212 THE POPULAR SCIENCE MONTHLY. 



torn of the cylinder, and kept from turning by an iron bar, m; and 

 thus disposed for the experiment the apparatus is represented in 

 Fig. 2. 



In Rumford's first determination the borer was forced against the 

 bottom with a pressure of about 10,000 pounds, and the cylinder was 

 rotated at the rate of thirty-two turns in a minute, by the labor of 

 two horses. To prevent also as far as possible any loss of heat 

 by radiation, the exposed parts were protected by thick coverings of 

 flannel. 



At the beginning of the experiment the temperature throughout, 

 as well as that of the surrounding air, was 60 Fahr. ; at the end of 

 thirty minutes, when 960 revolutions of the cylinder had been made, 

 the temperature, as indicated by a thermometer introduced into the 

 small hole, had risen to 130. 



Collecting the metallic dust or, as lie described it, scaly matter 

 which had been detached, he found upon a careful weighing that it 

 amounted to but 837 grains, or 54.2 grammes. Its inadequacy to 

 account for the large excitation of heat fully impressed him, and he 

 exclaims : 



" Is it possible that the very considerable quantity of heat that was produced 

 in this experiment (a quantity which actually raised the temperature of above 

 113 pounds of gun-metal at least TO of Fahrenheit's thermometer, and which, of 

 course, would have been capable of melting six pounds and a half of ice, or of 

 causing nearly five pounds of ice-cold water to boil) could have been furnished by 

 so inconsiderable a quantity of metallic dust, and this merely in consequence of 

 a change of its capacity for heat ? 



"As the weight of this dust (837 grains, Troy) amounted to no more than 

 -g^g- part of that of the cylinder, it must have lost no less than 948 of heat, to 

 have been able to raise the temperature of the cylinder 1 ; and consequently it 

 must have given off 60,360 of heat to have produced the effects which were 

 actually found to have been produced in the experiment ! 



" But without insisting on the improbability of this supposition, we have 

 only to recollect that from the results of actual and decisive experiments, made 

 for the 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 would only be superficial, the cylinder would by degrees be ex- 

 hausted ; or the quantities of heat produced in any given short space of time 

 would be found to diminish gradually 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 ex- 

 haustion in the metal, notwitbstanding the large quantities of heat actually 

 given off. 



" Finding so much reason to conclude that the heat generated in these ex- 



