Thus a continuous rotation of the wheels, with an equable force, is obtained from the rectilinear and intermitting action of the engine.

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Both Allen's and Hulls' plans were sufficiently clear and explicit, and had they been judiciously carried into execution, even with the means then at command, must have been attended with a moderate share of success, but neither were acted upon, and for nearly half a century, the subject of steam navigation seems to have remained in abeyance. But during this interval, Watt had introduced his stupendous improvements in the steam engine, by which he not merely augmented its effectiveness, but also, infinitely enlarged the sphere of its applicability, by showing that its utility was not limited to the draining of mines, to which purpose alone it had been hitherto confined, but that it was universally applicable as a prime mover of machinery.

As men became acquainted with the powers of the engine in its improved form, it was gradually called into requisition for various purposes, and attempts to apply it to propel vessels seem to have been instituted at nearly the same period in various countries.

About the year 1783, Mr. John Fitch, an American, appears to have succeeded in moving a boat on the Delaware by paddles worked by a steam-engine; and he subsequently constructed another vessel of larger size; but ultimately the scheme was abandoned.

Contemporaneously with Fitch, a Mr. Rumsey of Virginia appears to have been occupied with the idea of navigating by steam. In 1787 he made some short trips upon the Potomac, in a vessel about fifty feet long, which was propelled by pumps worked by a steam engine - the plan (as we have just seen) originally proposed by Doctor Allen. The experiment being eventually given up, he came to England, where he found parties to advance the funds for another experiment; and although he unfortunately died before the whole of the arrangements were completed, the vessel was got afloat early in the year 1793, and made several trial voyages on the Thames, realising, it is said, a speed of four knots an hour against wind and tide. If this were really the fact, it seems inconceivable that the attempt should have been relinquished (as it unfortunately was), for such a performance could scarcely be deemed a failure at that period, especially if considered as a first attempt.

It has been stated, that the earliest attempts to propel vessels by steam power in this country were made by Mr. Miller, at Dalswinton, in Scotland. But there is some ground for believing that Mr. Miller's agency was rather in the character of a patron, than that of an inventor. It seems that Mr. Miller, in 1787, published a description of a triple boat moved by wheels, with which he had been experimenting, to ascertain the comparative velocity with those moved by ordinary oars; and in this pamphlet he observed that the power of steam might be employed to give them a quicker motion. A similar suggestion has been attributed to Mr. Taylor, who was a tutor in the house at Dalswinton, and for which he has been regarded, by some writers, as the inventor of steam navigation. Under the impression that such was the fact, Lord Brougham advocated the claims of the widow of the late Mr. Taylor, and succeeded in obtaining a small pension for her, in consideration of her husband's public services. A third claimant, however, having a better title to the honour of originating this important invention, appears in the person of Mr. Symington, who was introduced to Mr. Miller in the early part of his experiments on the comparative merits of oars and paddle wheels; and by which of these three gentlemen the idea of applying steam power to move the paddles originated, is quite immaterial.

But it is not questioned that Symington actually applied his steam engine to turn Miller's paddle wheels, attached to a twin boat, lying in a lake near Dalswinton-house. Symington had previously obtained a patent for his steam engine, and shown its application in a small model of a steam carriage. The transition of turning the wheels of a boat, instead of those of a carriage, was so easy and obvious, that Symington did it out of hand, and made several trials of it in 1788, which proved so satisfactory, and so delighted Mr. Miller and his numerous visitors, that he immediately determined to commence another boat on a greater scale than the first. The machinery required for this purpose was constructed at the Carron works, under the direction of Symington, and was applied to a double boat sixty feet long, which had been used for Miller's previous experiments. A trial of this vessel was made on the Forth and Clyde canal, in October 1789, and was found so efficacious, that she glided through the water at the rate of nearly six miles per hour.

The mechanical arrangement of this vessel was precisely the same as the former, the only alteration being its increased dimensions, affording strong presumptive evidence of practical success, and hence rendering a description of its construction of the deepest interest in a scientific point of view; which we shall now proceed to give, with reference to the annexed sketch, which represents a longitudinal section of the vessel and its machinery.

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At a a are the cylinders of the engines, which are a modification of the atmospheric engine as patented by Mr. Symington; bb are the nozzles; c the plug beam for working the valves; d d the air pump rods; e e connecting chains; ffdirection pulleys; gg the paddle wheels, situated and wrought in a trough, extending from the stem to the stern of the boat, and allowing free ingress and egress to the water; hh ratchet wheels, for communicating motion to the paddle wheels. The level of the water is expressed by the horizontal line at dd; the boiler is at k.