from coal and other mines, was obviously unfitted for extension to other purposes in which a continuous rotatory motion was desired. By a slight modification of the valves of his engine, Watt was enabled to overcome the difficulty; and in the "double-acting engine," for which we are indebted to his genius, the piston is both raised and depressed by the action of the steam, a vacuum being alternately made above and below the piston. In 1781 he took out a patent for this modification, but his attention had been drawn to it many years before; in fact, while prosecuting his petition for a prolongation of his original patent in 1774, he had exhibited a drawing of the plan to the House of Commons. In this drawing he explained how, after the piston had been pressed by the steam to the bottom of the cylinder, by shutting off the connexion beween the upper part and the boiler, and opening a communication between it and the under side of the cylinder, the steam by this means could be made to raise as well as depress the piston into a vacuous space, which might be made above and below it alternately. For the introduction of this form of engine, by which the dead-weight of the counterpoise was got rid of, and the efficacy of the engine as a general motive power so vastly increased, and the range of its powers so much extended, we are probably indebted to the rivalry which existed between the firm of Bolton and Watt and other engine-makers, and to the machinations which many of them condescended to employ for the purpose of obtaining a share of the public patronage. Holding such an extensive monopoly, a monopoly not only of legal power, but also, it may be said, of mechanical genius, and of a vast experience such as no others could lay claim to, it need not be wondered at that the firm encountered a vast amount of obloquy and reproach from various interested sources, and that angry feelings and bitter animosity on the part of their rival brethren in the trade existed to a large extent. Some notion of the state of matters thus existing may be derived from the statement of a late engineer (whose mind and talents should, we think, have prompted more generous feelings), who declared that, "when men of better judgment had constructed engines as good, or better than their own, they have (i.e. Bolton and Watt) just candour enough to admit the fact, and pride and avarice enough to claim them as their invention;" and who even went the length of trying much "to make it clear that Mr. Watt had no right to any patent whatever !" But this state of matters, however much to be deplored, was not the only thing Bolton and Watt had to contend against their own feelings of rectitude and just principle, which undoubtedly characterised them in all their dealings, bore them up against all the attacks of slander and detraction; but an extensive and powerful combination to wrest from them the pecuniary advantages of their invention touched them in another way, and called forth another and more public reprisal. As already mentioned, the profits derived by Bolton and Watt from their engines was exactly in proportion to the saving which they effected to the proprietors who had them erected. Nothing in commerce could be fairer than this; yet to the discredit of a large number of them, they, forgetting the two-thirds which by the use of the engines were put into their pockets, they grudged the third which the patentees asked for the great benefits thus conferred. By a species of sophistry, which we see often acted upon by men who, in other matters, fulfil to the letter the moral law of the rights of property, they thought it no wrong to apply to

their own use freely, and without consulting the rightful owners, the property which mental labour had created. They covertly, if not openly, therefore, supported a horde of " pirates," who endeavoured to wrest the invention of Watt from his grasp. Bolton and Watt for a length of time took no steps to stop this flood of wrong; but at last it reached to such a height, that a due regard to their own social rights, as well as to the claims of public morality, rendered it imperative upon them to take some public and decided steps to put, at once and for ever, a stop to these proceedings. An engine having been erected on Watt's plan at a mine at Cornwall, an action was begun against Mr. Bull, by whom several of the Cornish miners were represented. The principal plea put in, in defence, was the vagueness and want of precision in the specification, and through this the invalidity of the patent. The judges were divided on this point, and no judgment was given. Advantage, however, having been taken of this, and reckoning on it as a legal defect sustained by the patentees, the attempts to evade the patent rights again became numerous; and further steps, to put a stop to this, were again taken by the patentees. The trial before the Court of King's Bench this time resulted in their favour. The immediate effect of this "Cornish conspiracy," as it has been termed, was doubtless the introduction of the double-acting engine; for Watt, foreseeing the extent to which it could be applied in a vast range of manufacturing operations, was no doubt anxious to occupy this field also, and not to depend altogether on that of Cornish pumping-engines. It was in connection with the double-acting engine that Watt introduced those beautiful and philosophical inventions which we are now about to notice.

66

In the application of the steam-engine to the production of a continuous motion, the first step to be taken was the changing of the reciprocating motion of the piston-rod into a continuous rotatory one. If the reader will turn to pp. 47-49 of the companion treatise to the present volume, Mechanics and Mechanism, in this series, he will there find a description of the method of effecting this purpose by means of what is called a crank." Although the works of philosophy and mechanics published at periods long anterior to the time of Watt and his contemporaries contained illustrations of this contrivance, and although, moreover, evidence of its use could be seen in almost every street in the knife-grinder's wheel (see p. 48, fig 72, Mechanics and Mechanism), or in many houses in the country in the "housewife's spinning-wheel," the animated rivalry which existed between several mechanics who claimed the honour of its discovery, as an important appliance of the steam-engine, is very remarkable; the great importance which was thus attached to its exclusive possession may be viewed, therefore, " as one of the many curious illustrations afforded, in the progress of this machine, of the great value of even an apparently trifling improvement." We may here trace the history of its application to the steam-engine.

In the year 1779, a Mr. Matthew Wasbrough, of Bristol, patented a contrivance by which the balanced beam of the atmospheric engine could produce a rotatory motion. This was effected by the employment of one or more pulleys, wheels, or segments of wheels, to which were fastened ratchets or checks. In another case he shifted a wheel and its axis from one set of teeth to another. A third method was, employing racks with teeth, which tumbled or moved on their own axis or centre; and these

racks he fastened to the working beam or great lever, or they were connected with it by means of chains. "For other purposes, instead of a working beam, he substituted a wheel or pulley, working by racks or chains from the steam piston; and to regulate the motion, he in some cases added a fly." Wasbrough fitted up one of his machines at Birmingham for a Mr. John Pickard. This party was instrumental, however, in introducing a much simpler method of producing rotatory motion; this was by substituting the crank. For this he took out a patent in 1780; and associated with him, in carrying its application into practice, the inventor of the previously mentioned mechanism, Wasbrough. They succeeded in introducing the method of working into several mills.

From Mr. Watt's own statement there appears every reason to conclude, that the idea of using the crank had been borrowed from his factory at Soho. The following is the statement alluded to:

"I had very early turned my mind to the producing continued motions round an axis; and it will be seen, by reference to my first specification in 1769, that I there described a steam-wheel, moved by the force of steam acting in a circular channel against a valve on one side, and against a column of mercury, or some other fluid metal, on the other side. This was executed upon a scale of about six feet diameter at Soho, and worked repeatedly; but was given up, as several practical objections were found to operate against it. Similar objections lay against other rotative engines which had been contrived by myself and others, as well as to the engines producing rotatory motions by means of ratchet-wheels. Having made my reciprocating engines very regular in their movements, I considered how to produce rotative motions from them in the best manner; and amongst various schemes which were subjected to trial, or which passed through my mind, none appeared so likely to answer the purpose as the application of the crank in the manner of the common turning-lathe (an invention of great merit, of which the humble inventor, and even its era, are unknown). But as the rotative motion is produced in that machine by the impulse given to the crank in the descent of the foot only, and behoves to be continued in its ascent by the momentum of the wheel, which acts as a fly, and being unwilling to load my engine with a fly heavy enough to continue the motion during the ascent of the piston (and even were a counterweight employed, to act during that ascent of a fly, heavy enough to equalise the motion), I proposed to employ two engines acting upon two cranks fixed on the same axis, at an angle of one hundred and twenty degrees to one another; and a weight placed upon the circumference of the fly at the same angle to each of the cranks, by which means the motion might be rendered nearly equal, and a very light fly only would be requisite. This had occurred to me very early; but my attention being fully employed in, making and erecting engines for raising water, it remained in petto until about the year 1778 or 1779, when Mr. Wasbrough erected one of his ratchet -wheel engines at Birmingham, the frequent breakages and irregularities of which recalled the subject to my mind, and I proceeded to make a model of my method, which answered my expectations; but having neglected to take out a patent, the invention was communicated, by a workman employed to make the model, to some of the people about Mr. Wasbrough's engine, and a patent was taken out by them for the application of the crank to steam-engines. This fact the said

workman confessed; and the engineer who directed the works acknowledged it, but said, nevertheless, the same idea had occurred to him prior to his hearing of mine, and that he had even made a model of it before that time; which might be a fact, as the application of a single crank was sufficiently obvious. In these circumstances I thought it better to endeavour to accomplish the same end by other means than to enter into litigation; and if successful, by demolishing the patent, to lay the matter open to every body. Accordingly, in 1781, I invented and took out a patent for several methods of producing rotative motions from reciprocating ones, amongst which was the method of the sun-and-planet wheels.

"This contrivance was applied to many engines, and possesses the great advantage of giving a double velocity to the fly; but is, perhaps, more subject to wear, and to be broken under great strains, than the crank, which is now more commonly used, although it requires a fly-wheel of four times the weight, if fixed upon the first axis. My application of the double engine to these rotative machines rendered unnecessary the counter-weight, and produced a more regular motion; so that, in most of our great manufactories, these engines now supply the place of water, wind, and horsemills; and, instead of carrying the work to the power, the prime agent is placed wherever it is most convenient to the manufacturer.

"I do not exactly recollect the date of the invention of the double engine; but a drawing of it is still in my possession, which was produced in the House of Commons when I was soliciting the act of parliament for the prolongation of my patent in 1774 and 1775. Having encountered much difficulty in teaching others the construction and use of the single engine, and in overcoming prejudices, I proceeded no further in it at that time; nor until, finding myself beset with a host of plagiaries and pirates in 1782, I thought it proper to insert it and some other things in the patent above mentioned."

The mechanism of the "sun-and-planet" wheels above alluded to, for the purpose of obtaining continuous rotatory motion from the reciprocating movements of the piston-rod, the reader will find explained in pp. 70-77, fig. 142, Mechanics and Mechanism. The method employed in the singleacting engine for connecting the piston-rod with the end of the working beam was obviously (see p. 84, fig. 164, Mechanics and Mechanism) incapable of being applied to the double-acting engine; where the piston was pushed up by the pressure of the steam, not pulled up by the counterpoise, as in the single-acting engine. The

mechanism which Watt at first employed will be understood from an inspection of the diagram in fig. 26. Let a be the piston-rod, furnished with a rack at its upper end,. working into teeth of a segment fixed on the rod of the working beam; as the pistonrod moved up and down, the teeth actuated those of the segment, and made the beam c reciprocate. In working expansively, a small fly-wheel, shown by the dotted lines d, was applied to the mechanism; on the centre of this was fixed a small toothed wheel, which was worked by the rack, of

fig. 26,

E

the piston; the fly moved alternately from side to side as the piston ascended and descended. This contrivance was found possessed of many disadvantages on being carried into practice, especially in large engines, not the least of which was the great noise and jar occasioned by the teeth of the rack and segment engaging as the direction of motion of the piston-rod was changed. Some more elegant contrivance was therefore desiderated, and Watt's genius and mechanical ability no more failed him here than at other and more trying times; and the result of his cogitations was the production of that most beautiful and philosophical mechanism known as the " parallel motion." The principle of this contrivance the reader will find in p. 84, fig. 165, Mechanics and Mechanism; and an exemplification of its arrangement as carried out in practice in the diagram,

fig. 27.

fig. 63, p. 44 of the same work. The diagram here given, fig. 27, illustrates the arrangement of the parallel motion as first applied to the double-acting engine. Let a a be the working beam, ƒ is the pistonrod, g the air-pump rod, bed the links. Other exemplifications of this motion will be found in the diagrams in succeeding chapters of this volume.

In order to render the doubleacting engine as perfect in its arrangements as possible, and independent of the attention of careless workmen, Watt introduced a method by which the engine itself This he effected by adopting what is now known as the "governor," a description of which will be found in pp. 87-89, Mechanics and Mechanism, and illustrations showing its application to the opening and closing of the valve by which the steam is admitted to the engine. In the single-acting engines the throttle-valve was opened and shut by hand, a

regulated its own motion.

sufficient uniformity of motion being thus obtained. A view of the valve is