The cliff railway at the Centre for Alternative Technology near Machynlleth is amazing. The two cars are joined by a large cable which is wound around a large drum to provide braking. The cars cannot move independently of each other. The blue compartment in the top car is filled with water from a reservoir until that car is heavier than the lower one. Gravity means that the top car will fall and it will drag the lower car up. At the start of the day when people are predominantly going up the hill more water must be put into the tank than later in the day when people start going downhill.
