Traversing platforms are used when it is desired simply to pass engines or carriages from one line of rails to another situated parallelly to it. They are exclusively fixed in stations where no through traffic can possibly be admitted ; because they consist of a platform suscep tible of movement only in a direction transversal to that of the line of rails, and moving on rollers in a deep pit extending the whole length of the lines thus put in communication with one another.
Water-tanks, water-cranes, pumping-engines, and wells, constitute useful adjuncts of railways, but they hardly require special notice iu this article. The signal posts, for both day and night services ; the provisions for the establishment of the electric telegraph ; the watch boxes even for the guardians of the way in particular positions, must also occupy the serious attention of the railway engineer. Local cir cumstances must, however, so modify the manner of dealing with all these questions of detail, that it would be dangerous to attempt to lay down any absolute principles with respect to them, otherwise than by saying that every convenience should be provided to facilitate the discharge of duties upon which the safety of the public so materially depends. It may bo added that, with respect to the service of the water columns for the supply of tenders, the tendency of modern practice is to make them with reservoirs able to hold about 200 cubic feet of water, and to place those reservoirs immediately over the delivery-pipe, so as to ensure the rapid filling of the tenders; the reservoirs are them selves filled during the intervals of the trains. Heating apparatus are also provided for the water-columns, in order to prevent the freezing of the water. Good signals are especially required at the entrances of long tunnels, and at the points of the turn-outs of single lines of railway, or at embranehments.
On some lines, or portions of lines, as on the old Birmingham and the Blackwall Railways, upon the goods lines at Liverpool, and upon the line from Liege to the Prussian frontiers, it was thought advisable to substitute fixed machinery for the locomotives employed on the other parts of the line. These machines, in fact, gave motion to end less ropes, passing over grooved wheels and running from station to station upon friction-rollers, to which ropes the carriages were attached, and were thus hauled along. In almost every case, but those at Liege and at Liverpool, these engines have been abandoned ; and indeed, the improvements lately introduced in the details of locomotive engines have rendered their intervention unnecessary ; and it may be suspected that at Liege, even the fixed engines would have been abandoned, had they not been placed on n line in the direct control of the state. The same description of remark may also be extended to the atmospheric railway, which has been so universally abandoned by engineers, that it may suffice here to refer those who desire to make themselves acquainted with its practical and theoretical defects, to the Late Mr. R. Stephenson's report upon the subject. The system thus referred to was tried on the largest scale, both in England and in France ; and in both countries it has signally failed (when compared, economically) with locomotive traction. (ATMOSPHERIC RAILWAY.] Stock.—Railway carriages for the conveyance of passengers are usually very capacious, the bodies being made to project over the wheels, which in ordinary lines are made 3 feet, or 3 feet 6 inches in diameter; but as the centre of gravity of the carriages is kept very low, the oversailing of the frame produces no evil effects. On account of the rapid speed at which the carriages travel, and the violent shocks to which they aro occasionally exposed, their frames are necessarily made of great strength ; and every precaution is taken by the intro duction of springs and buffers to diminish the violence of the blows they receive, or the effect they themselves might produce upon the rails. Elasticity in the traction is also necessary as well for the safety and comfort of the passengers, as for the preservation of the carriages; and even in order to economise engine power, for if it did not exist, the engine would be obliged to exercise a greater power to start the trains than it would do for the maintenance of the speed once attained.
Various contrivances, more or less successful, have been adopted to secure these conditions ; but the system represented in Fig. 17, is the the engine, and upon the same frame ; and sometimes with the tenders entirely detached, and carried upon a distinct set of four wheels, as is the case with any ordinary carriage. In America, and on the lines in Germany with very steep gradients, the engines are made with eight, or even with ten wheels ; the tenders being, in either of those cases, upon the same frame as the engines, but the wheels working upon two bogie axle frames. In ordinary passenger engines the cylinders are placed internally, and the piston-head communicates motion directly to the crank upon the large centre wheels, which thus become the driving-wheels, leaving the fore and hind pairs of wheels simply to act as trailers. Figs. 13 and 19 will convey a tolerably correct notion of one usually adopted ; it represents the plan of the framework of a carriage, the body being supposed to be removed. The frame is carried on springs fixed outside the wheels, and resting on brass bushes, which hear directly on the Balm : a, a, a, a, are the buffers, or discs of wood or metal, covered with cushions, and fixed to the ends of metal rods, working between guides against the ends of very strong horizontal springs c, c. In such cases, when the train is suddenly the springs are forced against one another, and serve thus to soften the blow to an extent dependent upon the force of the spring. The draw-bars are also'attached to the centre of the horizontal springs, and thus prevent any sudden jar to the frames of the carriages at their starting, and the several draw-bars of a train are attached to one another by a coupling chain, bearing a double thread, so as to force the buffers into close contact; loose chains are also placed by the sides of the buffers, in case the couplin; chains should break. Many varieties of springs have been applied for both the purposes described above ; but experi ence has led engineers to resort to the old-fashioned plate springs, of course of considerable thickness, and of the very best quality of steel. The ordinary first-class carriages have three compartments, able to contain from six to eight passengers in each compartment ; the second class carriages mostly have three or four compartments with ten pas sengers in each compartment; whilst the third-class carriages are made to contain from fifty to sixty passengers each. The weight of the best modern first-class carriages, on the narrow-gauge, is about tons; that of the sec6nd-class is about 6; tons ; and that of the third-class 6 tons : or, in other words, the ratios of the dead weights of the carriages to the loads transported are, in the several classes, as to 1; as 2.1 to 1 ; and as to 1. A certain number of the car riages in each train is made with breaks, and a guard's van, with occa sionally an extra luggage van, are added. Horse-boxes, carriage-trucks, and post-office waggons are made upon the same principles of framing and suspension, as the ordinary traveller's carriages, so as to allow of their being added to the same trains as the latter. Aa the goad; waggons do not travel at the same velocity as the waggons for the conveyance of passengers, there is not the same attention paid either to their modes of suspension, or to their drawbars; but every waggon which is added to a train moved by a locomotive engine is hung upon springs, even when there is no spring draw-bar; there is very rarely any buffing apparatus attached to merchandise waggons. On ordinary narrow-gauge lines the weights of goods carriages range between 3 and 5 tons; they carry about 5 tons each.