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We now come to the description of a machine of great singularity, and which strongly attests the ingenuity of the contriver, William Brunton, of the Butterly Iron Works, in Derbyshire, and for which he took out patents.
It consists in a curious combination of levers, the action of which nearly resembles that of the legs of a man in walking, whose feet are alternately made to press against the ground of the road or railway, and in such a manner as to adapt themselves to the various inclinations or inequalities of the surface. The following engraving represents this engine, which the inventor called his "Mechanical Traveller".
The boiler is nearly similar to that which we last described. The cylinder a is placed on one side of the boiler; the piston rod is projected out behind horizontally, and is attached to the leg a-b at a, and to the reciprocating jointed bent lever above; at the lower extremity of the leg a-b, feet are attached by a joint at b; these feet lay a firmer hold on the ground, being furnished with short prongs, which prevent them from slipping, and are sufficiently broad to prevent their injuring the road.
On inspecting the drawing, it will be seen that when the piston rod is projected out from the cylinder, it will tend to push the end of the lever or leg a from it, in a direction parallel to the line of the cylinder; but as the leg a-b is prevented from moving backwards by the end is being firmly fixed upon the ground, the reaction is thrown upon the carriage, and a progressive motion given to it, and this will be continued to the end of the stroke.
Upon the first reciprocating lever is fixed at 1, a rod, 1-2-3, sliding horizontally backwards and forwards upon the top of the boiler; from 2 to 3 it is furnished with teeth, which work into a cog-wheel, lying horizontally; on the opposite side of this cog-wheel a sliding-rack is fixed, similar to 1-2-3, which, as the cog-wheel is turned round by time sliding-rack 2-3, is also moved backwards and forwards. The end of this sliding-rod is fixed upon the other reciprocating lever of the leg d-e, at 4.
When, therefore, the sliding-rack is moved forwards in the direction 3-2-1, by the progressive motion of time engine; and, when the piston-rod is at the farthest extremity of the stroke, the leg d-e will be brought close to the engine; the piston is then made to return in the opposite direction, moving with it the leg a-b, and also the sliding-rack 1-2-3; the sliding-rack, acting on the toothed wheel, causes the other sliding-rod to move in the contrary direction, and with it the leg d-e.
Whenever, therefore, the pistols is at the extremity of the stroke, and one of the legs is no longer of use to propel the engine forward, the other, immediately on the motion of the piston being changed, is ready, in its turn, to act as a fulcrum or abutment for the action of the moving power, to secure the continued progressive motion of the engine.
The feet are raised from the ground during the return of the legs to the engine, by straps of leather or rope fastened to the legs at f-f, passing over friction sheaves, movable in one direction only, by a ratchet and catch, worked by the motion of the engine. The feet are described of various forms in the specification, the great object being to prevent them front injuring the road, and to obtain a firm footing, that no jerks should take place at the return of the stroke, when the action of the engine came upon them; for this purpose they were made broad, with short spikes to lay hold of the ground.
It is proper to record that this strange machine was actually put to work. 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 two and a half 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 45 lbs. pressure upon the square inch, the machine was propelled at the rate of two and a half miles per hour, and raised 112 lbs. at the same speed; thus making the whole power 896 lbs. at two and a half 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.