A deserted tower at the Uithof Campus of Utrecht University used to be an astronomical observatory, purpose-built for Marcel Minnaert’s famous undergraduate course in practical astronomy. The tower, which was opened in 1964, has hardly been used, however. This was in part because of unforeseen campus development, but also because of shifting teaching priorities. This paper reconstructs the history of Minnaert’s ‘Sterrentoren’, which illustrates how failed observatories can shed as much light on the history of astronomy as successful ones.

This essay examines the transformation of a local rule of thumb into a widely acknowledged meteorological law, generally known as Buys Ballot’s law. This law relates wind direction to atmospheric pressure. From 1857 to 1867, Christophorus Buys Ballot (1817–1890) actively lobbied in the international arena for his wind rule, which he regarded as a promising basis for a system of storm warnings. At the same time he was reluctant to generalize his rule beyond the Dutch boundaries or to make strong claims about its predictive nature. Initially he failed to interest foreign meteorologists in his work, partly because of a widespread scepticism with regard to meteorological predictions, and partly because some of his foreign colleagues favored competing theories. One of his main rivals in this respect was Robert Fitzroy, director of the British Meteorological Office, who had set up his own warning system. This practice provoked the wrath of the Royal Society, as its members regarded Fitzroy’s theories and the resulting predictions as unscientific. After his death the Society took the British Meteorological Office under its control and abolished the practice of storm warnings. The resulting wave of protests from people who felt they had benefitted from the warnings landed the Society in an awkward predicament. The warnings could only be reintroduced without losing face if they had a ‘‘scientific’’ basis, and therefore finding a sound basis for storm predictions became a matter of urgency. At last Buys Ballot found a willing ear for his campaign. A rapid verification of his wind rule in Britain sufficed for the introduction of the unprecedented expression ‘‘Buys Ballot’s law’’ in the Royal Society reports. From these authoritative reports the designation rapidly spread all over the world, thus becoming a current expression.

Like many of their contemporaries Bernard Nieuwentijt (1654–1718) and Pieter van Musschenbroek (1692–1761) were baffled by the heterodox conclusions which Baruch Spinoza (1632–1677) drew in the Ethics. As the full title of the Ethics—Ethica ordine geometrico demonstrata—indicates, these conclusions were purportedly demonstrated in a geometrical order, i.e. by means of pure mathematics. First, I highlight how Nieuwentijt tried to immunize Spinoza’s worrisome conclusions by insisting on the distinction between pure and mixed mathematics. Next, I argue that the anti-Spinozist underpinnings of Nieuwentijt’s distinction between pure and mixed mathematics resurfaced in the work of van Musschenbroek. By insisting on the distinction between pure and mixed mathematics, Nieuwentijt and van Musschenbroek argued that Spinoza abused mathematics by making claims about things that exist in rerum natura by relying on a pure mathematical approach (type 1 abuse). In addition, by insisting that mixed mathematics should be painstakingly based on mathematical ideas that correspond to nature, van Musschenbroek argued that René Descartes’ (1596–1650) natural-philosophical project (and that of others who followed his approach) abused mathematics by introducing hypotheses, i.e. (mathematical) ideas, that do not correspond to nature (type 2 abuse)

As a supplement to John L. Heilbron’s account, I will argue that, although the label ‘experimental physics’ can be rightfully used to describe aspects of Petrus van Musschenbroek’s (1692-1761) work, the latter’s understanding of ‘physica’ is to be situated within a broader framework in which theological, philosophical and teleological considerations continued to play an important role. First, I will draw attention to Musschenbroek’s views on the scope of physica and especially to his conception of a law of nature. It will be shown that by radicalizing certain aspects of Isaac Newton’s methodological ideas van Musschenbroek no longer considered physics as the discipline that uncovered causes from effects, as Newton did, but as the discipline that studies the effects of unknown causes. In addition, I will show that van Musschenbroek endorsed the view that the laws of nature are contingent on God’s free will and that they are knowable due to his goodness. Second, it will be argued that for van Musschenbroek physics, alongside with teleology, had clear physico-theological repercussions. Along the way, van Musschenbroek’s views on the principle of sufficient reason will be discussed for the first time.

According to a dominant view in the scholarly literature, Musschenbroek is to be considered a follower of Newton’s methodology, i.e. as a natural philosopher who, although he occasionally departed from Newton’s doctrines, aligned himself to Newton’s methodological views. Few scholars have, however, explained in full detail what it means to claim that Musschenbroek followed Newton’s method. The purpose of this essay is to get more grip on this matter.