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408 which should be referred to here, were it not for limited space. His observations on the moon's heat; on the solar eclipse of 1878 (at the summit of Pike's Peak); his direct comparison of the sun with the molten metal of a Bessemer converter; his investigations at Mount Etna, Pike's Peak, and Mount Whitney, on the conditions of vision at great altitudes, all deserve more than this brief notice.

His published scientific papers are very numerous. A list of the more important of these follows this article. There are forty-six separate papers in the years from 1869 to 1885. Besides these, the magazines have contained many more popular articles; and his courses of lectures at the Lowell Institute, the Peabody Institute, and elsewhere, have been most successful.

Professor Langley is a member of the National Academy of Sciences and of numerous American and foreign bodies, and has received the recognition of honorary degrees from various universities.