HEAT 557 mass of water at the boiling temperature, under standard atmospheric pressure ( 5), is 536J- thermal units centigrade. This number, which is no doubt very accurate, differs but little from Watt s final result, 960 thermal ^ units Fahr. (equal to 533 3 thermal units centigrade), obtained by him, in a repetition in 1781 of experiments which he had com menced in 1765 at the invitation of Black, whose pupil he was. 8. Preliminary regarding the Nature of Heat. Dyna mical Calorimetry. From the dawn of science till the close of last century two rival hypotheses had been entertained regarding the nature of heat, each with more or less of plausibility, but neither on any sure experimental basis : one that heat consisted of a subtle elastic fluid permeating through the pores or interstices among the particles of matter, like water in a sponge ; the other that it was an intestine commotion among the particles or molecules of matter. In the year 1791) Davy, in his first published work entitled An Essay on Heat, Light, and Combinations of Light j 1 conclusively overthrew the former of these hypotheses, and gave good reason for accepting as true the latter, by his celebrated experiment of converting ice into water by rubbing two pieces of ice together, without com municating any heat from surrounding matter. A few years earlier Rumford had been led to the same conclusion, and had given very convincing evidence of it in his observ ation of the great amount of heat produced in the process of boring cannon in the military arsenal at Munich, and the experimental investigation on the excitation of heat by friction 2 with which he followed up that observation. He had not, however, given a perfect logical demonstration of his conclusion, nor even quite a complete experimental basis on which it could be established with absolute certainty. According to the materialistic doctrine it would have been held that the heat excited by the friction was not gene rated? but was produced, squeezed out, or let flow out like honey from a broken honeycomb, from those parts of the solid which were cut or broken into small fragments, or rubbed to powder in the frictional process. If this were true, the very small fragments or powder would contain much less heat in them than an equal mass of continuous solid of the same substance as theirs. But unhappily the caloristic doctrine, besides its fundamental hypothesis, which we now know to be wrong, had given an absurd and illogical test for quantity of heat in a body, of which a not altogether innocuous influence still survives in our modern name " specific heat "; and Rum ford actually, in trying to disprove the materialistic doctrine, was baffled by this sophism. That is to say, he measured the specific heat or " capacity for heat " of the powder, and he found that the powder took as much heat to warm it to a certain degree as did an equal mass of the continuous solid, and from this he con cluded that the powder did not contain less heat than the continuous solid at the same temperature. This conclusion is so obviously unwarranted by the premises that it is diffi cult to imagine how Rumford could have for a moment put forward the " capacity for heat " experiment as proving it, or could have rested in the conclusion without a real proof, or at least the suggestion of a real proof. All that Rumford s argument proved was that the fundamental hypothesis of the " calorists " and their other altogether gratuitous doctrine of equality of "specific heat" as a test for equality of whole quantities of heat in matter could not be both true ; and any one not inclined to give up the 1 Published in 1799 in Contributions to Physical and Medical Knowledge, principally from the West of England, collected by Thomas Beddoes, M.D., and republished in Dr Davy s edition of his brother s collected works, vol. iL, London, 1836. "An Enquiry concerning the Source of Heat which is excited by Friction" (Phil. Trans., abridged, vol. xviii. p. 256). 3 Compare quotation from Cavendish, footnote, 2 above. materialistic hypothesis might have cheerfully abandoned the minor doctrine, and remained unmoved by Rumford s argument. If Rumford had but melted a quantity of the powder (or dissolved it in an acid), and compared the heat which it took with that taken by an equal weight of the continuous solid, he would have had no difficulty in proving that the enormous quantity of heat which he had found to be excited by the friction had not been squeezed, or rubbed, or pounded, out of the solid matter, but was really brought into existence, and therefore could not be a material sub stance. He might even, without experiment, have pointed out that, if the materialistic doctrine were true, it would follow that sufficiently long-continued pounding of any solid substance by pestle and mortar, whether by hand or by aid of machinery, would convert it into a marvellous powder possessing one or other of two properties about equally marvellous. Either the smallest quantity of it thrown into an acid would constitute a freezing mixture of unlimited intensity, the longer it had been pounded, the more intense would be its frigorific effect on being dissolved, or the powder would be incapable of being warmed by friction, because it had already parted with all the heat which friction could rub out of it. The real effect of Rumford s argument seems to have been to salve the intellectual consciences of those who were not inclined to give up the materialistic doctrine, and to save them from the trouble of reading through Rumford s paper and thinking for themselves, by which they would have seen that his philosophy was better than his logic, and would inevitably have been forced to agree with him in his conclusion. It is remarkable that Davy s logic, too, .was at fault, and on just the same point as Rumford s, but with even more trans parently logical fallaciousness, because his argument is put in a more definitely logical form. " Let heat be considered as matter, and let it be granted that the temperature of bodies cannot be increased unless their capacities are diminished from some cause, or heat added to them from some bodies in contact" ! !
" Experiment II. I procured two parallelepipedons of ice, 4 of the temperature of 29, 6 inches long, 2 wide, and of an inch thick ; they were fastened by wires to two bars of iron. By a peculiar mechanism their surfaces were placed in contact and kept in a continued and violent friction for some minutes. They were almost entirely converted into water, which water was collected and its temperature ascertained to be 35 after remaining in an atmo sphere of a lower temperature for some minutes. The fusion took place only at the plane of contact of the two pieces of ice, and no bodies were in friction but ice. From this experiment it is evident that ice by friction is converted into water, and, according to the supposition, its capacity is diminished ; but it is a well-known fact that the capacity of water for heat is much, greater than that of ice, and ice must have an absolute quantity of heat added to it before it can be converted into water. Friction consequently does not diminish the capacities of bodies for heat." Davy s Essay on Heat, Light, and Combinations of Light, pp. 10-12. [Delete from "and, according to the supposition," to " greater than that of ice " inclusive ; and delete the lame and impotent conclusion stated in the last eleven words. The residue constitutes an unanswerable demonstration of Davy s negative proposition that heat is not matter.] 9. Joule s Dynamical Equivalent of Heat. It is remark- able that, while Davy s experiment alone sufficed to over throw the hypothesis that heat is matter, and Rumford s, with the addition of just a little consideration of its relations to possibilities or probabilities of inevitable alternatives, did the same, fifty years passed before the scientific world be came converted to their conclusion, a remarkable instance of the tremendous efficiency of bad logic in confounding public opinion and obstructing true philosophic thought. 1 " The result of the experiment is the same if wax, tallow, resin, or any substance fusible at a low temperature be used ; even iron may
be fused by collision, as is evident by the first experiment."
