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“ and of his knowledge; for, indeed, the management of “ steam to perfection is the employment of an accomplished “ philosopher.

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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 knowledge 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

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 prin

ciple, 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,

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

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" 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.

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“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.”

CHAPTER VII.

MR. WATT'S NARRATIVE OF THE INVENTIONS DESCRIBED IN HIS SPECIFICA

TION OF 1769, GIVEN IN HIS NOTES ON ROBISON FURTHER ANECDOTES
OF HIS INVENTION OF THE SEPARATE CONDENSER HIS NARRATIVE
ENTITLED A PLAIN STORY."

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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

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

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Robison's Mechanical Works,' edited by Sir David Brewster.

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“ turned by hand, it was easy to see how it could be done by “ the machine itself, and to make it work with perfect regu

larity. 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. 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 regularly 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

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of larger engines, (generally covered on the inside with a

stony crust), and that considerable advantage could be

gained by making the cylinders of some substance that “ would receive and give out heat slowly. Of these, wood “ seemed to be the most likely, provided it should prove

sufficiently durable. A small engine was, therefore, con

structed, with a cylinder six inches diameter, and twelve “ inches stroke, made of wood, soaked in linseed oil, and “ baked to dryness. With this engine many experiments

were made; but it was soon found that the wooden cylinder “ was not likely to prove durable, and that the steam con“densed in filling it still exceeded the proportion of that “ required for large engines, according to the statements of

Desaguliers. It was also found that all attempts to produce "a better exhaustion by throwing in more injection, caused a

disproportionate waste of steam. On reflection, the cause “ of this seemed to be the boiling of water in vacuo at low “ heats, a discovery lately made by Dr. Cullen and some “ other philosophers, (below 100°, as I was then informed); “ and consequently, at greater heats, the water in the cylinder “ would produce a steam which would, in part, resist the pressure of the atmosphere.

By experiments which I then tried upon the heats at “ which water boils under several pressures greater than that “ of the atmosphere, it appeared that when the heats pro“ ceeded in an arithmetical, the elasticities proceeded in some “ geometrical ratio; and, by laying down a curve from my " data, I ascertained the particular one near enough for my

purpose. It also appeared, that any approach to a vacuum “ could only be obtained by throwing in large quantities of

injection, which would cool the cylinder so much as to

require quantities of steam to heat it again, out of propor“ tion to the power gained by the more perfect vacuum; and " that the old engineers had acted wisely in contenting them“ selves with loading the engine with only six or seven pounds “ on each square inch of the area of the piston. It being “ evident that there was a great error in Dr. Desaguliers' “ calculations of Mr. Beighton's experiments on the bulk of

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