280 PHILOSOPHICAL TRANSACTIONS. [ANNO 1798. 



the course of experiments made with it, and after it had been separated from the 

 cannon with which, during the experiments, it remained connected. 



Experiment I . — This experiment was made in order to ascertain how much heat 

 was actually generated by friction, when, a blunt steel borer being so forcibly shoved, 

 by means of a strong screw, against the bottom of the bore of the cylinder, that the 

 pressure against it was equal to the weight of about lOOOOlb. avoirdupois, the cy- 

 linder was turned round on its axis, by the force of horses, at the rate of about 32 

 times in a minute. At the beginning of the experiment, the temperature of the 

 air in the shade, as also that of the cylinder, was just 6*0° p. At the end of 30 

 minutes, when the cylinder had made 960 revolutions about its axis, the horses 

 being stopped, a cylindrical mercurial thermometer, whose bulb was -j^_ of an 

 inch in diameter, and 3^- inches in length, was introduced into the hole made to 

 receive it, in the side of the cylinder, when the mercury rose almost instantly 

 to 130°. 



To see how fast the heat escaped out of the cylinder, The heat, as 



1 1 1 • shown by the 



(in order to be able to make a probable conjecture re- At the end of thermometer, 



..,,,.., Min. was 



specing the quantity given off by it, during the time the 4 ' !2go 



heat generated by the friction was accumulating,) the 5 125 



machinery standing still, I suffered the thermometer to j 2 ' * [ ! ] * ..,..'. 120 



remain in its place near -§- of an hour, observing and 1* 119 



noting down, at small intervals of time, the height of the 20 * * " ' ' " ' " n g 



temperature indicated by it, as in the annexed tablet. 24 115 



rrn -cS •••.........1 14) 



AnUS, 31 113 



Having taken away the borer, I now removed the me- 3* 112 



tallic dust, or rather scaly matter which had been de- 41 .] no 



tached from the bottom of the cylinder by the blunt steel 



borer, in this experiment ; and, having carefully weighed it, I found its weight to 

 be 837 grains Troy. Is it possible that the very considerable quantity of heat that 

 was produced in this experiment (a quantity which actually raised the temperature 

 of above I13lb. of gun-metal at least 70 degrees of Fahrenheit's thermometer, 

 and which, of course, would have been capable of melting G^lb. of ice, or of causing 

 near 5 lb. of ice-cold water to boil,) could have been furnished by so inconsiderable 

 a quantity of metallic dust? and this merely in consequence of a change of its 

 capacity for heat ? As the weight of this dust, 837 grains Troy, amounted to no 

 more than -54-g-th part of that of the cylinder, it must have lost no less than 948 

 degrees of heat, to have been able to have raised the temperature of the cylinder 

 1 degree ; and consequently it must have been given off 66360 degrees of heat, 

 to have produced the effects which were actually found to have been produced in 

 the experiment ! 



But, without insisting on the improbability of this supposition, we have only to 

 recollect, that from the results of actual and decisive experiments, made for the 



