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THE THEORETICAL EXPLANATION BEHIND GALILEO S TELESCOPIC OBSERVATIONS . First edition, extremely rare, of this important early work on the optics of the telescope and related optical phenomena, and containing the first essentially correct theory of the rainbow to be published. Dominis and Galileo were both teaching mathematics and physics in Padua at the same time, and it is almost certain that they knew each other. The present work has the same publisher as Galileo s Sidereus nuncius of the previous year. Dominis sought to provide the theoretical explanation behind Galileo s telescopic observations, and his work appears to have been completed before Galileo s, although published later (see below). The work was edited by Dominis s friend Giovanni Bartolo. "In the preface, Bartolo says that the work is based on notes prepared by De Dominis for his lectures at Padua and Brescia twenty years before; but he adds that De Dominis himself had revised these notes and inserted an explanation of the newly-invented telescope" (Ockenden, p. 42). This preface is the source for the erroneous claim that Galileo invented the telescope. The second half of the book is taken up with the phenomena of refraction and reflection in raindrops and the rainbow. Newton owned a copy of this book (Harrison 535) and referred to it twice in his Opticks, stating that Dominis was the first to present a correct theory of the rainbow, involving double refraction and internal reflection of sunlight in raindrops. This led to a dispute with Descartes and his supporters, who held that the first correct explanation of the rainbow was given in Descartes s Discours (1637). ABPC/RBH list only one copy since the Honeyman copy sold in 1979 (both of these copies were in modern bindings). "Dominis had written two works on physics by the time he lectured on mathematics in Padua. The first one, De radiis visus et lucis, deals with lenses, telescopes, and the rainbow. Dominis knew how light was refracted in its passage from one medium to another, but he was not always consistent in his assertions. He held that it was possible that in some cases light could pass through the border of a medium without being refracted for instance, into a thin layer of water. In general, his observations on refraction in lenses were correct. "After the invention of the telescope Dominis added its theoretical explanation to his work. His explanation was not entirely satisfactory, however, because his knowledge of the law of refraction was incomplete. He concluded that the image of an object was enlarged by increasing the angle of sight, which he had previously defined correctly. Thus Dominis describes in particular detail the effect on the angle of sight of a lens of greater curvature or of a greater distance between the lens and the object being viewed. With the same thoroughness he examined lens combinations, in particular the combination of a convex object glass and a concave eyepiece. This work led to his discovery of the conditions under which the magnification of an image is possible" (DSB). The correct elementary explanation of the rainbow in terms of reflection and refraction of the Sun s rays in raindrops was given by the Persian astronomer and physician Qutb Al-Din and the Teutonic Dominican theologian Theodoric of Freiburg as early as the fourteenth century, but their work remained unpubished until the nineteenth century (although Regiomontanus had considered publishing Theodoric s work on optics). Many other scholars attempted explanations in the intervening centuries. Johannes Kepler gave a variey of incorrect and sometimes fanciful explanations, but in correspondence with Thomas Harriot in the years 1606-1609 he gave essentially the correct one. However, this was not included in his Dioptrice, published in the same year as the present work, nor in any of his other published works. So closely does Dominis s theory of the rainbow resemble Descartes s account in Les météores (appended. Seller Inventory # 5287
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