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6 Laboratory and Statistical Astronomy
there were students in mathematics and sometimes physics, who did some
practical work with him in the form of measuring of plates. In principle they
were not reimbursed for this, but it was some good experience. In 1896 Willem
de Sitter was one of those students. Jan Guichelaar has published an excellent
biography of Willem de Sitter in this series [62]. De Sitter was born in Sneek
(Friesland) in a family that mainly consisted of lawyers, but Willem broke with
this tradition and had come to Groningen to study mathematics. He attended
Kapteyn’s lectures and worked in Kapteyn’s laboratory when David Gill visited
Groningen. Later, in a letter to Gill, de Sitter mentioned that this took place
on October 2, 1896; he also mentioned his poor English, of which he was still
embarrassed. But with Kapteyn’s help—and when he had to lecture that of
Mrs Kapteyn—they had a conversation in which Gill became much impressed
by Willem de Sitter. So impressed in fact, that the next morning he asked de
Sitter to come and see him and offered him to come to Cape Town to do work
and prepare an astronomical PhD thesis.
De Sitter (see Fig. 6.11) did not have the intention at all of obtaining a
PhD in astronomy; he had come to Groningen to study mathematics. But after
Fig. 6.11 Willem de Sitter. This picture comes from the Album Amicorum, presented
to H.G. van de Sande Bakhuyzen on the occasion of his retirement as professor of
astronomy and director of the Sterrewacht Leiden in 1908 [47]