VOL. LXXXVIII.] PHILOSOPHICAL TRANSACTIONS. 281 



express purpose of ascertaining that fact, the capacity for heat, of the metal of 

 which great guns are cast, is not sensibly changed by being reduced to the form of 

 metallic chips, in the operation of boring cannon ; and there does not seem to be 

 any reason to think that it can be much changed, if it be changed at all, in being 

 reduced to much smaller pieces, by means of a borer that is less sharp. If the heat, 

 or any considerable part of it, were produced in consequence of a change in the 

 capacity for heat of a part of the metal of the cylinder, as such change could only 

 be superficial, the cylinder would by degrees be exhausted; or the quantities of 

 heat produced, in any given short space of time, would be found to diminish gra- 

 dually, in successive experiments. To find out if this really happened or not, I 

 repeated the last-mentioned experiment several times, with the utmost care; but I 

 did not discover the smallest sign of exhaustion in the metal, notwithstanding the 

 large quantities of heat actually given off. Finding so much reason to conclude, 

 that the heat generated in these experiments, or excited, as I would rather choose 

 to express it, was not furnished at the expence of the latent heat or combined 

 caloric of the metal, I pushed my inquiries a step further, and endeavoured to find 

 out whether the air did, or did not, contribute any thing in the generation of it. 



Exper. 1. — As the bore of the cylinder was cylindrical, and as the iron bar, to 

 the end of which the blunt steel borer was fixed, was square, the air had free 

 access to the inside of the bore, and even to the bottom of it, where the friction 

 took place by which the heat was excited. As neither the metallic chips produced 

 in the ordinary course of the operation of boring brass cannon, nor the finer scaly 

 particles produced in the last-mentioned experiments by the friction of the blunt 

 borer, showed any signs of calcination, I did not see how the air could possibly 

 have been the cause 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 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 circum- 

 stances 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. 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 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 considerable degree of friction, when the hollow cylinder was turned 



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