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ciently strong for the purpose of keeping up the intensity of the fire in the furnace, so as to produce high pressure steam with the required velocity. 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 jet 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; and their efficiency was tested by the amount of vacuum that was produced in the smokebox. The degree of rarefaction was determined by a glass tube fixed to the bottom of the smoke-box, and descending into a bucket of water, the tube being open at both ends. 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
• The alteration afterwards made in the blast of the “ Rocket,” after the competition at Rainhill, by which the two separate exit pipes were thrown into CHAP. xxv.] CONSTRUCTION OF THE “ROCKET.”
below the area of the steam-ports; and before the engine left the factory, the water rose in the glass tube three inches above the water in the bucket.
The other arrangements of the “Rocket” were briefly these: - The boiler was cylindrical with flat ends, six feet in length, and three feet four 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, twenty-five copper tubes of three 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, two feet wide and three 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 connexion 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 four tons and a quarter; and it 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 completed, 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
one, as in the original Killingworth engines, was adopted rather with the view of lessening the space occupied by them in the chimney than because of any increased effect thereby secured, though it is probable that the jet of steam is rather more efficient when thrown upwards in the exact centre of the chimney than when slightly on one side.
quantity which then appeared marvellous. The same evening a letter was dispatched to George Stephenson 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 shipped for Liverpool.
THE COMPETITION OF LOCOMOTIVES AT RAINHILL.
The time, so much longed for by George Stephenson, had now arrived, when the merits of the passenger locomotive were about to be put to the test. He had fought the battle for it until now almost single-handed. Engrossed by his daily labours and anxieties, and harassed 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 circumstance 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 competition. 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 idle spectators either. The populations 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. On the day appointed for the great competition of locomotives at Rainhill, the following engines were entered for the prize: –
1. Messrs. Braithwaite and Ericsson's “ Novelty."
4. Mr. Burstall's “ Perseverance." Another engine was entered by Mr. Brandreth of Liverpool — the “ Cycloped,” weighing three tons, worked by a horse in a frame; but it could not be admitted to the competition. The above were the only four exhibited, out of a considerable number of engines which had been built in different parts of the country in anticipation of this contest, but which could not be satisfactorily completed by the day fixed for the competition.
The ground on which the engines were to be tried was a level piece of railroad, about two miles in length. Each engine was to make twenty trips, or equal to a journey of seventy miles, in the course of the day; and the average rate of travelling was to be not under ten miles an hour. It was determined that, to avoid confusion, each engine should be tried separately, and on different days.
The day fixed for the competition was the first of October, but to allow the engines sufficient time to get into good working order, the directors extended it to the 6th. The judges were Mr. Nicholas Wood, Mr. Rastrick, and Mr. Kennedy. On the morning of the 6th, the ground at Rainhill presented a lively appearance, and there was as much excitement as if the St. Ledger were about to be run. Many thousand spectators looked on, amongst whom were some of the first engineers of the day. A stand was provided for the ladies; and the “ beauty and fashion ” of the neighbourhood were present, whilst the side of the road was lined with carriages of all descriptions.
It was quite characteristic of Mr. Stephenson, that, although