evident mistrust of its real import, he never could be prevailed on to produce it, or say where it was to be found. Mr. Brown's executor has lately brought forward, as the writing in question, no new or unpublished MS. document, but a mere quotation from a printed book open to all the world, and very well known to many besides Mr. Robert Brown, viz., De Luc's Idées sur la 'Météorologie,' published in 1786-7. The quotation is as follows:-"Vers la fin de l'année 1782 j'allai à Birmingham, où le "Dr. Priestley s'étoit établi depuis quelques années. Il me com"muniqua alors; que M. Cavendish, d'après une remarque de "M. Warltire; qui avoit toujours trouvé de l'Eau dans les Vases "où il avoit brûlé un mêlange d'Air inflammable et d'Air atmosphérique; s'étoit appliqué à decouvrir la Source de cette Eau, et "qu'il avoit trouvé: qu'un mêlange d'Air inflammable et d'Air "dephlogistiqué, en proportion convenable, étant allumé par l'étin“celle électrique, se convertissoit tout entier en Eau.' Je fus 'frappé au plus haut degré de cette découverte." (Idées,' &c., tom. ii. p. 206-7.)

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It is only at first sight, however, and when taken in an isolated form, apart from the rest of De Luc's narrative, that the passage cited could bear the interpretation suggested by Mr. Brown's executor. How unwise, as well as unfair, it would be so to view it, can at once easily be shown from the rest of the same history. Dr. Priestley's communication of Cavendish's experiment is said by M. De Luc to have been made "towards the end of 1782." In the continuation of his narrative, De Luc then mentions the experiments of Priestley, the formation of Mr. Watt's theory of April, 1783, and Blagden's report of his communication to Lavoisier, at Paris, in June of the same year. But, in the same section of the same volume, he distinctly and positively says, that when in September [1783] he returned to Birmingham, "Nous igno"rions, M. Watt et moi, que M. Cavendish eût eu des idées fort "semblables aux siennes sur la Cause de ce Phénomène."— Idées,' &c., tom. ii. p. 224. Now, we may well ask, how could this possibly have been the case with De Luc in 1783, if Priestley's communication to him in 1782 had extended to the conclusions, as well as to the experiments, of Cavendish? Yet that is really the whole point at issue; for no one has ever denied the performance of Cavendish's experiments in 1781; and the communication of them, with the result of an equivalent weight of water, (though not of any conclusions), to Priestley, is mentioned in Cavendish's own paper of 1784.

De Luc adds, on the next page of his work, that "Au mois

"de Juin," (an evident mistake for Janvier), "1784, M. Caven"dish remit à la Société Royale un Mémoire, dans lequel il “joignit, au récit de ses Expériences de 1781, sa Théorie sur la "formation de l'Eau.”—‘Idées,' &c., tom. ii. p. 225. Here, for the first time, in De Luc's narrative, (with the exception of the allusion, already noticed, to Blagden's statement at Paris, in June, 1783), occurs a clear and distinct notice of Cavendish's theory or conclusions, as distinguished from his experiments. What M. De Luc's opinion of the Memoir was, in which those conclusions were announced, when he perused it in March, 1784, and sent an analysis of it to Mr. Watt, is well known from his letters already published. He thought it probable that Cavendish, in his Memoir of 1784, was "pillaging" from Mr. Watt's prior letters of the 26th of April and the 26th of November, 1783, then unpublished, but the contents of which are admitted to have been well known both to Blagden and to Cavendish himself, for months before the reading of Cavendish's Memoir. Étant ici de ma "lettre," De Luc writes, "j'ai reçu le mémoire de M. Cavendish, "et je l'ai lu !! Attendez-vous à quelque chose qui vous "étonnera dès que je pourrai vous écrire."-M. De Luc to Mr. Watt, 1st of March, 1784. And again, vos propres termes, dans votre lettre d'Avril au Dr. Priestley, donné pour quelque chose "de nouveau, par quelqu'un qui doit connoître cette lettre, connue "de tous les membres actifs de la Société Royale; du Dr. Blag"den surtout, (puisqu'il dit en avoir parlé à MM. Lavoisier et "De La Place), qui a eu pleine connoissance du mémoire de "M. Cavendish avant qu'il fut lû à la Société Royale, et à sa "lecture, et qui m'en a entretenu, comme je vous le disois dans "ma précédente,-moi qu'il sait être votre ami zélé."-M. De Luc to Mr. Watt, 1st and 4th of March, 1784.

**

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We are thus enabled to set against the interpretation attempted to be put on the passage in question, the most conclusive of all testimony; that, namely, of De Luc himself. For, if he had intended to say that in the end of 1782 the conclusions of Cavendish had along with his experiment been communicated by Priestley, he could not possibly have gone on to say, as he has done, a few pages later in the same volume, that in September, 1783, he was ignorant of Cavendish having entertained any such ideas. Nor would he have felt the astonishment, and entertained the suspicions, which he so strongly expresses, on his perusal of Cavendish's memoir in March, 1784.

What, then, it may be asked, did he mean, when he wrote the passage now quoted from the Météorologie? The answer is

obvious. He only meant, and can have only meant, to describe the mere fact of Cavendish's experiment, which is all that appears, from any other evidence in the case, to have been then known either to Priestley, or to Cavendish himself; an experiment, with its result of an equivalent weight of water, in itself doubtless a very remarkable phenomenon, or, as De Luc calls it, a "découverte," which greatly struck him, but which, it must always be remembered, is a very different thing from the conclusions which were afterwards stated as to its cause, by Watt, by Cavendish, and by Lavoisier.

De Luc's account, it must also be observed, is not a contemporaneous one, published at the time of Priestley's communication and before the all-important conclusions of Watt were made known. Writing at an interval of some years after his interview with Priestley, and also after the true interpretation of the experiments had been arrived at, and the cause of the phenomenon established, he has used language, in describing Cavendish's experiment, which he could scarcely have applied to it in 1782; as when he says that the two gases 66 se convertissoient:" the only fact then observed being the appearance of an equivalent weight of water, and the idea of conversion being as yet unsuggested by any one. M. De Luc also laboured under the disadvantage of translating Priestley's English communication into French, in which language his work was published; and in which the smallest variation from the precise terms used by Priestley or by Cavendish might be of the greatest importance.

No one who reads the whole of De Luc's narrative, and also his published letters to Mr. Watt, will doubt for a moment what was his real opinion as to both the originality and the priority of the theory, or conclusions, of the latter. And, viewed as a whole, his account corresponds in a very satisfactory manner with that given in a passage in Cavendish's paper, (inserted by Dr. Blagden after Mr. Watt's papers had been read, in 1784), in which it is said that the experiments made in 1781 were mentioned by Cavendish to Dr. Priestley, but that some account of both the experiments, and the conclusions drawn from them, was given to Lavoisier in the summer of 1783. It thus appears, on Blagden's and Cavendish's own statement, that no conclusions were mentioned to Priestley, and therefore none could have been repeated by him to De Luc; while, by the summer of 1783, both Dr. Blagden and Mr. Cavendish had become well acquainted with Mr. Watt's letter of April, 1783, containing his conclusions.

Besides, we know that Dr. Priestley, to whom the commu

nication of December, 1782, is said to have been made, looked on Lavoisier's memoir of November, 1783, as a plagiarism not from Cavendish, but from Watt: "He thinks, as I do," writes Mr. Watt to Mr. De Luc, "that Mr. Lavoisier, having heard some "imperfect account of the paper I wrote in the Spring, has run away with the idea," &c.* And Blagden, well informed of all Cavendish's proceedings, and desirous to name the earliest date of his drawing his conclusions, has assigned to them, not December, 1782, but "the Spring" of 1783.

The idea that the narrative of De Luc, contained in his Météorologie,' remained for more than half a century unknown to all engaged in researches on the water controversy, till it was "discovered" by the late Mr. Robert Brown, is as incorrect, as the interpretation sought to be put on a partial quotation from it is evidently mistaken. We can answer for ourselves that, many years ago, we read the whole of the narrative in question, and formed in regard to it the opinion which we have now stated. Twice, at least, in a work published in 1846— Correspondence of Watt on his Discovery of the Theory of the Composition of Water,' pp. liv. and lvi.-we had occasion to quote it, accompanying our quotations with particular references to it. By others who have maintained the cause of Watt, it was not brought forward because it could only have introduced apparent confusion, and no real fresh evidence, into the controversy. Nay, we can inform our readers, from a copy of one of his letters preserved among his correspondence, that Mr. Watt himself saw De Luc's narrative while yet in MS., and on this part of it only remarked that "Mr. Cavendish was not the first "who observed that phenomenon, it was Mr. "Warltire and "Dr. Withering"-that the latter put in no claim to it, but that "Mr. Warltire's observation is very clearly established by the Appendix to Dr. P.'s fifth volume, the second of what he calls "Observations,' &c., and by Mr. C.'s own acknowledgment." It is thus plain that Mr. Watt, like Priestley, understood De Luc's expressions, as De Luc himself intended them, to apply only to the observation of the fact or phenomenon irrespective of any conclusion.

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If not hitherto cited by the supporters of Mr. Cavendish, doubtless it has been because they also observed that any argument which the quotation might at first sight appear to furnish on their side is only apparent; that there can be no real question

30th November, 1783. See p. 328, suprà.

of De Luc's decision having been strongly against Cavendish; that when the whole of the statement is considered, it leaves the case exactly where it was before, or rather, corroborates the rest of the evidence, which establishes the priority of Watt. These, also, are excellent reasons why the late Mr. Brown, although often asserting that he knew of some document favourable to the cause of Cavendish, uniformly declined to produce it. When we find De Luc positively declaring that, in September, 1783, he was ignorant of Cavendish's conclusions, the inference attempted to be drawn in favour of Cavendish, from the terms in which at a later period De Luc describes the communication in 1782, falls to the ground.

J. P. M.

END OF THE APPENDIX.