Mr. Woolf, a short time after, made a series of experiments, to develope the law of action of steam, at different degrees of elasticity, which he explained, in his patent of June 7, 1804.

Art. 1.-Trevithick and Vivian's Engine.

Messrs. Trevithick and Vivian, in the specification of their patent, gave a drawing of their engine, applied to move a carriage upon the common roads, which may be seen in the fourth vol. Rep. Arts. 2d Series, p. 241. The carriage there delineated resembles, in form, the common stage coaches, used for the conveyance of passengers; a square iron case, containing the boiler and cylinder, is placed behind the large, or hinder, wheels of the carriage, and is attached to a frame, supported from the axles of those wheels. The cylinder was in a horizontal position; and the piston-rod was projected backwards and forwards, in the line of the road towards the front of the carriage. Across the square frame, supported by the wheel of the carriage, an axle was extended, reaching a little beyond the frame on each side; this axle was cranked in the middle, in a line with the centre of the cylinder, and a connecting rod, passing from the end of the piston, turned this axle round, and produced a continued rotatory motion of it, when the piston was moved backwards and forwards in the cylinder. Upon both ends of this axle, cog-wheels were fixed, which worked into similar cog-wheels upon the axle of the wheels of the carriages, so that, when a rotatory motion was produced in the cranked axle by the piston-rod, the rotatory motion was communicated to the axle of the larger, or hinder, wheels of the carriage; and these wheels being fixed upon, and turning

round with the axle, gave a progressive motion to the carriage. Upon one end of this axle was fixed a flywheel, to secure a rotatory motion in the axle, at the termination of each stroke.

The fore wheels of the carriage were of the usual form, which, turning to different angles with the body of the carriage, directed its motion upon the road; and, in cases where abrupt turns of the road required sudden changes in the direction of the carriage, the toothed or cog wheels, on either side, could be thrown out of geer, and the opposite wheel made to drive the carriage into the proper obliquity of the road.

Upon the periphery of the fly-wheel, a brake was attached, to regulate the descent of the carriage down steep hills. The contrivances, to effect the requisite motions of the various parts of this machine, are extremely ingenious; and, considered as the first attempt of the application of steam to carriages, upon common roads, it is entitled to great commendation.

The many objections to its application, upon public turnpike roads, would, we presume, operate in preventing the patentees from carrying it into practice, in the manner described in their specification; they, therefore, it appears, directed their attention to its use upon railroads.

Two years after the date of this patent, we find, that Mr. Trevithick made an engine in South Wales, which was tried upon the Merthyr Tydvil railroad. The engine is stated to have had an eight-inch cylinder, with a four-feet six-inches stroke, and "drew after it, upon the railroad, as many carriages as carried ten tons of bar-iron, from a distance of nine miles; which it performed without any supply of water, to that contained

in the boiler at the time of setting out; travelling at the rate of five miles an hour."

As there is no account given of the inclination of the road, we cannot judge of the real performance of the engine. It had, it appears, only one cylinder, and, from what we can learn, did not materially differ, in construction, from that previously described, except in the form of the carriage.

The great obstacle, to the introduction of steam carriages upon railroads, at that time, was the supposed want of hold, or adhesion, of the wheels upon the rails, to effect the locomotion of the engine. Messrs. Trevithick and Vivian, in their patent, recommended making the external periphery of the wheels rough or uneven, by using projecting heads of nails, bolts, or cross-grooves; or, in case of a hard pull, to cause a lever, bolt, or claw, to project through the rim of one, or both of the wheels, driven by the engine, to take hold of the ground. But it will appear obvious to any one, that this mode of remedying one defect, would be the means of producing another; for any projections, would not only cause considerable resistance to the progressive motion of the engine, but would also tend to injure the rails of the road.

Art. 2.-Blenkinsop's Engine.

To obviate these defects, Mr. Blenkinsop, of Middleton colliery, near Leeds, in 1811, obtained a patent for the application of a rack, or toothed rail, stretched along the whole distance to be travelled; into which cog-wheels, turned by the engine, worked, and thus produced a progressive motion, in the carriages.

The annexed drawing, No. 1, will convey a pretty correct idea of the mode of action, of this kind of engine. R R, represents a portion of the rails, constituting the railroad, on the side of which were cast the semicircular protuberances, or projections, 111, &c. These semicircular teeth projected, from the side of the rail, two or three inches, thus forming a longitudinal toothed rack, which was extended the whole length of the road. a a, are the cylinders, placed within the boiler. The action was communicated, by the pistons, to the connecting rods, bb, which transferred the motion to the cranks, cc, turning axles, attached to the inside of the frame of the carriage. Upon the axles, on which these cranks were fixed, were also fixed the pinion-wheels, dd, which were turned round by the cranks; these two pinion-wheels communicated with a larger cog-wheel, e, in such a manner, that both contributed in producing a rotatory motion in it. The action of this cog-wheel, e, extended to the outside of the frame of the engine, and upon the end of it was affixed the larger toothed

wheel, f, which was thus turned round by the large cog-wheel, and, consequently, by the action of the engine; and the teeth of this cogwheel, being made to correspond with, and lay hold of, the toothed projections, on the side of the rail, a progressive motion of the carriage was thereby effected. The steam, after performing its office, in the cylinder, was allowed to escape into the atmosphere, through the pipe, s. The boiler was cylindrical, and heated by a circular tube passing through it, terminated, at one end, by the chimney. The toothed or rack rail, was only laid on one side of the road, the other being common rails. The cog-wheels were varied in size, according to the different velocity with which it was required to travel.

By the use of this rack-rail, Mr. Blenkinsop's engine was enabled to ascend acclivities, which Mr. Trevithick's engine, from the want of adhesion, could not surmount. Mr. Blenkinsop, soon after the date of his patent, erected some of those engines, and employed them upon the Middleton colliery railroad, in conveying coals to Leeds, where they were used for several years; but it having been since proved, that the adhesion of the wheels was sufficient, to accomplish the progressive motion, the rack-rail has been abandoned.

The engine, erected by Mr. Trevithick, had one cylinder only, with a fly-wheel, to secure a rotatory motion in the crank, at the end of each stroke. An engine of this kind was sent to the North, for Mr. Blackett, of Wylam, but was, for some cause, or other, never used upon his railroad, but was applied to blow a cupola, at an iron foundry, in Newcastle. Mr. Blackett, however, had, in 1813, an engine of this kind made, and set upon his railroad, which worked by the adhesion of its wheels upon the rails. Still, the supposed want of adhesion formed the great obstacle to their introduction, and the attention of