MODERN THEORIES OF HEAT AND LIGHT 



inside of the bore of the cylinder, was effectually pre- 

 vented. I did not find, however, by this experiment 

 that the exclusion of the air diminished in the smallest 

 degree the quantity of heat excited by the friction. 



"There still remained one doubt, which, though it 

 appeared to me to be so slight as hardly to deserve any 

 attention, I was, however, desirous to remove. The 

 piston which choked the mouth of the bore of the cylin- 

 der, in order that it might be air-tight, was fitted into 

 it with so much nicety, by means of its collars of leather, 

 and pressed against it with so much force, that, not- 

 withstanding its being oiled, it occasioned a consider- 

 able degree of friction when the hollow cylinder was 

 turned round its axis. Was not the heat produced, or 

 at least some part of it, occasioned by this friction of 

 the piston ? and, as the external air had free access to 

 the extremity of the bore, where it came into contact 

 with the piston, is it not possible that this air may have 

 had some share in the generation of the heat produced ? 



" A quadrangular oblong deal box, water-tight, being 

 provided with holes or slits in the middle of each of its 

 ends, just large enough to receive, the one the square 

 iron rod to the end of which the blunt steel borer was 

 fastened, the other the small cylindrical neck which 

 joined the hollow cylinder to the cannon; when this 

 box (which was occasionally closed above by a wooden 

 cover or lid moving on hinges) was put into its place- 

 that is to say, when, by means of the two vertical open- 

 ings or slits in its two ends, the box was fixed to the 

 machinery in such a manner that its bottom being in 

 the plane of the horizon, its axis coincided with the 

 axis of the hollow metallic cylinder, it is evident, 



211 



