454 



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 " Dic- 

 tionary 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 improve- 

 ment was to make the wheel with several pieces nailed together, which 

 would be less liable to sj^lit. The ancient Roman farm-carts were 

 mostly made with such w^heels, as are their successors which are used 

 to this day with wonderfully little change, as in Greece and Portugal. 



Fig. 11. 



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-argu- 

 ment, 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 



