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MOTIVE POWER AND DISPOSITION

resistance opposed to the progressive motion ofthe wheels, were greater than the friction oradhesion of the exterior surface of the peri-phery of the wheels upon the rail, the wheelswould then slide round, and the engine wouldstand still; but so long as the former does notexceed the latter, the wheels will always rollforward along the rails, and effect the progres-sive motion of the engine.

In this engine, the small cog-wheels eg fwere each twelve inches diameter, and the coir-wheels upon the axles of the travelling wheelstwenty-four inches diameter; so that the cranksmade two revolutions for one revolution of theengine-wheels.

This engine was tried upon the Killing-worthColliery llail-road, July 27, 1814, upon apiece of road with the edge-rail, ascendingabout one yard in four hundred and fifty, todraw after it, exclusive of its own weight, eightloaded carriages, weighing altogether aboutthirty tons, at the rate of four miles an hour ;and, after that time, continued regularly atwork.

The application of the two cylinders renderedthe action of the engine regular, and securedthe continual progressive motion ; thus reme-dying the imperfection caused by the irregularaction of the single cylinder and fly-wheel.