This collection includes numerous Darwin writings, in manuscript and typescript, as well as letters to him from Niels Bohr, Max Born, M. Frenkel, Oskar Klein, J. E. Littlewood, H. Moseley, H. R. Robinson. The writings include such topics as magnetic storms, atom mechanics, and wave theory. There is also a copy of a paper in Darwin's hand by Henri Poincaré, "On the theory of Quanta" (published in Journal de Physique, 1912).

Primary source materials for the history of quantum physics in the twentieth century, collected under the auspices of the American Philosophical Society and the American Physical Society, with a grant from the National Science Foundation.