See in this Supplement, Chemistry, Part I. chap. v. where we have endeavoured to establish the modern doctrine respecting Caloric or latent heat. In n° 309, &c. of that article, we have given an account of Count Rumford's ingenious experiments, instituted with a view to determine whether or not caloric be a substance, and have stated our reasons for differing from his opinion. It has been suggested to us, however, by a friend, to whose judgment we are inclined to pay great deference, that it would be proper, in this place, to give the Count's arguments at full length, and in his own words; and the propriety of this is the more apparent, that in the supplementary article Electricity, we have hinted our own suspicions of the non-existence of an electrical fluid. The Count then reasons from his experiments in the following words:
"By meditating on the results of all these experiments, we are naturally brought to that great question which has so often been the subject of speculation among philosophers, namely, What is heat?—Is there any such thing as an igneous fluid?—Is there anything that can with propriety be called caloric?
"We have seen that a very considerable quantity of heat may be excited in the friction of two metallic surfaces, and given off in a constant stream or flux in all directions, without interruption or intermission, and without any signs of diminution or exhaustion.
"From whence came the heat which was continually given off in this manner in the foregoing experiments? Was it furnished by the small particles of metal detached from the larger solid masses on their being rubbed together? This, as we have already seen, could not possibly have been the case.
"Was it furnished by the air? This could not have been the case; for in three of these experiments, the machinery being kept immersed in water, the access of the air of the atmosphere was completely prevented.
"Was it furnished by the water which surrounded the machinery? That this could not have been the case is evident; first, because this water was continually receiving heat from the machinery, and could not at the same time be giving to and receiving heat from the same body; and, secondly, because there was no chemical decomposition of any part of this water. Had any such decomposition taken place (which indeed could not reasonably have been expected), one of its compound elastic fluids (most probably inflammable air) must at the same time have been set at liberty, and, in making its escape into the atmosphere, would have been detected; but though I frequently examined the water to see if any air bubbles rose up through it, and had even made preparations for catching them in order to examine them if they should appear, I could perceive none; nor was there any sign of decomposition of any kind whatever, or other chemical process going on in the water.
"Is it possible the heat could have been supplied by means of the iron bar to the end of which the blunt steel borer was fixed? or by the small neck of gunmetal by which the hollow cylinder was united to the cannon? These suppositions appear more improbable even than either of those before mentioned; for heat was continually..." continually going off or out of the machinery, by both these last passages, during the whole time the experiment lasted.
"And, in reasoning on this subject, we must not forget to consider that most remarkable circumstance, that the source of the heat generated by friction in these experiments appeared evidently to be inexhaustible.
"It is hardly necessary to add, that any thing which any insulated body or system of bodies can continue to furnish without limitation, cannot possibly be a material substance; and it appears to me to be extremely difficult, if not quite impossible, to form any distinct idea of any thing capable of being excited and communicated in the manner the heat was excited and communicated in these experiments, except it be motion.
"But although the mechanism of heat should in fact be one of those mysteries of nature which are beyond the reach of human intelligence, this ought by no means to discourage us, or even lessen our ardour, in our attempts to investigate the laws of its operations. How far can we advance in any of the paths which science has opened to us, before we find ourselves enveloped in those thick mists which on every side bound the horizon of the human intellect? But how ample and interesting is the field that is given us to explore!
"Nobody, surely, in his sober senses has ever pretended to understand the mechanism of gravitation; and yet what sublime discoveries was our immortal Newton enabled to make, merely by the investigation of the laws of its action! The effects produced in the world by the agency of heat are probably just as extensive and quite as important, as those which are owing to the tendency of the particles of matter towards each other; and there is no doubt but its operations are in all cases determined by laws equally immutable."