80 TBEVITHICK'S STEAM-CARRIAGE. CHAP. VI. 



the hind axle. The motion of the piston was trans- 

 mitted to a separate crank-axle, from which, through 

 the medium of spur-gear, the axle of the driving-wheel 

 (which was mounted with a fly-wheel) derived its mo- 

 tion. The steam-cocks and the force-pump, as also the 

 bellows used for the purpose of quickening combustion 

 in the furnace, were worked off the same crank-axle. 



John Petherick, of Camborne, has related that he 

 remembers this first English steam-coach passing along 

 the principal street of his native town. Considerable 

 difficulty was experienced in keeping up the pressure of 

 steam ; but when there was pressure enough, Trevithick 

 would call upon the people to "jump up," so as to 

 create a load upon the engine. It was soon covered 

 with men attracted by the novelty, nor did their num- 

 ber seem to make any difference in the speed of the 

 engine so long as the steam could be kept up ; but it 

 was constantly running short, and the horizontal bel- 

 lows failed to keep it up. 



This road-locomotive of Trevithick' s was one of the 

 first high-pressure working engines constructed on the 

 principle of moving a piston by the elasticity of steam 

 against the pressure only of the atmosphere. Such an 

 engine had been described by Leopold, though in his 

 apparatus it was proposed that the pressure should act 

 only on one side of the piston. In Trevi thick's engine 

 the piston was not only raised, but was also depressed 

 by the action of the steam, being in this respect an 

 entirely original invention, and of great merit. The 

 steam was admitted from the boiler under the piston 

 moving in a cylinder, impelling it upward. When the 

 motion had reached its limit, the communication between 

 the piston and the under side was shut off, and the 

 steam allowed to escape into the atmosphere. A pas- 

 sage being then opened between the boiler and the 

 upper side of the piston, which was pressed down- 

 wards, the steam was again allowed to escape as before. 



