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Kepler and the telescope. (English) Zbl 1042.01005

“There is an uncanny unanimity about the founding role of Kepler’s Dioptrice for the theory of optical instruments and for classical geometrical optics generally” (S. 107). Der vorliegende Beitrag behandelt darüberhinaus auch physiologische Fragen im Zusammenhang mit Keplers Dioptrice, Augsburg 1611, wobei ein deutlicher Gegensatz zu gängigen Ansichten hervortritt. Entsprechend wie “Galileo had no theoretical understanding of why and how telescopes worked” (S. 108), heißt es: “Kepler did not have a quantitative solution for the focus of lenses in general. He only had a largely qualitative knowledge of the location of focal points” (S. 109), denn: “Ignoring the physical causes of refraction, Kepler states the basic facts about refractions as ‘axioms’ ” (S. 109).
In elf Abschnitten geht Verf. auf Details ein, wobei er seine Überlegungen
“It is obvious, therefore, that what Kepler calls ‘image’ cannot be identified with the notions of ‘real’ and ‘virtual’ geometrical images that would come to dominate geometrical optics from the last decades of the seventeenth century on” (S. 114); “While he can develop no geometrical and quantitative theory’ of the telescope, because he lacks the crucial notion of geometrical image, yet he manages to provide a rationalization or ‘explanation’ of some features of the telescope and of its main visual effects” (S. 123f.); in Kepler’s Methode “there is no way to deal geometrically or theoretically with optical images. Kepler shows how to deal with geometrical properties of pictures (their sizes and distances to the lens), but all this he cannot apply to images seen through telescopes, because images are produced within the mind only” (S. 127); “In any case, whenever Kepler needed to introduce experimental data in demonstrations, he used axioms that stated factual experience. Kepler did not test or check any proposition by means of experiments…On the other hand, he used experimental arrangements to investigate physical properties of lenses” (S. 130). usw.
auf beigegebene Figuren stützt.
Verf. resümiert schließlich in “11. The legacy of Kepler’s Dioptrice”, wobei auf die wort- bzw. sinngetreue Wiedergabe lateinischer termini technici Keplers Wert gelegt wird: “Kepler wants to understand the interaction of lenses and telescopes with human vision…Keplerian ‘images’ are not physical or mathematical entities, rather they are acts of vision” (S. 133). “On the other hand, Kepler’s pictures, not formally introduced or defined in Dioptrice, play no role in his account of vision through lenses and telescopes…Geometrical optical images, a crucial notion in classical geometrical optics, are missing in Kepler’s treatise. As a consequence, the whole family of problems related to geometrical image formation, so characteristic of classical optics, is not even adumbrated in Kepler’s dioptrics…It is hard therefore to claim that Kepler’s Dioptrice inaugurates classical geometrical optics and the ‘modern’ understanding of how telescopes work…This body of results apparently nobody questioned before the 1660s. That his results articulated theoretical as well as practical descriptions of optical instruments for more than fifty years is the real measure of Kepler’s achievement” (S. 134).

MSC:

01A45 History of mathematics in the 17th century
78A05 Geometric optics

Biographic References:

Kepler, Johannes
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