200

entered, as was sufficient to fill the glass within about th part of its whole contents; and this small residuum may safely be concluded to have been occasioned by some impurity in one or both kinds of air. The moisture adhering to the glass, after these deflagrations, being wiped off, or sucked up, by a small piece of sponge paper, first carefully weighed, was found to be exactly, or very nearly, equal in weight to the airs employed. In some experiments, but not in all, a small quantity of a sootylike matter was found adhering to the inside of the glass. The whole quantity of sooty-like matter was too small to be an object of consideration, particularly as it did not occur in all the experiments.

"Let us now consider what obviously happens in the case of the deflagration of the inflammable and dephlogisticated air. These two kinds of air unite with violence; they become red-hot, and upon cooling totally disappear. When the vessel is cooled a quantity of water is found in it equal to the weight of the air employed. The water is then the only remaining product of the . process, and water, light, and heat are all the products.

"Are we not, then, authorised to conclude that water is composed of dephlogisticated air and phlogiston, deprived of part of their latent or elementary heat; that dephlogisticated or pure air is composed of water deprived of its phlogiston, and united to elementary heat and light; and that the latter are contained in it in a latent state, so as not to be sensible to the thermometer or to the eye; and if light be only a modification of heat, or a circumstance attending it, or a component part of the inflammable air, then pure or dephlogisticated air is composed of water deprived of its phlogiston and united to elementary heat."

In enclosing it, Mr. Watt adds, "As to myself, the more I consider what I have said, I am the more satisfied with it, as I find none of the facts repugnant."

"To those," wrote Mr. James Watt, junr., in an interesting letter addressed to the author of this biography,* "who may

* Dated Aston Hall, 5 February, 1846, and printed with Mr. Watt's 'Corre

HIS LETTER TO PRIESTLEY.

267

wish to form a just appreciation of the circumstances in which this correspondence took place, and of the merit that attaches to my father for the discovery it records, I beg to state, in the words of the great master of the English tongue, that 'it was written, not in the soft obscurities of retirement, or under the shelter of academick bowers; but amidst inconvenience and distraction, in sickness and in sorrow.' About the beginning of the year, when the correspondence commences, he had returned from planning and superintending the erection of his steam-engines, during a long sojourn in Cornwall, where he had been much harassed by attempts to pirate his improvements; and he was, through the greater part of the subsequent period, laboriously engaged in making out drawings and descriptions for the long specifications of his three great patents for mechanical improvements and inventions, taken out in the years 1781, 1782, and 1784, besides giving the constant attention necessary to the concerns of a nascent manufactory, and himself writing volumes of other letters on business, which alone would have furnished full employment even to an industrious intellect. His mind had been greatly affected by his unavoidable absence from the death-bed of his aged father; and during the greater part of the time, I well remember seeing him suffer under most acute sick head-aches, sitting by the fire-side for hours together, with his head leaning on his elbow, and scarcely able to give utterance to his thoughts. It was unquestionably the busiest, as well as the most anxious, period of his life, and fraught with the most important results. I need not attempt to do justice to them, for time has sanctioned the judgment of his contemporaries, who had done it already.”

But,—to return to Mr. Watt's letter to Dr. Priestley, of 26th April, 1783,-"This letter," as is stated in Mr. Watt's Note published in the Philosophical Transactions, "Dr. Priestley received at London; and, after showing it to several members of the Royal Society, he delivered it to Sir Joseph Banks, the

spondence on his Discovery of the Theory of the Composition of Water,' published in the same year, pp. i. to xvi.

President, with a request that it might be read at some of the public meetings of the Society."

But, as it happened, the public reading which had been so requested by Mr. Watt did not take place at that time. "Before that could be complied with," the note continues, “the author, having heard of Dr. Priestley's new experiments, begged that the reading might be delayed."

The new experiments alluded to in the note, Priestley had announced in these terms:-"Behold with surprise and indignation the figure of an apparatus that has utterly ruined your beautiful hypothesis," † giving a rough sketch with his pen of the apparatus employed. But Mr. Watt immediately and unhesitatingly replied, "I deny that your experiment ruins my hypothesis. It is not founded on so brittle a basis as an earthen retort, nor on its converting water into air. I founded it on the other facts, and was obliged to stretch it a good deal before it would fit this experiment. * */ I maintain my hypothesis

until it shall be shown that the water formed after the explosion of the pure and inflammable airs, has some other origin." So to Mr. De Luc:-"I do not see Dr. Priestley's experiment in the same light that he does. It does not disprove my theory. * * My assertion was simply, that air" [i. e., dephlogisticated air, or oxygen, which was also commonly called vital air, pure air, or simply air,] "was water deprived of its phlogiston, and united to heat, which I grounded on the decomposition of air by inflammation with inflammable air, the residuum, or product of which, is only water and heat."§ Even when writing to Dr. Black that he had withdrawn his paper, he adds, "I have not given up my theory." ||

But he did withdraw, or rather reserve the public reading of

* Philosophical Transactions,' 1784, p. 330.-Note.

† Dr. Priestley to Mr. Watt, 29th April, 1783.

Mr. Watt to Dr. Priestley, 2nd May, 1783.

§ To Mr. De Luc, 18th May, 1783.

| To Dr. Black, 23rd June, 1783.

LETTER READ BEFORE THE ROYAL SOCIETY. 269

his paper, till he should further examine the new experiments which were said to be hostile to the doctrine which it unfolded; and also, as he adds with his usual modesty, because he was "informed that that theory was considered too bold, and not sufficiently supported by facts."* “Mr. Watt then wished,” as

it is more fully expressed in a work published shortly afterwards, "that the letter should not be read at the public meeting of the Society, because he learned that his theory was thought too bold, or that a substance such as water, till then considered as of the nature of an element, was there placed in the class of compounds.” † But the letter itself, after being read by many members, remained in the custody of the President till the day when it was read to the Society, 22nd April, 1784, as is well ascertained from Mr. Watt's letter to Blagden of 27th May, 1784.

But in the meantime, baving by additional experiments still further satisfied himself of the correctness of his theory, in which he had never been able to detect error, and the truth of which he now held to be abundantly confirmed, he proceeded, towards the end of November, tranquilly to occupy himself in preparing a more full statement of it, to be sent to his friend De Luc, for the purpose of being read to the Royal Society. By the 1st of December, however, we find that he had received accounts of an occurrence which appeared to stand much in need of explanation; and which, after that had been obtained, proved little to the credit of some of those concerned. "I was," he says, in writing to Mr. De Luc, ‡ "at Dr. Priestley's last night. He thinks, as I do, that Mr. Lavoisier, having heard some imperfect account of the paper I wrote in the Spring, has run away with the idea, and made up a memoir hastily, without any satisfactory proofs. How that may be, I cannot take on me to say; but if you will read the 47th and 48th pages of Mr. De la Place's and his Memoir on Heat, you will be convinced that they had no such ideas then, as

* Mr. Watt to Sir Joseph Banks, 12th April, 1784.

+ De Luc, 'Météorologie,' tom. ii., p. 216. 1786.

† 30th November, 1783.

4

they speak clearly of the nitrous acid being converted into air. I therefore put the query to you of the propriety of sending my letter to pass through their hands to be printed; for even if this theory is Mr. Lavoisier's own, I am vain enough to think that he may get some hints from my letter, which may enable him to make experiments, and to improve his theory, and produce a memoir to the Academy before my letter can be printed, which may be so much superior as to eclipse my poor performance, and sink it into utter oblivion; nay, worse, I may be condemned as a plagiary, for I certainly cannot be heard in opposition to an Academician and a Financier. * But, after all, I may be

doing Mr. Lavoisier injustice.

*

I see it, on the one hand,

so difficult to satisfy those nice chemists, and, on the other hand, so difficult to be allowed even the honour of the discovery, that I am nearly discouraged, either from publishing at all, or trying any more experiments; as it seems to be losing my labour and procuring myself disquiet." "M. Lavoisier," he also writes, "has read a memoir opening a theory very similar to mine on the composition of water; indeed, so similar, that I cannot help suspecting he has heard of the theory I ventured to form on that subject, as I know that some notice of it was sent to France."*

To this conjecture, Mr. Kirwan was able, in his reply, to add the most positive assurance. "M. Lavoisier," he writes, "certainly learned your theory from Dr. Blagden, who first had it from Mr. Cavendish, and afterwards from your letter to Dr. Priestley, which he heard read, and explained the whole minutely to M. Lavoisier last July." [June.]†

The letter was, of course, well known to Dr. Priestley, who received it, perused it, and at once occupied himself in answering it, and to Sir Joseph Banks, in whose hands it long remained. But that it was also read by many other members of the Royal Society, though not then at a public meeting of the body, there cannot be any manner of doubt. For we have not only the

* To Mr. Kirwan, 1st December, 1783.

+ Mr. Kirwan to Mr. Watt, 13th December, 1783.