78 LETTERS ON NATUEAL MAGIC. 



be obtained by varying the distance of the lens D 

 from EF. 



When the image is received on an opaque 

 ground, as is commonly the case, the spectators 

 are placed in the same room with the lantern ; 

 but, for the purposes of deception, it would be 

 necessary to place the lantern in another apart- 

 ment like the mirror in Fig. 4, and to throw the 

 magnified pictures on a large plate of ground 

 glass, or a transparent gauze screen, stretched 

 across an opening EF, Fig. 4, made in the parti- 

 tion which separates the spectators from the 

 exhibitor. The images might, like those of the 

 concave mirror, be received upon wreaths of 

 smoke. These images are of course always 

 inverted in reference to the position of the painted 

 objects ; but in order to render them really erect, 

 we have only to invert the sliders. The repre- 

 sentations of the magic lantern never fail to 

 excite a high degree of interest, even when ex- 

 hibited with the ordinary apparatus ; but by 

 using double sliders, and varying their move- 

 ments, very striking effects may be produced. 

 A smith, for example, is made to hammer upon 

 his anvil, a figure is thrown into the attitude of 

 terror by the introduction of a spectral appari- 

 tion, and a tempest at sea is imitated, by having 

 the sea on one slider, and the ships on other 

 sliders, to which an undulatory motion is com- 

 municated. 



The magic lantern is susceptible of great im- 

 provement in the painting of the figures, and in 

 the mechanism and combination of the sliders. 

 A painted figure, which appears well executed to 

 the unassisted eye, becomes a mere daub when 



