TARGET 080220 How to connect two rivers which flow at different levels.

What with Loch Ness and Loch Lomond and all the other lochs in Scotland, you'd expect them to build a simple set of locks (ship-locks, that is). But no, they had to come up with something new and, actually, very wonderful. They invented a new use for the wheel. The Falkirk Wheel lies at the end of a reinforced concrete aqueduct that connects, via the Roughcastle tunnel and a double staircase lock, to the Union Canal.

The process starts with boats entering each of the cradles, or "gondolas" - one from the upper river and one from the lower river. Then, the wheel turns, raising the lower boat up to the upper river and the upper boat down to the lower river.

Boats entering the gondolas are raised and lowered, along with the water that they float in on. This works on the Archimedes principle of displacement. That is, the mass of the boat sailing into the gondola will displace an exactly proportional volume of water so that the final combination of ‘boat plus water’ is the same for both gondolas, even though the boats may be of vastly different sizes and weights.

Each gondola runs on small wheels that fit into a single curved rail fixed on the inner edge of the opening on each arm. In theory, this should be sufficient to ensure that they always remain horizontal, but any friction or sudden movement could cause the gondola to stick or tilt. To ensure that this could never happen and that the water and boats always remain perfectly level throughout the whole cycle, a series of linked cogs acts as a back up. Hidden at each end, behind the arm nearest the aqueduct, are two 8 meter diameter cogs to which one end of each gondola is attached. A third, exactly equivalent sized cog is in the centre, attached to the main fixed upright. Two smaller cogs are fitted in the spaces between, with each cog having teeth that fit into the adjacent cog and push against each other, turning around the one fixed central one. The two gondolas, being attached to the outer cogs, will therefore turn at precisely the same speed, but in the opposite direction to the Wheel. Given the precise balancing of the gondolas and this simple but clever system of cogs, a very small amount of energy is actually then required to turn the Wheel. In fact, it is a group of ten hydraulic motors located within the central spine that provide the small amount, just 1.5 kw, (the electricity of fifteen 100 watt light bulbs) of electricity to turn it.

And not only is the entire complex beautifully designed, but when a ship enters the gondola at night, it is truely a beautiful sight to behold. FEEDBACK MAP Many thanks to Ray McClure for this target