An expert in stellar spectroscopy, Walter Sydney Adams (1876-1956, APS 1915) made important empirical contributions to the analysis of the physical conditions of stellar and planetary atmospheres, determining the distances to extragalactic objects, and understanding stellar evolution. Adams succeeded his mentor George Ellery Hale as director of the Mount Wilson Observatory, serving in that capacity from 1923 to 1946. The Adams Papers contains approximately 100 letters addressed to the astronomer Walter Sydney Adams, dating primarily from the period after his move to Mount Wilson Observatory in 1904. Much of the correspondence is relatively perfunctory, however a few letters include interesting scientific content, including Harlow Shapley discussing his photometric study of HV 3435 and interest in Alpha Circini, Arthur Compton's comments on Keener's photoelectric method, Svante Arrhenius on the possibilities of constructing a new observatory for the Swedish Academy of Sciences, and Arthur Eddington discussing the implications of the spectrum of the companion to Sirius. Among Adams' other correspondents are J. C. Kapteyn, James H. Jeans, Henry Norris Russell, Elihu Thomson, and Willem de Sitter.

An electrical engineer, inventor, and entrepreneur, Elihu Thomson was an innovator in electrification in both a technical and corporate sense. With interests that ranged from the technical (electrical meters, high-pressure steam engines, dynamos, generators) to scientific (fused quartz optics, X-rays), Thomson acquired over 700 patents in his career, and in 1882, founded one of the early electrical corporations in the United States, the Thomson-Houston Company, which merged with the Edison Electric Company in 1892 to form the General Electric Company. The Thomson Papers are a massive and nearly comprehensive collection documenting the wide range of Thomson's scientific and technical interestsm from his electrical experiments, inventions, and patents, to his interests in astronomy, geology, and medicine, as well as his role in the development of two major corporations involved in electrification, the Thomson-Houston Electric Company and General Electric Company. Roughly three quarters of the collection is dated between 1890 and 1920 when Thomson was associated with General Electric, and was active in professional groups such as the American Institute of Electrical Engineers (AIEE), International Electrotechnical Commission. His research interests. The balance of the collection is comprised of eight boxes and five volumes relating to Thomson's patents; a series of notebooks kept at Central High School; 43 letterbooks, 1882-1936; diaries of trips to Europe; notebooks on genealogy; scrapbooks of cards, photographs, clippings, and other souvenirs; and 2 vols. of tributes on his eightieth birthday, etc.