22
2 Boarding School and University
the ceremony. In total there were eighteen, of which the numbers 10 to 16 are
astronomical in nature—a clear indication of his strong interest in this field.
Among the non-astronomical ones there was a remarkable proposition, because of the person involved, Dutch author Multatuli (pseudonym for Eduard
Douwes Dekker, 1820–1887). The proposition deals with the use of the ‘zero’
in roulette. The details are not so important here. But the fact that he quoted
Multatuli shows that he had read his work. It is known from other sources
that Multatuli was an important source of inspiration for Kapteyn and that
Multatuli’s non-conformist view of society and religion appealed to him particularly. In Henriette Hertzsprung–Kapteyn’s biography [1] Multatuli’s work
does not appear in the inventory of the library in Barneveld, so Kapteyn may
have read Multatuli later during his student days. Nevertheless, Multatuli will
have influenced Kapteyn’s development and almost certainly played a role in
his rejection of his parents’ religion.
I will go into two of the astronomical propositions in more detail. Number
X reads: The best photometer is that of Zöllner. A photometer is an instrument
to measure the brightness of a star in the sky. The proposition suggests that
Kapteyn was aware of the properties of such photometers and had experience
using them. Johann Karl Friedrich Zöllner (1834–1882) had developed a stellar
photometer in 1858 (see Fig. 2.6), which compared a star with an image of
a flame from a so-called Bunsen burner [30, 31]. This is designed to give a
gas flame that is particularly stable and not flickering. One could then adjust
the brightness of the resulting image with a polarizer to match that of the star.
Light can be interpreted as a wave and can be polarized when it passes through
a transmitting thin plate, which, due to the orientation of the crystals, only
allows light to pass that oscillates in a certain plane. A second plate is then
placed behind it; if it is ‘parallel’, it allows all the light to pass through, but it
can be rotated, so that only a part or nothing passes through. In this way one
can adjust the brightness of the ‘artificial star’ to that of the star of which the
brightness has to be determined. Of course, one must first observe a star of
known brightness to calibrate the instrument. In Sect. 10.3 a photograph of
Willem de Sitter has been reproduced (Fig. 10.11), where he is depicted next
to a telescope with a Zöllner photometer mounted on it.
Until then, the brightness of stars was measured by means of visual comparison with one or more other stars. John Frederick William Herschel (1792–
1871) used what he called an ‘astrometer’, with which he compared a star with
a downsized image of the Moon in his field of view in the telescope, which he
obtained after reflection in a prism and focusing with a lens. Another method
was that of Carl August von Steinheil (1801–1870) in München, who had
developed a device with which he compared the brightness of out-of-focus
2 Boarding School and University
the ceremony. In total there were eighteen, of which the numbers 10 to 16 are
astronomical in nature—a clear indication of his strong interest in this field.
Among the non-astronomical ones there was a remarkable proposition, because of the person involved, Dutch author Multatuli (pseudonym for Eduard
Douwes Dekker, 1820–1887). The proposition deals with the use of the ‘zero’
in roulette. The details are not so important here. But the fact that he quoted
Multatuli shows that he had read his work. It is known from other sources
that Multatuli was an important source of inspiration for Kapteyn and that
Multatuli’s non-conformist view of society and religion appealed to him particularly. In Henriette Hertzsprung–Kapteyn’s biography [1] Multatuli’s work
does not appear in the inventory of the library in Barneveld, so Kapteyn may
have read Multatuli later during his student days. Nevertheless, Multatuli will
have influenced Kapteyn’s development and almost certainly played a role in
his rejection of his parents’ religion.
I will go into two of the astronomical propositions in more detail. Number
X reads: The best photometer is that of Zöllner. A photometer is an instrument
to measure the brightness of a star in the sky. The proposition suggests that
Kapteyn was aware of the properties of such photometers and had experience
using them. Johann Karl Friedrich Zöllner (1834–1882) had developed a stellar
photometer in 1858 (see Fig. 2.6), which compared a star with an image of
a flame from a so-called Bunsen burner [30, 31]. This is designed to give a
gas flame that is particularly stable and not flickering. One could then adjust
the brightness of the resulting image with a polarizer to match that of the star.
Light can be interpreted as a wave and can be polarized when it passes through
a transmitting thin plate, which, due to the orientation of the crystals, only
allows light to pass that oscillates in a certain plane. A second plate is then
placed behind it; if it is ‘parallel’, it allows all the light to pass through, but it
can be rotated, so that only a part or nothing passes through. In this way one
can adjust the brightness of the ‘artificial star’ to that of the star of which the
brightness has to be determined. Of course, one must first observe a star of
known brightness to calibrate the instrument. In Sect. 10.3 a photograph of
Willem de Sitter has been reproduced (Fig. 10.11), where he is depicted next
to a telescope with a Zöllner photometer mounted on it.
Until then, the brightness of stars was measured by means of visual comparison with one or more other stars. John Frederick William Herschel (1792–
1871) used what he called an ‘astrometer’, with which he compared a star with
a downsized image of the Moon in his field of view in the telescope, which he
obtained after reflection in a prism and focusing with a lens. Another method
was that of Carl August von Steinheil (1801–1870) in München, who had
developed a device with which he compared the brightness of out-of-focus