that of Trevithick and Vivian in 1804. Their engine for this purpose, was on the same principle as that described in 335, differing a little in the arrangement. The cylinder was horizontal, the piston moving parallel to the road, and turning cranks by which the motion was transformed from rectilinear to circular motion, and transmitted to the wheels. This locomotive engine seems to have been very successful; and yet, for nearly thirty years afterwards, little was done to extend the use of steam as a locomotive power. Indeed, until the opening of the Manchester and Liverpool Railway in 1830, it could not be said that the public were at all aware of the practicability and advantages of locomotive steam-engines on railways.

339. At first, it was proposed to draw waggons on railways, by ropes attached to stationary engines at convenient distances. This plan was considered necessary from the idea entertained that, if the power were in the carriage to be moved, the wheels would slip on the rail, and be turned round and round, while the carriage would remain still. This would no doubt be the case, if the surfaces of the wheel and rail were perfectly smooth, and there were no friction between them. It was supposed that there was not enough friction to give a resistance sufficient to cause the wheel to move onwards, instead of turning on its axis. This is termed skidding of the wheels. It was pro

posed to make the wheel and rail toothed, which was tried, but the motion found so rough, and the tear and wear so great, that it was abandoned. Next, to the engine propellers were attached, which took hold of a fixed point, and thus gave a resistance by which the carriage was impelled onwards. But all these schemes were given up when it was ascertained that there really is sufficient friction or resistance between the rail and wheel, to prevent any skidding of the latter,

340. The following figure represents a locomotive engine for a railway. The frame (A) is of wrought iron, and very strong. Its length is fifteen feet, breadth seven; and it rests on four springs, which are supported by the four wheels. The boiler (B) is of

wrought iron; at the left, is the furnace (C); at the right, the chimney. On the top of the chimney is a wire-net capping (D), which arrests the ignited bits of coke, carried upwards by the rapid draught. The boiler is a long, somewhat cylindrical vessel, with a number of tubes of thin sheet copper or brass within it, traversing the lower half. The tubes are surrounded by the water, and through them the hot air from the furnace passes; so that, besides the direct heat of the furnace, considerable heating effect is procured from the hot air, as it passes through the tubes on its way to the chimney. The tubes are about ninety in number, and one and a-half inch in diameter. The boiler has two safety-valves (G and H); the first is under the control of the engineer, and he can load it to any extent up to a certain limit, and thus regulate the power of the engine. The other is not under his control, and is always loaded so that it does not permit the steam to acquire strength beyond a certain point, a little beyond what is required to work the engine. The tubes I convey the steam from the boiler to the cylinder. These tubes are provided with throttlevalves, under the control of the engineer; so that he can, as necessary, shut altogether or contract the connection between the cylinder and boiler, so as to stop the engine, or adjust the quantity of steam admitted, so as to produce any desired rate of motion. In these engines, the engineers perform the part of the governor in engines for impelling machinery. E, E, are gauge cocks, by which the height of water in the boiler may be learned in the usual manner.

341. The steam from the boilers enters the valve-box (K), from which it is admitted alternately above and below the piston. From the cylinder, the steam passes by the pipe R to the chimney, after it has produced its action on the piston, rushing there with great force, and producing a powerful draught through the furnace.

342. At the top of the piston-rod is a cross-bar or cross-head, from which two side rods (M), descend to work the bell crank (N N); the triangular frame N' N turns at N'. The rods M act on one lever of this bell crank, while to the other extremity is attached the rod O, which by the usual crank turns the wheel like a common spinning-wheel. The cranks on each wheel are at right angles to each other, so that they are not both at the dead points at the same time. To the perpendicular lever of the bell crank is attached a rod (P), which it works. This is the rod of the forcepump by which the boiler is supplied. The water is contained in a carriage called a tender, behind the engine. The pipe which conveys the water to the force-pump is seen at the left, below the engineer. The bell crank movement requires no parallel motion; the lever to which the side-rod M is attached is long, so that the segment it describes is nearly a straight line at least does not deviate materially from the vertical. By the levers F, F, the engine is directed by the engineer, these levers acting upon the valve, and directing the course of the steam, so that the engine may be moved backwards or forwards as required.

343. In many locomotive engines now constructed, the cylinders are not exposed to the air, by which a considerable saving of heat is effected. They are placed in a casing immediately under the chimney, which is kept warm, both by its being near to the end of the boiler, and by the heated air rushing to the chimney. By successive improvements in the boiler and other parts of the engine, the fuel required has been reduced from about 2.41 lbs. coke to transfer a ton a mile, (which was the quantity required in Mr Stephenson's engine, the Rocket, at the time of the opening of the Liverpool and Manchester Railway,) to 0.33. lb. per ton transferred a mile, or even less-about one-third of a pound of coke.

SECTION IX.

LOCOMOTIVE ENGINES FOR COMMON
ROADS.

344. In 1831, a steam-carriage plied between Gloucester and Cheltenham regularly for four months, on the common turnpike-road. This carriage was constructed by Mr GOLDSWORTHY GURNEY, whose invention it was. Dr Robison, Mr Watt, Oliver Evans in America, and Mr Symington of Falkirk, had projected the idea of using steam for carriages on common roads. Also, previously to Mr Gurney, attempts to construct a steam-carriage for common roads had been made by Mr Trevithick in 1802, Mr Griffiths in 1821, Mr Gordon in 1824, Messrs J. and S. Seaward, and Messrs Hill and Burstall. But none can be said to have led to a successful result, till that of Mr Gurney's patent in 1827. The first sufficient trial of steam-propelled carriages on common roads was by Mr Gurney, who, in 1829, travelled from London to Bath, and back, in his steam-carriage. To the disgrace of the individuals who had charge of the roads where Mr Gurney's carriage was running in 1831, the difficulties encountered were so great, from heavy tolls imposed, and obstructions placed on the road, that, after running successfully for four months, it was abandoned. Mr Gurney petitioned Parliament, and a committee was appointed to inquire and report upon the subject.

345. The following extracts from their report contain some interesting information on the subject :

Mr Gurney states, "that he has kept up steadily the rate of twelve miles an hour; that the extreme