As narrow wheels always sink into the ground, espec•tlly when the heaviest part of the load lies upon them, they must be considered as going constantly up-hill, even on level ground. And their aides most sustain a great deal of fric tion by rubbing against the ruts made by others. But both these inconve niences are avoided by broad wheels ; which, instead of cutting and ploughing up the roads, roll them smooth and har den them, as experience testifies, in places where they have been used; espe cially either on wettish or sandy ground. The fore-wheels of all carriages ought to be so high as to have their axles even with the breasts of the horses, which would not only give the horses a fair draught, but likewise cause the machine to be drawn by a less degree of power. When the spokes are inclined to the the wheels are said to be connive, or dishing. But it is allowed, on all hands, that perpendicular spokes are pre ferable on level ground. The inclination of the spokes, therefore, which may ren der concave wheels advantageous in rug ged and unequal roads, renders them dis advantageous when the roads are in good order.
M. Camus showed that the line of trac tion should be a horizontal line, or rather, that it should always be parallel to the ground on which the carriage is moving, both because the horse can exert his greatest strength in this direction, and because the line of draught, beingper pendicular to the vertical spoke of the wheel, acts with the greatest possible leverage. M. Deparcieux shows, in the most satisfactory manner, that animals draw by their weight, joined to the force of their muscles. In four-footed animals,
the hind-feet are the fulcrum of the le ver by which their weight acts against the load, and when the animal pulls hard, it depresses its chest, and thus in creases the lever of its weight, and di minishes the lever by which the load resists its efforts.
Noiseless wheels.—A patent has been taken out for dulling the sound of wheels. IA this instance the invention consists in the application of a solid band of vulcanized. Over the iron tire of the wheel. The India-rubber is held it, its place by the tire having a rais ed rim on both sides, and by its own elasticity. The band of an ordinary carriage wheel is about an inch to one inch and a half in thickness, and, un less on close inspection, no difference from the common iron-shod wheel is per ceptible. We have driven some distance in a with the wheels so shod, and were struck, not only with its noise lessness, but at the perfect smoothness of the motion—the wheels being, in fact, springs, and, by their elasticity, giving a lighter draught than with the iron tire. One set of wheels, which have been driven 4000 miles, have here and there a trifling cut, but show no appearance of being worn out, and seem quite ca pable of another three or four thousand. An iron tire is generally worn out in 8,000 miles, so that the India rubber tire has so far proved itself the more lasting. It is certainly a great addition to the lux ury of a carriage to have it run without jar or noise ; and it would be a universal comfort to have the streets of cities without the present incessant rattle of carriages, omnibuses, &c.