der was divided into two chambers quite distinct from each other --that above and that below the piston. Now, in addition to the former communications between the cylinder and the boiler and condenser, a tube was made to connect the boiler with the upper chamber, so as to introduce steam above the piston. This steam, by its elastic force, and no longer the atmosphere by its pressure, drove down the piston when the vacuum had been formed by the condensation of the steam beneath; and as soon as the descending stroke was complete, the turning of a cock could admit steam from the boiler equally into both chambers, thus restoring the balance, and enabling the piston to ascend, as before, by the mere counterpoise of the beam. The engine with this improvement Watt named the Modified Engine; it was, however, properly the first real steam-engine; for in it, for the first time, steam, besides serving to produce the vacuum, acted as the moving force. In this substitution of steam as the moving force instead of the atmosphere, there was, moreover, this peculiar advantage—that whereas the force of the atmosphere was uniform, and could, in no case, exceed fifteen pounds on every square inch of the piston's surface, the force of the steam could, within certain limits, be varied.

Another improvement less striking in appearance, but of value in economising the consumption of fuel, was the enclosing of the cylinder in a jacket or external drum of wood, leaving a space between which could be filled with steam. By this means the air was prevented from acting on the outside of the cylinder so as to cool it. A slight modification was also necessary in the mode of keeping the piston air-tight. This had been done in Newcomen's engine by water poured over the piston; but in the closed cylinder this was obviously impossible; the purpose was therefore effected by the use of a preparation of wax, tallow, and oil, smeared on the piston-rod and round the piston-rim.

The improvements which we have described had all been thoroughly matured by Mr Watt before the end of 1765, two years after his attention had been called to the subject by the model of Newcomen's engine sent him for repair. During these two years he had been employing all his leisure hours on the congenial work, performing his experiments in a delft manufactory at the Broomielaw quay, where he set up a working model of his engine, embodying all the new improvements, and having a cylinder of nine inches diameter. One would anticipate, as M. Arago remarks, that when the fact of the construction of so promising and economical an engine was made generally known, "it would immediately displace, as a draining apparatus, the comparatively ruinously expensive machines of Newcomen. This, however, was far from being the case. Watt's grand invention and most felicitous conception, that steam might be condensed in a vessel quite separated from the cylinder, was completed in the year 1765; and in two years scarcely any progress

was made to try its applicability upon the great scale." Watt himself did not possess the necessary funds for that purpose. "At length," says Lord Brougham, "he happily met with Dr Roebuck, a man of profound scientific knowledge, and of daring spirit as a speculator. He had just founded the Carron iron-works, not far from Glasgow, and was lessee, under the Hamilton family, of the Kinneil coal-works." Such a man, so extensively employed in engineering, was precisely the person to introduce Watt's invention into practice; and accordingly a partnership was formed between him and Watt, according to the terms of which he was to receive two-thirds of the profits in return for the outlay of his capital in bringing the new machines into practice. A patent was taken out by the partners in 1769, and an engine of the new construction, with an eighteen-inch cylinder, was erected at the Kinneil coal-works with every prospect of complete success; when, unfortunately, Dr Roebuck was obliged by pecuniary embarrassments to dissolve the partnership, leaving Watt with the whole patent, but without the means of rendering it available.

WATT'S OCCUPATIONS AS A GENERAL ENGINEER-HIS

PARTNERSHIP WITH MR BOULTON OF SOHO.

Watt, rather than apply to the money-lenders for funds, which they would very probably have been glad to invest in so hopeful a speculation, devoted himself for some time exclusively to the proper business of his profession as a civil engineer, allowing his steam-engine model to lie like mere lumber in the Broomielaw delft work. Between the years 1769 and 1774 he was employed in various engineering enterprises of great importance" the extensive operations of which Scotland then became the scene giving," says Lord Brougham, "ample scope to his talents. He was actively engaged in the surveys, and afterwards in the works for connecting by a canal the Monkland coal-mines with Glasgow. He was afterwards employed in preparing the canal, since completed by Mr Rennie, across the isthmus of Crinan; in the difficult and laborious investigations for the improvement of the harbours of Ayr, Greenock, and Glasgow; in improving the navigation of the Forth and Clyde; and in the Campbeltown Canal; besides several bridges of great importance, as those of Hamilton and Rutherglen." "What Johnson said of Goldsmith, may with equal justice be applied to Watt-' he touched not that which he did not adorn.' In the course of his busy surveys his mind was ever bent on improving the instruments he employed, or in inventing others, to facilitate or correct his operations. During the period of which we have been speaking, he invented two micrometers, for measuring distances not easily accessible,

* Memoir of Watt in Lord Brougham's " Men of Letters of the Reign of George III."

such as arms of the sea. Five years after the invention of these ingenious instruments, one Mr Green obtained a premium for an invention similar to one of them from the Society of Arts, notwithstanding the evidence of Smeaton, and other proofs, that Watt was the original contriver.

"In 1773, the importance of an inland navigation in the northern part of Scotland between the eastern and western seas became so great, that Mr Watt was employed to make a survey of the Caledonian Canal, and to report on the practicability of connecting that remarkable chain of lakes and valleys. These surveys he made, and reported so favourably of the practicability of the undertaking, that it would have been immediately executed, had not the forfeited lands from which the funds were to be derived been restored to their former proprietors. This great national work was afterwards executed by Mr Telford, on a more magnificent scale than had been originally intended."

At the end of the year 1773, Watt was left a widower by the death of his wife in Glasgow while he was absent on his survey of the Caledonian Canal. Two children, a son and a daughter, survived their mother. This event would probably have the effect of withdrawing his attention still more from his steam inventions. For five years his patent " for methods of lessening the consumption of steam, and consequently of fuel in the steamengine," had been running, without bringing him any returns, the dissolution of his partnership with Dr Roebuck having thrown the entire risks of introducing the new machine into practice upon himself, and either his cautious temperament, or his actual want of means, preventing him from abandoning the certainties of his profession for the sake of pushing his steamengine into public notice. This indifference is certainly in itself not entitled to be considered a merit; we point it out merely as characteristic.

At length, in 1774, Mr Watt entered into a partnership most fortunate for himself and for the world. This was with Mr Matthew Boulton of the Soho foundry near Birmingham-a gentleman of remarkable scientific abilities, of liberal disposition, and of unbounded enterprise, who, having his attention called to the improvements on Newcomen's steam-engine effected by the Glasgow surveyor, immediately formed a connexion with him, sharing the patent as Dr Roebuck had formerly done.

Almost the first business of the partners was to procure a prolongation of Watt's patent, which, having commenced in 1769, had but a few years to run. Whether because the value of Watt's improvements had, by the mere course of time, become more generally recognised than at first, or because the enthusiasm with which so well-known an individual as Mr Boulton patronised them, roused many parties to a sense of their importance, it was only after a very keen opposition in parliament, that the extension of the patent for twenty-five years was obtained. At the

head of those who opposed the renewal of the patent in the House of Commons was the celebrated Edmund Burke; the opponents out of the House were the engineers and miners whom the patent would prevent from employing the engine without paying the inventor for permission to do so.

The extension of the patent having been procured, the partners began to construct, at their manufactory at Soho, draining machines of the largest dimensions, which immediately supplanted Newcomen's engines in all the mining districts. The bargain which the partners made with those mine proprietors who applied for permission to use the improved engine, was certainly the most reasonable that could have been expected. They stipulated for receiving “a third part of the value of the coal saved by the use of the new engine." Yet this agreement brought ample profits to the partners, as may be judged from the fact, that the proprietors of the single mine of Chasewater in Cornwall, where three pumps were employed, commuted the proposed third of the coal saved into £2500 a-year for each of the engines. Thus the saving effected by one engine amounted to at least £7500, which had been expended formerly in waste fuel. As there was a possibility that, if the mine proprietors had been left to estimate for themselves the value of the saving, they might cheat the partners of their fair dues, Watt rendered himself independent of them by confiding the duty of rendering an account to a meter, invented on purpose, and which, kept in a box under a double lock, registered every stroke of the engine.

As the engine was one of large dimensions, it was scarcely possible to pirate it secretly; but so numerous were the attempts made to plagiarise it, or, by ingenious ways, to infringe the patent right, that Messrs Watt and Boulton were almost perpetually engaged in lawsuits to defend their property. In several cases, the opposition which Mr Watt experienced on account of his defending his rights, amounted to positive persecution--to attacks on his character. These attacks, however, failed; and in their lawsuits the partners were uniformly successful. "I have been so beset with plagiaries," says Mr Watt in one of his letters, "that if I had not a very distinct recollection of my doing it, their impudent assertions would lead me to doubt whether I was the author of any improvement on the steam-engine."

As the foundry at Soho was one of the largest establishments in Great Britain, Watt's new position, as a partner with Mr Boulton, was one of great wealth and consequence. He had hardly entered upon it when, in the year 1775, after two years of widowhood, he married Miss Macgregor, the daughter of a rich Glasgow merchant.

The first consequences of the introduction of Watt's improved steam-engine into practice was to give an impulse to mining speculations. New mines were opened; and old mines, which could not be profitably worked when taxed with such a consump

tion of fuel for draining as Newcomen's engines required, now yielded a return. This was the only obvious consequence at first. Only in mines, and generally for the purpose of pumping water, was the steam-engine yet used; and before it could be rendered applicable to other purposes in the arts-before it could promise, even to the most sanguine expectation, to perform such a universal part in machinery as that which we now witness it performing, the genius of Watt required once again to stoop over it, and bestow on it new creative touches.

IMPROVEMENTS RENDERING THE STEAM-ENGINE APPLICABLE FOR GENERAL PURPOSES.

Any one on considering the steam-engine, will perceive that the original motion in it, and the source of all others, is that of the piston up and down in the cylinder. It is by connecting the piston-rod with other pieces of machinery through a beam that the work is done. Now, in the draining-engine the piston-rod was attached to the beam by a flexible chain. Where the purpose was the mere pumping of water, the inconvenience of this was not so great; but to render the steam-engine useful for other purposes, it was necessary to do away with the flexible chain, and connect the piston-rod with the end of the beam by some rigid communication. Watt effected this by that most graceful and beautiful invention, the sight of which in operation produces a feeling of pleasure, like that derived from contemplating a fine work of art the parallel motion. At the end of the beam of a steam-engine may be observed a curious jointed parallelogram, with the piston-rod attached to one of its angles. When the engine is in action, if the movements of this parallelogram be watched attentively, it will be perceived that while three of the angles of the parallelogram move in small circular arcs, the fourth-that to which the piston-rod is attached-is so pulled upon by opposite forces, that although tending to move in a curve, it moves in a straight line. This result depends on a very recondite mathematical principle; the contrivance, however, practically, is one of the most simple imaginable. "I myself," says Watt, speaking of his first trial of the parallel motion, "have been much surprised with the regularity of its action. When I saw it in movement, it afforded me all the pleasure of a novelty, and I had quite the feeling as if I had been examining the invention of another."

Another improvement, which, in point of the additional power gained, was more important than the parallel motion, and which indeed preceded it in point of time, was the Double-acting Engine. In the steam-engine, so far as we have yet described it, the whole force consisted in the downward stroke; in the depression of the piston in Newcomen's engine by the atmosphere; and in Watt's improved engine by the steam admitted into the upper chamber of the cylinder. When the piston had reached the bottom