Part 14 (1/2)
They then resolved to call to their aid two professional engineers of high standing, who should visit the Darlington and Newcastle railways, carefully examine both modes of working-the fixed and the locomotive,-and report to them fully on the subject. The gentlemen selected were Mr.
Walker of Limehouse, and Mr. Rastrick of Stourbridge. After carefully examining the modes of working the northern railways, they made their report to the directors in the spring of 1829. They concurred in the opinion that the cost of an establishment of fixed engines would be somewhat greater than that of locomotives to do the same work; but thought the annual charge would be less if the former were adopted. They calculated that the cost of moving a ton of goods thirty miles by fixed engines would be 6.40d., and by locomotives, 8.36d.,-a.s.suming a profitable traffic to be obtained both ways. At the same time it was admitted that there appeared more ground for expecting improvements in the construction and working of locomotives than of stationary engines.
On the whole, however, and looking especially at the computed annual charge of working the road on the two systems on a large scale, the two reporting engineers were of opinion that fixed engines were preferable, and accordingly recommended their adoption. And, in order to carry the system recommended by them into effect, they proposed to divide the railroad between Liverpool and Manchester into nineteen stages of about a mile and a half each, with twenty-one engines fixed at the different points to work the trains forward.
Such was the result, so far, of George Stephenson's labours. Two of the best practical engineers of the day concurred in reporting substantially in favour of the employment of fixed engines. Not a single professional man of eminence supported the engineer in his preference for locomotive over fixed engine power. He had scarcely an adherent, and the locomotive system seemed on the eve of being abandoned. Still he did not despair.
With the profession as well as public opinion against him-for the most frightful stories were abroad respecting the dangers, the unsightliness, and the nuisance which the locomotive would create-Stephenson held to his purpose. Even in this, apparently the darkest hour of the locomotive, he did not hesitate to declare that locomotive railroads would, before many years had pa.s.sed, be ”the great highways of the world.”
He urged his views upon the directors in all ways, and, as some of them thought, at all seasons. He pointed out the greater convenience of locomotive power for the purposes of a public highway, likening it to a series of short unconnected chains, any one of which could be removed and another subst.i.tuted without interruption to the traffic; whereas the fixed engine system might be regarded in the light of a continuous chain extending between the two termini, the failure of any link of which would derange the whole. {206} He represented to the Board that the locomotive was yet capable of great improvements, if proper inducements were held out to inventors and machinists to make them; and he pledged himself that, if time were given him, he would construct an engine that should satisfy their requirements, and prove itself capable of working heavy loads along the railway with speed, regularity and safety. At length, influenced by his persistent earnestness not less than by his arguments, the directors, at the suggestion of Mr. Harrison, determined to offer a prize of 500 for the best locomotive engine, which, on a certain day, should be produced on the railway, and perform certain specified conditions in the most satisfactory manner. {207}
It was now felt that the fate of railways in a great measure depended upon the issue of this appeal to the mechanical genius of England. When the advertis.e.m.e.nt of the prize for the best locomotive was published, scientific men began more particularly to direct their attention to the new power which was thus struggling into existence. In the mean time public opinion on the subject of railway working remained suspended, and the progress of the undertaking was watched with intense interest.
During the progress of the discussion with reference to the kind of power to be employed, Mr. Stephenson was in constant communication with his son Robert, who made frequent visits to Liverpool for the purpose of a.s.sisting his father in the preparation of his reports to the Board on the subject. They had also many conversations as to the best mode of increasing the powers and perfecting the mechanism of the locomotive.
These became more frequent and interesting, when the prize was offered for the best locomotive, and the working plans of the engine which they proposed to construct came to be settled.
One of the most important considerations in the new engine was the arrangement of the boiler and the extension of its heating surface to enable steam enough to be raised rapidly and continuously, for the purpose of maintaining high rates of speed,-the effect of high-pressure engines being ascertained to depend mainly upon the quant.i.ty of steam which the boiler can generate, and upon its degree of elasticity when produced. The quant.i.ty of steam so generated, it will be obvious, must depend chiefly upon the quant.i.ty of fuel consumed in the furnace, and by necessary consequence, upon the high rate of temperature maintained there.
It will be remembered that in Stephenson's first Killingworth engines he invented and applied the ingenious method of stimulating combustion in the furnace, by throwing the waste steam into the chimney after performing its office in the cylinders, thus accelerating the ascent of the current of air, greatly increasing the draught, and consequently the temperature of the fire. This plan was adopted by him, as we have already seen, as early as 1815; and it was so successful that he himself attributed to it the greater economy of the locomotive as compared with horse power. Hence the continuance of its use upon the Killingworth Railway.
Though the adoption of the steam-blast greatly quickened combustion and contributed to the rapid production of high-pressure steam, the limited amount of heating surface presented to the fire was still felt to be an obstacle to the complete success of the locomotive engine. Mr.
Stephenson endeavoured to overcome this by lengthening the boilers and increasing the surface presented by the flue-tubes. The ”Lancas.h.i.+re Witch,” which he built for the Bolton and Leigh Railway, and used in forming the Liverpool and Manchester Railway embankments, was constructed with a double tube, each of which contained a fire and pa.s.sed longitudinally through the boiler. But this arrangement necessarily led to a considerable increase in the weight of the engine, which amounted to about twelve tons; and as six tons was the limit allowed for engines admitted to the Liverpool compet.i.tion, it was clear that the time was come when the Killingworth locomotive must undergo a further important modification.
For many years previous to this period, ingenious mechanics had been engaged in attempting to solve the problem of the best and most economical boiler for the production of high-pressure steam. As early as 1803, Mr. Woolf patented a tubular boiler, which was extensively employed at the Cornish mines, and was found greatly to facilitate the production of steam, by the extension of the heating surface. The ingenious Trevithick, in his patent of 1815, seems also to have entertained the idea of employing a boiler constructed of ”small perpendicular tubes,”
with the same object of increasing the heating surface. These tubes were to be closed at the bottom, and open into a common reservoir, from which they were to receive their water, and where the steam of all the tubes was to be united.
About the same time George Stephenson was trying the effect of introducing small tubes in the boilers of his locomotives, with the object of increasing their evaporative power. Thus, in 1829, he sent to France two engines constructed at the Newcastle works for the Lyons and St. Etienne Railway, in the boilers of which tubes were placed containing water. The heating surface was thus found to be materially increased; but the expedient was not successful, for the tubes, becoming furred with deposit, shortly burned out and were removed. It was then that M.
Seguin, the engineer of the railway, pursuing the same idea, adopted his plan of employing horizontal tubes through which the heated air pa.s.sed in streamlets. Mr. Henry Booth, the secretary of the Liverpool and Manchester Railway, without any knowledge of M. Seguin's proceedings, next devised his plan of a tubular boiler, which he brought under the notice of Mr. Stephenson, who at once adopted it, and settled the mode in which the fire-box and tubes were to be mutually arranged and connected.
This plan was adopted in the construction of the celebrated ”Rocket”
engine, the building of which was immediately proceeded with at the Newcastle works.
The princ.i.p.al circ.u.mstances connected with the construction of the ”Rocket,” as described by Robert Stephenson to the author, may be briefly stated. The tubular principle was adopted in a more complete manner than had yet been attempted. Twenty-five copper tubes, each three inches in diameter, extended from one end of the boiler to the other, the heated air pa.s.sing through them on its way to the chimney; and the tubes being surrounded by the water of the boiler, it will be obvious that a large extension of the _heating surface_ was thus effectually secured. The princ.i.p.al difficulty was in fitting the copper tubes within the boiler so as to prevent leakage. They were made by a Newcastle coppersmith, and soldered to bra.s.s screws which were screwed into the boiler ends, standing out in great k.n.o.bs. When the tubes were thus fitted, and the boiler was filled with water, hydraulic pressure was applied; but the water squirted out at every joint, and the factory floor was soon flooded. Robert went home in despair; and in the first moment of grief, he wrote to his father that the whole thing was a failure. By return of post came a letter from his father, telling him that despair was not to be thought of-that he must ”try again;” and he suggested a mode of overcoming the difficulty, which his son had already antic.i.p.ated and proceeded to adopt. It was, to bore clean holes in the boiler ends, fit in the smooth copper tubes as tightly as possible, solder up, and then raise the steam. This plan succeeded perfectly, the expansion of the copper tubes completely filling up all interstices, and producing a perfectly watertight boiler, capable of withstanding extreme internal pressure.
The mode of employing the steam-blast for the purpose of increasing the draught in the chimney, was also the subject of numerous experiments.
When the engine was first tried, it was thought that the blast in the chimney was not strong enough to keep up the intensity of the fire in the furnace, so as to produce high-pressure steam in sufficient quant.i.ty.
The expedient was therefore adopted of hammering the copper tubes at the point at which they entered the chimney, whereby the blast was considerably sharpened; and on a further trial it was found that the draught was increased to such an extent as to enable abundance of steam to be raised. The rationale of the blast may be simply explained by referring to the effect of contracting the pipe of a water-hose, by which the force of the jet of water is proportionately increased. Widen the nozzle of the pipe, and the force is in like manner diminished. So is it with the steam-blast in the chimney of the locomotive.
Doubts were, however, expressed whether the greater draught secured by the contraction of the blast-pipe was not counterbalanced in some degree by the negative pressure upon the piston. A series of experiments was made with pipes of different diameters; the amount of vacuum produced being determined by a gla.s.s tube open at both ends, which was fixed to the bottom of the smoke-box, and descended into a bucket of water. As the rarefaction took place, the water would of course rise in the tube; and the height to which it rose above the surface of the water in the bucket was made the measure of the amount of rarefaction. These experiments proved that a considerable increase of draught was obtained by the contraction of the orifice; accordingly, the two blast-pipes opening from the cylinders into either side of the ”Rocket” chimney, and turned up within it, were contracted slightly below the area of the steam-ports; and before the engine left the factory, the water rose in the gla.s.s tube three inches above the water in the bucket.
[Picture: The ”Rocket”]
The other arrangements of the ”Rocket” were briefly these:-the boiler was cylindrical with flat ends, 6 feet in length, and 3 feet 4 inches in diameter. The upper half of the boiler was used as a reservoir for the steam, the lower half being filled with water. Through the lower part, 25 copper tubes of 3 inches diameter extended, which were open to the fire-box at one end, and to the chimney at the other. The fire-box, or furnace, 2 feet wide and 3 feet high, was attached immediately behind the boiler, and was also surrounded with water. The cylinders of the engine were placed on each side of the boiler, in an oblique position, one end being nearly level with the top of the boiler at its after end, and the other pointing towards the centre of the foremost or driving pair of wheels, with which the connection was directly made from the piston-rod, to a pin on the outside of the wheel. The engine, together with its load of water, weighed only 4 tons, and was supported on four wheels, not coupled. The tender was four-wheeled, and similar in shape to a waggon,-the foremost part holding the fuel, and the hind part a water-cask.
When the ”Rocket” was finished, it was placed upon the Killingworth railway for the purpose of experiment. The new boiler arrangement was found perfectly successful. The steam was raised rapidly and continuously, and in a quant.i.ty which then appeared marvellous. The same evening Robert despatched a letter to his father at Liverpool, informing him, to his great joy, that the ”Rocket” was ”all right,” and would be in complete working trim by the day of trial. The engine was shortly after sent by waggon to Carlisle, and thence s.h.i.+pped for Liverpool.
The time so much longed for by George Stephenson had now arrived, when the merit of the pa.s.senger locomotive was to be put to a public test. He had fought the battle for it until now almost single-handed. Engrossed by his daily labours and anxieties, and hara.s.sed by difficulties and discouragements which would have crushed the spirit of a less resolute man, he had held firmly to his purpose through good and through evil report. The hostility which he experienced from some of the directors opposed to the adoption of the locomotive, was the circ.u.mstance that caused him the greatest grief of all; for where he had looked for encouragement, he found only carping and opposition. But his pluck never failed him; and now the ”Rocket” was upon the ground,-to prove, to use his own words, ”whether he was a man of his word or not.”
Great interest was felt at Liverpool, as well as throughout the country, in the approaching compet.i.tion. Engineers, scientific men, and mechanics, arrived from all quarters to witness the novel display of mechanical ingenuity on which such great results depended. The public generally were no indifferent spectators either. The inhabitants of Liverpool, Manchester, and the adjacent towns felt that the successful issue of the experiment would confer upon them individual benefits and local advantages almost incalculable, whilst populations at a distance waited for the result with almost equal interest.