Haarlem, Joh. Enschede, 1946, in-4°, II + 121 p., with 26 figures and 3 maps, and bibliography of 202 titles + 1 leaf (Stellingen), original wrappers.
Thesis for the doctor degree in the mathematical and natural sciences at the University of Leyden. A study of stars in the region, Pleiades
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