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CAMERA OBSCURA 517 About the same time Maurolycus, the eminent mathe- how by placing a mirror behind the aperture unreversed matician of Messina, in his Theoremata, de Lv/nvine et Umbra, images might be obtained, illustrating the two effects with fully investigated the optical problems connected with diagrams. vision, the passage of rays of light through small apertures Risner, who died in 1580, has also in his Opticce (1606) with and without lenses. Risner says he has described very clearly explained the reversal of the images in the the application of the darkened room to the observation of camera obscura. He notes the conveniences of the method eclipses. In any case his theoretical work was a great for solar observations, and its previous use by the observers advance on that of his predecessors. It is possible that already mentioned. He further points out its advantages for Reinhold got this method of observing eclipses from easily and accurately copying on an enlarged or reduced scale, Maurolycus, through Purbach. He is said to have used especially for chorographical or topographical documents. it to observe an eclipse of the sun at Wittenberg, in 1540, Ihis seems to be the first notice of the application of the and he certainly did so in 1544 and 1545. He has de- camera to cartography and reproduction of drawings on scribed his method in his edition of Pvirbach’s Theoricce various scales, which, perhaps more than anything else, is Jovce Planetarum, and says it can also be applied to its prime use at the present day. In the Diversarum observing terrestrial objects, though he only used it for the opeculationum Adathematicarum et Physicarum, written in sun. Gemma Frisius has fully described the application of 1585 by the Venetian nobleman Benedetti, there is a letter Reinhold s method to making measurements and drawings to Piiro de Arzonis, in the course of which, after discussing of the sun during eclipses, or otherwise, and gives a figure the destruction or weakening of the images of the camera of the arrangements he adopted in observing the eclipse of obscura by the admission of extraneous light, he tells him January 1544 at Louvain, in his De Radio Astronomico et of an improvement in that sort of thing some one had Geometrico (1545), p. 31. He says it can also be used for carried out by the use of a double convex glass in the observations of the moon and stars and for longitudes. aperture of the dark room, and that the images could be Moestlin adopted the same method later, and handed it on made erect by reflexion from any plane mirror. This was to Kepler. It had the advantage of being simple and four years before Porta published it, and may refer to avoiding injury to the eyes. It is interesting to note this Barbaro. The account of the camera obscura given in early application of the camera obscura to the field of Porta s second edition of the ATagia Naturalis, in 1589 astronomical research, in which its latest achievements have is expanded from the first. The use of the lens, which is been of such pre-eminent value. given as a great secret, in place of the concave speculum of The addition of optical appliances to the simple dark the first edition, is not so clearly described as by Barbaro; chamber seems to have been first described by Cardan, in the concave speculum is used for making the images larger a passage in his treatise De Subtilitate (1550), p. 107, which and clearer, and also for making them erect, but no details Libri has noted : 11 Quod si libeat spectare ea quod in via are given. He describes some peep-show arrangements, fiunt, sole splendente, in fenestra orbem e vitro collocabis, and indicates how the camera with a concave speculum inde occlusa fenestra videbis imagines per foramen trans- can be used for observing eclipses. There is no mention latas in opposite piano . . . atque alia mira non solum of a portable box or construction beyond the darkened sphaericum sed et conicum ac cylindricum.” From this it room. In his treatise De Refractione Optices Parte (1593), would appear that he used spherical mirrors, and not a lens, he goes into the theory of vision and the optics of the which might be implied by the use of the word “orbem.” camera. He brought forward no novelty in the camera We now come to Porta. In his first account of the obscura, he did not improve it, his descriptions of it are camera obscura in the Afagia Naturalis, in four books, vague, but were published in a book which became popular, Naples, 1558, no mention is made of a lens, but he discloses and so he acquired credit for the invention. as a great secret, that by a proper arrangement of a concave The first to take up the camera obscura after Porta’s speculum in front of the aperture the colours of objects second edition was Kepler, who used the method for solar could be seen much better. This seems, however, to be observations in 1600, and in his Ad Vitellionem Paralivery similar to Cardan’s arrangement published eight years poviena (1604) discusses all the old problems of the earlier. Porta also alludes to the application of the passage of light through small apertures and the rationale method to painting by persons ignorant of drawing who of the camera obscura. He was the first to make up an could lay on colour. His second edition, in which he in instrument fitted with a sight and paper screen for the same words claims the discovery of the use of a convex observing the diameters of the sun and moon in a dark lens in the aperture as his own, and a secret he intended to room. In his later book Dioptrice (1611) he fully diskeep, was not published till 1589, thirty-one years after the cusses refraction and the use of lenses, showing the first. In this interval the use of the lens was discovered and action of the double convex lens in the camera obscura, clearly described by Daniele Barbaro, a Venetian, Patriarch and the principles which regulate its use, with the reason of Aquileia, in his work on geometrical perspective, La of the reversal of the image. He also shows that enlarged Pratica della Prospettiva, p. 192, published in 1568, or images can be produced by using a concave lens at a suittwenty-one years before Porta mentioned it. The lens used able distance behind the convex, as in modern telephotoby Barbaro was an ordinary convex, or old man’s, spectacle graphy. He extended the work of Maurolycus, and glass ; concave, he says, will not do. He shows how the demonstrated the exact analogy between the eye and the paper must be moved till it is brought into the focus of camera and the arrangements by which an inverted image the lens, the use of a diaphragm to make the image is produced on the retina. clearer, and also the application of the method for drawing About this time the telescope came into use, and the objects in true perspective. That Barbaro was really the danger of observing the sun with it was soon discovered. first to apply the lens to the camera obscura is supported In 1611 Fabricius published his observations of sun-spots, by Bettinus in the Apiaria, and by Schott in his Magia and describes how he and his father fell back on the old Universalis, the former taunting Porta with the appropria- method of observing the sun’s image through a small hole tion. In an Italian translation of Euclid’s Optics, published in a darkened room, finding that they could observe the by Egnatio Danti in 1573, after discussing the effects of spots just as well as in the telescope. They do not seem plane, convex, and concave reflectors, he gives a full to have used a lens, or thought of using the telescope for description of the method of showing reversed images projecting an enlarged image. This was done by Scheiner passing through an aperture in a darkened room, and shows who has fully described and illustrated his method in the