Lighthouse

Lighthouse, a conspicuous building carrying at night a light for the warning or guidance of mariners. Lighthouses were of very early adoption, and were at first merely towers with open fires upon their summits. Candles, and then oil lamps, behind glass were next used. Oil lamps are still retained in many localities, but are supplemented with scientifically-constructed lanterns and powerful reflectors or refractors, and elsewhere gas or electricity supply the illumination. Simple concave mirrors were originally used to direct the light, spherical parabolic mirrors were next employed. All systems by which the light is thus reflected are termed "catoptric." Early in the 19th century Fresnel introduced the "dioptric" or refracting system of lenses, by the use of which the light is much economised. He also introduced the "catadioptric" system, whereby mirrors and lenses are combined. The "holophotal" system of Mr. T.Stevenson causes the rays from the side of the flame opposite to the mirrors or lenses, as the case may be, to fall upon a series of prisms, from the internal surfaces of which they are reflected back through the lenses. The lights of different lighthouses are distinguished by their colour, by their nature or intensity, or by their periodicity if they be revolving; and they can thus be easily recognised. Those on the coasts of the United Kingdom number about five hundred. English lights are under the Corporation of the Trinity House [Trinity House], Scottish ones under the Commissioners of Northern Lights, and Irish ones under the so-called Ballast Board, or Corporation for Preserving and Improving the Port of Dublin; but all are subordinate to the Board of Trade. Among celebrated British lighthouses are the Eddystone (q.v.), and the following: Smalls Rock, built of wood in 1776, and of granite in 1861; Maplin, built on iron screwed piles in 1838; Bishop Rock, completed in 1858, and raised and altered in 1889; St. Catherine's, built in 1780, reduced in 1840, and furnished with electric light in 1888; Inch Cape, or Bell Rock, finished in 1811; Skerryvore, finished in 1844; North Unst, temporarily erected in 1854, and permanently completed in 1858; and Dhu Heartach, finished in 1872.