'Salter's Duck', a wave energy device, undergoing tests in a wave tank at Edinburgh University. This device was designed by Professor Stephen Salter, and has been proposed as a source of electricity from the sea. The scale model seen here clearly shows the effectiveness of the design, waves generated at the right have their energy almost totally absorbed by the 'duck', leaving calm water behind (left). The waves cause the leading edge of the device to bob up and down, rotating around the submerged axle. This oscillating rotary motion is converted into electricity by a double-acting dynamo, so power is generated on both the up and down strokes.