two 

 metallic surfaces, and given off in a constant stream or flux, in all directions, 



