[806] On the obligations of Watt to Black, compare Brougham's Life of Watt (Brougham's Works, vol. i. pp. 25, 36–38, edit. Glasgow, 1855), with Muirhead's Life of Watt, second edit. London, 1859, pp. 66, 83. At p. 301, Mr. Muirhead says of Watt, that ‘his principal inventions connected with the steam-engine, with all their prodigious results, were founded, as we have seen, on the attentive observation of great philosophical truths; and the economy of fuel, increase of productive power, and saving of animal labour, which gradually ensued, all originated in the sagacious and careful thought with which he investigated the nature and properties of heat.’ But whatever investigations Watt made into heat, he discovered no new law respecting it, or, at all events, no new law which is large enough to be noted in the history of thermotics, considered purely as a science, and apart from practical application. Mr. Muirhead, in his interesting work which I have just quoted, has published (pp. 484–486) some remarks made on the subject by Watt, several years after the death of Black, which, though perfectly fair and candid, show that Watt had a rather confused notion of the real difference between an invention and a discovery.
[807] Mr. Muirhead, in his Life of Watt, pp. 301–370, seems to have put the priority of Watt beyond further doubt; though he is somewhat hard upon Cavendish, who, there can be little question, made the discovery for himself.
[808] I would not wish to diminish one jot of the veneration in which the great name of Watt is justly held. But when I find the opinion of Dr. Withering, the botanist, quoted, to the effect that his ‘abilities and acquirements placed him next, if not superior, to Newton.’ (Muirhead's Life of Watt, p. 302), I cannot but protest against such indiscriminate eulogy, which would rank Watt in the same class as one of those godlike intellects of which the whole world has not produced a score, and which are entitled to be termed inspired, if ever human being was so. Another instance of this injudicious panegyric will be found in the same otherwise excellent work (Muirhead, pp. 324, 325), where we read that Watt's discovery that water consists of oxygen and hydrogen, was ‘the commencement of a new era, the dawn of a new day in physical inquiry, the real foundation of the new system of chemistry; nay, even a discovery “perhaps of greater importance than any single fact which human ingenuity has ascertained either before or since.”’
[809] That there was no plagiarism on the part of Watt, we know from positive evidence; that there was none on the part of Cavendish, may be fairly presumed, both from the character of the man, and also from the fact that in the then state of chemical knowledge the discovery was imminent, and could not have been long delayed. It was antecedently probable that the composition of water would be ascertained by different persons at the same time, as we have seen in many other discoveries which have been simultaneously made, when the human mind, in that particular department of inquiry, had reached a certain point. We are too apt to suspect philosophers of stealing from each other, what their own abilities are sufficient to work out for themselves. It is, however, certain that Watt thought himself ill-treated by Cavendish. See Watt's Correspondence on the Composition of Water, London, 1846, pp. 48, 61.
[810] On 26th November 1783, he writes: ‘For many years I have entertained an opinion that air was a modification of water; which was originally founded on the facts, that in most cases where air was actually made, which should be distinguished from those wherein it is only extricated from substances containing it in their pores, or otherwise united to them in the state of air, the substances were such as were known to contain water as one of their constituent parts, yet no water was obtained in the processes, except what was known to be only loosely connected with them, such as the water of the crystallization of salts. This opinion arose from a discovery that the latent heat contained in steam diminished, in proportion as the sensible heat of the water from which it was produced, increased; or, in other words, that the latent heat of steam was less when it was produced under a greater pressure, or in a more dense state, and greater when it was produced under a less pressure, or in a less dense state; which led me to conclude, that when a very great degree of heat was necessary for the production of the steam, the latent heat would be wholly changed into sensible heat; and that, in such cases, the steam itself might suffer some remarkable change. I now abandon this opinion, in so far as relates to the change of water into air, as I think that may be accounted for on better principles.’ See this remarkable passage, which is quite decisive as to the real history of Watt's discovery, in Correspondence of James Watt on the Composition of Water, London, 1846, pp. 84, 85. Compare p. cxxiv. and p. 248 note.
[811] In the paper which he communicated to the Royal Society, announcing his discovery, he, well knowing the empirical character of the English mind, apologizes for this; and says, ‘I feel much reluctance to lay my thoughts on these subjects before the public in their present indigested state, and without having been able to bring them to the test of such experiments as would confirm or refute them.’ Watt's Correspondence on the Discovery of the Composition of Water, pp. 77, 78. Eleven months earlier, that is in December 1782, he writes (Ibid. p. 4): ‘Dr. Priestley has made a most surprising discovery, which seems to confirm my theory of water's undergoing some very remarkable change at the point where all its latent heat would be changed into sensible heat.’
[812] ‘He’ (i.e. Cavendish) ‘here omits entirely the consideration of latent heat; an omission which he even attempts to justify, in one of the passages interpolated by Blagden. But it is well known to every one acquainted with the first principles of chemical science, even as it was taught in the days of Black, and it was indisputably familiar to Mr. Watt, that no aëriform fluid can be converted into a liquid, nor any liquid into a solid, without tho evolution of heat, previously latent. This essential part of the process, Mr. Cavendish's theory does not embrace; but without it, no theory on the subject can be complete; and it will presently be seen, that Mr. Watt took it fully into account.’ Muirhead's Life of Watt, p. 315.
[813] ‘Cavendish and Watt both discovered the composition of water. Cavendish established the facts; Watt the idea.’ … ‘The attaching too high a value to the mere facts, is often a sign of a want of ideas.’ Liebig's Letters on Chemistry, London, 1851, p. 48. The last sentence of this illustrious philosopher, which I have put in italics, should be well pondered in England. If I had my way, it should be engraved in letters of gold over the portals of the Royal Society and of the Royal Institution.
[814] ‘Organic substances, whether directly derived from the vegetable or animal kingdom, or produced by the subsequent modification of bodies which thus originate, are remarkable as a class for a degree of complexity of constitution far exceeding that observed in any of the compounds yet described.’ Fownes' Chemistry, 3rd edit., London, 1850, p. 353. I quote this, as the first authority at hand, for a doctrine which is universally admitted by chemists, and which is indubitably true, so far as our experiments have at present extended.
[815] ‘As the organic world is characterized by the predominance, in quantity, of carbon, so the mineral or inorganic world is marked by a similar predominance of silicon.’ Turner's Chemistry, edited by Liebig and Gregory, vol. ii. p. 678, London, 1847.