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The Prehistory of the Invention of the Telescope

1.1 - The Perspectivist Tradition

G. Parigi, Archimedes' burning mirror, early 17th c. (Galleria degli Uffizi , Sala delle Matematiche, Firenze) Witelo, Peri Optike..., 1535: frontispiece Ibn al_Haytham & Witelo, Opticae Thesaurus ..., 1572: frontispiece

In Antiquity the chief concern of optics had been that of explaining the phenomenon of visual perception. Euclid (4 th century B.C.E.) had restricted himself to the problem of direct vision, while Claudius Ptolemy (2 nd century C.E.) extended his studies to the reflection of "visual rays" on a mirror-like surface and their refraction through the surfaces separating two transparent media. The results obtained were re-elaborated by the Islamic mathematician Ibn al-Haytham (965-1039), whose Kitab al-Manazir constituted the reference text for the perspectivist tradition of optics in the 13 th century.

Like the ancients, the perspectivists were interested only in the perception of images through mirrors and glass spheres. This is not to say that the problems associated with the behaviour of light reflected from a mirror or refracted by a glass sphere were ignored. The study of "burning mirrors" in particular was urgently pursued in the 16 th century, especially in view of the military applications foreseen, inspired by the name of Archimedes (287-212 B.C.E.). This study was however conducted independently of those concerned with images perceived in a mirror or a glass sphere.

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