1911 Encyclopædia Britannica/Wheel

WHEEL (O. Eng. hwēol, hweohl, &c., cognate with Icel. hjōl, Dan. hiul, &c.; the Indo-European root is seen in Sanskrit chakra, Gr. κύκλος, circle, whence "cycle"), a circular frame or solid disk revolving on an axis, of which the function is to transmit or to modify motion. For the mechanical attributes and power of the wheel and for the modification of the lever, known as the "wheel and axis," and of the mechanical powers, see Mechanics. The most familiar type of the wheel is of course that used in every type of vehicle, but it forms an essential part of nearly every kind of mechanism or machinery. Vehicular wheels in the earliest times were circular disks either cut out of solid pieces of wood, or formed of separate planks of wood fastened together and then cut into a circular shape. Such may be still seen in use among primitive peoples to-day, especially where the tracks, if any exist, are of the roughest description, and travelling is heavy. The ordinary wheel consists of the nave (O. Eng. nafu, cf. Ger. Nabe, allied with "navel"), the central portion or hub, through which the axle passes, the spokes, the radial bars inserted in the nave and reaching to the peripheral rim, the felloe or felly (O. Eng. felge, Ger. Felge, properly that which fitted together, Teut. felhan, to fit together). From the monuments we see that the ancient Egyptian and Assyrian chariots had usually six spokes; the Greek and Roman wheels from four to eight. (See further Carriage and Chariot; also Tire; and articles on Bicycle; Tricycle; and Motor Vehicles.)