lighthouse

lighthouse, a building or other construction erected to display a characteristic light as a warning of danger at sea and an aid to navigation.

The lighthouse has a long history, and no doubt owes its origin to the beacon fires which were maintained by priests in ancient Egypt. There is a description of a lighthouse at Sigeum (the present Cape Inchisari) in the writings of the poet Lesches in 660 bc. The most famous of the older lighthouses is the Pharos of Alexandria, which was built in the reign of Ptolemy II (283–247 bc) by Sostratus of Cnidus. This was well authenticated as one of the seven wonders of the world. Contemporary claims that the tower, which carried the light at the top, was 183 metres (600 ft) high are, however, open to some doubt and probably 45 metres (150 ft) is nearer the mark.

The oldest lighthouses in western Europe are said to be those erected by the Romans at Dover and Boulogne, in the 1st and 2nd centuries ad. There were famous lighthouses in Italy in the 1st century, those at Ostia, Ravenna, and Messina being the best known. The light exhibited at Cordouan, a rock in the sea in the Gironde estuary, is recognized as the first example of a lighthouse built out at sea. The earliest of the Cordouan towers dates from about ad 800.

One Chinese geographer, writing around the close of the 8th century, in describing the sea route from Canton to the Persian Gulf, mentions that the people living near the entrance to the Gulf ‘set up ornamental pillars in the sea, on which at night they place torches so that people travelling on board ships shall not go astray’. By 1562 there were 711 beacons along the Chinese coast between western Kuangtun and northern Chiangsu.

For centuries lighthouses in the west were lit by wood or coal fires in braziers. Then, in 1763, the first catoptric system, which reflected oil light off parabolic mirrors, was designed and set up by Liverpool's dockmaster, William Hutchinson (1715–1801), a system later improved by the Scottish Lighthouse Board's engineer, Robert Stevenson (1772–1850). The next development, the dioptric system, where light rays were refracted through optic glass, was first described by the Scottish scientist Sir David Brewster (1781–1868) in 1812. But it was the French physicist Augustin Fresnel (1788–1827) who, independently, perfected it in 1822, while Stevenson promoted its installation, and invented a revolving dioptric apparatus which emitted intermittent and flashing light. A further refinement, Fresnel's catadioptric system, both refracted and reflected the light rays which intensified them so that they could be seen at a greater distance.

Until the 1990s most lighthouse using these systems were manned. However, because of the work of the Swedish scientist Gustaf Dalén (1869–1937), which won him the Nobel prize for physics in 1912, some had become automated by the 1930s, as nearly all are nowadays.