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72 INVENTION OF THE STEAM-BLAST. Chat. V.
tions were made with the view of ascertaining this important point. The result was, that it was found the working of the engine was at first barely economical; and at the end of the year the steam power and the horse power were ascertained to be as nearly as possible upon a par in point of cost. The fate of the locomotive in a great measure depended on this very engine. Its speed was not beyond that of a horse's walk, and the heating surface presented to the fire being comparatively small, sufficient steam could not be raised to enable it to accomplish more on an average than about three miles an hour. The result was anything but decisive; and the locomotive might have been condemned as useless, had not Mr. Stephenson at this juncture applied the steam-blast, and at once more than doubled the power of the engine.
The eduction steam was originally allowed to escape into the open atmosphere with a hissing blast, which was the terror of horses and cattle, and was generally complained of as a nuisance. A neighbouring squire even threatened an action against the colliery lessees if it were not put an end to. But Mr. Stephenson's attention had already been drawn to the circumstance of the much greater velocity with which the steam issued from the exit pipe, compared with that at which the smoke escaped from the chimney of the engine. He then thought that, by conveying the eduction steam into the chimney by means of a small pipe after it had performed its office in the cylinders, and allowing it to escape in a vertical direction, its velocity would be imparted to the smoke from the fire, or to the ascending current of air in the chimney.
The experiment was no sooner made than he found that the combustion of the fuel in the furnace was greatly stimulated by the blast; consequently the capability of the boiler to generate steam was much increased, and the effective power of the engine was augmented in precisely the same proportion, without in any way adding to its weight.
This simple but beautiful expedient, though it has hitherto Chap. V. HIS SECOND LOCOMOTIVE. 73
received but slight notice as an original idea on the part of its author, was really fraught with the most important consequences to railway communication; and it is not too much to say that the success of the locomotive depended upon its adoption. Without the steam-blast, the advantages of the "multitubular boiler" could never have been fairly tested; and it was these two improvements, working together, which afterwards secured the triumph of the locomotive on the opening of the Liverpool and Manchester Eailway. Without the steam-blast, by which the intensity of combustion was kept up to the highest point, and the evolution of steam thus rapidly effected, high rates of speed could not have been maintained, and locomotives might still have been dragging themselves unwieldily along at little more than five or six miles an hour.
The steam-blast had scarcely been adopted, with so decided a success, when Mr. Stephenson, observing the numerous defects in his engine, and profiting by the experience which he had already acquired, determined to construct a second engine, in which to embody his improvements in their best form. Careful and cautious observation of the working of his locomotive had convinced him that the complication arising out of the action of the two cylinders being combined by spnrwheels would prevent its coming into practical use. He according directed his attention to an entire change in the construction and mechanical arrangements of the machine ; and in the following year, conjointly with Mr. Dodds, who provided the necessary funds, he took out a patent, dated the 28th of February, 1815, for an engine which combined in a remarkable degree the essential requisites of an economical locomotive; that is to say, few parts, simplicity in their action, and directness in the mode by which the power was communicated to the wheels supporting the engine.
This locomotive, like the first, had two vertical cylinders, which communicated directly with each pair of the four wheels that supported the engine, by means of a cross head and a pair of connecting rods. But, in attempting to 74 HIS SECOND LOCOMOTIVE. Chap. V.
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 pistonrod 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 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. Another important point was, to combine each pair of wheels by means of some simple mechanism, instead of by 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 Chap. V. HIS SECOND LOCOMOTIVE. 75
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.
76 EXPLOSIONS OF FIRE-DAMP. Chap. VI
Invention Of The "Geordy" Safety-lamp.
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 suifering 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 appeared from the graphic account which he gave to a committee of the House of Commons, which sat on the subject of Accidents in Coal Mines, some thirty years after the event.
Another explosion of a similar kind occurred in the same pit in 1809, by which twelve persons lost their lives. George Stephenson was working at the pit when the accident occurred, but the blast did not reach the shaft as in the former case; the unfortunate persons in the pit having been suffocated by the after-damp. But more calamitous explosions than these occurred in the neighbouring collieries; one of the worst being that which took place in May, 1812, in the Felling Pit, near Gateshead, a mine belonging to Mr. Brandling, by which no fewer than ninety men and boys were suffocated or burnt to death. And a similar ao