"that Dr. Priestley has formed water without suspecting it." It will presently be seen that Dr. Priestley's first intelligence of any idea being entertained that water is a compound body, came from Mr. Watt; and was received not only with surprise, as being entirely novel, but also with incredulity, as being quite erroneous. The real state of the case is very well explained by him in his paper, read 24th February, 1785, and printed in the Philosophical Transactions' for that year, where he says, "Mr. Watt concluded from some experiments of which I gave an account to the Society, and also from some observations "of his own, that water consists of dephlogisticated and in"flammable air, in which Mr. Cavendish and M. Lavoisier 66 concur with him." *

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There is thus no statement put on record by Mr. Cavendish, so far as we have yet gone, of his conclusions having been either drawn by himself, or made known to a single human being, previous to the summer of 1783; while the only intimation to be derived from the printed papers in the Philo'sophical Transactions,' of his having drawn his conclusions at even so early a period, is contained in the above passage, which was written by Blagden, interpolated after the paper had been read in January, 1784, and not till then adopted by Cavendish.

It is, further, apparent from the very title of his paper, • Experiments on Air,' that the composition of water was not the principal object to which Mr. Cavendish's attention had been directed. In this respect, his paper presents an obvious contrast to that of Mr. Watt, which bears the much more unequivocal title of Thoughts on the Constituent Parts of • Water, and of Dephlogisticated Air;' and of which the great object is to maintain that doctrine of the composition of water which is distinctly stated in its outset.

Moreover, some of the expressions used by Mr. Cavendish in further treating of the subject, are marked by no small ambiguity, and even inconsistency; for his theory is thus expressed in his own paper:-" From what has been said there

*Phil. Trans.' for 1785, p. 280.

"seems the utmost reason to think, that dephlogisticated air "is only water deprived of its phlogiston, and that inflam"mable air, as was before said, is either phlogisticated water, "or else pure phlogiston; but in all probability the former." Now, besides the strange supposition as to inflammable air being phlogisticated water, which shows that Mr. Cavendish had then no very clear ideas on the subject of water being composed of oxygen and hydrogen, it is evident that he 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 the 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.

We have the authority of one of the best informed practical and theoretical chemists of this country for declaring, that "ideas exactly similar to those of Mr. Watt are entertained "by the most distinguished philosophers of the present day.” "Dr. Black," says Professor Graham of University College, "made it appear probable, that metals owe their malleability " and ductility to a quantity of latent heat combined with "them." And the learned Professor carries the same doctrine further; where, in referring to change in the physical condition and crystalline configuration of bodies, without any alteration in their ponderable constituents, he says,"The loss of heat observed will afford all the explanation "necessary, if heat be admitted as a constituent of bodies, equally essential as their ponderable elements." This may serve as another illustration of the masterly grasp of Mr.

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Watt's comprehensive mind, which could so early foresee all that subsequent inquiry has fully confirmed.

M. Lavoisier, in his celebrated Memoir, admits that a partial communication was made by Blagden, to him and some other members of the French Academy, when, on the 24th of June, 1783, along with M. La Place, he tried the experiment which they reported to the Academy on the following day. "He informed us," says Lavoisier, "that Mr. Cavendish "had already attempted to burn inflammable air in close " vessels, and that he had obtained a very sensible quantity of "water." He thus confines the extent of the communication within very narrow limits; for neither the experiment nor the result, as thus reported, was anything more than had been effected by Warltire and Priestley. Evidently he did not intend to admit that he knew of any conclusion, as to the real origin of the water, having been drawn by Cavendish ; for in a subsequent part of the same memoir, he takes to his coadjutor and himself the credit of drawing such conclusion: -"we did not hesitate to conclude from it that water is not a simple substance, and that it is composed, weight for weight, of inflammable air, and of vital air." He adds also, that they were then ignorant, and did not learn for some days, that M. Monge was occupied on the same subject.

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It may be observed in passing, that as compared with Lavoisier and Cavendish, sufficient justice does not appear to have been done by writers on this subject, to the valuable labours of Monge. It is true, that when we consider the whole contents of his paper, which includes some deductions both hesitating and obscure, and even, so far as we can judge, incorrect; and recollect the comparatively late period at which it was first given to the world, in the Memoirs of the Academy, we find it impossible, without showing an undue excess of favour to his memory, to rank him, in respect either of the precision, or of the early date of his conclusions, along with any of the other three great philosophers who have been candidates, in either country, for the credit of the discovery. But his experiments, performed in the laboratory of the school at Mézières, were on a great scale; and are

admitted, by Lavoisier and Meusnier,* to have been conducted with a very exact apparatus, and the most scrupulous attention. They are described in his paper in the Memoirs of the Academy for 1783, published in 1786; it is not stated when that paper was read, but a note mentions that they were made in June and July, and repeated in October, 1783, in ignorance of those of Cavendish in England, which were on a smaller scale, and of those of Lavoisier and La Place at Paris, which were made with an apparatus not fitted to attain so great exactness. Lavoisier and Monge thus declare their mutual ignorance of each other's proceedings: but Monge has never been accused, and may safely be acquitted, while the other has been frequently, and with too much justice, convicted, of concealing previous knowledge of other men's proceedings, in order to increase the estimated amount of his own merits. Of Lavoisier, indeed, it has been said, with equal severity and justice, by an ingenious author and excellent chemist, "He has done sufficient, and been praised suffi"ciently for what he has done, to satisfy a mind the most "avaricious of fame; he is deservedly placed in the first rank among the philosophers of his day; and he ought not to "have thrown a shade over his well-earned reputation, by claiming for himself the honour of those discoveries which "he had learned from another."†

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The want of any date for either the authorship or the reading of M. Monge's paper, between the end of the year 1783, in which his experiments were made, and that part of 1786 in which it was published, leaves us in doubt as to how far he may have profited by the lights which were during that interval thrown upon the subject. Certainly his words, as there given, are very similar to those of Mr. Watt's letter of April, 1783, hereafter to be particularly noticed. "It fol"lows," says Monge, "from this experiment, that when we "detonate inflammable gas and dephlogisticated gas, each "considered as pure, we obtain no other result than pure

* Mémoires de l'Académie' for 1781, pp. 269, 270.
† Appendix to 'Memoirs of Priestley,' 1806, p. 258.

"water, the matter of heat, and that of light." But his conclusions, as further explained in the same paper, are less clear and decided than Mr. Watt's, or than those of Lavoisier and Cavendish; for he hesitates whether to consider water as not a simple substance, or fire as a compound one, and is encumbered with the uncertainty of an alternative theory; -either, of different substances being held in solution by the fluid of fire considered as a common solvent, and combining to produce water; or else, of the two gases being solutions of water in different elastic fluids, which quit the water they held in solution, in order to combine and form the fluid of fire and light, which escapes through the sides of the vessel in which the detonation takes place.

Lavoisier's paper having been in part read in November, 1783, was afterwards published with additions, which are not specifically distinguished from the original memoir, but are said to refer to the labour undertaken in common with M. Meusnier relative to the same subject. The volume in which it appears was published in 1784, and is known in the series of the Mémoires de l'Académie' as that for 1781. It arrived in this country after Mr. Cavendish's paper had been read on 15th January, 1784, but before it was published in that year; and it is alluded to in another addition to Mr. Cavendish's paper, which was unquestionably made after its arrival in England, and in which the theory of the composition of water is more clearly stated than it had been by him previous to the enunciation and exposition of it by the enlightened French chemist.* A point of internal evidence that seems to fix within very narrow bounds the period at which that volume of the French Memoirs was printed, is, that Lavoisier therein speaks of Blagden as "aujourd'hui Secrétaire de la "Société Royale de Londres;" an office to which he was not appointed till the 5th of May, 1784.

Now, there can be little doubt, that the passage already cited, in which Blagden, in his own hand, but in Cavendish's name, detailed his communication to Lavoisier, was written

*Phil. Trans.' for 1784, pp. 150-153.