We are told by some writers that the rolling log (the one-wheeled cart) was followed by the two-wheeled cart, on which the wheels were the ends of a log and the axle was the middle portion of the log hewn down to a proper size (Fig. 8). Here wheels and axle turned together precisely like a modern car wheel. This makes a very pretty story but I am afraid the solid two-wheeled affair represented in Figure 8 is only imaginary, and that in a true account of the development of the cart it has no place. The true beginning of the two-wheeled cart may be learned from Figure 9. Here the wheels are two very short logs through the center of which are holes in which the round ends (axles) of a piece of timber (the axle-tree) fit. When the cart moves, the wheels turn upon the axle. The one-wheeled cart had at first one log turning with the axle; the two-wheeled cart at first had as its wheels two very short logs turning on the axles.
FIG. 10.—CART WITH WHEEL PARTLY SOLID.
(From a Model in the National Museum.)
FIG. 11.—WHEELS WITH SPOKES.
(From National Museum.))
FIG. 12.—AN ANCIENT EGYPTIAN CHARIOT SHOWING HUB, SPOKES, FELLY AND RIB.
(From National Museum.)
The first two-wheeled carts were a great improvement upon the single rolling log, yet they were exceedingly heavy and clumsy. The trouble was with the wheel. This was very thick and with the exception of the hole in which the axle went it was entirely solid. Wheelwrights at a very early date saw that the problem was to make the wheel light and at the same time to keep it strong. Little by little this problem was solved. At first crescent-shaped holes were made in the wheel (Fig. 10). This made the wheel lighter, but did not weaken it. In its next form the wheel was even less solid than before. It now consisted of four curved pieces of wood (Fig. 11) held together by four spokes. In this wheel there was a hub, but the spokes were not inserted in it; they were fastened about it. In the Egyptian chariot (Fig. 12) we find the wheel in the last stage of its interesting and remarkable development. Here the spokes, six in number, are inserted in the hub from which they radiate to the six pieces of the felly or inner rim. Around the felly is the outer rim or tire made of wood and fastened to the felly with thongs. The wheel of to-day has more iron in it, and has more spokes and is lighter and stronger than the old Egyptian wheel, yet in its main features it is made like it.
