Page:Popular Science Monthly Volume 12.djvu/224

212 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 he 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 70° 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 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 exhausted; 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 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