HADLEY'S ENGINE, WYLAM RAILWAY, 1815

     This engine was practically the same as the "Puffing Billy," but was of greater power as the cast iron rails, then employed, were only able to support then when their weight was distributed upon eight wheels, also geared to work together so as obtain the adhesion of them all.

     These engines embodied two improvements of much importance, the first being the return flue boiler to give additional heating surface and to render the course of the flame more effective, the other of adopting a chimney of small diameter (12 inches) which materially increased the draft.

     Trevethick was perhaps, the author of both these improvements but Hadley was the first to bring both into practical use.