In heavy vehicles the wheels are not set perpendicularly to the axis of the hub, but in such a manner as to incline outwardly, as seen in Figure 35 (AL 2o), giving- them what is technically called " dish." In connection with this it is found necessary to give a slight downward inclination to the axle, varying in deg-ree to correspond with the amount of dish given to the wheel (fig. 35). In the case of lig-lit vehicles the spokes are set straight in the hub, but receive dish by the shrinking on of the tire. This artifice is claimed to afford the following advantages—namely, it pro vides increased space for the wagon-body, the mud and dirt are more readily thrown off and away from the wagon, and a certain elasticity and lateral stiffness are obtained, and, where the roadway is strongly arched, better contact between roadway and tire is assured.
It is customary to make the bearing portion of the axle slightly taper ing, and (at least in American practice) the axle-box is adjusted as snugly as possible, especially with the lighter class of vehicles. The axle, made of wrought iron or steel, is given a square section between the bearing ends, and is secured by means of clips to the axle-bed (fig. 34). In the case of carts this axle-bed serves as a carrier of the wagon-body as well as for the attachment of the shafts (fii. 24, fig. 90).
The running--gear of a four-wheeled wagon comprises a front and back carriage part, usually joined together by the perch. Figure 32 (AL 2o) ex hibits a side view of a heavy wagon with the wagon-body removed; Figure 33 is a half g-round-plan of the same; Figure 34 exhibits half of the front running-gear; and Figure 35, the same of the back. The axle-bed of the front part, as shown in the illustration, is connected by iron bands with the woodwork immediately above it, forming a species of truck through which the futchels pass for receiving the pole, and to which the pole is firmly fastened. A suitable slot is provided in the fore truck for the attach ment of the front end of the perch, which likewise is firmly secured to the hind truck. The wag-on-body, of which only the two horizontal support ing beams are shown in the figure, rests, with these, directly upon the hind truck; in front, however, the supporting beams are joined to a cross-piece —the transom—which, in turn, is supported upon the truck of the fore axle. This transom is connected with the truck and with the front end of the perch by the kingbolt, which is passed through them, forming a pivot.
It is plain that by this artifice the wagon may be turned about with great ease, since it permits of considerable lateral deflection of the front axle with its truck independently of the wagon-body.
The above-described construction is now very generally modified by dispensing with the perch. Figure 38 zo), for example, represents an English farm-wagon of this description, in which the front wheels are car ried entirely under the wagon-body. It admits of being moved and turned about with great ease.
Upon pleasure-vehicles the omission of the perch is quite common, and lias certain advantages: it permits the body of the vehicle to be set lower, thus facilitating getting in and out, and, by lowering the centre of gravity, makes the strncture more stable. Much attention has also been bestowed on the construction of the axle-box, and numerous patenteci inventions have been introduced having for their object the attainment of greater se cnrity against the coming off of the wheels when driven at high speed, and the protection of the axle against rapid wear and cutting by more or less effective methods of excluding dirt and grit.
Classes of Carriages.—The variety of pleasure-carriages is legion, and the names by which they are distinguished are often quite arbitrary. The more recent models embrace the vehicles called, respectively, the landau, Berlin coach, English coach, extension-front brougham (pi. r, fig. 9), coupe, landaulette (fig. 12), wagonette, calash, phaeton (fig. 15), buggy (fig. 1), Whitechapel, dog-cart, cabriolet (fig. 13), surrey (fig. 14), rock away (jig. ro), T-cart, and numerous others.
Public Conveyances for the transportation of passengers and mail fall in this category. As early as the beginning of the seventeenth century the English had instituted a systematic public service of coaches for the trans portation of passengers between the principal cities, and the stage-coach has reached its highest state of perfection in that country. In France they had for the same purpose, first the slow " diligence," then the " malle-poste," and the coaches of the " Messageries Royales" and " Lafitte." In Ger many it appears that passenger-posts were first introduced after the Thirty Years' War, and the " Eilwagen," which came into use at the beginning of the present century, appears to have been modelled after the practice of the French.