THE PEDRAIL: A WALKING STEAM-ENGINE

Too Long; Didn't Read

Have you ever watched carefully a steam-roller's action on the road when it is working on newly laid stones? If you have, you noticed that the stones, gravel, etc., in front of the roller moved with a wave-like motion, so that the engine was practically climbing a never-ending hill. No wonder then that the mechanism of such a machine needs to be very strong, and its power multiplied by means of suitable gearing. Again, suppose that an iron-tyred vehicle, travelling at a rapid pace, meets a large stone, what happens? Either the stone is forced into the ground or the wheel must rise over it. In either case there will be a jar to the vehicle and a loss of propulsive power. Do not all cyclists know the fatigue of riding over a bumpy road—fatigue to both muscles and nerves? As regards motors and cycles the vibration trouble has been largely reduced by the employment of pneumatic tyres, which lap over small objects, and when they strike large ones minimise the shock by their buffer-like nature. Yet there is still a great loss of power, and if pneumatic-tyred vehicles suffer, what must happen to the solid, snorting, inelastic traction-engine? On hard roads it rattles and bumps along, pulverising stones, crushing the surface. When soft ground is encountered, in sink the wheels, because their bearing surface must be increased until it is sufficient to carry the engine's weight. But by the time that they are six inches below the surface there will be a continuous vertical belt of earth six inches deep to be crushed down incessantly by their advance.