in Academia Marpurgensi Professoris publici, litteris ad de Novo Pulveris Pyrii usu.

Act. Erud. for 1688, p. 497-501.

9. Additamentum ad Disquisitionem Dn. Papini de novo pyrii pulveris usu, mense proximo Septembri in Actis hisce pag. 497, exhibitam: De usu tuborum prægrandium ad propagandam in longinquum vim motricem fluviorum, &c. Communicatum a laudato Dn. Papino.

Ibid. p. 643-646.

10. Dionysii Papini Descriptio Torcularis, cujus in Actis Anni 1688, pag. 646, mentio facta fuit: Excerpta ex ejusdem litteris ad. . Marburgi d. 23 Dec. A. 1688, exaratis.

Ibid. 1689, p. 96-101.

11. D. Papini De gravitatis causa et proprietatibus observationes.

Ibid. p. 183-188.

12. Ejusdem Examen machinæ Domini Perrault.

Ibid. p. 189-195.

13. Dion. Papini Rotatilis Suctor et pressor Hassiacus, in Serenissima aula Cassellana demonstratus et detectus.

Ibid. p. 317-322.

14. In J. B. Appendicem illam ad Perpetuum Mobile, Actis Novemb. A. 1688, pag. 592 sqq. insertam, Observationes D. P.

Ibid. p. 322-324.

15. Excerpta ex litteris Dn. Dion. Papini ad Instrumentis ad flammam sub aqua conservandam.

Ibid. p. 485-489.

de

16. Examen Siphonis Wurtemburgici in vertice effluentis. Excerpta ex Litteris Dn. Dion. Papin. ad

Ibid. 1690, p. 223-228.

17. Dion. Papini Nova Methodus ad vires motrices validissimas levi pretio comparandas.

Ibid. 1690, p. 410-414. sententia, asserta a

18. Mechanicorum de viribus motricibus Dn. Papino adversus Cl. G. G. L. objectiones.

19. Dion. Papini observationes quædam circa materias ad Hydraulicam spectantes, Mensi Februario hujus anni insertas.

Ibid. p. 208-213.

20. [Account of] Fasciculus Dissertationum de novis quibusdam machinis atque aliis argumentis philosophicis. Autore Dionysio Papino, Med. Doct. Matheseos Prof. Publ. Marpurgensi. Marpurgi, 1695, in 8, plagg. 20, cum tribus plagg. figurarum.

No. II.

HISTORICAL NOTE ON THE DISCOVERY OF THE THEORY OF THE COMPOSITION OF WATER. BY THE RIGHT HON. HENRY LORD BROUGHAM, F.R.S., AND MEMBER OF THE NATIONAL INSTITUTE OF FRANCE.

THERE can be no doubt whatever, that the experiment of Mr. Warltire, related in Dr. Priestley's 5th volume,* gave rise to this inquiry, at least in England; Mr. Cavendish expressly refers to it, as having set him upon making his experiments.-(Phil. Trans. 1784, p. 126.) The experiment of Mr. Warltire consisted in firing, by electricity, a mixture of inflammable and common air in a close vessel, and two things were said to be observed: first, a sensible loss of weight; second, a dewy deposit on the sides of the vessel.

Mr. Watt, in a note to p. 332 of his paper, Phil. Trans. 1784,

Mr. Warltire's letter is dated Birmingham, 18th April, 1781, and was published by Dr. Priestley in the Appendix to the 2nd Vol. of his Experiments and Observations relating to ' various branches of Natural Philosophy; 'with a continuation of the Observations on Air,'-forming, in fact, the 5th volume of his Experiments and Observations on different kinds of Air;' printed at Birmingham in 1781.

Mr. Warltire's first experiments were made in a copper ball or flask, which held three wine pints, the weight 14 oz.; and his object was to determine "whether heat "is heavy or not." After stating his mode of mixing the airs, and of adjusting the balance, he says, he "always ac"curately balanced the flask of common "air, then found the difference of weight "after the inflammable air was intro"duced, that he might be certain he had "confined the proper proportion of each. "The electric spark having passed through "them, the flask became hot, and was "cooled by exposing it to the common air "of the room: it was then hung up again "to the balance, and a loss of weight was "always found, but not constantly the same; upon an average it was two grains."

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He goes on to say, "I have fired air in "glass vessels since I saw you (Dr.

"Priestley) venture to do it, and I have "observed, as you did, that, though the "glass was clean and dry before, yet, "after firing the air, it became dewy, and "was lined with a sooty substance.”

As you are upon a nice balancing of claims, ought not Dr. Priestley to have the credit of first noticing the dew?

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In some remarks which follow, by Dr. Priestley, he confirms the loss of weight, and adds, "I do not think, however, that "so very bold an opinion as that of the "latent heat of bodies contributing to "their weight, should be received without more experiments, and made upon a still larger scale. If it be confirmed, it will "no doubt be thought to be a fact of a very remarkable nature, and will do the "greatest honour to the sagacity of Mr. "Warltire. I must add, that the moment " he saw the moisture on the inside of the "close glass vessel in which I afterwards "fired the inflammable air, he said, that "it confirmed an opinion he had long "entertained, viz. that common air de"posits its moisture when it is phlogisti"cated."

It seems evident, that neither Mr. Warltire, nor Dr. Priestley, attributed the dew to anything else than a mechanical deposit of the moisture suspended in common air.-[NOTE BY MR. JAMES WATT, JUN.]

inadvertently states, that the dewy deposit was first observed by Mr. Cavendish; but Mr. Cavendish himself, p. 127, expressly states Mr. Warltire to have observed it, and cites Dr. Priestley's 5th volume.

Mr. Cavendish himself could find no loss of weight, and he says that Dr. Priestley had also tried the experiment, and found none. But Mr. Cavendish found there was always a dewy deposit, without any sooty matter. The result of many trials was, that common air and inflammable air being burnt together, in the proportion of 1000 measures of the former to 423 of the latter, "about "one-fifth of the common air, and nearly all the inflammable air, "lose their elasticity, and are condensed into the dew which lines "the glass." He examined the dew, and found it to be pure water. He therefore concludes, that "almost all the inflam"mable air, and about one-sixth of the common air, are turned "into pure water."

Mr. Cavendish then burned, in the same way, dephlogisticated and inflammable airs, (oxygen and hydrogen gases), and the deposit was always more or less acidulous, accordingly as the air burnt with the inflammable air was more or less phlogisticated. The acid was found to be nitrous. Mr. Cavendish states, that "almost the whole of the inflammable and dephlogisticated air "is converted into pure water." And, again, that "if these airs "could be obtained perfectly pure, the whole would be con"densed." And he accounts for common air and inflammable air, when burnt together, not producing acid, by supposing that the heat produced is not sufficient. He then says that these experiments, with the exception of what relates to the acid, were made in the summer of 1781, and mentioned to Dr. Priestley; and adds, that "a friend of his, (Mr. Cavendish's), last summer,' (that is, 1783), gave some account of them to Mr. Lavoisier, as well as of the conclusion drawn from them, that dephlo"gisticated air is only water deprived of its phlogiston; but, "at that time, so far was Mr. Lavoisier from thinking any such opinion warranted, that till he was prevailed upon to repeat "the experiment himself, he found some difficulty in believing "that nearly the whole of the two airs could be converted into "water." The friend is known to have been Dr., afterwards Sir Charles Blagden; and it is a remarkable circumstance, that this passage of Mr. Cavendish's paper appears not to have been in it when originally presented to the Royal Society; for the paper is apparently in Mr. Cavendish's hand, and the paragraph, pp. 134, 135, is not found in it, but is added to it, and directed

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to be inserted in that place. It is, moreover, not in Mr. Cavendish's hand, but in Sir Charles Blagden's; and, indeed, the latter must have given him the information as to Mr. Lavoisier, with whom it is not said that Mr. Cavendish had any correspondence. The paper itself was read 15th January, 1784. The volume was published about six months afterwards.

Mr. Lavoisier's memoir, (in the Mém. de l'Académie des Sciences for 1781), had been read partly in November and December, 1783, and additions were afterwards made to it. It was published in 1784. It contained Mr. Lavoisier's account of his experiments in June, 1783, at which, he says, Sir Charles Blagden was present; and it states that he told Mr. Lavoisier of Mr. Cavendish having 66 already burnt inflammable air in close "vessels, and obtained a very sensible quantity of water." But he, Mr. Lavoisier, says nothing of Sir Charles Blagden having also mentioned Mr. Cavendish's conclusion from the experiment. He expressly states, that the weight of the water was equal to that of the two airs burnt, unless the heat and light which escape are ponderable, which he holds them not to be. His account, therefore, is not reconcilable with Sir Charles Blagden's, and the latter was most probably written as a contradiction of it, after Mr. Cavendish's paper had been read, and when the Mémoires of the Académie were received in this country. These Mémoires were published in 1784, and could not, certainly, have arrived, when Mr. Cavendish's paper was written, nor when it was read to the Royal Society.

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But it is further to be remarked, that this passage of Mr. Cavendish's paper in Sir Charles Blagden's handwriting, only mentions the experiments having been communicated to Dr. Priestley; they were made," says the passage, "in 1781, and communi"cated to Dr. Priestley;" it is not said when, nor is it said that "the conclusions drawn from them," and which Sir Charles Blagden says he communicated to Mr. Lavoisier in summer 1783, were ever communicated to Dr. Priestley; and Dr. Priestley, in his paper, (referred to in Mr. Cavendish's), which was read June, 1783, and written before April of that year, says nothing of Mr. Cavendish's theory, though he mentions his experiment.

Several propositions then are proved by this statement.

First, That Mr. Cavendish, in his paper, read 15th January, 1784, relates the capital experiment of burning oxygen and hydrogen gases in a close vessel, and finding pure water to be the produce of the combustion.

Secondly, That, in the same paper, he drew from this experiment

the conclusion, that the two gases were converted or turned into water.

Thirdly, That Sir Charles Blagden inserted in the same paper, with Mr. Cavendish's consent, a statement that the experiment had first been made by Mr. Cavendish in summer 1781, and mentioned to Dr. Priestley, though it is not said when, nor is it said. that any conclusion was mentioned to Dr. Priestley, nor is it said at what time Mr. Cavendish first drew that conclusion. A most material omission.

Fourthly, That in the addition made to the paper by Sir Charles Blagden, the conclusion of Mr. Cavendish is stated to be, that oxygen gas is water deprived of phlogiston; this addition having been made after Mr. Lavoisier's memoir arrived in England.

It may further be observed, that in another addition to the paper, which is in Mr. Cavendish's handwriting, and which was certainly made after Mr. Lavoisier's memoir had arrived, Mr. Cavendish for the first time distinctly states, as upon Mr. Lavoisier's hypothesis, that water consists of hydrogen united to oxygen gas. There is no substantial difference, perhaps, between this and the conclusion stated to have been drawn by Mr. Cavendish himself, that oxygen gas is water deprived of phlogiston, supposing phlogiston to be synonymous with hydrogen; but the former proposition is certainly the more distinct and unequivocal of the two; and it is to be observed that Mr. Cavendish, in the original part of the paper, i. e. the part read January, 1784, before the arrival of Lavoisier's, considers it more just to hold inflammable air to be phlogisticated water than pure phlogiston, (p. 140).

We are now to see what Mr. Watt did; and the dates here become very material. It appears that he wrote a letter to Dr. Priestley on 26th April, 1783, in which he reasons on the experiment of burning the two gases in a close vessel, and draws the conclusion, "that water is composed of dephlogisticated air and "phlogiston, deprived of part of their latent heat."* The letter

It may with certainty be concluded from Mr. Watt's private and unpublished letters, of which the copies taken by his copying-machine, then recently invented, are preserved, that his theory of the composition of water was already formed in December, 1782, and probably much earlier. Dr. Priestley, in his paper of 21st April, 1783, p. 416, states, that Mr. Watt, prior to his (the Doctor's) experi

ments, had entertained the idea of the possibility of the conversion of water or steam into permanent air. And Mr. Watt himself, in his paper, Phil. Trans. p. 335, asserts, that for many years he had entertained the opinion that air was a modification of water, and he enters at some length into the facts and reasoning upon which that deduction was founded.[NOTE BY MR. JAMES WATT, JUN.]