porary barrack, and another had to be erected in its place. The foundations of the tower involved the excavation of two thousand tons of material. The first stone was laid in July 1840, and the light exhibited in 1843. The rearing of this structure, containing upwards of 4,300 tons of granite, occupied three seasons, each extending to about two months, and was personally superintended by its author. The tower rises to a height of 138 ft., is 42 ft. in diameter at the base, gradually decreasing to 16 ft. at the top. The ‘solid’ or monolithic part extends to 26 ft. above the rock, the cubic contents of which are double the entire contents of Smeaton's Eddystone tower. The walls, as they spring from the solid, are 9¼ ft. in thickness, gradually diminishing to 2 ft. The interior is divided into ten floors, including the light-room, each 12 ft. in diameter. The optical apparatus is dioptric revolving, the most complete which had hitherto been constructed; the height of the eight central lenses was extended to 3 ft. 3 in., and, instead of Fresnel silvered mirrors below the lenses, Stevenson designed prismatic rings, which were introduced for the first time in this apparatus. Stevenson designed and carried out some notable improvements on dioptric apparatus used in lighthouses. For the central portion of the fixed apparatus he converted Fresnel's narrow lenses into a truly cylindrical drum, which he divided into sections with helical joints; and he introduced prismatic rings above and below the central belts, thus securing equal distribution of light all round, and extending dioptric action throughout the whole height of the apparatus. He also suggested the spherical mirrors placed on the landward arcs of dioptric apparatus.
In 1830 Stevenson became a member of the Institution of Civil Engineers, and in 1838 a fellow of the Royal Society of Edinburgh, acting as a member of its council from 1843 to 1845. In 1840 the university of Glasgow conferred on him the honorary degree of LL.B. The emperor of Russia and the kings of Prussia and Holland presented him with medals in acknowledgment of his merit as a lighthouse engineer. In 1848 was published his ‘Account of the Skerryvore Lighthouse, with Notes on the Illumination of Lighthouses,’ 4to. It still remains a standard book. The notes on lighthouse illumination were subsequently extended and published in 1850 under the title of ‘A Rudimentary Treatise on the History, Construction, and Illumination of Lighthouses.’
Stevenson had fine literary tastes. He knew Italian, Spanish, French, Greek, and Latin literatures thoroughly. In 1852 he was seized with paralysis, and thenceforth beguiled his suffering by translating the ten hymns of Synesius, bishop of Cyrene. These translations, along with other poems, were printed for private circulation the year before his death. He wrote articles for the ‘Encyclopædia Britannica’ (8th edit.) on lighthouses and other subjects. Stevenson died at Portobello on 23 Dec. 1865. On 3 Jan. 1866 the commissioners of northern lighthouses recorded in their minutes ‘their deep and abiding regrets for the loss of a man whose services had been to them invaluable,’ and whose works combined profound science and practical skill.
STEVENSON, DAVID (1815–1886), civil engineer, born at Edinburgh on 11 Jan. 1815, was third son of Robert Stevenson [q. v.], and was brother of Alan Stevenson [q. v.] and of Thomas Stevenson [q. v.] He was educated at the high school and university of Edinburgh, but spent some time in youth in the workshops of millwrights, where he acquired much manual skill. While a pupil he conducted extensive land and marine surveys, in the almost entire absence of trustworthy charts and maps, and made tidal and other hydrometric observations for lighthouses, piers, harbours, docks, and for river and estuarial improvements. His results he published in ‘The Application of Marine Surveying and Hydrometry to the Practice of Civil Engineering,’ the first book of its kind (1842). On completing his apprenticeship he was engaged with Mr. Mackenzie, the contractor on the Liverpool and Manchester railway, and gave a description of the railway in 1835 to the Royal Scottish Society of Arts. A paper on the ‘Dublin and Kingston Railway’ followed in 1836. In 1837 Stevenson made a professional tour in Canada and the United States, and published on his return next year a ‘Sketch of the Civil Engineering of North America’ (republished in 1859 with additions, and now forming one of Weale's ‘Engineering Series’). On the outward and homeward voyages he made daily observations on the temperature of the sea and air. In 1838 Stevenson entered into partnership with his father and brother Alan. His father then gave little attention to business, and Alan confined himself to the lighthouse department; the entire management of the general business of the firm consequently devolved on David. He soon was a recognised authority in reference to the improvement of rivers and estuaries, harbours, the construction of docks, and other marine works. He was called on to report