Stephenson's Engine, 1815.
Twining’s Model of Stephenson’s Engine
This engine had vertical cylinders immersed within the boiler, each piston rod being secured to a long crosshead spanning the whole width of the engine and having a pair of connecting rods working downward and turning one pair of wheels by means of crank pins fixed in their arms. It was proposed to couple the wheels together by a pair of coupling rods working on cranks forged in both axles and the adhesion of the wheels of the tender was to be also obtained by coupling them to one pair of the engine by means of an endless chain. The attempt was abandoned and the engine wheels were coupled by an endless chain until, after some years, outside coupling rods were adopted. This engine was constructed under Geo. Stephenson's directions, in the workshops of the Killingworth Colliery in 1815.
The 26-year-old George Stephenson actually worked on two engines at the Killingworth Colliery. The first was tested in 1814 and the second, was patented in 1815. Details of the two engines are given in Brown, William H., The History of the First Locomotives In America.