An experiment by the London and Croydon Railway. Pumping stations were built which created a vacuum in a pipe laid between the rails. Each carriage had a piston that entered a slot in the tube, sealed by a leather seal. As air was sucked from the tube the carriages were drawn along the track.
As part of the construction works, the world's first railway viaduct was built, carrying the railway over the conventional steam line below. After the experiment was abandoned, the stationary engine-house at Forest Hill railway station was largely demolished and an electricity sub-station built on the site. This image shows the viaduct above the conventional steam railway.
Credit for this entry to: Alan Patient of www.plaquesoflondon.co.uk