LANGLEY, Samuel Pierpont, astronomer, born in Roxbury, Boston, Massachusetts, 22 August, 1834. He was graduated at the Boston Latin school, and then turned his attention to civil engineering, after which he was occupied with the practice of architecture. As a boy he showed a decided fondness for astronomy, not only reading books on that science, but also experimenting and making small telescopes for his own use. In 1865, after spending two years in Europe, he returned to the United States, was for a few months an assistant in the Harvard observatory, and then was called to a chair of mathematics in the United States naval academy at Annapolis. In 1867 he was invited to fill the professorship of astronomy in the Western university of Pennsylvania in Pittsburg, with charge of the observatory in Allegheny City. Here he has since remained, and in January, 1887, received the appoint-meat of assistant secretary of the Smithsonian institution, succeeding to the full secretaryship in August, 1887. His work at the Allegheny observatory began in 1869 with the establishment of a complete time service, then a novel feature, which has since been widely copied. The present extended systematic distribution of time began then at Pittsburg. Professor Langley accompanied the parties that were sent out by the United States coast survey to observe the total eclipses of 1869 and 1870, being sent during the former year to Oakland, Kentucky, and to Xeres, Spain, during the latter year. He also observed the solar eclipse of 1878 from Pike's Peak. In 1870 he began his series of brilliant researches on the sun which have since led to his being recognized as one of the foremost authorities on that body. His first paper was on the structure of the photosphere, and included a plate giving the most detailed representation of a sun-spot that had appeared up to that time. This he followed with a study of the heat of the solar surface by means he showed among his conclusions that the direct effect of sunspots on terrestrial temperatures is sensible. Finding that the thermopile was not sufficiently sensitive for his work, he invented the bolometer, with which exceedingly delicate measurements of heat were made. He spent the winter of 1878-'9 on Mount Etna, Sicily, obtaining excellent results. In 1881 he organized an expedition, which was fitted out at the cost of a citizen of Pittsburg; but went also under the auspices of the United States signal service to the top of Mount Whitney, in California, and there made important observations in solar heat and its absorption by the earth's atmosphere. In 1885 he was invited to lecture at the Royal institution, London, and there gave an account (if the novel results that he had obtained on Mount Whitney. His scientific papers have been very numerous and include more than fifty important titles. Of these, aside from those directly of scientific value, the most interesting are a series of popular expositions entitled " The New Astronomy "that he contributed to the "Century" in 1884-'6. Professor Langley has delivered courses of lectures before the Lowell and Peabody institutes, and in 1882 was invited to address the British association for the advancement of science at Southampton. He has received the degree of Ph. D. from Stevens institute of technology in 1882, and that of LL.D. from the Universities of Wisconsin in 1882, Michigan in 1883, and Harvard in 1885. In 1886 he received the first Henry Draper medal that was awarded by the National academy of sciences, for his work on astronomical physics. During the present year (1887) he received the Rumford medal from the Royal society, London, and also the Rumford medal from the American academy of arts and sciences, two distinct foundations, whose awards were conferred independently. Professor Langley is a member of numerous foreign and American scientific societies, and in 1876 received an election to the National academy of sciences. In 1878 he was elected vice president of the American association for the advancement of science, delivering his retiring address at its Saratoga meeting, and in 1886 was elected president of that association, presiding over the deliberations of its New York meeting in August, 1887.--His brother, John Williams, chemist, born in Boston, Massachusetts, 21 October, !841, was graduated at the Lawrence scientific school of Har-yard in 1861, and then served as assistant surgeon in the United States navy during the civil war, after which he visited Europe. In 1867 he became assistant professor of natural philosophy and chemistry in the United States naval academy, where he remained for three years, becoming, in 1872, professor of chemistry in the Western university of Pennsylvania. Since 1875 he has filled the chair of chemistry in the University of Michigan. Professor Langley's scientific work has been principally in connection with the development of the chemistry of iron-ores, and his results have been published in the " American Journal of Science" and elsewhere. In 1877 he received the honorary degree of M. D. from the University of Michigan, and, besides being a member of several societies, held the office of vice president of the American association for the advancement of science in 1884.