1. Research and Teaching.- 1.1. Research, general.- 1.2. Specific research for special lectures.- 1.3. Book reviews, biographies etc.- 1.4. Popular lectures and articles.- 1.5. Courses of lectures at Leiden Observatory.- 1.6. Other lectures.- 1.7. Research of colleagues and students.- 1.8. Lecture notes when a student.- 1.9. Chapter 21 of Stars and Stellar Systems V; Book.- 1.10. Notes on literature.- 2. Correspondence.- 2.1. General correspondence.- 2.2. Personal correspondence.- 2.3. Strange letters and wild theories.- 2.4. Correspondence with foreign visitors.- 2.5. Correspondence on travel arrangements.- 2.6. Correspondence on projects financed by ZWO.- 2.7. Letters of recommendation.- 3. Leiden Observatory.- 3.1. Correspondence on the Observatory at Hartebeespoortdam.- 3.2. Correspondence Rockefeller Telescope.- 3.3. Leids Sterrewacht Fonds.- 3.4. Leids Kerkhoven-Bosscha Fonds (LKBF).- 3.5. Assistant Director.- 3.6. Director, 1945-1947.- 3.7. Kenya Expedition.- 3.8. Bosscha Observatory at Lembang.- 3.9. Diaries; day-to-day appointments.- 3.10. Jan Hendrik Oortfonds.- 4. Leiden University.- 4.1. Baccalaureate Committee, 1957-1960.- 4.2. Committee for the Development of Scientific Research.- 4.3. Boerhaave Museum for the History of Science.- 4.4. Academic Arts Committee.- 4.5. Curatoren.- 4.6. Senate, 1951-1955, 1963-1969.- 4.7. Faculty of Science.- 4.8. Bachiene Foundation.- 4.9. Civitas Academica.- 5. Astronomy in the Netherlands.- 5.1. Netherlands Foundation for Radio Astronomy.- 5.2. Benelux Cross Antenna Project, 1958-1967.- 5.3. Space Research.- 5.4. Bulletin of the Astronomical Institutes of the Netherlands.- 5.5. Eclipse Commission.- 5.6. Summer course at Nijenrode, 1960.- 5.7. Scientific meetings.- 5.8. Dutch Telescope in Southern Europe.- 5.9. Academic Council, section Astronomy (SSAR).- 6. Netherlands.- 6.1. KNAW (Royal Dutch Academy of Sciences).- 6.2. Other learned societies and organizations, both national and foreign.- 6.3. Speeches.- 6.4. Teacher's degree examinations, 1930-1941.- 6.5. Academic Council.- 6.6. KNMI (Royal Dutch Meteorological Institute).- 6.7. Editorial Board of Natuur en Techniek.- 6.8. Christiaan Huygens.- 7. Europe.- 7.1. European Southern Observatory.- 7.2. Astronomy and Astrophysics, 1968-1972.- 7.3. Astronomy and Astrophysics, correspondence and referee reports.- 7.4. European Conferences.- 7.5. Foreign Programme committees, 1971-1977.- 7.6. Astronomy in Germany, 1967.- 7.7. Pontifical Academy.- 7.8. Jury membership Prix Docteur A. de Leeuw.- 8. International (World).- 8.1. International Astronomical Union (IAU).- 8.2. Inter-Union Committee for the Allocation of Frequencies.- 8.3. International Council of Scientific Unions (ICSU).- 8.4. Symposia.- 8.5. Foreign Visits, lectures, and seminars.- 8.6. Honours and prizes.- 8.7. International Computation Centre.- 8.8. Copernicus 500th Anniversary celebrations.- 8.9. Periodical publications.- 8.10 Humanitarian Issues.- 9. Personal Archives.- 9.1 Correspondence.- 9.2 Documents and notes.- 9.3 Personal notes and diaries.- 9.4 Press cuttings.- List Of Publications.- List Of Abbreviations.- Name Index.
