WALDO, Leonard, astronomer, born in Cincinnati, Ohio, 4 March, 1853. He was graduated at Marietta in 1873, and, after spending a few months at the Cincinnati observatory, entered the Columbia college school of mines and became assistant in astronomy in 1873. In the following year he was appointed assistant astronomer on the expedition that was sent to Hobart Town, Tasmania, to observe the transit of Venus. He was appointed assistant at the Harvard observatory in 1875, and continued there until 1880, after which, until 1887, he was astronomer in charge of the horological bureau of the Winchester observatory of Yale, where his work included the comparison of thermometers with standard instruments. He was also active in causing the introduction of a uniform time system in Connecticut. The degree of S. D. was conferred on him by Harvard for original investigations in 1879, and he received the degree of A.M. from Yale in 1880. He has contributed reports of his astronomical researches to scientific journals, and is the author of cyclopaedia articles and popular papers on technical subjects.