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Abstract

Frederik Kaiser (1808-1872) was one of the most inspiring directors of the Leiden astronomical observatory. In Dutch astronomy he introduced a systematic observing and research program. Furthermore he succeeded in founding a new observatory after years of struggle. This paper describes how Kaiser's urge for precision led the way in his research, in his selection of instruments and in the design of the new observatory.

Kaiser was educated in astronomy by his uncle, the Amsterdam mathematician and astronomer Jan Frederik Keijser. He introduced young Frederik also into the world of instruments, theory and influential persons. At the age of eighteen Frederik succeeded in getting appointed as an observer at Leiden Observatory. However, the bad relationship with its director and the lousy state of the instruments at this observatory made observing almost impossible. Instead, Frederik took up a study in physics and mathematics at Leiden University. In 1835 Kaiser's chances turned with the predicted return of Halley's comet. With borrowed equipment, Kaiser observed the comet at home. More important, Kaiser had rightfully predicted the perihelium-passage of the comet (the closest approach to the sun). His calculation differed only two hours with the actual moment. This exact computation enhanced Kaiser's reputation as a scholar and led in 1837 to his appointment as director of the Leiden Observatory.

From the very outset Kaiser tried to incorporate 'statistal astronomy' in his research, imitating German scientists as Gauss, Bessel, Encke and Hansen. He therefore applied for a new observatory and instruments, but in first instance only some money for new instruments was granted. For his research on double stars and the trajectories of comets Kaiser bought some new instruments, like a Fraunhofer refractor with a precision micrometer and two transit instruments. In his publications Kaiser not only described his observations, but also meticulously investigated instrumental and personal errors. These errors brought Kaiser to improve and design instruments by himself.

Kaiser's precision talents were noticed by the Dutch Naval Minister. He appointed Kaiser as 'Verificator of the National Maritime Instruments'. In this capacity Kaiser used his talent to reorganize naval research and redesign instruments used by the navy. Although his astronomical work brought Kaiser and the Leiden Observatory international prestige, he strived for more: a new building. Finally, in 1860, after numerous pleas, a new observatory was built.The most important instrument in this building was a large meridian circle, not surprisingly a very precise instrument. Together with the most accurate astronomical clock of that time, Kaiser started ambitiously with his 'absolute measurements'. Within the European zone program he was able to pinpoint the positions of some 10,000 stars.

In 35 years Kaiser managed to bring the Leiden Observatory at the top of the international astronomical league, with his precise observation, critical analyses and lobby work. Kaiser therefore has been of enormous importance to Leiden Observatory.