66 66 "conversations with Dr. Black I frequently introduced Watt's steam-engine. I one day asked him why Mr. Watt never thought of impelling the piston by steam much stronger "than common steam, mentioning the way in which I would "introduce and manage it. He then corrected me in some parts of my proposed construction, and described Mr. Watt's "with accuracy; and bade me reflect on the enormous size " and strength which must be given to the boiler, and the ex"pense of fuel in supplying steam so dense and so hot. All "this I had thought on already, and only wanted to learn “what he had just now told me; and now I am fully entitled "to say, that in the summer of 1767 the whole contrivance "was perfect in Mr. Watt's mind, although he had neither "executed the double stroke, nor that most beautiful con"trivance of cutting off the steam before the piston reaches "the bottom of the cylinder; a contrivance which in a "moment fits the engine, however great and powerful, to any the most trifling task, and makes it more manageable than "any other engine whatever that is not immediately actuated "by the hand of man. Indeed, any person who deserves the "name of engineer must see, and, if he speak from the con"viction of his conscience, must acknowledge, that the whole "contrivance was perfect in Mr. Watt's mind in his very first "trial. 66 66 During the two following winters, notwithstanding Mr. "Watt's frequent absence from Glasgow, and my constant "occupation with my chemical lectures, I had many oppor"tunities of conversing with him, and learned all his diffi"culties and embarrassments. He struggled long to condense "with sufficient rapidity without injection, and exhibited many beautiful specimens of ingenuity and fertility of re"source. Many pretty schemes occurred to him for a rota"tory engine. Some of these I am sorry to find that he has "neglected. I am confident of their complete success; and though I agree with him in thinking that his engine with a "double stroke is superior to them all, I should have been "glad that they had been executed, because they would have "given a most brilliant specimen of his wonderful ingenuity 66 "and of his knowledge; for, indeed, the management of "steam to perfection is the employment of an accomplished philosopher. 66 66 66 During my residence in Glasgow I was in habits of con"tinual intimacy with Mr. Watt. All who knew him know "that it is his greatest pleasure to communicate his know. ledge to those who have a relish for it. I have reason to "think that he never, from any kind of jealousy, concealed anything from me. From the day that he-I may almost "say we began to play with the College model, I knew "almost every step of his thoughts. He was confined to his "business; I was more at large, and going about the College. "I ransacked the libraries for every book that he wanted; "and every quotation that he met with made him impatient "till he got at the original. I saw every book that he got by "any other channel besides the public libraries. So I may safely say that I knew the whole extent of his reading. "Our abode was too far out of the circle of business for allow 66 66 ing us to be informed of the numberless projects that are every day born and buried in this busy country. I can say, "with great confidence, that nothing ever occurred to Mr. "Watt, either by reading or information, of his leading principle, of a steam-vessel perpetually and universally hot. "All the other contrivances, of separate condenser,—air and "water-pumps,-amalgam, or rosins, or fats for keeping the "piston air-tight,-are but so many emanations from this "first thought; and I will venture to say they all came into "his mind in succession, and nearly in the order I have stated, "after he said to himself, Let me make an engine, working 'by a piston, in which the cylinder shall be continually hot "and perfectly dry.' I will venture to say that in no book previous to that date is there any account or proposal of "such a thing, if we except some attempts to put the steam"vessel of Worcester's or Savery's engine in this predicament, 66 6 66 66 by means of a travelling mass of oil or air, which was to be "interposed between the steam and the water that was to be "raised. Of these, Mr. Watt and I had some very imperfect "account; but they never interested him, because the very "nature of the operation made it impossible to do anything "more than approximate to the desired object. "I must say, further, that the thought was wholly Mr. "Watt's. For this I have every authority that can be wished "for. I am certain that when I went out of town in (May, I "think,) 1765, he had not thought of the method of keeping "the cylinder hot; and I am as certain that a fortnight after "he had completed it, and confirmed it by experiment. Dr. "Black, the first philosophical chemist of his time, and the "most scrupulous man upon earth with respect to claims of originality, gave this to Mr. Watt in the most unqualified "terms, the first time I saw him after I had learned it from "Mr. Brown, and long before I saw Mr. Watt and got it more distinctly from himself." 66 66 CHAPTER VII. MR. WATT'S NARRATIVE OF THE INVENTIONS DESCRIBED IN HIS SPECIFICA- OF HIS INVENTION OF THE SEPARATE CONDENSER THE account given by Mr. Watt himself, in his Notes on Professor Robison's Dissertation on Steam-engines,* is as follows: 66 "My attention was first directed, in the year 1759, to the subject of steam-engines, by the late Dr. Robison, then a "student in the University of Glasgow, and nearly of my own age. He at that time threw out an idea of applying the "power of the steam-engine to the moving of wheel-carriages, "and to other purposes; but the scheme was not matured, " and was soon abandoned on his going abroad. 66 "About the year 1761, or 1762, I tried some experiments "on the force of steam in a Papin's digester, and formed a species of steam-engine by fixing upon it a syringe, one-third "of an inch diameter, with a solid piston, and furnished also "with a cock to admit the steam from the digester, or shut "it off at pleasure, as well as to open a communication from "the inside of the syringe to the open air, by which the steam "contained in the syringe might escape. When the commu"nication between the digester and syringe was opened, the "steam entered the syringe, and by its action upon the piston "raised a considerable weight (15 lbs.) with which it was “loaded. When this was raised as high as was thought "proper, the communication with the digester was shut, and "that with the atmosphere opened; the steam then made its escape, and the weight descended. The operations were repeated, and, though in this experiment the cock was 66 * Robison's Mechanical Works, edited by Sir David Brewster. 66 66 66 "turned by hand, it was easy to see how it could be done by "the machine itself, and to make it work with perfect regularity. But I soon relinquished the idea of constructing an engine upon its principle, from being sensible it would be "liable to some of the objections against Savery's engine, "viz., the danger of bursting the boiler, and the difficulty of making the joints tight, and also that a great part of the power of the steam would be lost, because no vacuum was "formed to assist the descent of the piston. I, however, "described this engine in the fourth article of the specifica"tion of my patent of 1769; and again in the specification "of another patent in the year 1784, together with a mode "of applying it to the moving of wheel-carriages. "The attention necessary to the avocations of business pre"vented me from then prosecuting the subject further; but "in the winter of 1763-4, having occasion to repair a model "of Newcomen's engine belonging to the Natural Philosophy "class of the University of Glasgow, my mind was again "directed to it. At that period my knowledge was derived "principally from Desaguliers, and partly from Belidor. I "set about repairing it as a mere mechanician; and when "that was done, and it was set to work, I was surprised to "find that its boiler could not supply it with steam, though apparently quite large enough, (the cylinder of the model "being two inches in diameter, and six inches stroke, and "the boiler about nine inches diameter). By blowing the "fire it was made to take a few strokes, but required an "enormous quantity of injection water, though it was very lightly loaded by the column of water in the pump. 66 66 66 It "soon occurred that this was caused by the little cylinder exposing a greater surface to condense the steam, than "the cylinders of larger engines did in proportion to their respective contents. It was found that by shortening the "column of water in the pump, the boiler could supply the cylinder with steam, and that the engine would work regu 66 66 66 larly with a moderate quantity of injection. It now "appeared that the cylinder of the model, being of brass, "would conduct heat much better than the cast-iron cylinders |