This guide incorp. entries from the guide pub. in 1966 (Memoirs of the APS, Vol. 66). The earlier entries have been updated and listings for all new collections, microfilm holdings, sound recordings (esp. in Native Amer. lang.), and maps are now included. Since the first guide, the Library has increased its holdings significantly -- adding the papers of many distinguished scholars -- among them George Gaylord Simpson, Herman Goldstine, Salvador E. Luria, Elsie Clews Parsons, Theodosius Dobzhansky and Hanry DeWolf Smyth. Other major collections have also been enhanced, notably those for Darwin, Native Amer. studies, linguistics, genetics, the histories of med., technology, 20th-cent. physics, and natural history. This last includes a large collection of the prints of Benjamin Smith Barton.