The boiler was a cylinder of wrought iron, 5 feet 6 inches long, 3 feet in diameter, and of such strength as to be capable of sustaining a pressure of upwards of 400 pounds per square inch. The working cylinder was 6 inches in diameter, and the piston had a stroke of 24 inches, the step of the feet was 26 inches, and the whole machine, including water, weighed about 45 cwt. When placed upon a railway, Mr. Brunton found that it required to move it at the rate of 2 1/2 miles per hour, a power equal to the constant pressure of 84 pounds. He then applied a chain to the hinder part of the machine, by which as the machine moved forward, a weight was raised at the same time and rate; and he found that with steam equal to 40 or 451bs. pressure upon the square inch, the machine was propelled at the rate of 2 1/2 miles per hour, and raised 112lbs. at the same speed; thus making the whole power 896lbs., at 2 1/2 miles, which, at 150 lbs. the horse power, is equal to about six horses; but the machine was only designed to insure 4 horses' power, and to work upon a railway rising one in thirty-six.
To get rid of the cumbrous wheels and pistons, and avoid the jerks and concussions consequent upon Mr. Blenkinsop's arrangement, we find Mr. Ralph Dodd and Mr. George Stephenson taking out a joint patent "for various improvements in the construction of locomotive engines," which was dated Feb. 28, 1815. It consisted of the application of a pin upon one of the spokes of the running wheels that supported the engine; the lower end of the connecting-rod being attached to the pin. and the upper end to the cross-head of the piston rod, worked up and down by the piston. (The following engraving serves to explain this invention, although it belongs to the patented improvements subsequently introduced by Mr. Losh, in conjunction with Mr. Stevenson; Mr. Dodd's previous invention being combined therein.) ah represents the connecting-rod, the end a attached to the cross-head, and the end b to one of the spokes of the wheel; in like manner the end d of the other connecting-rod is attached to the beam of the other piston, and the lower end to a pin fixed in the spokes of the wheel B. By these means the reciprocating motion of the piston and connecting-rod is converted, by the pin upon the spokes acting as a crank, into a rotatory motion, and the continuation of this motion secured by the one pin or crank being kept at right angles to the other as shown in the drawing.
To effect this, the patentees had two methods; - to crank the axles, on which each of the wheels were fixed, with a connecting-rod between, to keep them always at the angle with respect to each other; or to use a peculiar sort of endless chain passing over a toothed wheel on each axle. This endless chain consisted at first of one broad and two narrow Jinks, alternately fastened together at the ends with bolts; the two narrow links were always on the outside of the broad link; consequently, the distance they were separated laterally would be equal to the breadth of the broad link, which was generally about two inches, and their length three inches. The periphery of the wheels fixed upon the axles of the engine, was furnished with cogs, projecting from the rim of the wheels (otherwise perfectly circular and flat) about an inch or an inch and a half. When the wheel turned round, these projecting cogs entered between the two narrow links, having a broad link between every two cogs, resting on the rim of the wheel; these cogs, or projections, caused the chain to move round with the wheel, and completely prevented it from slipping round upon the rim.
When, therefore, this chain was laid upon the two toothed wheels, one wheel could not be moved round without the other moving round with it, and thus secured the proper angles to the two cranks. This mode of communicating the action of the engine from one wheel to another, is shown in the drawing, the wheels A and B having each projecting cog-wheels, round which the endless chain passes. When the chain got worn by frequent use, or was stretched, so as to become too long, one of the chairs of the axles could be moved back to tighten it again, until a link could be taken out, when the chair was moved back again to its former situation.
In the following year, 1816, a joint patent was obtained by Messrs. Stevenson and Losh, of Newcastle, for a variety of improvements in the carriages, wheels, rails, etc. of a railway. In that part which relates to locomotive engines, the very singular proposition is made of "sustaining the weight or a part of the weight of the engine, upon pistons moveable within cylinders, into which the steam or water of the boiler is allowed to enter, in order to press upon such pistons; and which pistons are, by the intervention of levers and connecting-rods, made to bear upon the axles of the running wheels of the engine." The annexed section of a locomotive engine, exhibits the application of the " Steam-springs," as they were called. At a a are the steam-cylinders, containing the floating pistons b b, connected with rods, cc, the ends of which rest upon the brasses of the axles of the wheels dd. "These pistons, pressing equally on all the axles, cause each of the wheels to press with an equal stress upon the rails, and to act upon them with an equal degree of friction, although the rails should not all be in the same plane; for the bearing brasses have the liberty of moving in a perpendicular direction in a groove or slide, and carrying the axles and wheels along with them, free the wheels to accommodate themselves to the inequalties of the railway.
The objects of these floating pistons are, to prevent the engine from receiving shocks, and preserve a steadiness of motion; the inventors considering, that by acting on an elastic fluid, they produce the desired effect " with much more accuracy than could be obtained by employing the finest springs of steel to support the engine." A longitudinal section of this locomotive engine is given in the preceding figure, in the description of Dodd and Stephenson's improvements, which it equally illustrates.