In the drawing produced by Mr. Watt before the House of Commons in 1774, he shewed a method of applying the steam to press on both sides of the piston. This was brought forward by a Dr. Falck in 1779 as a new idea. The Doctor published a pamphlet enumerating the advantages of this kind of engine, stating it to be equal to perform double the work of the usual lever Engines of the same size; but he does not appear to have proved the assertion by constructing a model.

The only novelty in the Doctor's scheme was the way he produced this double action. He proposed using two cylinders fitted with pistons, connected with the same boiler. Steam was introduced under both pistons, and a vacuum was formed by its condensation, by the same methods as those practised in the Atmospheric Engines. Only, that while the steam was admitted from the boiler into one cylinder, it was prevented from flowing into the other by a regulator. The piston-rods were kept (by means of a wheel fixed into an arbour) in a continual ascending and descending motion, in the same manner as the rods of a common air-pump, by which they move a common axle, having another wheel affixed to it; this wheel moves the pump rods, in the same alternate directions as the piston rods, by which the pistons of the pumps are kept in constant action. "We have seen both the Atmospheric and single Engine of Mr. Watt working in this arrangement, but his double Engine is much preferable." *

*Farey in Rees' Cyclopedia, art. Steam Engine.

About this time Mr. Watt's condensing Engine was introduced into France. In 1779 a M. Perrier, who was associated with his brother in the manufacture of machines at Paris, was commissioned by a company then recently established to supply that city with water, to proceed to England and to endeavour to procure a Steam Engine manufactured on the best principle; those which were constructed in France being exceedingly defective in arrangement and workmanship. M. Perrier ultimately succeeded in purchasing from Bolton and Watt an engine in which were combined their improvements. By the sanction of the English Government, it was sent to France, and erected by MM. Perrier at Chaillot, near Paris. The French engineer Prony, in his elaborate work on the Steam Engine, describes this identical engine; is minute even to prolixity in his enumeration of the peculiarities of its construction and its economical advantages; yet with a detestable illiberality and utter disregard to every thing like candour or truth, he attributes all the merit of the improvements in the Chaillot Engine -to his friend Perrier, the person who merely put together the pieces he had brought from Soho, without once alluding to Mr. Watt's labours, or once mentioning his name in his quarto book, as being the person who constructed it,* or even as having

* "Mr. Watt was too inoffensive a man to attack Prony; and when the injustice done was mentioned to him in 1810 or 1811, when he was in London, he said that it was true, but that he had seen de Prony, who had made a sort of an apology, or entered

made any improvement in steam meehanism! This attempt to award to his countryman the honour due to another is entitled to still more unqualified reprobation, from M. Prony's personal knowledge of the whole transaction; for we believe he was the person under whose immediate direction Perrier was sent to England, and who was in correspondence with that gentleman when he was residing at Birmingham, during the execution of the Chaillot Engine; and who superintended Perrier when he put the Engine together in France.*

The Engine invented by Mr. John Hornblower presents no novelty in its principle or even in the

into an explanation. Mr. Watt did not appear to wish to enter on the subject." Playfair's Memoir. Nothing more strongly marks the equanimity and greatness of Mr. Watt's mind, than his indifference to the attempts of those who would detract from his claim as an inventor. Prony, however, never had either the candour or the grace to make an apology through the same medium that he attempted to do the injury.

"Prony's work," says Mr. Farey, in Rees' Cyclop. "is little more than a description of the plates. These engines are not the best specimens of Mr. Watt's invention; they were all constructed in France by M. Perrier of Paris, who, in 1780, erected a large engine at Chaillot, to pump up the water of the Seine for the supply of the town, and another of smaller dimensions on the opposite side of the river at Gros Caillou. These engines are still (1817) at work, and I visited them in 1814. They are upon the plan of Mr. Watt's first Engines, though, for want of some attention to minute particulars, they do not produce any great effects. M. Perrier had visited England to obtain the requisite instructions for making these engines." "Frenchmen," says Playfair, "are at great pains to conceal the origin and country of the Chaillot Engine;" they have even succeeded in concealing it from Mr. Farey.

arrangement, combining Mr. Watt's expansion Engine with the two cylinders of Dr. Falck. The steam, after it was admitted to elevate or depress the piston in the first cylinder, was then admitted to perform the same action in the second cylinder, which in dimension considerably exceeded the first cylinder, and thus was allowed to operate by its expansion to raise the piston. Our Thirtieth Figure will give a general idea of this contrivance, without shewing any of the smaller parts, which, as being similar to those of common engines, and not to confuse the Figure, are omitted. A, the small cylinder, having a piston, a, attached by a rod to the lever-beam, this cylinder communicates with the boiler by the pipe c Other pipes and cocks, X, Y, (Hornblower arranged his parts more compactly, but, in order to explain this machine in one Figure, we arrange them somewhat differently,) are attached to each cylinder, and open a communication with both sides of their pistons. E, is a pipe with a stop cock, which opens a communication between the bottom of the small cylinder A, and the top of the large cylinder B. F, is a pipe and cock leading to the condenser G, its pump H, placed as usual in cold water; these are the same as those in Mr. Watt's Engines. Steam comes from the boiler by the pipe c, and its flow may be prevented by the cock K. We will now suppose the cock K, to allow the passage of steam from the boiler, and the cocks E, X, Y, to be all open, which will allow the steam to fill both cylinders. The cocks x and y must now be closed, E and K remaining open.