But Kaiser was not only important to the department of astronomy in Leiden, his impact on
Dutch science was far more profound. This had everything to do with the fact that he was an
ardent proponent of a new methodology: taking his cue from German astronomer Friedrich
Bessel, Kaiser insisted that precise, quantitative measurement should serve as the basis of
astronomy. The astronomer’s task then lay in the computational and statistical analysis of
this data.
This shift in focus of the astronomer’s work, away from observation of the skies towards
apparently more mundane calculation and number-crunching on the basis of observational
data that had been obtained through standardised methods of observationB- which could
therefore also be obtained by less well-trained observers - was taking place throughout the
astronomical community. The Astronomer Royal George Biddell Airy for instance took a
similar stance.
The emergence of this new methodological approach coincided with a period of gradual
specialisation of the natural sciences, and the rise of disciplinary borders between the
specialised communities of researchers. In the Netherlands this was only iully reflected in the
organisational structure of the universities long after van der Willigen had completed his
studies, after a series of educational reforms in the 1860s and 1870s. However, in the same
way that those involved in the (experimental) study of nature in the Anglo-Saxon world began
adopting the label “man of science” or even “scientist” as a badge of honour as early as the
1830s, their Dutch counterparts were equally eager to gain recognition of the fact that their
field of study was not only expanding rapidly, but also becoming so vast that specialisation
was becoming necessary. In an - ultimately unsuccessful - attempt to push through reform of
the Dutch universities rules of examination, the deans of the faculties of philosophy drafted a
joint letter suggesting reform, which contained the following key argument:
“The practice of those branches of science associated with Mathematics and Physics
[Natuurkunde] is increasing more and more, as is, correspondingly, the size of these fields.
While as a result some parts of the larger whole increasingly grow closer and need each
other’s support, the whole of science is in the meantime growing so large that a single person
can no longer be familiar with it. On the contrary, because of the nature of the situation, a
subdivision is, more and more, urgently required.”25
On this see: Elly Dekker, “Een procesverbaal van verhoor,” Gewina 15 (1992): 153-162; and also: Hans
Hooijmaijers, “Een passie voor precisie: Frederik Kaiser en het instrumentarium van de Leidse Sterrewacht,”
Studium: tijdschrift voor wetenschaps- en universiteitsgeschiedenis 4, no. 2 (2011): 109.
On the situation in England see for instance: Simon Schaffer, “Astronomers Mark Time: Discipline and the
Personal Equation,” Science in Context 2, no. 1 (1988): 115-145.
De beoc fcning der taken van wetenschap welke tot Wis- en Natuurkunde gebragt worden, neemt steeds meer
en meer toe, en in dezelfde mate ook de uitgebreidheid van elk deel der wetenschappen hetwelk hiertoe behoort.
Terwijl hierdoor sommige deelen van het groote geheel elkander meer en meer naderen, en elkanders hulp
behoeven, wordt het geheel intusschen veel te groot, dan dat een mensch daarmede goed vertrouwd zou kunnen
worden. Integendeel eene splitsing wordt door den aard der zaak hoe langer hoe meer met dringende
noodzaakelijkheid geboden.” “Aan Zijne Excellence den Minister van Binnenlandsche Zaken”, 11.03.1842,
Leiden, UBL BC, Archieven van Senaat & Faculteiten, nr. 488.
Even more important than this latent dissatisfaction with a lack of formal specialisation within
the sciences - certainly as far as van der Willigen was concerned - was the fact that Kaiser’s
methodological approach began to affect other areas of science as well. Physicists in
particular began to apply these methods, pioneered by their close colleagues the astronomers,
to their own research. It has been shown that almost all the main proponents of quantitative
methods in physics in Germany and the Netherlands during the 19th century were strongly
influenced by what Bessel (in Germany) and Kaiser (in the Netherlands) had initiated in
astronomy.26 In many cases, they had received some training in astronomy as part of their
scientific education, before specialising in physics.
This brings us back to the future physicist van der Willigen. All evidence suggests that Kaiser
was a good teacher, and van der Willigen evidently was impressed and enamoured with this
energetic young professor’s groundbreaking ideas.27 Inspired by Kaiser, van der Willigen
adopted the same approach to all of his scientific studies throughout his career, i.e. insisting
that precise, quantitative measurements could serve as the only basis for any legitimate claim
in physics. As such, he provided an important and largely overlooked contribution to the
development of physics in the Netherlands. His impact becomes tangible through his own
pupil and acolyte Johannes Bosscha, who has been identified as one of the pioneers of
experimental physics in the Netherlands alongside Herman Haga and Heike Kamerlingh
Onnes.28 Bosscha’s interest in scientific instruments and the precision that could be achieved
with them is sure to have been rooted at least to some extent in the classes given by van der
Willigen which he attended.
The two first met shortly after van der Willigen had completed his studies in Leiden. He
graduated with a final dissertation on the aberration of light, in which he discussed the
theories of Stokes and Challis.29 He had chosen Kaiser as his supervisor. He graduated in
1847 with the highest distinction (magna cum laude), which was exceptional. That same
year he received a job as a teacher of physics at the Latin School in Amsterdam - which
Bosscha attended.
26 Frans van Lunteren, ‘“Van meten tot weten’: De opkomst der experimentele fysica aan de Nederlandse
universiteiten in de negentiende eeuw,” Gewina 18, no. 2 (1995): 1 0 2 ||||P :lr „
27 On Kaiser as a teacher see: Zuidervaart, “Frederik Kaiser (1808-1872), een gekweld man met een misste, 72-
73 On the impression he made on his student van der Willigen see: Hendricus Gerardus van de Bakhuyzen,
“Nekrolog: Volkert Simon Maarten van der Willigen,” Vierteljahrsschrift der astronomischen Gesellschaft 14
(1879): 98. Van der Sande Bakhuyzen also mentions other teachers (Verdam and Uylenbroek), but singles out
Kaiser as having impressed van der Willigen the most. For a specific example in which van der Willigen
acknowledges that he was strongly influenced by Kaiser’s methodology see: Willigen, “Memoire sur la
détermination des indices de réfraction et sur la dispersion des mélanges d’acide sulfürique et d eau, 75.
28 On Bosscha’s reputation as a pioneer and his interest in instruments and precise measurements see: Lunteren,
‘“Van meten tot weten’: De opkomst der experimentele fysica aan de Nederlandse universiteiten m de
negentiende eeuw,” 73 & 54; Bastiaan Willink, De tweede Gouden Eeuw: Nederland en de Nobelprijzen voor
natuurwetenschappen, 1870-1940 (Amsterdam: Bert Bakker, 1998), 30.
29 Volkert Simon Maarten van der Willigen, Dissertatio inauguralis de aberratione lucis (Leiden: O.G. Menzel,
1847).
30 On his final graduation see: “Catalogus candidatorum qui gradum adepti sunt 1813-1850”, 1847, UBL BC,
Archieven van Senaat en Faculteiten, nr. 351, fol. 329-330.