Box-folder 90:21

Scope and Contents From the Sub-Series: Contains both incoming and outgoing professional correspondence, organized under four headings for each administrative unit or department with which Tombaugh was affiliated. Under each heading (Physical Science Laboratory; Research Center; Department of Earth Sciences and Astronomy; and Department of Astronomy), the files are arranged alphabetically by correspondent, with internal correspondence, form letters, letters of reference for former students, and reprint requests and acknowledgments...