Page:Encyclopædia Britannica, Ninth Edition, v. 20.djvu/243

Rh RAILWAY 225 because it was first laid on bridges was that first used on the Great Western Railway, and is of a shallow section, but wide, and possessed of lateral stiff- ness. The first line was a series of beech piles, 12 inches square, driven into the FIG. 5. The bridge ground, to which were bolted at the sur- rail - face level cross balks of timber, one on each side of the pilehead on which they were shouldered. Longitudinal balks, 1 5 feet long, were laid on the cross balks. The longi- tudinals were covered with oak or elm planking screwed down to the surface. When the ballast was packed under the longitudinal balks, the surface of the oak planks was planed level, and the bridge rails screwed down on them, with felt between. It was supposed that there would be no yielding whatever, but a very short time demonstrated that the piles formed a series of solid resistances, while the balks between sprang, and it was found necessary to cut away the piles. Transoms were then framed into the longitudinals and secured by strap -bolts, and the whole resembled a long ladder laid on the ground. Eight different sections of rails were tried in succession ; one section measured 1 J inches in height by 7 inches in width, weighing 44 K> per yard ; and the last section 2f inches high by 6 inches wide, weighing 62 Ib per yard. The screws which held down the rails were counter-sunk be- neath the wheel-flanges, and nut-headed on the other side (see fig. 6). In consequence of the ^a want of depth in the rails, they bent longitudinally under the wheels, QSE3 and the horizontal flanges curled up at the sides, while the holes Fig. 6. Bridge rail on through them bent into angles. One Great Western Railway. remedy tried was to cross-board the longitudinal timbers on the surface, and thus the fibre was made less yielding. The double-headed rail (fig. 7) was originated by Joseph Locke, and was first laid on the Grand Junction Railway. It also weighed 62 Ib per yard. The two tables were equal ; the rail was more easily rolled than others, and, being reversible, it was in fact two rails in one. But as it was laid in cast-iron chairs the lower table was exposed to FIG. 7. The damage under the hammering of the traffic ; and double- many engineers were led to make the lower table of smaller size, as in fig. 8, merely as a support, not as a surface to be used by the wheels. This rail, which acquired the title of " bull-headed," was, like the flat-foot and bridge rails, used as a prop supported on its base. There was a waste of metal in these early rails, both flat-foot and double-headed, owing to the excessive thickness of the vertical web, which has been corrected in recent designs. It was found, naturally, that rails would not rest in their chairs at the joints, but were loosened and bruised at the ends by the blows of the traffic. The fish-joint Fr - 8 ;T The, b V" was therefore devised in 1847 by Mr W. a pw y.d). ( Bridges Adams, the intention being by "fishing" the joints to convert the rails into continuous beams. In the original design two chairs were placed, one under each rail, a few inches apart, as in fig. 9. The joint was thus suspended between the two chairs, and two keys of iron, called " fishes," fitting the side channels of the rails, were driven in on each side between the chairs and the rails. In subsequent modifications the fishes were, and they continue to be, bolted to and through the rails, the sleepers being placed further apart, and the joint sus- pended between them. In the employment of steam-power for traction on rail- ways rapid progress was made in response to the demand headed rail. for power. The year 1829 is famous in the annals of rail- ways not only for the opening of the Liverpool and Mau- FIG. 9. The original fish-joint, by W. Bridges Adams. Chester line but for the invention and construction of the first high-speed locomotive of the standard modern type. Robert Stephenson's engine, the "Rocket," was made under competition for the Liverpool and Manchester Rail- way, and it gained the prize for lightness, power, and speed awarded by the directors. The two steam-cylinders of the "Rocket" were 8 inches in diameter, with 16^ inches of stroke, and the driving-wheels were 4 feet 8| inches in diameter. The engine weighed 4 tons 5 cwt., the tender following it 3 tons 4 cwt., and two loaded carriages drawn by it on the trial 9 tons II cwt. : thus the weight drawn was 12 tons 15 cwt., and the gross total 17 tons. The pressure of steam in the boiler was 50 Bb per square inch. An average speed of 14 miles per hour was attained, the greatest velocity being 29 miles per hour ; and the boiler evaporated 18| cubic feet, or 114 gallons, of water per hour. The " Rocket " possessed the three elements of effi- ciency of the modern locomotive, the internal water- surrounded fire-box and the multitubular flue in the boiler, or a number of small tubes in place of one large tube ; the blast-pipe, by which the waste steam of the engine was exhausted up the chimney ; and the direct connexion of the two steam-cylinders, one on each side of the engine, with the driving or propelling wheels, on one axle. The subdivision of the single large flue, up to that time in general use in locomotives, into a number of small tubes greatly accelerated the generation of steam without adding to the size or weight of the boiler. But the evaporating tubes would have been of little avail practically had they not been supplemented by the blast-pipe, which, by ejecting the steam from the engine after it had done its work in the cylinder straight up the chimney, excited a strong draught through the boiler and caused a brisk and rapid combustion of fuel and generation of heat. The heat was absorbed with proportional rapidity through the newly applied heat- ing-tubes. The blast-pipe, thus applied, in conjunction with the multitubular flue, vastly improved the capacity and usefulness of the locomotive. And, taking into account the direct connexion of the steam-cylinder with one axle and pair of wheels, the improvements were tantamount to a new and original machine. The " Rocket " subsequently drew an average gross load of 40 tons behind the tender at a speed of 13'3 miles per hour. The old Killingworth engine, one of the earlier type of locomotives constructed by George Stephenson, weighing with its tender 10 tons, could only work at a maximum of 6 miles per hour with 50 tons. For many years engines belonged to two general classes. In one class there were six wheels, of which one pair was placed behind the boiler, typified in the engines of the day made by Robert Stephenson ; in the other class there were but four wheels, placed under the barrel of the boiler, leaving the fire-box overhung, typified in the engines made by Bury for the London and Birmingham Railway. Ex- perience demonstrated the disadvantage of an overhanging mass, with a very limited wheel-base, in the four-wheeled engine running at high speed; and now it is the general XX. 29