8.3 Character
163
afterward. Here, too, the divine rhythm of the great, multifaceted life can reveal
itself to those who have an eye for it.
8.4 Weersma, Yntema, van Rhijn
It took a long time before Kapteyn delivered his first Ph.D. student, Willem
de Sitter in 1901. After that it took a long time again for number two to
present himself. It is true that Cornelis Easton received his doctorate in 1903,
but as said, that was honoris causa. In total Kapteyn, not counting Easton,
only had eight Ph.D. students. Adriaan van Maanen (1884–1946) obtained
his Ph.D. in 1911 in Utrecht with Albertus Antonie Nijland (1868–1936) as
supervisor, but van Maanen actually worked in Groningen for some time on
his dissertation (on the proper motions of stars) and in fact saw Kapteyn as his
real teacher. With Adriaan van Maanen added, the number comes to nine. For
Kapteyn’s contemporaries in mathematics and natural sciences in Groningen,
the average per professor was roughly one Ph.D. every three years. Kapteyn,
who has been a professor for 43 years, even if Adriaan van Maanen is counted,
does not get more than one Ph.D. student per almost five years. But when
in 1908 his second Ph.D. student Herman Albertus Weersma (see Fig. 7.9)
defended his thesis, he was far behind even on that schedule.
Herman Weersma’s dissertation was about a new determination of the Apex
‘according to the method of Bravais’. Weersma went back to the original formulation of the problem, using the spatial positions, velocities and masses of
the stars, to determine the center of gravity of a system. This was not very
practical of course, because the distance and spatial velocity of only a few
stars had been measured; the mass of stars and the variation among them were
largely unknown. So Weersma developed an adapted method, in which he took
into account the missing data as well as possible and as a first approximation
ascribed equal masses to all the stars. That was indeed an improvement on
earlier work and he obtained a more accurate result, working with the care that
Kapteyn expected of him. The knowledge of the position of the Apex (and
the velocity of the Sun relative to the collective of stars in its vicinity) was,
as we have already seen, an essential part of Kapteyn’s program using secular
parallaxes as a step towards determining the construction of the heavens.
Weersma was appointed on a permanent position as Kapteyn’s assistant
in 1908; he succeeded de Sitter when he moved to Leiden in that year. When
Weersma left Groningen in 1912, his place (in 1913) was taken by Frits
Zernike (1888–1966), who was later to win the Nobel Prize in physics for his
invention of the phase contrast microscope. Zernike did not work for Kapteyn
163
afterward. Here, too, the divine rhythm of the great, multifaceted life can reveal
itself to those who have an eye for it.
8.4 Weersma, Yntema, van Rhijn
It took a long time before Kapteyn delivered his first Ph.D. student, Willem
de Sitter in 1901. After that it took a long time again for number two to
present himself. It is true that Cornelis Easton received his doctorate in 1903,
but as said, that was honoris causa. In total Kapteyn, not counting Easton,
only had eight Ph.D. students. Adriaan van Maanen (1884–1946) obtained
his Ph.D. in 1911 in Utrecht with Albertus Antonie Nijland (1868–1936) as
supervisor, but van Maanen actually worked in Groningen for some time on
his dissertation (on the proper motions of stars) and in fact saw Kapteyn as his
real teacher. With Adriaan van Maanen added, the number comes to nine. For
Kapteyn’s contemporaries in mathematics and natural sciences in Groningen,
the average per professor was roughly one Ph.D. every three years. Kapteyn,
who has been a professor for 43 years, even if Adriaan van Maanen is counted,
does not get more than one Ph.D. student per almost five years. But when
in 1908 his second Ph.D. student Herman Albertus Weersma (see Fig. 7.9)
defended his thesis, he was far behind even on that schedule.
Herman Weersma’s dissertation was about a new determination of the Apex
‘according to the method of Bravais’. Weersma went back to the original formulation of the problem, using the spatial positions, velocities and masses of
the stars, to determine the center of gravity of a system. This was not very
practical of course, because the distance and spatial velocity of only a few
stars had been measured; the mass of stars and the variation among them were
largely unknown. So Weersma developed an adapted method, in which he took
into account the missing data as well as possible and as a first approximation
ascribed equal masses to all the stars. That was indeed an improvement on
earlier work and he obtained a more accurate result, working with the care that
Kapteyn expected of him. The knowledge of the position of the Apex (and
the velocity of the Sun relative to the collective of stars in its vicinity) was,
as we have already seen, an essential part of Kapteyn’s program using secular
parallaxes as a step towards determining the construction of the heavens.
Weersma was appointed on a permanent position as Kapteyn’s assistant
in 1908; he succeeded de Sitter when he moved to Leiden in that year. When
Weersma left Groningen in 1912, his place (in 1913) was taken by Frits
Zernike (1888–1966), who was later to win the Nobel Prize in physics for his
invention of the phase contrast microscope. Zernike did not work for Kapteyn