'Delineated Plan of a Cone', 1787.
© Science Museum / Science & Society Picture Library
Hand-coloured engraving depicting sectioned views of a wooden cone, or caison, to be used in the construction of a breakwater. Caisons of this type were used in the construction of the breakwater built to enclose the harbour at Cherbourg, France. This began in 1783 under the direction of Alexandre de Cesart. Each caison was about 60 feet tall and designed to be filled with 194,000 lbs of stone, which would then anchor the caison to the sea bed. The caisons were moved into place by attaching sufficient wooden barrels to give them bouyancy and then towing them. Once in position, the ropes attaching the barrels to the caison were cut, causing the caison to sink to the sea floor. The gaps between the caisons were to be filled with more stone, forming a solid wall.