RAILWAYS.

663. THE great resistance offered to the force of traction on common roads, where the traffic is of a heavy character, naturally suggested the idea of trying other means, which would afford a more even and durable track for the wheels than the road-coverings in ordinary use. Various methods have been resorted to, with greater or less success, to accomplish this object: in some instances tracks have been formed of long narrow stone blocks; in others, heavy beams of timber, covered on the surface with sheet iron to protect them from wear, have been used; and finally, both the stone and wooden ways were replaced by iron plates and bars, and that system of road-covering, now so well known as the railway, or railroad, has been the result.

For these successive stages of improvement, by which, in the short period of less than a quarter of a century, so great a revolution has been made both in the speed and the amount of transportation on land, by means which bid fair to supersede every other, the civilized world is indebted to England, in whose mining districts the railway system first sprung up.

664. A railway, or railroad, is a track for the wheels of vehicles to run on, which is formed of iron bars placed in two parallel lines and resting on firm supports.

665. Rails. The iron ways first laid down, and termed tramways, were made of narrow iron plates, cast in short lengths, with an upright flanch on the exterior to confine the wheel within the track. The plates were found to be deficient in strength, and were replaced by others to which a vertical rib was added under the plate. This rib was of uniform breadth, and of the shape of a semi-ellipse in elevation. This form of tramway, although superior in strength to the first, was still found not to work well, as the mud which accumulated between the flanch and the surface of the plate presented a considerable resistance to the force of traction. To obviate this defect, iron bars of a semi-elliptical shape in elevation, which received the name of Fig. 157-Represents a cross section a, of the fish-bellied rail of the Liverpool and Manchester Railway, and the method in which it is secured to its chair. The rail is formed with a slight projection at bottom, which fits into a corresponding notch in the side of the chair b. An iron wedge c is inserted into a notch on the opposite side of the chair, and confines the rail in its place.

edge rails, were substituted for the plates of the tramway. The cross sections of these rails were of the form shown in Fig. 157,

the top surface being slightly convex, and sufficiently broad to preserve the tire of the wheel from wearing unevenly. This change in the form of the rail introduced a corresponding one in the tires of the wheels, which were made with a flanch on the interior to confine them within the rails of the track.

The cast-iron edge-rail was found upon trial to be subject to many defects, arising from the nature of the material. As it was necessary to cast the rails in short lengths of three or four feet, the track presented a number of joints, which rendered it extremely difficult to preserve a uniform surface. The rails were found to break readily, and the surface upon which the wheels ran wore unevenly. These imperfections finally led to the substitution of wrought-iron for cast-iron.

666. The wrought-iron rails first brought into use received nearly the same shape in cross section and elevation as the castiron rail. They were formed by rolling them out in a rollingmill so arranged as to give the rail its proper shape. The length of the rail was usually fifteen feet, the bottom of it (Fig. 158)

Fig. 158-Represents a side elevation of a portion of a fish-bellied rail.

presenting an undulating outline so disposed as to give the rail a bearing point on supports placed three feet apart between their centres. This form, known as the fish-belly rail, was adopted as presenting the greatest strength for the same amount of metal. It has been found on trial to be liable to some inconveniences. The rails break at about nine inches from the supports, or one fourth of the distance between the bearing points, and from the curved form of the bottom of the rail they do not admit of being supported throughout their length.

667. The form of rail at present in most general use is known by the name of the parallel, or straight rail, the top and bottom of the rail being parallel; or as the T, or H rail, from the form of the cross section.

A variety of forms of cross section are to be met with in the parallel rail. The more usual form is that (Fig. 159) in which

the top is shaped like the same part in the fish-belly rail, the bottom being widened out to give the rail a more stable seat on

its supports. In some cases the top and bottom are made alike to admit of turning the rail. The greatest deviation from the usual form is in the rail of the Great Western Railway in England, (Fig. 160.)

Fig. 160-Represents a cross section of the rail of the Great Western Railway in England. This rail is laid on a continuous support, and is fastened to it by screws on each side of the rail. A piece of tarred felt was inserted between the base of the rail and its support.

The dimensions of the cross section of a rail should be such that the deflection in the centre between any two points of support, caused by the heaviest loads upon the track, should not be so great as to cause any very appreciable increase of resistance to the force of traction. The greatest deflection, as laid down by some writers, should not exceed three hundredths of an inch, for the usual bearing of three feet between the points of support. The top of the rail is usually about two and a half inches broad, and an inch in depth. This has been found to present a good bearing surface for the wheels, and sufficient strength to prevent the top from being crushed by the weight upon the rail. The breadth of the rib varies between three fourths of an inch to an inch; and the total depth of the rail from three to five inches. The thickness and breadth of the bottom have been varied according to the strength and stability demanded by the traffic.

668. Supports. The rails are laid upon supports of timber, or stone. The supports should present a firm unyielding bed to the rails, so as to prevent all displacement, either in a lateral or a vertical direction, from the pressure thrown upon them.

Considerable diversity is to be met with in the practice of engineers on this point. On the earlier roads, heavy stone blocks were mostly used for supports, but these were found to require great precautions to render them firm, and they were, moreover, liable to split from the means taken to confine the rails to them. Timber has, within late years, been generally preferred to stone. It affords a more agreeable road for travel, and gives a better lateral support to the rails than stone blocks.

The usual method of placing timber supports is transversely to the track. Each support, termed a sleeper, or cross-tie, being formed of a piece of timber six or eight inches square. The ordinary distance between the centre lines of the supports, is three feet for rails of the usual dimensions. With a greater bearing, rails of the ordinary dimensions do not present sufficient stiffness. The sleepers, when formed of round timber, should be squared on the upper and lower surface. On some of the recent railways in England, sleepers presenting in cross section a right-angled triangle have been used, the right angle being at the bottom. They are represented to be more convenient in setting, and to

offer a more stable support than those of the usual form. The sleepers are placed either upon the ballasting of the roadway, or upon longitudinal beams laid beneath them along the line of the rails. The latter is now the more usual practice with us, and is indispensable upon new embankments to prevent the ends of the sleepers from settling unequally. Thick plank, about eight inches broad and three or four inches thick, is usually employed for the longitudinal supports of the sleepers.

On some of the more recent railways in England, the rails have been laid upon longitudinal beams, presenting a continuous support to the rail, the beams resting upon cross-ties.

669. Chairs. The rails are firmly fastened to their supports by cast-iron chairs, (Figs. 157, 159,) wrought-iron spikes, or screws. The chair is cast in one piece, and consists of a bottom-plate, upon which the rail rests, and two side pieces between which the rail is confined by wedges of iron, or of wood. The chairs are fastened to the supports by iron bolts, or wooden pins. A variety of forms have been given to the chairs, and different methods adopted for confining the rail firmly within them. Iron wedges having been found to work loose, wooden wedges, or keys, have been substituted for them. They are made of kiln-dried timber, and are forced through cutters, by which they receive the proper shape, and are at the same time strongly compressed. The key, prepared in this manner, gradually swells by imbibing moisture after being inserted, and forms a very strong fastening. Chairs are generally placed upon each support. In some cases they are only placed at the points of junction of the rails; iron spikes with a bent head being driven into the supports, to confine the rails at the intermediate points between the chairs.

A joint of sufficient width is left between the ends of the rails, to allow for the expansion of the bars. Various methods of forming this joint have been tried; the more usual forms are the square joint, and the oblique joint.

670. Ballast. A covering of broken stone, of clean coarse gravel, or of any other material that will allow the water to drain off freely, is laid upon the natural surface of the excavations and embankments, to form a firm foundation for the supports. This has received the appellation of the ballast. Its thickness is from nine to eighteen inches. Open or broken-stone drains should be placed beneath the ballasting to convey off the surface water. The parts of the ballasting upon which the supports rest should be well rammed, or rolled; and it should be well packed beneath and around the supports. After the rails are laid, another layer of broken stone or gravel should be added, the surface of which should be slightly convex and about three inches below the top of the rails.

671. Temporary railways of wood and iron. On the first introduction of railways into the United States, the tracks were formed of flat iron bars laid upon longitudinal beams. The iron bars were about two and a half inches in breadth, and from one half to three fourths of an inch in thickness, the top surface being slightly convex. They were placed on the longitudinal beams, a little back from the inner edge, the side of the beam near the top being bevelled off, and were fastened to the beam by screws or spikes, which passed through elliptical holes with a countersink to receive the heads of the spikes; the holes receiving this shape to allow of the contraction and expansion of the bar, without displacing the fastenings. The longitudinal beams were supported by cross sleepers, with which they were connected by wedges that confined the beams in notches cut into the sleepers to receive them. The longitudinal beams were usually about six inches in breadth, and nine inches in depth, and in as long lengths as they could be procured. The joints between the bars were either square or oblique, and a piece of iron or zinc was inserted into the beams at the joint, to prevent the end of the rail from being crushed into the wood by the wheels.

In some instances the bars were fastened to long stone blocks, but this method was soon abandoned, as the stone was rapidly destroyed by the action of the wheels; besides which, the rigid nature of the stone rendered the travelling upon it excessively disagreeable.

This system of railway, whose chief recommendation is economy in the first cost, has gradually given place to the solid rail. Besides the want of durability of the structure, it does not possess sufficient strength for a heavy traffic.

672. Gauge. The distance between the two lines of rails of a track, termed the gauge, which has been adopted for the great majority of the railways in England, and also with us, is 4 feet 8 inches. This gauge appears to have been the result of chance, and it has been followed in the great majority of cases up to the present time, owing to the inconvenience that would arise from the adoption of a different gauge upon new lines. The greatest deviation yet made from the established gauge is in that of the Great Western Railway, in which the gauge is seven feet. Engineers are generally agreed that a wider gauge is desirable, as with it the wheels of railway cars could be made of greater diameter than they now receive, and be placed outside of the cars instead of under them as at present; the centre of gravity of the load might be placed lower, and more steadiness of motion and greater security at high velocities be attained.