CHAP. IX.] 



THE LOCOMOTIVE. 



479 



has been of course to avoid the ruts occasioned by the weight of 

 the engines. With this object Boydell employed an endless rail, 

 which placed itself in front of the wheel, and rested on the ground by 

 means of broad shoes. The complication of the machinery arid the 

 small velocity obtained led to the abandonment of this system. 

 Bray adopted iron wheels of large dimensions, provided along the 

 circumference with movable grippers, but the result was that the 

 roads were quickly spoiled. To solve the same problem Thomson of 

 Edinburgh covered the fellies of the driving-wheels of his engine with 

 vulcanized India-rubber bands 5 inches thick and 1 foot broad. 



FIG. 322. Larmanjat's road- engine. 



These bands l perfectly support the weight of the engine, and roll 

 on ordinary roads without breaking the stones that lie on the surface. 

 Owing to the elasticity of the india-rubber, the contact between the 

 felly and the ground is not confined to a line, but takes place on a 

 surface over which the pressure is distributed. The wheels therefore 

 do not bury themselves in the ground, and even if it is made to pass 

 over newly-made roads, it will traverse the freshly broken stones 

 without the band being cut or spoiled. The force necessary to drive 

 a locomotive of this sort is therefore much less than that necessary 



1 See an article by M. Sauvee in the Industrial Annals, an excellent review, from 

 which we borrow the drawing of Thomson's locomotive. 



