Experiment

The Stockton & Darlington Railway, opened on 27 September 1825, had been authorised primarily as a coal-carrying line, but from its first day it also carried fee-paying passengers in a small four-wheeled coach known as "Experiment". For the railway's first months these passenger workings were in fact horse-hauled, and it was only in 1826 that a locomotive specifically capable of working passenger trains at higher speeds was commissioned.

The new engine, also named Experiment after the coach, was built at Robert Stephenson's Forth Street works in Newcastle in 1826. It followed the general Stockton & Darlington pattern established by Locomotion No. 1 but with refinements aimed at smoother running for passenger service.

Experiment entered service in 1826 and worked the Stockton & Darlington's pioneering passenger services through the late 1820s. It was eventually superseded by the more sophisticated Planet-pattern engines from 1830 onwards. The locomotive was withdrawn during the 1830s and has not been preserved.

0-4-0 chassis with vertical in-boiler cylinders, side-rod coupled wheels, and a tall front-mounted chimney; broadly similar in appearance to Locomotion No. 1.

• Experiment (1826, not preserved)