480 Iiiqidry concerning the Source of 



leave the subject as naked and open to inspection as 

 possible. 



In order, by one decisive experiment, to determine 

 whether the air of the atmosphere had any part, or not, 

 in the generation of the Heat, I contrived to repeat the 

 experiment under circumstances in which it was evidently 

 impossible for it to produce any effect whatever. By means 

 of a piston exactly fitted to the mouth of the bore of 

 the cylinder, through the middle of which piston the 

 square iron bar, to the end of which the blunt steel borer 

 was fixed, passed in a square hole made perfectly air- 

 tight, the access of the external air to the inside of the 

 bore of the cylinder was efi^ectually prevented. (In 

 Fig. 3, this piston (^) is seen in its place; it is likewise 

 shown in Fig. 7 and 8.) 



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 ap- 

 peared to me to be so slight as hardly to deserve any at- 

 tention, I was however desirous to remove. The piston 

 which closed the mouth of the bore of the cylinder, 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, notwithstand- 

 ing its being oiled, it occasioned a considerable 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 in contact with the piston, is it not 

 possible that this air may have had some share in the 

 generation of the Heat produced ? 



