The amount of heat given out in a continual stream by his borer he estimated at that of nine wax candles each of three-quarters of an inch in diameter. This was produced by the work of two horses. ‘But,’ he adds, ‘no circumstances can be imagined in which this method of procuring heat would not be disadvantageous; for more heat may be obtained by using the fodder necessary for the support of a horse as fuel.’ He concludes thus: ‘Anything 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 anything capable of being excited and communicated in these experiments except it be MOTION. ‘I am far from pretending to know how that particular kind of motion which has been supposed to constitute heat is excited, continued, and propagated. Nobody surely in his sober senses has ever pretended to understand the mechanism of gravitation, and yet what sublime discovery was our immortal Newton enabled to make merely by the investigation of the laws of its action!’ The account of these experiments was read to the Royal Society, January 25, 1798. Some interesting facts regarding this paper are to be found in the correspondence of Sir C. Blagden with Sir J. Banks. DEAR SIR JOSEPH,--Count Rumford’s paper on Friction, together with your letter, were safely delivered to me by Lord Palmerston. The paper is by no means incorrect in itself, nor has the copyist made any remarkable blunders, and it is valuable from the large scale on which the experiments were tried, and the quantity of heat produced in consequence. As the result of the experiments was such as the Count himself foresaw, and as every other philosopher would have expected, they do not furnish any _new_ argument in favour of the opinion he has adopted that heat is motion, though perhaps they add force to the old ones. There is, however, an experiment of some consequence if it can be depended upon; namely, _that_ which seemed to show that the shavings cut by the borer out of the cannon had the same capacity for heat as the metal on which the borer had not acted; but I do not feel much confidence in experiments of this nature. You will recollect that one opinion pretty much adopted on this subject is that the heat produced in boring a cannon depends on the compression of the metal of the cannon by the borer, in consequence of which it gives out heat; on the principle that the same body has a less capacity for heat when it is in a denser than when it is in a rarer state. I wish the Count had ascertained whether the metal shavings he tried had really a greater specific gravity than that of the chips of metal he had sawed off.