A very simple expedient tends to remove all considerable irregularity or concussion from the common paddle-wheel. It is to allow the extremity of the paddle board nearest the side of the boat, to descend from six to twelve inches deeper in the water than the outer extremity. This plan was carried into effect by the writer of this treatise on a steam vessel in 1836. The desired object was attained without any sacrifice of power or speed. For distinction we may call this the conical paddle wheel. It is shown in figs. 40, 41.

In the three following figures we have represented the single oblique paddle wheel. Fig. 44 shows the development or stretch-out of a part of the circumference of the wheel, to exhibit more clearly the arrangement of the paddle boards.

In figs. 45, 46, the double oblique paddle wheel is represented; and in figure 47 the development of a portion of its circumference is given.

The Reefing Paddle.-One of the greatest improve. ments on paddle wheels, and one of especial importance to steam navigation, still remains to be invented. We mean such a mechanism as shall enable the steam commander to set out on a long voyage deeply laden, with a small diameter of paddle wheel; that is, with the paddle boards near to the axis, and to increase the effective diameter of the paddle, that is, to remove the paddle boards further from the axis, as the vessel proceeds on her voyage and is lightened by the consumption of coal. The invention of a durable, economical, and safe apparatus still remains to be made. In the infancy of steam navigation, Mr Buchanan of Glasgow published an account and drawing of a reefing paddle; Messrs Bolton and Watt are also in possession of a very old method of reefing paddles; the Society of Arts in Scotland offered a prize several years ago for the invention, without obtaining, out of many plans, one to be recommended for practice; and, finally, the indefatigable inventor, Mr Hall of Basford, has patented a very elegant mechanism for the same purpose. It still, however, remains to introduce and establish a perfect reefing apparatus, and the author of such a system will render the common paddle wheel a perfect propeller.

HISTORICAL SKETCH OF STEAM LOCOMOTION.

THE history of locomotives is inseparable from that of the high-pressure engine, first hinted at by the Marquis of Worcester, and brought into practical use by Savary, who proposed it for propelling carriages.

After the magnificent improvements of James Watt, highpressure engines were neglected for many years. With reference to locomotion, however, the next suggestion seems to have come from Dr Robison, then a student in the university of Glasgow, who proposed, in 1759, the steamengine to Watt as a means of moving wheel carriages. Murdoch, in 1782, to whom Trevithick was a pupil, made a model of a steam carriage, which was exhibited to many persons. In 1784, Watt explains, in his patent, the manner in which, among other things, he proposes his engine to propel carriages. This method, although a curiosity at the present day, bears the full impress of his mind. The boiler was to be of wooden staves hooped together with iron like a cask; the iron furnace was to be inside the boiler and almost entirely surrounded by the water, the whole being placed on a carriage, the wheels of which were to be worked by a piston, the reciprocating motion being converted into a rotatory one by toothed wheels and a sun and planet motion. His system of wheels was a double one, their proportions differing, and by this contrivance he proposed to overcome the variable resistance to be found on the road. The cylinder was to be seven inches diameter, the number of strokes sixty per minute, and their length one foot. The carriage thus constructed was to carry two persons. Watt, however, never built it, and continued till his death an opponent of high-pressure steam.

The first person who may properly be said to have reduced the theory to practice was Richard Trevithick, who seeing that lightness and portability were indispensable in any attempt at locomotion, either on common roads or on railroads, at once adopted the high-pressure principle.

This was in 1802, when, in conjunction with Vivian, he took out a patent. The condenser, cistern, air-pump, and cold water pump were omitted and the engine thus lightened, became not only considerably cheaper, but had the power to move itself, as well as to carry a load as a wheel carriage. At first it was tried on common roads, and was exhibited before thousands of people; among other places, near Euston square, where the London and Birmingham railway company's station is now fixed. The carriage presented a handsome appearance, having two small wheels in front by which it was guided, and two large ones behind by which it was driven. It had but one cylinder, and this, together with the boiler and fire, which were all enclosed in a case, was situated low down and in the rear of the hind axle; each driving wheel could be worked separately, or one could be reversed while the other went forward, their motion being produced by spur gear, to which was added a fly-wheel. The piston-rod outside the cylinder was double, and drove a cross piece, working in guides, on the opposite side of the cranked axle to the cylinder, and the crank of the axle revolved between the double parts of the piston rod. To this axle was attached the first of the toothed wheels; and to the axle on which were the driving wheels was attached the other, similar in size to the first, and worked by it. The steam cocks were opened and shut by a connexion with the crank axle. The force pump,

by which a supply of hot water, contained in the casing which enclosed the cylinder, fire box, &c., was injected into the boiler, was also worked from it, as were the bellows to produce sufficient combustion. The specification of his patent also adverts to contrivances for increasing