Apart from its importance for the study of Hale's personal and professional life, the collection is one of the richest sources for the history of science in the United States in the early twentieth century. It contains a good deal of significant material relating to the theoretical and instrumental development of astrophysics and the history of the Mount Wilson and Palomar Observatories. The collection is of singular importance for the study of science and government, particularly with respect to the affairs of the National Academy of Sciences and the National Research Council. It documents much of the early history of the California Institute of Technology. Finally, it contains substantial material on the general affairs of the scientific community in the United States and Europe [from Kevles 1968].

These documents cover the years 1847 to 1953, the year of Millikan's death, but the core of the collection consists of the official papers generated by Millikan after his move to Pasadena in 1921. The collection includes more than 125,000 pages of letters, notebooks, unpublished speeches, addresses, lecture notes, and family papers.

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.