^4© 'lExptt'iments on Heat excited hy Friclian. 



.from flie axis of the Cylinder to near its furface, the heat indicated by it could not be very 

 different from that of the mean temperature of the cylinder ; and it was on tliis account 

 -that a thermometer of that particular form was chofen for this experiment. 



To fee how fad the heat efcaped out of tlie cylinder, (in order to be able to make a 

 probable conjefture refpeding the quantity given off by it during the time the heat genc- 

 •rated by the friftion was accumulating,) the machinery (landing ftill, I fuffcred the ther- 

 mometer to remain in its place near three quarters of an hour, obferving and noting dowuj 

 Mt fmall intervals of time, the height of the temperature indicated by it. Thus, 

 At the end of 4 minutes, the heat, as (hown by the thermometer, was laC" 

 After 5 minutes, always reckoning from the firft obfervation, J 25 

 At the end of 7 minutes, — — — 123 



12 — — — — 120 



14 — -- — — "9 ' 



,6 — — — — "8 



20 — — — — ' J 16 



,4 — _ — — 115 



28 — — — — "4 



31 - - - - i'3 



34 - - - - "2 



37. _ - _ _ III 



And when 41 minutes had elapfed — — no 



Having taken away the borer, I now removed the metallic duft, or rather fcaly matter, 

 which had been detached from the bottom of the cylinder by the blunt fteel borer, in thi« 

 experiment, and, having carefully weighed it, I found its weight to be 837 grains Troy. 



Is it poflible that the very confiderable quantity of heat that was produced in this expe- 

 riment (a quantity which aftually raifed the temperature of above 113 lb. of gun-metal at 

 lead 70 degrees of Fahrenheit's thermometer, and which, of courfe, would have been ca- 

 pable of melting 6^ lb. of ice, or of caufmg near 5 lb. of ice-cold water to boil,) could 

 have been furniflied by fo inconfiderable a quantity of metallic duft ? and this merely in 

 confequence of a change of its capacity for heat ? 



As the weight of this duft (837 grains Troy) amounted to no more than ^^th part of 

 that of the cylinder, it muft have given off 948 degrees to raife the temperature of the 

 cylinder i degree i and confequently it muft have given off 66360 degrees of heat to have 

 produced that of the experiment ! 



But, without infilling on the improbability of this fuppofitlon, we have only to recolle£l, 

 that from the refults of a£lual and decifive experiments, made for the exprefs purpofe of 

 afcertaining that fa£l, the capacity for heat, of the metal of which great guns are caft, is 

 pot fenfibly changed by being reduced to the form of metallic chips, in the operation of 

 boring cannon ; and there does not feem to be any reafon to think that it can be much 

 changed, if it be changed at all, in being reduced to much fmaller pieces by means of a 

 J)Orer that is lefs {harp. 



If 



