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102 Mr. Langley commenced the active work of life as an architect in 1856. This profession was followed for several years. In 1864 he went to Europe and on his return to this country, in the following year, he became assistant at the Harvard college observatory and entered upon the course of scientific study and investigation which he has followed with unwavering devotion and in which he has been eminently successful and useful. In 1866 he became an assistant professor of mathematics on the academic staff of the United States naval academy at Annapolis. Beside performing the duties of an instructor he placed in serviceable condition the observatory, which during the civil war had been practically useless. In 1867 he removed to Pittsburg, where he remained for nearly twenty years. Here he became director of the Allegheny observatory, which was connected with the Western university of Pennsylvania. The situation there, as he found it, was discouraging. The equipment of the observatory was very poor. There was hardly a dollar with which to purchase the instruments which were imperatively needed or to pay the expenses which original research would involve. With the aid of a generous friend and by the use of several of his own inventions, Professor Langley did much toward placing the observatory on a good working basis; and in 1869, in the face of many difficulties, he established the paid "time service" from which funds were secured for the prosecution of his investigations along independent lines. This service, by means of which "standard" time is accurately kept at all connecting points, was at first adopted only by a few railroads and by business houses in large cities; but it proved so valuable that its use has become common at the smaller centers of population and in numberless public and private offices throughout the country.

Professor Langley has been one of the most persistent and successful investigators of the nature of the sun, and has been very prominent, especially in laying foundations and indicating the most promising lines of study, in developing the science of aerostatics. He was a member of expeditions to observe eclipses of the sun in Kentucky, 1869; in Spain, 1870; and at Pike's Peak in 1878. In the year last named he also visited Mount ^Etna to observe the character of the astronomic vision at that altitude. In 1881, under the auspices of the United States Signal Service, he organized and conducted an expedition to the station on Mount Whitney, in Southern California (one of the highest in the country), to learn certain important facts