I do not wish to keep any remarkable effect of this system a secret from you ... the round opening the size of one small mirror may be filled in with one of those spectacles which are made for old people (but not the kind for those of short sight), but one whose both surfaces are convex, not concave. Then set up a white sheet of paper (as the screen), so far back from the opening that the objects on the outside may appear on it. And if indeed these outside objects are illuminated by the sun they will be seen so clearly and distinctly that nothing will seem to be more beautiful or more delightful. The only objection is that the objects will appear inverted. But if we wish to see those objects upright, this can be done best by interposing another plane mirror. In the revised and expanded edition of his _Natural Magic_, Porta gave a more complete description of the uses of the camera. Part of the text was identical with the earlier accounts; part was new. [Illustration: Ars Magna Lucis et Umbrae, 1646 _CAMERA OBSCURA, the natural room camera, was accidentally discovered in antiquity, probably in the Far East. Here is shown an improved version by Giovanni Battista della Porta, 16th Century Neopolitan writer, scientist and showman. A translucent sheet was the screen. The images were upside down and indistinct as no lenses were used. Artists and entertainers found the apparatus of value._] Porta had learned how to make his opening in the single window better by this time--“make the opening a palm’s size in width and breadth and glue over this a sheet of lead or bronze which has in the middle an opening about the size of a finger.” He next pointed out that the outside objects can be seen clearer and sharper if a crystalline lens is put in the opening of the camera as suggested by Barbaro and Benedetti. Porta also mentioned that the insertion of another mirror in the system would make the images appear upright instead of upside down. [Illustration: Wissenschaftliche Abhandlungen, 1878 _JOHANNES KEPLER developed the scientific principles of the camera and its use in astronomy._] But Porta showed himself a real showman by his final word--describing how hunting, battles and other illusions may be made to appear in a room. Here artificial objects and painted scenes were substituted for the natural outdoors as the pictures for the room camera in a method originally suggested by Alberti. Porta said, “Nothing can be more pleasing for important people, dilettants and connoisseurs to behold.”--An early premiere audience of invited guests!