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pair of connecting-rods. But, in attempting to establish a direct communication between the cylinders and the wheels that rolled upon the rails, considerable difficulties presented themselves. The ordinary joints could not be employed to unite the parts of the engine, which was a rigid mass, with the wheels rolling upon the irregular surface of the rails; for it was evident that the two rails of the line of way— more especially in those early days of imperfect construction of the permanent road — could not always be maintained at the same level,- that the wheel at one end of the axle might be depressed into one part of the line which had subsided, whilst the other wheel would be comparatively elevated; and, in such a position of the axle and wheels, it was obvious that a rigid communication between the cross head and the wheels was impracticable. Hence it became necessary to form a joint at the top of the piston-rod where it united with the cross head, so as to permit the cross head to preserve complete parallelism with the axle of the wheels with which it was in communication. In order to obtain that degree of flexibility combined with direct action, which was essential for ensuring power and avoiding needless friction and jars from irregularities in the road, Mr. Stephenson made use of the “ball and socket” joint (so called from its resemblance to the hip-joint of the human body) for effecting a union between the ends of the cross heads where they united with the connecting rods, and between the ends of the connecting rods where they were united with the crank-pins attached to each driving wheel. By this arrangement the parallelism between the cross head and the axle was at all times maintained and preserved, without producing any serious jar or friction on any part of the machine. The next important point was, to combine each pair of wheels by means of some simple mechanism, instead of by
cHAP. IX.] HIS SECOND LOCOMOTIVE. 95
the cogwheels which had formerly been used. And, with this object, Mr. Stephenson began by making in each axle cranks at right angles to each other, with rods communicating horizontally between them. A locomotive was accordingly constructed upon this plan in the year 1815, and it was found to answer extremely well. But at that period the mechanical skill of the country was not equal to the task of forging cranked axles of the soundness and strength necessary to stand the jars incident to locomotive work. Mr. Stephenson was accordingly compelled to fall back upon a substitute, which, although less simple and efficient, was within the mechanical capabilities of the workmen of that day, in respect of construction as well as repair. He adopted a chain which rolled over indented wheels placed on the centre of each axle, and so arranged that the two pairs of wheels were effectually coupled and made to keep pace with each other. The chain, however, after a few years' use, became stretched; and then the engines were liable to irregularity in their working, especially in changing from working back to working forward again. Eventually the chain was laid aside, and the front and hind wheels were united by rods on the outside, instead of by rods and crank axles inside, as specified in the original patent. This expedient completely answered the purpose required, without involving any expensive or difficult workmanship. Thus, in the year 1815, Mr. Stephenson, by dint of patient and persevering labour, by careful observation of the works of others, and never neglecting to avail himself of their suggestions,—had succeeded in manufacturing an engine which included the following important improvements on all previous attempts in the same direction:-viz., simple and direct communication between the cylinder and the wheels rolling upon the rails; joint adhesion of all the wheels, attained by the use of horizontal connecting rods; and finally, a beautiful method of exciting the combustion of the fuel by employing the waste steam, which had formerly been allowed uselessly to escape into the air. Although many improvements in detail were afterwards introduced in the locomotive by Mr. Stephenson himself, as well as by his equally distinguished son, it is perhaps not too much to say that this engine, as a mechanical contrivance, contained the germ of all that has since been effected. It may in fact be regarded as the type of the present locomotive engine.
EXPLOSIONS of fire-damp were unusually frequent in the coal mines of Northumberland and Durham about the time when George Stephenson was engaged in the construction of his first locomotives. These explosions were frequently attended with fearful loss of life and dreadful suffering to the colliery workers. Killingworth Colliery was not free from such deplorable calamities; and during the time that Stephenson was employed as a brakesman at the West Moor, several “blasts” took place in the pit, by which many workmen were scorched and killed, and the owners of the colliery sustained heavy losses. One of the most serious of these accidents occurred in 1806, not long after he had been appointed brakesman, by which ten persons were killed. Stephenson was working at the mouth of the pit at the time, and the circumstances connected with the accident seem to have made a deep impression on his mind, as will appear from the following graphic account which he gave to a committee of the House of Commons, some thirty years after the event": — “The pit had just ceased drawing coals, and nearly all the men had got out. It was some time in the afternoon, a little after midday. There were five men that went down the pit; four of them for the purpose of preparing a place
* Evidence given before the Select Committee on Accidents in Mines, 26th
for the furnace. The fifth was a person who went down to set them to work. I sent this man down myself, and he had just got to the bottom of the shaft about two or three minutes, when the explosion took place. I had left the mouth of the pit, and had gone about fifty or sixty yards away, when I heard a tremendous noise, looked round, and saw the discharge come out of the pit like the discharge of a cannon. It continued to blow, I think, for a quarter of an hour, discharging everything that had come into the current. There was wood came up, stones came up, and trusses of hay that went up into the air like balloons. Those trusses had been sent down during the day, and I think they had in some measure injured the ventilation of the mine. The ground all round the top of the pit was in a trembling state. I went as near as I durst go; everything appeared cracking and rending about me. Part of the brattice, which was very strong, was blown away at the bottom of the pits. Very large pumps were lifted from their places, so that the engine could not work. The pit was divided into four by partitions; it was a large pit, fourteen feet in diameter, and partitions were put down at right angles, which made four compartments. The explosion took place in one of those four quarters, but it broke through into all the others at the bottom, and the brattice or partitions were set on fire at the first explosion. After it had continued to blow for a quarter of an hour the discharge ceased, and the atmosphere all round poured into the pit to fill up the vacant place that must have been formerly occupied by the flame. In one of the other pits, that was connected by some doors in a drift with that in which the explosion took place, were several men, some of whom succeeded in getting up safe. The ropes in the first pit were shattered to pieces by the force of the blasts, but the ropes in the other pits were still left comparatively uninjured. Nobody durst go near the shafts for some time, for