what is the city and south london railway?
The first deep-level underground "tube" railway in the world
City and South London Railway
The City and South London Railway (C&SLR) was the first deep-level underground "tube" railway in the world, and the first major railway to use electric traction. 
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City and South London Railway [SEP] Introduction
The City and South London Railway (C&SLR) was the first deep-level underground "tube" railway in the world, and the first major railway to use electric traction. The railway was originally intended for cable-hauled trains, but owing to the bankruptcy of the cable contractor during construction, a system of electric traction using electric locomotives—an experimental technology at the time—was chosen instead. When opened in 1890, the line had six stations and ran for in a pair of tunnels between the City of London and Stockwell, passing under the River Thames. The diameter of the tunnels restricted the size of the trains, and the small carriages with their high-backed seating were nicknamed "padded cells".