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].