« PoprzedniaDalej »
that he has been furnished with a coat of mail from the hostile armoury, and that, in taking his place in the forlorn hope, he has escaped from its dangers. s:The most recent defenee of the claims of Cavendish has just been published in the Notes to the new edition of Dr. Whewell's History of the Inductive Philosophy. We feel it a duty to enroll Dr. Whewell's name in the list of his friends, and, though the Note be full of errors, to give to liis cause all the support which it can derive from the great talents and acquirements of the Master of Trinity. “ In the philosophy of the Inductive Sciences,” says Dr. Whewell,
c. 4) “ I have stated, with reference to recent attempts to deprive Cavendish of the credit of his discovery of the composition of water, and to transfer it to Watt—that Watt not only did not anticipate, but did not fully appreciate the discovery of Cavendish and Lavoisier ; and I have expressed my concurrence with Mr. Vernon Harcourt's views, when he says (Address to the British Association, 1839) that "Cavendish pared off from the current hypotheses their theory of combustion, and their affinities of imponderable for ponderable matter, as complicating chemical with physical considerations; and he then corrected and adjusted them with admirable skill to the actual phenomena, not binding the facts to the theory, but adapting the theory to the facts.'
“I conceive that the discussion which the subject has recently re. ceived has left no doubt on the mind of any one who has perused the documents, that Cavendish is justly entitled to the honour of this discovery, which, in his own time, was never contested. The publication of his Journals of Experiments (Appendix to Mr. V. Harcourt's Address) shows that he succeeded in establishing the point in question in July 1781. His experiments are referred to in an abstract of a paper of Priestley's, made by Dr. Maty, the Secretary of the Royal Society, in June 1783. In June 1783, also, Dr. Blagden communicated the result of Cavendish's experiments to Lavoisier at Paris. Watt's letter, containing his hypothesis that water is composed of dephlogisticated air and phlogiston, deprived of part of their latent or elementary heat, and that deplilogisticated, or pure air, is composed of water deprived of its phlogiston, and united to elementary heat and light,' was not read till November 1783.; and even if it could have suggested such an ext periment as Cavendish's, (which does not appear likely) is proved, by the dateş, to bave had no share in doing so.
« Mr. Cavendish's experiment was suggested by an experiment in which Warltire, a lecturer on chemistry at Birmingham, exploded a ñixture of hydrogen and common air in a close vessel, in order to determine whether heat were ponderable.”—Notes, pp. 206, 207.
From this brief history of the controversy, we now pass to what we hope will be its last stage, namely, the publication of the Correspondence of Mr. Watt, on his discovery of the theory of the
composition of water.” We shall endeavour to give a short and perspicuous abstract of this correspondence, in order to put our readers in possession of all the facts and circumstances under which Mr. Watt's opinions and views were developed, and in order to make this more intelligible, we shall substitute, as MM. Arago and Dumas have done, the term oxygen for dephlogisticated air, and hydrogen for phlogiston. Mr. Harcourt, indeed, has objected to such a substitution ; but M. Arago has satisfactorily re: plied to the objection ; and we hold that Mr. Cavendish's friends are not only debarred from making any such objection by tlie fact that Cavendish himself uses the very same language, but that they are bound to regard Mr. Watt's theory of the composition of water as the very same as that of Cavendish, because Cavendish himself unequivocally declares that the difference between them is only apparent, and consists of a form of speaking which may be either used or avoided, as the parties think best. **
In the year 1776, Volta fired inflammable'air by a simple electric spark. In 1776-7, Macquer burned mixtures of inflainmable air and oxygen in glass vessels, and observed that the part of the saucer which the flame licked was moistened with small drops of a liquor as clear as water, and which appeared to him to be pure water. Macquer, however, drew no conclusion from his experiments; and it was not till sometime before the 18th April 1781, that a similar experiment was made by Priestley and Warltire, who fired a mixture of common and inflammable airs, and of inflammable air and oxygen, and observed a deposit of water on the side of the vessel. After the publication of these experiments, Mr. Cavendish repeated them in the summer of 1781, and observed that though the glass globe was dry before firing, it was immediately
covered with dew on firing. * These experiments,” says Mr. Cavendish in his paper of 1784, were mentioned by me to Dr. Priestley, who, in consequence of it, made some experiments of the same kind, as he relates in a paper printed in the preceding volume of the Transactions." 1. It appears from a letter of Priestley to Watt, of 18th December 1782, that Mr. Watt conceived water to consist of gases. “I have the pleasure," says he,“ to inforın you, that I readily convert water into a permanent air, which agrees with your idea on the subject.” Mr. Watt, in writing to Mr. De Luc, five days afterwards, assures him, that “ Dr. Priestley has made a most surprising discovery, which seems to confirm my theory of water's
Philosophical Transactions, 1784, p. 140. + This passage occurs in the paragraph interpolated by Dr. Blagden in Caven. dish's paper, after it had been read. The time when the experiments were mey.. tioned to Priestley is not stated, and the experinjents are said to be of the same kind with Priestley's,
undergoing sucli a remarkable change (that it would become air) at the point where all its latent heat would be changed into sensible heat." "I have observed," continues Mr. Watt,“ several other processes by which I now believe air is generated from water.'
“ If this process contains no deception, here is one element dismissed from the list .!” On the 26th March 1783, Mr. Watt writes to Mr. Hamilton, that Dr. Priestley kindles dry oxygen and dry hydrogen by electricity; that no air remains if the two airs are pure, and that on the side of the vessel he found a quantity of water equal in weight to the air employed; and on the 21st of April 1783, he informs Dr. Black that Priestley has made more experiments on the conversion of water into air, and that "he believes he (Mr. Watt) has found out the cause of it, which he has put in the form of a letter to him, to be read at the Royal Society.” The conclusion or theory to be drawn from these experiments, is given in the same letter, namely, that water is composed of oxygen and hydrogen deprived of part of their latent heat. On the 26th April 1783, he sends a corrected copy of his letter above referred to, to Dr. Priestley, who having received it while in London, shews it to several members of the Royal Society, among whom was Dr. Blagden, Mr. Cavendish's intimate friend, and afterwards delivered it to Sir J. Banks to be read to the Society. A few days afterwards, however, namely on the 29th April, Dr. Priestley announces to Mr. Watt, on the authority of an experiment afterwards found to be erroneous, that it “ has utterly ruined his beautiful hypothesis,” Mr. Watt replies, on the 2nd May, that “he maintains his hypothesis, until it shall be shewn that the water found after the explosion of pure and inflammable air has some other origin;" but deeming it prudent to reconsider the bearing of Dr. Priestley's experiment, he requests, prior to the 23rd June, that the public reading of his paper should be delayed.
After having seen Mr. Watt's paper, Dr. Blagden goes to Paris in the summer of 1783, and communicates to M. Lavoisier an accountof the experiments made by Cavendish on the firing of oxygen and hydrogen, and, as he says, of the conclusion drawn from them, that oxygen is only water deprived of hydrogen. This statement of what Dr. Blagden had done, is made in Cavendish's paper of 1784, in a paragraph interpolated by Dr. Blagden after the paper had been read, and of course adopted by Cavendish; and it is very important to notice the terms in which it is made, because they mark, in the clearest manner, the difference between the experiments themselves, and the conclusion drawn from them. Lavoisier gives a different account of the communication then made to him. “Mr. Blagden, says he, informed us that Mr. Cavendish had already fired inflammable air in closed vessels,
and that he had obtained a very sensible quantity of water."* This statement of Lavoisier is corrected, and, to a certain extent, contradicted in the following letter from Dr. Blagden to Dr. Lorenz Crell
, who published it in his Chemische Annaley, for 1786,-a letter which throws no inconsiderable light on the most important features of the controversy:
“ I can certainly give you the best account of the little dispute about the first discoverer of the artificial generation of water, as I was the principal instrument through which the first news of the discovery that had been already made was communicated to Mr. Lavoisier, The following is a short statement of the history :
“ In the spring of 1783 Mr. Cavendish communicated to me and other members of the Royal Society, his particular friends, the result of some experiments with which he had for a long time been occupied. He shewed us, that, out of them, he must draw the conclusion, that dephlogisticated air was nothing else than water deprived of its phlo, giston; and, vice versa, that water was dephlogisticated air united with phlogiston. About the same time the news was brought to London, that Mr. Watt of Birmingham had been induced by some observations, to form a similar opinion. Soon after this I went to Paris, and in the company of Mr. Lavoisier, and of some other members of the Royal Academy of Sciences, I gave some account of these new experiments, and of the opinions founded upon them. They replied that they had already heard something of these experiments; and, particularly, that Dr. Priestley had repeated them. They did not doubt that in such manner a considerable quantity of water might be obtained ; but they felt convinced that it did not come near to the weight of the two species of air employed; on which account it was not to be regarded as water formed or produced out of the two kinds of air, but was already contained in, and united with the airs, and deposited in their combustion. This opinion was held by Mr. Lavoisier, as well as by the rest of the gentlemen who conferred on the subject; but, as the experiment appeared to them very remarkable in all points of view, they unanimously requested Mr. Lavoisier, who possessed all the necessary apparatus, to repeat the experiment on a somewhat larger scale, as early as possible. This desire he complied with on the 24th June 1783, (as he relates in the latest volume of the Paris memoirs.) From Mr. Lavoisier's own account of his experiment, it sufficiently appears, that at that period he had not yet formed the opinion, that water was composed of dephlogisticated and inflammable airs; for he expected that a sort of acid would be produced by their union. In general, Mr. Lavoisier cannot be convicted of having advanced any thing contrary to truth; but it can still less be denied, that he concealed a part of the truth. For he should have acknowledged that I had some days before apprised him of Mr. Cavendish's experiments; instead of which the expression, " il nous apprit," gives
* Mem. Acad. Par. 1711. p. 472 (Printed in 1784).
rise to the idea that I had not informed him earlier than that very day. In like manner, Mr. Lavoisier has passed over a very remarkable circumstance, namely, that the experiment was made in consequence of what I had informed him of. He should likewise have stated in his publication, not only that Mr. Cavendish had obtained
une quantité d'eau très sensible,” but that the water was equal to the weight of the two airs added together. Moreover, he should have added, that I had made him acquainted with Messrs. Cavendish and Watt's conclusions ; namely, that water, and not an acid or any other substance, arose from the combustion of the inflammable and dephlogisticated airs. But those conclusions opened the way to Mr. Lavoisier's present theory, which perfectly agrees with that of Mr. Cavendish; only that Mr. Lavoisier accommodates it to his old theory, which banishes phlogiston. Dr. Monge's experiments, (of which Mr. Lavoisier speaks as if made about the same time,) were really not made until pretty long, I believe at least two months, later than Mr. Lavoisier's own, and were undertaken on receiving information of them. The course of all this history will clearly convince you, that Mr. Lavoisier, (instead of being led to the discovery, by following up the experiments which he and Mr. Bucquet had commenced in 1777,) was induced to institute again such experiments, solely by the accounts he received from me, and of our English experiments; and that he really discovered nothing, but what had before been pointed out to him to have been previously made out, and demonstrated in England.”
In this very important letter, written no doubt with the knowledge and sanction of his friend and patron Mr. Cavendish, Dr. Blagden has established several important facts in the history of this dispute. We have already seen that, early in the spring, (26th April,) Mr. Watt's letter to Priestley, containing his theory, or his conclusions, respecting the composition of water, was sent to London, and shown to Dr. Blagden; and it now appears, that it was not till the spring of that year that Mr. Cavendish communicated to his particular friends the result of the experiments with which he had long been occupied. “He showed them, that he must draw the conclusion, that water consisted of oxygen and hydrogen”_a clear proof that he had not drawn the conclusion till then, and that his experiments in 1781 were not considered as involving the theory of the composition of water. The acknowledgment, that about the same time news came to London that Mr. Watt had been induced, by some observations, to form a similar opinion, shows also that the conelusion drawn by both the philosophers had, in 1783, only the character of an opinion; and that, even in the mind of Dr. Blagden, the opinion of Mr. Watt and the opinion of Mr. Cavendish were of the same value, and contemporaneously formed. The reply of the Parisian academicians, that they had already