Correspondence; diaries; manuscripts; notes and notebooks; apparatus. The correspondence (1917-1922, 1956) concerns World War I defense research, as well as the development of the paper cone loudspeaker and geological subterranean sounding; the diaries (1914-1916, 1927-1928, 1930-1932) describe both social and academic activities, and negotiations and technical projects at Hughes Tool Company (1928-1933). The manuscripts (1919-1966) are of articles and addresses concerning acoustical and geophysical research as well as the history of science. Notebooks and notes (1919-1931) include student notebooks from undergraduate years at Rice University and seismographic studies. The apparatus is an example of the Hughes' plunger lift. Correspondents include: Karl K. Darrow, Robert A. Millikan, C. N. Scott, and Augustus Trowbridge.