fice, no part is condensed until the whole effect has been obtained in the cylinder; and when it has acted there, it is fo condenfed in the feparate vessel that no resistance remains: Accordingly, the barometer proves a vacuum, nearly as perfect as by the exhauftion of the air-pump. The whole of the team and heat is usefully employed; and the contrivance appears scarcely to admit of improvement.

Such is the history of this valuable invention, which we have extracted from Dr Black and Professor Robison's testimonials, who were privy to Mr Watt's discovery; as well as from some early letters of his own to confidential friends, to, which we have had access.

We have entered thus minutely into the subject, from a desire to do that justice which is due to Mr Watt, by showing that this great improvement was not the effect of accident, or of casual observation, but the result of deep reflection, of great ingenuity, and much philosophical investigation.

It did not, at the early period we have been speaking of, escape him, that great benefit might be derived from the direct application of the power of steam to driving mills, instead of using it to raise water to act on a wheel, as had heretofore been done; and with this view, he invented and executed the model of a steam wheel, for giving a circular motion to an axis.

His occupations in the business of a civil engineer which he had now taken up, perhaps also the indifferent state of his health, his want of funds, and his apprehension of the prejudices and opposition he might have to encounter, prevented his applying for a patent for the invention we have described, until the year 1769. He had, we believe, previous to, or about that time, erected an engine for his friend Dr Roebuck of Kinneil, near Borrowstounness, which, upon a large scale confirmed his expectations; the proportionate saving of fuel being from two thirds to three fourths of that of engines on Newcomen's construction. Dr Roebuck, whose spirit for enterprise and improvement in the arts is well known, foresaw all the advantages likely to result from this invention, and became associated in the prospects which it opened. But some of his own projects having failed, he soon after disposed of his interest to Mr Boulton the celebrated founder of Soho manufactory, with whose aid Mr Watt, in 1774, solicited and obtained an act of Parliament for the extension of the term of his patent for twenty-five years; and the business of making steam-engines was soon after commenced by the firm of Boulton and Watt.

In executing his invention on a large scale, Mr Watt felt the necessity of improving the construction of several of the parts of New comen's engine. With this view, he induced Mr Wilkinson

X 4

to

to erect an apparatus for boring the cylinders with more precision than had hitherto been done; he adopted a new mode of constructing the piston and screwing down the packing, and secured the rod in the piston in a more perfect manner; he introduced puppet valves into the steam boxes or nozles, instead of the old sliding regulators; he used better means of opening these valves, and added various improvements in the working gear; he suspended the working beam, so that the centre of motion was below the centre of gravity, instead of being above it, as in the old engines; and he improved the mode of setting the boilers on the grates, as well as the apparatus for keeping the boilers regularly supplied with water.

He introduced also into some of his earliest reciprocating engines, the principle of using the steam to act expansively, which he had discovered so early as the 1769% year

*

The character of his engines being now fully established by the erection of several large ones in Cornwall, and other parts of the kingdom, Mr Watt recurred to his favourite idea of applying the power of steam to produce motions round an axis.

He had, upon trial, found practical objections to the steam wheel described in his patent; and a second one which he had contrived was also given up: for, upon very full consideration of the subject, it appeared to him, that the object would be better attained by deriving the rotative motion from the rectilinear motion of the piston in the reciprocating engine.

Something of this kind had been attempted by others. An atmospheric engine had been employed at Hartley coalery, in Northumberland, as early as 1768, to draw coals out of a pit. It had a

toothed

*This appears by a letter from him to his friend the late Dr Small of Birmingham, dated Glasgow, 28th May, 1769; of which the following is an extract.

'I mentioned to you a method of still doubling the effect of the steam, and that tolerably easy, by using the power of steam rushing into a vacuum, at present lost. This would do little more than double the effect, but it would too much enlarge the vessels to use it all. It is peculiarly applicable to wheel engines, and may supply the want of a condenser where force of steam only is used: for, open one of the steam valves, and admit steam until one fourth of the distance between it and the next valve is filled with steam; shut the valve, and the steam will continue to expand, and to press round the wheel with a diminishing power, ending in one fourth of its first exertion. The sum of the series you will find greater than one half, though only one fourth steam was used. The power will indeed be unequal; but this can be remedied by a Ay, or several other ways,

toothed sector on the end of the working beam, working into a trundle, which, by means of two pinions with ratchet wheels, produced a rotative motion, in the same direction, by both the ascending and descending stroke of the arch;, and, by shifting the ratchets, the motion could be reversed at pleasure. This engine had no fly-wheel, and went sluggishly and irregularly. Who the inventor was, we do not know.

t

A patent was taken out in 1769, by a gentleman of the name of Stewart, for an engine which produced a rotative motion, by a chain going round a pully, and also round two barrels furnished. with ratchet wheels, with a weight suspended to the free end of the chain, which served to continue the motion during the return of the engine. In 1778, Mr Matthew Washbrough also obtained a patent for communicating a rotative motion from the steam engine, by a method which was virtually the same as that at Hartley; only, he had added a fly-wheel, which we believe was then for the first time employed in the steam engine, though it is evident, from the letter we have quoted from Mr Watt to Dr Small, that the former had conceived the idea long previous to: this period. Two or three of these engines were erected; but, owing to the defective mode of communicating the motion, were subject to such irregularities and accidents, as rendered them of little use.

The idea of communicating motion from the beam of the steam engine to a crank, in the same manner as is done in the common foot-lathe, had, as we are informed, early occurred to Mr Watt; but we believe he did not seriously set about reducing his ideas to practice until the year 1778 or 1779. In the first model he then made, in order to equalize the power, two cylinders, acting upon two cranks were fixed upon the same axis, at an angle of 120° from each other; and a weight was placed upon the circumference of the fly-wheel, at an angle of 120° from each of the cranks; which weight was to be so adjusted, as to act when neither of the cranks could do so, and consequently to render the power nearly equal. This model performed to satisfaction; but Mr Watt having neglected to take out a patent immediately, the essential part of the contrivance was communicated, as we understand, by a workman employed to make the model, to the persons engaged about one of Washbrough's engines; and a patent was taken out for the application of the crank by the engineer there employed. This did not dishearten Mr Watt; and, without troubling himself with setting aside a patent which, so ong as it continued attached to the common atmospheric engine, uld do him little harm, he set about other modes of effecting same thing; and, in 1781, took out a patent for several new

methods

1

methods of applying the vibrating or reciprocating motion of steam engines to produce a continued rotative motion round an axis; one of which was that beautiful contrivance of the revolving motion of one wheel round another. These and the crank were indifferently used in his engines, without any molestation on the part of the piratical patentee.

This, however, was only a part of what Mr Watt saw to be necessary, in order to perfect this application of the steam-engine. The steam had hitherto been used only to press down the piston, which was returned by a weight at the opposite end of the beam, so that the power of the steam may be said to have been inactive during that period. Mr Watt remedied this, by applying the power of the steam to press the piston down, as well as to press it up, thus forming alternately a vacuum above and below the piston. This he called the double engine; and, in fact, it doubled the power exerted within the same cylinder. He had long had in his mind the idea of this improvement; and had even produced a drawing of it to the House of Commons in 1774, at the time he procured the act to prolong his original patent; but the first he executed was, we believe, at Soho in the year 1781 or 1782, and the first public exhibition of it at the Albion Mills a few years later.

About the same period, finding double chains or racks and sectors very inconvenient for communicating the motion of the piston rod to the angular motion of the beam, he invented and applied what has been called the parallel motion, one of the most ingenious and most perfect contrivances in mechanics.

To prevent irregularities in the speed of the engine, arising from variations in the quantum of power used at different intervals in the works to which it was applied, he made an application of the centrifugal force of what is called the governor, (before used in wind and water mills), to regulate the admission of the steam; by this means keeping the engine always at an uniform velocity, and diminishing the consumption of steam in proportion to the power exerted; thus giving the finishing stroke to the perfection of the motion of this machine, and rendering its regularity nearly correspondent with that of the pendulum of a clock,

These inventions are detailed amongst many other contrivances, both relative to steam engines, and the applications of their power, in two patents, dated 1782 and 1784. Some of these are highly ingenious: a few may have been first ideas, not yet reduced to practice; and others were no doubt inserted for the purpose of guarding against evasion.

Such is the general outline of the improvements introduced by Mr Watt into the steam engine; but it would lead us too far, to go into the detail of the applications of this power, or to enu

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merate the advantages which the country has derived from it. We shall content ourselves with observing, that by means of it, many of the principal mines in the kingdom have been kept open, and rendered productive, when otherwise they must have ceased to work. By the construction of the rotative engine, a new era has been introduced into the manufactures of the kingdom; and it has been in a great measure owing to it, that those manufactures have been carried to an extent unprecedented in the history of nations. The merit and success of these improvements, however, created (as success and merit will always do) an host of imitators and detractors, from whom Messrs Boulton and Watt, during the greater part of the term of their exclusive privilege, experienced the most harassing and obstinate opposition.

Having given this short history of Mr Watt's improvements, we shall proceed to consider the view that Mr Gregory and his associate have taken of the same subject. These gentlemen have both animadverted with great severity, and, we think, with very little reason, on the mode adopted by Boulton and Watt for describing the force of the steam engine by a comparison with the power of horses. What is called,' say they, the horses' power, is of so fluctuating and indefinite a nature, that it is perfectly ridiculous to assume it as a common measure by which 'the force of steam engines and other machines should be appre'ciated.' II. pp. 78. 357.

Now, we are ready to admit, that if nothing more definite were said of any engine than that it did the work of a certain number of horses, this would not convey an idea of its power sufficiently accurate for many of the purposes of science. It might, however, be accurate enough for many of the purposes of common life. Now, if the thing wanted was an approximate and popular standard of comparison, such as might be intelligible to every body, and sufficiently exact for ordinary purposes, it is certain, that a more convenient expression could not easily be found than that which is here referred to. Prior to Mr Watt's application of the steam engine to produce rotative motion, the great manufactories of the kingdom had their mili-work set in motion by the agency of water, of wind, or of horses; and the latter had, for many years, been almost exclusively employed in the breweries and distilleries of the metropolis. It was therefore natural for one who wished to substitute the power of steam for the power of horses, to state the number of the latter to which the new power, under given conditions, would be equivalent; and it probable that Boulton and Watt felt that such a mode of comison would be more intelligible to common apprehensions than re accurate and scientific formula. It gave the power of an

engine