the Source of the Heat excited by Friction . 8 g 
of the heat that was produced ; but, in an investigation of this 
kind, I thought that no pains should be spared to clear away 
the rubbish, and leave the subject as naked and open to inspec- 
tion as possible. 
In order, by one decisive experiment, to determine whether 
the air of the atmosphere had any part, or not, in the genera- 
tion of the heat, I contrived to repeat the experiment, under cir- 
cumstances 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 effectually prevented. (In fig. 3. this piston 
(p ) is seen in its place ; it is likewise shown in fig. 7 and 8. ) 
I did not find, however, by this experiment, that the exclu- 
sion 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 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, notwithstanding 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 in contact with the piston, is it not possible that 
MDCCXC VIII . N 
