Page:The Kinematics of Machinery.djvu/623

Rh shows them to be simply the nails which had been driven into the wooden rim rusted together! The collection at Sigmaringen contains some beautiful specimens of them. They form evidently a very early step in the direction of making tires out of one piece.

I have found what appears to be a confirmation of Lindenschmidt's view in a model of a two-wheeled Chinese cart which was sent to the Vienna Exhibition of 1873. The tires are here made of iron, drawn out under the hammer; they are, however, very narrow, and on their outer surfaces are deeply stamped into forms resembling strings of beads. This appears to be simply a transference of the traditional outward form to the solid tire. The stamping is a fashion only, use and wont give value to this external form, although the new construction has made it worthless a process which fashions of every kind experience. It may be noted here, also, that in the great Pompeian mosaic, the "Alexander-schlacht," the Persian chariot in .the centre is represented as having a tire of nails made in the way we have described.

[The ancient wheels in the British Museum form a very interesting study. The Egyptian paintings show but few chariots ; their wheels have always six spokes, and only one drawing (so far as I have noticed) shows any constructive details. This belongs to the 18th or 19th dynasty. The nave is made in one piece, and has sockets for the (round) spokes ; at the end of each spoke is a tee-piece, which forms a socket both for the spoke and for the segments of the tire. Spokes and tire segments are coloured red, the nave and tee-pieces are left white.

The ancient Greek vases (circa 800 500 ) show numerous racing chariots, sometimes in very great detail. A great number of their wheels have four spokes only, but the way in which the wheel is put together is not shown. The tires are very narrow and apparently (from some of the end views) made in segments. A number of the drawings seem to indicate that the spokes are flat, and very much wider (in the plane of the axle) at the nave than at the rim. Strengthening pieces are always used at the junction of the spokes with the rim. Upon one vase, a prize at an Athenian chariot-race about 700, chariot-wheels are very distinctly shown as having one pair of radial spokes only, these being crossed at right angles by two bars passing at a considerable distance on each side of the nave. In the bronze room there is a four-wheeled bronze brazier from Vulci, and two others from Eschara, none of them probably later than 600 The wheels are four or five inches diameter.

The most interesting wheels are, however, those of the Assyrian sculp- tures. Here the uses of three different forms of wheel can be distinctly noticed. The vehicles used for heavy carriages and drawn by oxen have four spokes only. The sculptor has not thought it worth while to show their con- structive details, but the spokes are very broad and clumsy, and probably square in section, the tires or rims are also very heavy. The ordinary war chariot-wheels have commonly eight spokes. These are apparently round and fit in sockets formed upon the nave. The rim of the wheel is very deep, and is always shown as consisting of three concentric rings, of which the outer one, the tire, is much the deeper, and is made in segments. The rims are generally strengthened by two pairs of clips slipped on from the inside and

�