mist's great injection-syringe for a cylinder,) the piston-rod passed through a collar of leathers in the cover of the cylinder, and the steam was admitted through another aperture in the same cover, and it escaped into the condenser by a similar aperture in a cover on the other end of the cylinder. Long after this I found that the little apparatus which I saw on his knee, and which he shoved under the table with his foot, was the condenser in this first experiment. I discovered that I had not comprehended the whole contrivance so completely as I imagined. But though I was ashamed of my ignorance, my vanity would not let me acknowledge it, and I took circuitous ways of learning more exactly the precise state of the engine. I was living in Edinburgh during the summer of 1767, near Dr. Black, in order to prepare myself for my arduous task, and in my 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 could 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 expense 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, 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 contrivance 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 conviction of his conscience, must acknowledge that the whole contrivance was perfect in Mr. Watt's mind in his very first trial. PROFESSOR ROBISON'S NARRATIVE. 57 "During the two following winters, notwithstanding Mr. Tatt's frequent absence from Glasgow, and my constant occupaon with my chemical lectures, I had many opportunities of conersing with him, and learned all his difficulties and embarrassients. He struggled long to condense with sufficient rapidity ithout injection, and exhibited many beautiful specimens of inenuity and fertility of resource. Many pretty schemes occurred › him for a rotatory engine. Some of these I am sorry to find hat he has neglected. I am confident of their complete success, nd though I agree with him in thinking that his engine with a ouble stroke is superior to them all, I should have been glad that hey had been executed, because they would have given a most rilliant specimen of his wonderful ingenuity and of his knowldge; for, indeed, the management of steam to perfection is the mployment of an accomplished philosopher. "During my residence in Glasgow I was in habits of coninual intimacy with Mr. Watt. All who knew him know that it s his greatest pleasure to communicate his knowledge to those vho have a relish for it. I have reason to think that he never, rom any kind of jealousy, concealed anything from me. From he 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 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 allowing 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, any 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, 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, confirmed it by experiment. Dr. Black, the first philo sophical 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." : CHAPTER VII. MR. WATT'S NARRATIVE OF THE INVENTIONS DESCRIBED IN HIS SPECIFICATION OF 1769, GIVEN IN HIS NOTES ON ROBISON-FURTHER ANECDOTES OF HIS INVENTION OF THE SEPARATE CONDENSER-HIS NARRATIVE ENTITLED A PLAIN STORY." THE account given by Mr. Watt himself, in his Notes on Professor Robison's Dissertation on Steam-engines,* is as follows: "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. "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 communication 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, * Robison's Mechanical Works, edited by Sir David Brewster. 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 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 specification 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 prevented 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. 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 |