. The art of projecting. A manual of experimentation in physics, chemistry, and natural history, with the porte lumière and magic lantern. e lumiere through asmall hole. It goes straight across the room, and itscourse can be tracked through the room by the dustparticles, or a little smoke, which it will light up. Also,by having the room otherwise quite dark, permit thelight to come in the round orifice, half an inch in diam-eter, as it is reflected from the landscape outside, andnot reflected from the mirror. The room is thus a largemmera obscura, and an inverted image of the landscapewill be
. The art of projecting. A manual of experimentation in physics, chemistry, and natural history, with the porte lumière and magic lantern. e lumiere through asmall hole. It goes straight across the room, and itscourse can be tracked through the room by the dustparticles, or a little smoke, which it will light up. Also,by having the room otherwise quite dark, permit thelight to come in the round orifice, half an inch in diam-eter, as it is reflected from the landscape outside, andnot reflected from the mirror. The room is thus a largemmera obscura, and an inverted image of the landscapewill be seen upon the walls, or upon a small screen helda foot or two from the orifice. This image will be par-ticularly strong if the ground be covered with snow, asmuch more light is reflected from that than from grassor foliage. If persons are passing their forms will beseen, and appear as if walking head downward. Parallel rays A will be reflected from the mirror of 82 THE ART OF PROJECTING. \Q converging b and diverging c rayswill be obtained by interposing a convex lens of anysize in the path of the parallel Fig. 61. Transparent substances, like glass, some crystals,gases, and water permit the rays a to go through themand appear upon the screen. Translucent substances,like paper, ground glass, milk, allow but a few scatteredrays to go through them, and a diffused light appearson the screen. Opaque substances, such as metals,thick pieces of wood, stones, etc., stop all the light,reflecting some and absorbing the rest. INTENSITY OF ILLUMINATION. When the lens is interposed in the path of the beamthe light appears as a circular disk upon the screen,and as the rays cross each other at the focus f^ thatpoint may be considered as the source of light. Cut asheet of paper or a board s, one foot square, and holdit any distance from the focus, say two feet. Its shadowupon the screen will be bounded by «, e, which maybe measured in square feet. Now move the pap
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Keywords: ., bookcentury1800, bookdecade1870, bookpublisherbosto, bookyear1877
