Page:Popular Science Monthly Volume 12.djvu/222

210, the additional phenomena of latent or specific heats were not at all irreconcilable or difficult of explanation.

Thus Lavoisier and Laplace, in their famous "Mémoire sur la Chaleur" of 1780, though still retaining and defending the ideas of caloric, admitted the frictional excitation of heat to be "favorable" to the dynamical hypothesis. But it is, on the other hand, to be remembered that the earlier experiments devoted to the study of this point had been by no means unmistakable in their indications, directed as they had been rather to the detection of some suspected influence of the rubbing surfaces than to the investigation of any possible relation between the heat produced and the energy expended in producing it.

The material hypothesis was, therefore, the prevailing one, when about the year 1797 Count Rumford, while engaged in superintending the construction of cannon at the military arsenal at Munich, became impressed by the considerable generation of heat accompanying their boring. And as he thought upon the explanation of the phenomenon consistent with the then prevailing ideas as to the intimate nature of heat, it seemed to him impossible that an apparently unlimited supply of any substance could be separated from so inconsiderable a quantity of borings. The doubt increased when, upon making the determination, he found the specific heat of this débris to be the same, apparently, as that of the mass of metal from which it had been separated: for in some obscure manner the "capacity" for heat of any body, or the total quantity of it which it might hold in any particular state, was considered to be intimately connected with, if not entirely defined by, its specific heat.

But, though he quoted this experiment as sufficiently conclusive that the heat set free by friction could not have been produced at the expense of any caloric latent in the metal, he undertook the following more elaborate investigation to determine all the circumstances which might possibly exert an influence on its production: and it appears, both from his method of procedure and the arguments with which he supplemented his results, that he had fully comprehended the philosophical consequences of each rival theory.

In view of the preëminent importance of these first conclusive and well-understood experiments, both with respect to the establishment of the dynamic theory upon an experimental basis, and the undoubted claim of their author to be considered as its founder, we here give as detailed an account of his investigations as may be thought admissible in a work intended merely for didactic purposes; and we conceive a full statement upon this most important point to be the more desirable, from the fact that the completeness with which he then demolished the material hypothesis, and the maturity of his views respecting the dynamical nature of heat, do not of late seem to