97 
the Source of the Heat excited by Friction * 
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 
Experiment No. 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 ren- 
ders it necessary for me to be very particular in my account of 
it. Heat was generated, as in the former experiments, and, to 
all appearance, quite as rapidly ; and I have no doubt but the. 
water in the box would have been brought to boil, had the ex- 
periment been continued as long as the last. The only circum- 
stance that surprised 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 sur- 
faces rubbed together were wet with water, as when they were 
in contact with air. 
By meoitating 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, 
MBCCXCVIII* 
o 
