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Page:Popular Science Monthly Volume 18.djvu/470

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THE POPULAR SCIENCE MONTHLY.

this is to saw two broad drums off a tree-trunk, and connect them by a stout bar through their centers, pinned fast, so that the whole turns as a single roller. The solid drum-wheel was used in the farm-carts of classic times (see the article "Plaustrum," by Yates, in Smith's "Dictionary of Greek and Roman Antiquities"). The ox-wagon here shown is taken from the Antonine column (Fig. 11); it appears to have solid wheels, and the square end of the axle proves that it and its drum-wheels turned round together in one. A further improvement was to make the wheel with several pieces nailed together, which would be less liable to split. The ancient Roman farm-carts were mostly made with such wheels, as are their successors which are used to this day with wonderfully little change, as in Greece and Portugal.

Fig. 11.
PSM V18 D470 Ancient roman farm kart and oxen.jpg

The bullock-cart of the Azores (Fig. 12) (from Bullar, "Winter in the Azores," vol. i, p. 121) is a striking relic from the classic world; its wheels are studded with huge iron nails, by way of tire. From old times it was common to make wooden rings, sockets, or bearings underneath the cart for the axle to turn in, much as children's toy-carts are made, as has often been remarked. But a drawing of a modern bullock-cart, taken near Lisbon, represents only a pair of pieces of wood acting as stops, so that the body of the cart can be lifted off its wheels. In looking at these clumsy vehicles, we certainly seem to have primitive forms before us. There is, however, the counter-argument, which ought not to be overlooked, and which in some measure accounts for the lasting on of these rude carts, namely, that for heavy carting across rough ground they are convenient, as well as cheap and easily repaired. Considering that the railway-carriage builder gives up the coach-wheel principle, and returns to the primitive construction of the pair of wheels fixed to the axle turning in bearings, we see that our ordinary carriage-wheels turning independently on their axles are best suited to comparatively narrow wheels, and to smooth ground or made roads. Here they give greater lightness and speed, and especially have the advantage of easily changing direction and turning, which in