RAILWAY-CARS.
E.ar/y Rathvay-cars.—That the railway-cars (carriages, coupes) may be able to travel oyer the railway with safety at the high speed required in railway practice, they should be built with greater solidity than the road vehicles previously described (p. 164), and upon a different model. The earliest railway-cars resembled the ordinary road-wagon in the fact that the wheels turned free upon the axles, and to prevent the wheels from leaving the track they were guided by flanges on the rail (11. 22, jig. 4). With the introduction of the edge-rail (fig. 5), some fifty years later, cast-iron flanged wheels came into use, and it is now the universal practice to fasten the wheels immovably to the axles, so that they may revolve together. In Europe the general practice is to attach the pedestals of the axle-boxes directly to the bed of the car (fil. 3o, Jig. 5). In America the custom is to mount the car-body independently on wheel-trticks (fi/. 31, .fig. 2). This variation is explained by the difference in the length and weight of the cars, the European small and comparatively light vehicles (fi/. 3o, fig. 16) being in marked contrast with the long and heavy cars used on American roads (I./. 32, fig. 5). The number of wheels on which the car is borne will vary with the size and weight of the car. The earliest railway-cars were placed upon four wheels (pl. 23, jig. 5), and this remained the gen eral practice in Europe, where the small and light compartment-carriages are still almost universally in vogue (fi/. 3o, fig. 16), down to a compara tively recent date, when, with the gradual increase of the length and weight of the rolling-stock, the six-wheel system on three axles (fig. 14) has come into general use, as is notably' the case on the English railways.
American Sysion of ifounling on usual American prac tice is to support the car-body on two four-wheeled trucks placed respect ively under the front and rear part of the car, the axles of each truck being placed close together (fi/. 32, fig. 5). The principal feature of this form of support is that the connection between the truck and the car-body is not rigid (as where the axle-boxes on pedestals are attached directly to the car-frame), but is flexible, permitting the truck to turn, or swivel, beneath the car-bed as the car strikes a curve, this freedom of motion to a large extent relieving the car of jar and shock. This swivelling feature is
obtained by means of a mechanical device similar in principle to that emplo)ecl to give the swivelling movement to the front axle of the com mon road-vehicle. It is shown on Plate 31 (jig. 2), which represents a longitudinal view and a transverse section of an American passenger-car truck. It consists of a strong timber frame to which the wheels are suit ably attached; inside of this frame is a so-called " swinging-bolster," rest ing on elliptic springs. This bolster carries a centre-casting, which forms the bushing for the kingbolt, and for what may be called (by reason of its resemblance to the corresponding device upon the C0111111011 road-vehicle) a " fifth wheel." Upon this the end of the car oscillates. On the same principle, parlor and hotel cars on American railways are constructed with twelve (fi/. 32, fig. 5), and even with sixteen, wheels (fii. 3o, fig. 17). The best class of passenger-cars on American railways are now placed on two six-wheeled trucks (fii. 32, figs. 4, 5).
first it was the practice to give the tread of the wheels a cylindrical form, but it was soon observed that this form permitted too much lateral play between the flanges and the rails, and resort was had to the conical form, now universally in use (j5/. 3o, figs. 1-4). This construction not only corrects the above-nained defect, but also lessens to some extent the resistance in passing curves, inasmuch as by centrifugal force the outer on the curve mounts the rail and describes a larger circle than the inner one. The car-wheel and axle, which are made in many different ways, constitute the most iinportant parts of the structure of the rolling stock of a railway. Cast iron is largely used in the construction of the wheel, which may be either the spoke- or the disk-wheel. A form of the latter which is much used is seen in Figures and 2. Figure is the well known Washburn wheel. It is a cast wheel having an arch in its central part, said arch being joined to the rim by a curved web. Where the web joins the rim, the disk is strengthened by a series of curved ribs.