There is an uncanny unanimity about the founding role of Kepler's Dioptrice in the theory of optical instruments and for classical geometric optics generally. It has been argued, however, that for more than fifty years optical theory in general, and Dioptrice in particular, was irrelevant for the purposes of telescope making. This article explores the nature of Kepler's achievement in his Dioptrice . It aims to understand the Keplerian 'theory' of the telescope in its own terms, and particularly its links (...) to Kepler's theory of vision. It deals first with Kepler's way to circumvent his ignorance of the law of refraction, before turning to Kepler's explanations of why lenses magnify and invert vision. Next, it analyses Kepler's account of the properties of telescopes and his suggestions to improve their designs. The uses of experiments in Dioptrice , as well as the explicit and implicit references to della Porta's work that it contains, are also elucidated. Finally, it clarifies the status of Kepler's Dioptrice vis-à-vis , classical geometrical optics and presents evidence about its influence in treatises about the practice of telescope making during roughly the first two-thirds of the seventeenth century. (shrink)

Danish astronomy in the first half of the seventeenth century reflected the enduring legacy of Tycho Brahe and was dominated by his former assistant Longomontanus. This paper focuses on his successor as professor of astronomy, Jørgen From or Georgius Frommius in the Latin version, who was also the second director of the Round Tower observatory in Copenhagen. Before becoming a professor, Frommius travelled to the Netherlands and other countries. The letters from his journey cast light on the training of a (...) young astronomer at the time. He most likely was the first Dane to observe the heavens with a telescope. In the 1640s, he got involved in a controversy with the French astronomer and astrologist Jean Morin, and he later contributed to Pierre Gassendi’s pioneering biography of Tycho Brahe. Although Frommius died at the age of 46, his brief career as professor and astronomer is of interest to national as well as international history of science. (shrink)

SummaryThe Copernican system was condemned as heretical by a decree of the Roman Inquisition in 1633. This decree was effectively, though not officially, withdrawn in 1757, after which date Catholic astronomers felt themselves free to accept and propagate the system without reserve. Between these dates their attitudes varied greatly. In France the decree was never promulgated and was legally unenforceable. Astronomers could be Copernican without any fear of consequences and most of them were, though some, out of respect for the (...) Church, refrained from declaring themselves publicly. In Italy the possible risks were greater, but a few Copernican or near-Copernican works were published without hostile reactions. The ecclesiastical authorities were tolerant and made little positive effort to enforce conformity. By 1744, the system was being freely propagated in Rome itself. (shrink)

The aim of this paper is to offer an account of epistemic justification suitable for the context of theory pursuit, that is, for the context in which new scientific ideas, possibly incompatible with the already established theories, emerge and are pursued by scientists. We will frame our account paradigmatically on the basis of one of the influential systems of epistemic justification: Laurence Bonjour’s coherence theory of justification. The idea underlying our approach is to develop a set of criteria which indicate (...) that the pursued system is promising of contributing to the epistemic goal of robustness of scientific knowledge and of developing into a candidate for acceptance. In order to realize this we will (a) adjust the scope of Bonjour’s standards—consistency, inferential density, and explanatory power, and (b) complement them by the requirement of a programmatic character. In this way we allow for the evaluation of the “potential coherence” of the given epistemic system. (shrink)

While Newton tried to make his telescope into a proof of the supremacy of his theory of colours over older theories, his instrument was welcomed as a way to shorten telescopes, not as a way to solve the problem of chromatic aberration. This paper argues that the image published together with the report on Newton’s telescope in Philosophical Transactions (1672) encouraged this reception. The differences between this visualization and other images of Newton’s telescope, especially that published in Opticks (1704), are (...) discussed. This paper shows that the image in Opticks adopted characteristics of a Cartesian program of visualization of machines and instruments which complemented a rhetoric which attributed primacy to theory over practice. The differences between the images in Philosophical Transactions and Opticks are also considered within the broader institutional context of Newton’s attitude towards the Royal Society. (shrink)

As one of the least common, yet predictable astronomical occurrences, the transits of Venus were to become among the most keenly anticipated events for early modern cosmologists. Basing himself on Johannes Kepler’s Tabulae Rudolphinae (1627), former Cambridge student Jeremiah Horrocks (1616–1641) made the first recorded observation of a transit from Much Hoole, Lancashire in 1639. Alongside the description of his observations, Horrocks’ Venus in sole visa contains four poems alongside the work’s prose descriptions, figures, and tables. His verses call on (...) the long tradition of Latin scientific poetry employed for the predictable purposes of eulogy and homage, but they also serve to justify and clarify the author’s position on scientific issues of his time. Despite the long-recognized importance of Horrocks’ observations, his hexameter compositions have been largely ignored in later scholarship. In the latest translation of the Venus in sole visa (2012), one poem—the longest and arguably the best—is omitted altogether. This paper offers a study of Horrocks’ Latin poetry, his models and engagement with its subject matter. It reveals Horrocks’ efforts to promote his predecessors’ achievements, his position on questions central to the debates of his time, and the claims for authority he made for the work of others, as well as for his own. The present article also includes a new, modern translation of Horrocks’ longest, and recently forgotten poem as an appendix. (shrink)

In the Optics, Descartes claims that telescopes and microscopes lead to morally certain knowledge. It is unclear, however, that Descartes’s expressed confidence in these instruments is warranted. In this article, I show how a limited range of telescope and microscope observations could lead to morally certain knowledge for Descartes, and how observations beyond this range admit of enough reasonable doubt to undermine moral certainty. I also explain moral certainty as a form of knowledge in Descartes’s scientific practices, his epistemic commitment (...) to optical instruments, and I offer an explanation for why Descartes never used optical instruments in his scientific endeavours. -/- ---- -/- Dans la Dioptrique, Descartes prétend que les télescopes et les microscopes donnent accès à des connaissances moralement certaines. Cependant, il n’est pas certain que la confiance accordée par Descartes à ces instruments soit justifiée. Dans cet article, je montre comment une gamme limitée d’observations effectuées à l’aide d’instruments d’optique pourraient mener aux connaissances moralement certaines pour Descartes, et comment d’autres observations allant au-delà de cette gamme introduisent suffisamment de doute raisonnable pour saper cette certitude morale. Enfin, j’interprète la certitude morale comme une forme de connaissance dans l’empirisme de Descartes, j’explique son engagement épistémique envers les instruments d’optique, et j’éclaire les raisons pour lesquelles il n’a jamais employé d’instruments d’optique dans ses propres recherches scientifiques. (shrink)

According to the received view, the first spyglass was assembled without any theory of how the instrument magnifies. Galileo, who was the first to use the device as a scientific instrument, improved the power of magnification up to 30 times. How did he accomplish this feat? Galileo does not tell us what he did. We hold that such improvement of magnification is too intricate a problem to be solved by trial and error, accidentally stumbling upon a complex procedure. We construct (...) a plausibility argument and submit that Galileo had a theory of the telescope. He could develop it by analogical reasoning based on the phenomenon of reflection in mirrors—as it was put to use in surveying instruments—and applied to refraction in sets of lenses. Galileo could appeal to this analogy and assume Della Porta’s theory of refraction. He could thus turn the spyglass into a revolutionary scientific instrument—the telescope. (shrink)