Professional and personal correspondence, administrative records, manuscript lecture notes, and some miscellaneous printed materials. The general correspondence file contains letters, both personal and professional, with colleagues, with and about his students, about laboratory equipment, about weapons for the Army and Navy, and with industry concerning his research. The subject file contains some additional professional and personal correspondence, a number of administrative records on property control of laboratory equipment, particularly for government research projects, other Columbia Physics Department matters, several typescripts on cyclotron coil designs, Mitchell's personal records relating to employment, and other miscellaneous personal files. There are handwritten lecture notes for Mitchell's courses, the most complete being those for Physics R6 and General Studies Physics 18.