This is certainly a more skilful contrivance than either of the preceding ; but still the loss of steam, and, consequently, of &el, must be considerable Notwithstanding its plausible features, the engine was never carried into prac tical execution ; and Mr. Watt subsequently devised another roftryengine, which i is included in a patent obtained by him in 1784 : upon trial, however, it was Lund to have little or no power; and, therefore, a description of it is =nem sary. His attempts to produce an effective machine on this principle, were undoubted failures ; but still they opened up a path which led, and may lead, to other and more successful efforts by other engineers.
We shall close the narrative of Mr. Watt's inventions by a very brief notice of his dowbk-acting engine. The first engine of this kind, by which the machinery should be impelled equally in ascending and descending, was pro posed in 1779 by Dr. Falc, in a published account of a machine which, with the same quantity of &el, and in an equal space of time he suggested might be made to raise above double the quantity of water raised by any leveres of the same dimensions. It would appear, however, that Mr. Watt had previously contemplated an action of this kind, and had actually explained produced a drawing of it to the House of Commons, in 1774, upon the occa sion of his petition for a prolongation of the term of his patent. In that explanation he showed, that after the piston had been pressed by the steam to the bottom of the cylinder, by shutting off the connexion between 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; and thus, by a slight alteration in the office of his valves, and the introduction of another, a new and valuable action of his engine might be obtained, which should not only free it from the dead weight of counterpoises that bad previously encumbered the invention, but add most importantly to its efficacy. • Our limits are too restricted to describe this excellent modification of the single-impulse engine, nor, indeed, is it actually necessary. The reader, who has made himself acquainted with the details before given, will readily con ceive a manner of effecting it besides, the notices that will follow of the improvements made by other eminent persons, will necessarily involve parti culars which, of themselves, will supply the deficiency.
The first machine on this principle was executed somewhere about the year 1781, and the first public exhibition of it a few years after. In the patents of 1782 and 1784 the invention of the parallel motion before alluded to, with other inge nious contrivances, and the application of the governor are specified ; contrivances that, by diminishing the consumption of steam and of fuel, keeping the engine always at a uniform velocity, and rendering its regularity permanent and easy, completed the great achievements of this extraordinary man.
His reputation has been very freely attacked by other engineers, and his title to originality as freely doubted and denied. Much of this feeling may be ascribed, perhaps, to the manifest obscurity that runs throughout all his specifications, and to the claims set up by other persons for dreamy designs, the practicability of which they ingeniously enough speculated upon, but never carried into real effect.
Many of his plans, it is alleged, were the result of information surreptitiously obtained, or unfairly communicated to him, of the discoveries ofsuch persons. but of the truth of this allegation there appears to be no evidence beyond that of jealous conjecture. Certain it is, however, that either from the extent of patro nage and success which Bolton and Watt enjoyed in the manufacture of their engines, or from other unknown causes, a great deal of angry feeling was mani fested, the extent of which may be gathered from the declaration of the late Mr. Bramah, that when men of Letter judgment had constructed engines as good or better than their own, "they have just candour enough to admit the fact, and .pride and avarice enough to claim them as their invention I" Rugged it the 'path which merit has to walk in Great as was the degree of perfection to which the steam-engine had been brought by Mr. Watt, the discoveries which he, together with his predecessors, Savery and Newcomen, had made, furnished abundant materials for the exercise of future ingenuity ; and we now proceed to notice several of the most striking contributions towards its completion, subsequently made by other eminent en gineers, in the contrivance of various arrangements and combinations of me chanism for obtaining the most full and effective operation of steam power.