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“ managing Dr. Roebuck, who at that time had not become "a complete convert to the doctrine of latent heat. Accord

ingly, it was so; and Mr. Watt was obliged to yield for “ some time to the Doctor's confidence in his own great

experience. The Doctor thought to produce the condensa

tion, with sufficient rapidity and accuracy, by a very exten“ sive surface; and Mr. Watt knew that it also required

a great quantity of water, or other matter, to receive the “ emerging heat. I know that these differences of opinion “ retarded the completion of the engine.

“ But Dr. Roebuck had too much judgment not to see the “ conclusiveness of the experiments by which the doctrine of “ latent heat is established, and not to yield to their force; “and everything went on at last to their mutual satisfaction. “ Dr. Roebuck knew Mr. Watt's talents, and most liberally “ praised them. His timidity, his disposition to despond “ when under unforeseen difficulties, and his painful anxiety “ and diffidence in himself, were frequently the subjects of

friendly merriment at the Doctor's fireside ; and I have “often heard him say, that without his help, and even his “ instruction, on many points of the construction, Mr. Watt “could never have gone on. I have even heard him men“ tion some important, but subordinate, parts of the engine “ which were of his contrivance. But I never heard him “ lay the smallest claim to the leading thought of a hot and

dry cylinder for the piston to work in, and, therefore, a

separate condenser. I never knew him call it my engine,' “ nor 'our engine,' but uniformly · Watt's engine,' when he “ had occasion to speak of it as distinct from the old or Newcomen's engine. I remember Mrs. Roebuck saying one “ evening, Jamie is a queer lad, and without the Doctor his u invention would have been lost: but Dr. Roebuck won't “ • let it perish.' I mention all these trifling things because “ I have often heard gentlemen living in the neighbourhood of Borrowstoness speak of this new project as Dr. Roe

buck's, in which he was assisted by one Watt, from Glas“ gow. One gentleman in particular, Mr. Graham of Airth, " insisted with me that Dr. Roebuck was the inventor. But

H

“ one day Mr. Graham came home from Falkirk, where he “ had seen Dr. Roebuck, and engaged him in conversation on the subject. He told me that he now saw plainly that “ Mr. Watt was the sole author, and said that he would be “ at some pains to undeceive some gentlemen of the neigh“ bourhood, who were of the opposite opinion. This was “ very natural. Dr. Roebuck was a gentleman of uncommon knowledge in everything of this kind, and considered

as the first judge in all that country of all such matters ; “ whereas Mr. Watt was an entire stranger.

*

“I remember also, that in 1774, or 1775,* after my return “ from Russia, I had some conversation with Dr. Roebuck. “ The Doctor spoke with some dissatisfaction of Boulton and “ Watt. They were now, he said, amassing fortunes from a

project which his misfortunes had obliged him to cede to " them. They seemed to have forgotten that he had suffered “ all the anxieties attending the infant project; he had run “all the risk, and the risk had been very great, both from “ the novelty of the thing, and from Mr. Watt's delicate

health, and his timidity under difficulties ;—that without “ his continual encouragement and support it never would " have succeeded. He had ceded his right on very moderate “ terms, and he had expected some remembrance of this. “ In this disposition to repine at an opportunity which he “ had lost of benefiting himself, it would have been most “natural for Dr. Roebuck to put a high value on any part " that he had had in the discovery; and I listened with some “ anxiety to hear if he advanced any claim of this kind, for I “ knew that any such thing from Dr. Roebuck would be “ received with much deference. But I have the most dis“ tinct recollection that he made no claim whatever of this " sort; but, on the contrary, spoke in the highest terms of “Mr. Watt's ingenuity and inexhaustible resource of in“ vention.*

* This date probably was given by Boulton. It was several years before Dr. R. in mistake for a later one, as the manufacture of the improved Mr. Watt's Act of Parliament was steam- engines, which only comobtained in May, 1775 ; after which, menced in 1775, became in the least though in the same year, it was that degree remunerative. be entered into partnership with Mr.

« The duties of my profession call my attention to a great “ variety of very interesting objects. Of all these, my " favourite object is practical mechanics. I have, therefore, " hunted everywhere for information, and my opportunities “ have been considerable. Understanding most of the lan"guages of Europe, I have looked into almost every book " which treats of such things; and, in particular, I have ** searched for every project in mechanics, description of " machines, and schemes of public works. I can recollect " but one trace of anything like a separate condenser of “steam. This is in a volume of the Commentarii de * • Rebus in Medicinâ et Scientiâ Naturali gestis ;'I cannot “ now recollect the volume, and only remember that it is a “ late one; indeed this whole work is of a date posterior to “ 1769). In this volume there is a short account given of an

air-pump by M. Wilcke, of Upsal or Stockholm, precisely

• We understand these remarks which happened in 1794: and thus of Dr. Robison to have had reference he hoped to escape an effectual conto some stories told by a person of tradiction. Such folly and audacity, the name of Joseph Hately, who, however, were at once exposed, as having come into the employment of they deserve always to be; and we Dr. Roebuck some time after Mr. have now before us a letter from Dr. Watt had began to make his experi- R.'s son, Mr. John Roebuck, (to Mr. mental essays at Kinneil, but having Watt, 22nd Nov. 1796), in which he failed to give his employer satisfac- says, “ I never heard my father in tion, quitted it, or was discharged, “ the smallest degree claim any merit after a service of about eighteen or pretend to have any share in months. He seems to have after- "inventing or even in improving wards (16 Nov. 1790) taken out a upon your engine.

On the conpatent for a "Pneumatic fire-engine;" trary, he always represented the but would not bave been noticed “ whole invention to be yours." Also, here had it not been for a very ab- one from a gentleman who had been surd fable of which he was the clerk to Dr. R. at the time in quesauthor; which was to the effect that tion, and continued in strict friendthe improved engine had been in- ship with him from that period to vented not by Mr. Watt, but by Dr. the time of his death; who expresses Roebuck. This story he circulated his astonishment "that Mr. Hately on the eve of Boulton and Watt's " should pretend to attribute an inlitigation with the infringers of their “ vention to Dr. Roebuck, which on patent rights; the design of it ob- every occasion, during a twentyviously being, by an allegation of " seven years' intimate acquaintance prior invention, to * avoidMr. “ with the Doctor, he had avowed to Watt's patent. Before venturing to me, and to others in my hearing, promulgate such a creed he had

“ to be wholly yours."

(Mr. James waited, - no doubt wisely, as he Warrock to Mr. Watt, 26th Nov. thought, — till the Doctor's death, 1796.)

« such as I made when I heard of Mr. Watt's contrivance. “ It is mentioned as a thing which the Reviewers had forgot“ ten in its proper time, and they say, 'dudum fabricavit.' I “ mentioned this about a year ago to Dr. Black, when we “were speaking of some curious observations of M. Wilcke

on the cloud which appears in the receiver of an air-pump “ when damp air is suddenly rarefied. The Doctor told me, “ that when he was yet in Glasgow, he had a pupil of the " name of Williams, or Williamson, from the Mine College in “ Sweden; that this person was intimately acquainted in “ Dr. Roebuck's family, and, he believed, also with Mr. “ Watt; that he was in this country almost three years, and

fully understood all his theory; and he had no doubt that “ Dr. Wilcke owed to him all that he had published on that

subject. He thought it equally probable that this project “ of an air-pump had transpired in some of our conversations, “ it being a thing on which we put no value."

The following is evidently the notice intended to be referred to by Dr. Robison, which we here translate from the Latin, in which language it is printed in the Transactions of the Royal Academy of Sciences of Sweden :

“ 3. John Charles Wilke, Lecturer on Experimental Philosophy, proposes a new kind of air-pump. He makes use “ of the well-known property which the steam of boiling “ water possesses, of so expanding itself, as to drive out the “air from any space which it fills. Instead, therefore, of " that cylinder, in which, in common pumps, the sucker " moves, he takes a metallic vessel, into which, by means of " a tube, the steam of water, boiling over a fire, can ascend; “ by another aperture, the air contained in the vessel (which “ he calls a receiver) retires before the steam. The receiver “ is joined to a globe, on which a glass bell may be placed, “as in common [air-]pumps; and those three apertures of “ the receiver, by which the steam enters, the air escapes, and “ the globe is connected with it, may be closed by valves or “ cocks. The last of them, up to this point, is kept shut. “ When the steam, ascending into the receiver, has suffi" ciently expelled the air, the cock by which the air had “ escaped is closed, and the receiver is surrounded with cold "water. The steam, thus condensed, returns, in the form of “ drops, to the vessel whence it came; and the cock which, -“ when open, had permitted it to rise, being now closed, a

vacuum, to a great extent, is formed in the receiver. Then “ the cock by which it is joined to the globe, being opened, “ air will rush into it from the bell. This kind of exhaustion

may be repeated, till there remains under the bell [no “ more than) a one hundred and thirtieth portion of the air, “ in the machine with which Mr. Wilke made his experiment, “and which was by no means so perfect as it might be made “ by greater care. Even common air-pumps, as improved by " Nollet, rarefy air about 300 times ; (Wilke takes no notice * of John Smeaton's pump, mentioned in the ‘Philosophical

Transactions, vol. xlvii. Art. 69, by which air is said to be “ rarefied 500 or even 1000 times); so that this one, a little “ better made, will easily equal their performance; but its “principle is, that it will exhaust the air suddenly, not, as “ the common ones do, by degrees : (Nollet and others “ showed how a large receiver could be first emptied of air, “ and applied to the bell, so as to let the air from the “ latter suddenly rush into it). “But, it is added, “as it “ ' needs fire and water, its use is attended with some incon• veniences.'

Dr. Robison is not quite accurate in saying that the whole of the Commentarii' are of a date posterior to 1769. The work was published in a series of thirty-seven volumes, commencing in 1752, and ending in 1806; with three volumes of Supplementa,' 1763-96, and three of Indices, 1770-1793. But it is certain that the passage quoted above is of a date several years subsequent to Mr. Watt's invention of the separate condenser; and the circumstances through which it happened that Mr. Wilcke was even so early in possession of

* • Kongl. Vetenskaps Academiens mestre primum), printed in the Com* Handlingar för Aor 1769,' vol. xxx. 'mentarii de Rebus in Scientiâ &c. : i.e., Acta Academiæ Reg. Sc. Naturali et Medicinâ gestis,' voSuecicæ, anni 1769, vol. xxx. (Tri- luminis xviii. pars I. Lipsiæ, 1772.

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