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.
How much more favourably situated is the railway locomotive or truck. _Their_ wheels touch metal at a point but a fraction of an inch in length; consequently there is nothing to hamper their progression. So great is the difference between the rail and the road that experiment has shown that, whereas a pull of from 8 to 10 lbs. will move a ton on rails, an equal weight requires a tractive force of 50 to 100 lbs. on the ordinary turnpike.
In order to obviate this great wastage of power, various attempts have been made to provide a road locomotive with means for laying its own rail track as it proceeds. About forty years ago Mr. Boydell constructed a wheel which took its own rail with it, the rails being arranged about the wheel like a hexagon round a circle, so that as the wheel moved it always rested on one of the hexagon's sides, itself flat on the ground. This device had two serious drawbacks. In the first place, the plates made a rattling noise which has been compared to the reports of a Maxim gun; secondly, though the contrivance acted fairly well on level ground, it failed when uneven surfaces were encountered. Thus, if a brick lay across the path, one end of a plate rested on the brick, the other on the ground behind, and the unsupported centre had to carry a sudden, severe strain. Furthermore, the plates, being connected at the angles of the hexagon, could not tilt sideways, with the result that breakages were frequent.