DELARUE, GERVAIS (1751-1835), French historical in vestigator, formerly regarded as one of the chief authorities on Norman and Anglo-Norman literature, was a native of Caen who took refuge in England during the French Revolution. His prin cipal works are Essais historiques sur les Bardes, les Jongleurs, et les Trouveres normands et anglo-normands (3 vols., 1834), and books on the history of his native town.
(1815-1889), British astronomer and inventor of the photo-heliograph, son of Thomas De la Rue, was born in Guernsey on Jan. 18, 1815. He constructed in 185o a 13-in. reflecting telescope, mounted first at Canonbury, later at Cranford, Middlesex, and with its aid executed many drawings of the celestial bodies. In 1851 he saw a daguerrotype of the moon by G. P. Bond, shown at the great exhibition of that year. Employ ing the more rapid wet-collodion process, he succeeded before long in obtaining exquisitely defined lunar pictures, which remained un surpassed until the appearance of the Rutherford photographs in 1865. In 1854 he turned his attention to solar physics, and in order to obtain a daily photographic representation of the state of the solar surface he devised the photo-heliograph, described in his re port to the British Association, "On Celestial Photography in Eng land" (1859), and in his Bakerian Lecture (Phil. Trans. vol. clii.) . Regular work with this instrument, begun at Kew by De la Rue in 1858, was carried on there for 14 years; and was continued at Greenwich from 1873 to 1882. The results obtained in the years 1862-66 were discussed in two memoirs, entitled "Researches on Solar Physics," published by De la Rue, in conjunction with Pro fessor Balfour Stewart and Mr. B. Loewy, in the Phil. Trans. (vol. clix. and vol. clx.). The photographs which he took in Spain of the solar eclipse of July 18, 186o, proved beyond doubt the solar character of the prominences or red flames, seen around the limb of the moon during a solar eclipse. In 1873 De la Rue pre sented most of his astronomical instruments to the university ob servatory, Oxford ; in 1887 he provided it with a 13-in. refractor to enable it to take part in the International Photographic Survey of the Heavens. With Dr. Hugo Muller as his collaborator he pub lished many chemical papers between 1856 and 1862, and investi gated, 1868-1883, the discharge of electricity through gases by means of a battery of 14,60o chloride of silver cells. He was twice president of the Chemical Society, and also of the Royal Astro nomical Society (1864-66). He died in London on April 19, 1889.
