CLARK, Alvan, optician, born in Ashfield, Massachusetts, 8 March. 1804; died in Cambridge, Massachusetts, 19 August, 1887. He was the son of a farmer, and became, when young, an engraver for calico print-works in Lowell. This pursuit he followed at various places from 1827 till 1836, when he settled in Boston and became a successful portrait-painter. About 1844 he was interested in the manufacture of telescopes, and associated his sons with him. He was the first person in the United States to make achromatic lenses, and the most important modern telescopes have been constructed at his factory in Cambridge-port. Mr. Clark invented numerous improvements in telescopes and their manufacture, including the double eye-piece, an ingenious method of measuring small celestial arcs. A list of discoveries made by him with telescopes of his own manufacture is given in the "Proceedings of the Royal Astronomical Society" (London, vol. 17, No. 9).--His son, Alvan Graham, astronomer, born in Fall River, Massachusetts, 10 July, 1832. After a gram-mar-school education he became associated with his father in the firm of Alvan Clark & Sons, and in that capacity has successfully completed many famous lenses, among which are the Chicago refractor, the 26-inch lens in the Naval observatory at Washington, and the 30-inch refractor for the imperial observatory at St. Petersburg, for which the honorary medal of Russia was awarded --the only one ever conferred upon an American. During 1886 the 36-inch refractor, the largest in the world, was made for the Lick observatory on Mount Hamilton, near San Francisco, California Mr. Clark accompanied the total-eclipse expedition to Jerez, Spain, in 1870, and also the similar expedition to Wyoming in 1878. As an independent observer he has discovered fourteen intricate double stars, including the companion to Sirius, for which the Lalande gold medal was awarded him by the French academy of sciences in 1862. He has also made numerous inventions connected with the manufacture of refracting telescopes.