PICKERING, WILLIAM HENRY Ameri can astronomer, was born in Boston, Mass., on Feb. 15, 1858, and in 1879 graduated at the Massachusetts Institute of Technology. He served as an assistant and instructor in physics at his Alma Mater from 188o to 1887, and then became an assistant in astronomy at the Harvard college observatory. In 1889 he was made assistant professor of astronomy. He led expeditions for observing total solar eclipses to Colorado, 1878; Grenada, West Indies, 1886; California, 1889; Chile, 1893; and Georgia, 1900. While in southern California in 1889 he selected the Mt. Wilson site and established a temporary observatory there. In 1891 he established the Arequipa station of the Harvard observatory in Peru. He also established a meteorological station at an altitude of 16,65o ft. upon Mt. Chachani, and accomplished the ascent of El Misti, 19,200 feet. He surveyed and determined the alti tude of many other Peruvian mountains and returned to the United States by way of the Straits of Magellan in 1893. In 1894 he erected the observatory and telescope for Dr. Percival Lowell (q.v.) at Flagstaff, Ariz., and in 190o erected a station for
the Harvard observatory at Mandeville, Jamaica, in the West Indies. In 1899 he discovered Phoebe, 9th satellite of Saturn, anct explained its contrary revolution. The doubtful loth satel lite, Themis, which he announced in 1905, remains unconfirmed. In 1904 he again went to California to make observations of the moon, in 1905 to Hawaii, and in 1907 to the Azores to compare their crater formations with those in the moon. His work in planetary photography and photometry was especially notable. In later years he turned more and more to the study of Mars.
Besides many papers in astronomical journals (see especially Popular Astronomy), he wrote A Walking Guide to the Mt. Washington Range (1882) ; Investigations in Astronomical Photography (1895) Visual Observations of the Moon and Planets (19o3) ; An Atlas of the Moon (1903) ; Lunar and Hawaiian Physical Features Compared (1906) ; A Search for a Planet Beyond Neptune (1909) ; A Statistical Investigation of Cometary Orbits (19II) ; Mars (1921).