The Patent Cable Tramway Corporation owned the rights to the Hallidie cable-car system first invented and used in San Francisco in 1873; trains were attached to the cable with clamps, which would be opened and closed at stations, allowing the carriages to disconnect and reconnect without needing to stop the cable or to interfere with other trains sharing the cable. There were to be two independent endless cables, one between City station and Elephant and Castle moving at , and the other between Elephant and Castle and Stockwell, where the gradient was less, at . However, the additional length of tunnel permitted by the supplementary acts challenged the practicality of the cable system.