1 Table of Contents: “...Introduction -- Boarding School and University -- Astronomy Around 1875 -- Astronomer and Professor...”

2 Table of Contents: “... -- The Oort Limit and Galaxy Photometry -- Professor and Adjunct-Director -- World War II: The Watershed...”

3 Table of Contents: “... -- Chapter 3: Astronomer in Leiden -- Chapter 4: Professor in Groningen -- Chapter 5: From Kepler to Parallax...”