. The art of projecting. A manual of experimentation in physics, chemistry, and natural history, with the porte lumière and magic lantern. ous diameters. 38 THE ART OF PROJECTING. THE MEGASCOPE. Photographs that are taken especially for projectionwith the magic lantern are often called transparenciesbecause all of the lighter parts of the pictures are madeas transparent as possible, and they are shown by lightthat is transmitted through them. If one would ex-hibit a picture like a stereoscopic view or a commoncarte de visite^ it is evident that recourse must be had tosome other arrangement. Th
. The art of projecting. A manual of experimentation in physics, chemistry, and natural history, with the porte lumière and magic lantern. ous diameters. 38 THE ART OF PROJECTING. THE MEGASCOPE. Photographs that are taken especially for projectionwith the magic lantern are often called transparenciesbecause all of the lighter parts of the pictures are madeas transparent as possible, and they are shown by lightthat is transmitted through them. If one would ex-hibit a picture like a stereoscopic view or a commoncarte de visite^ it is evident that recourse must be had tosome other arrangement. The light must be reflectedfrom the picture, but when only the ordinary amountwhich is reflected from a surface of nine square inchesis distributed over seventy-five or a hundred square feet,it is evident that it will be but dimly visible. If a largeamount of light is concentrated upon the picture it will,of course, reflect more, and its image will be corres-pondingly brighter. This can be effected in two ways:first, by using a large lens, or second, by using a largeconcave mirror. The following figures will serve to show how this may. be done. When sunlight is used, the larger the con-denser the better. One seven or eight inches in diam-eter, if possible, should concentrate the light upon a PROJECTIONS. 39 second plain mirror at r, which should have such aninclination as to reflect the converging rays upon theobject to be shown at d^ and strongly illuminate it; theobjective at o will be used in the same way as for anyother projection. This apparatus should be in a boxmade with sides a foot square and six or eight inchesdeep. At the back of it a hole should be left at d, inwhich the various objects for exhibition may be held. In place of the condenser and the plain mirror, alarge concave reflector, such as is used behind lamps,may be placed at r, and the parallel rays from the portelumiere allowed to fall upon it. It should be placed atsuch a distance from the object d^ that it
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Keywords: ., bookcentury1800, bookdecade1870, bookpublisherbosto, bookyear1877
