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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.

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.”+

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 “ 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.

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

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 to supply the imperfect admission of the French author, and to prevent those inferences as to priority of the theory, which otherwise might have been drawn in favour of Lavoisier. Considering the object thus manifestly in view, here, if anywhere, we ought to look for an explicit statement of the earliest date at which Mr. Cavendish's theory could be said to have been formed, which, at that time, there was no difficulty in ascertaining, and there could have been little in establishing; and we are fairly entitled to hold, that the earliest date consistent with the fact would be assigned, if not by the author of the paper, at least by his zealous and assiduous friend who is so much mixed up with the transaction. All this we say on the supposition, that the question as to priority had arisen merely between Lavoisier and Cavendish: for that is the whole length that our statement has as yet gone. We shall presently see whether other circumstances had not in the meantime arisen, which called still more loudly for that full, clear, and precise declaration which was to have been expected; and which was absolutely indispensable, in order to authenticate for the theory which Mr. Cavendish stated to the Royal Society on the 15th January, 1784, an earlier date than its publication on that day could ensure.

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





MR. Watt, in whose neighbourhood Dr. Priestley says he had “the happiness to be situated,” and with whom, as has been mentioned, he was on terms of friendship and frequent intercourse, had, previous to 1783, for many years entertained an opinion that air was a modification of water; and that, if steam could be made red-hot, so that all its latent heat should be converted into sensible heat, either the steam would be converted into permanent air, or some other change would take place in its constitution. “You may remember," he writes to Mr. Boulton,* " that I have often said, that if “ water could be heated red-hot or something more, it would

probably be converted into some kind of air, because steam “ would in that case have lost all its latent heat, and that it “ would have been turned solely into sensible heat, and pro

bably a total change of the nature of the fluid would en“ sue." And, so early as 13th December, 1782, he talks of processes " by which," he says, “I now believe air is gene“rated from water;" using the expression, “if this process “ contains no deception, here is an effectual account of many phenomena, and one element dismissed from the list.|

Being thus, even at that time, prepared to expect that water was, in some way or other, convertible into air, he di

• 10th December, 1782.
† Mr. Watt to Mr. De Luc, 13th December, 1782.

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