Victorian hydraulic boat lifts - ingenious industrial archeology.
Houdeng-Goegnies boat lift, the first of the four Victorian lifts (elevators). These ingenious structures each contain two large tanks on large shafts. The shafts are pistons in columns of water, with the columns linked. To move them up and down, a foot (30 cm) of water is added to the upper tank and the connecting valve opened. The extra weight of the upper tank pushes it down and the other tank up. While in theory this should operate with no additional power, in reality the system is slightly inefficient and there are pumps that help push up the raising piston. The four lifts have heights of 15 to 17 m. On the photo is lift number 1.