THE MAGIC LANTERN. 



will be reproduced upon a screen, placed at a certain distance 

 behind the lens, that distance being greater the nearer the picture 

 in front of the lens is to its principal focus. This is the principle 

 upon which the magic lantern is constructed. 



2. It varies in form and arrangement, according to its price and 

 the circumstances under which it is used, but in general consists 

 of a dark lantern fig. 1, within which a strong lamp L is placed, 



Fig. i. 



having a bent chimney at the top, to allow the smoke and heated 

 air to escape, while the light is intercepted. In front of the lamp, 

 and on a level with its flame, a tube is inserted, in which a large 

 convex lens A is fixed, by means of which the light of the lamp is 

 condensed upon the picture placed opposite the lens A, by sliding 

 it through a groove, c D. From this mode of fixing the picture, 

 the latter has generally been called a " slider." In the tube 

 thus projecting from the lantern, another tube is fitted sliding in 

 it, as one tube of an opera-glass slides in the other. At the end 

 of this second tube a convex lens B is set, and the tube is so 

 adjusted, that the distance of B from the picture shall be a little 

 greater than the focal length of the lens B. A large screen r, 

 made of white canvas, which is much improved by covering it 

 with paper, is then placed at a distance from B, and at right 

 angles to the axis of the lens. By properly adjusting the tube B, 

 and the distance of the screen F, the picture upon the slider in c D 

 will be reproduced at E upon the screen, on an enlarged scale. 



It must be observed, however, that as the picture will be 

 inverted, with relation to the object, it will be necessary to turn 

 the slider in c D upside down, in order to have the picture on the 

 screen in its proper position. 



To increase the illumination of the slider, a concave reflector 

 M N is usually placed behind the lamp, by which the light pro- 

 jected upon the lens A is increased. A better effect, however, 

 may be produced by simply bending a sheet of white paper or 

 paste board round the inside surface of the lantern, 

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