82 LETTERS ON NATURAL MAGIC. 



before, suddenly advanced upon the spectators, 

 becoming larger as they approached them, and 

 finally vanished by appearing to sink into the 

 ground. The effect of this part of the exhibition 

 was naturally the most impressive. The spec- 

 tators were not only surprised but agitated, and 

 many of them were of opinion that they could 

 have touched the figures. M. Robertson, at 

 Paris, introduced along with his pictures the 

 direct shadows of living objects, which imitated 

 coarsely the appearance of those objects in a 

 dark night or in moonlight. 



All these phenomena were produced by vary- 

 ing the distance of the magic lantern AB, Fig 5, 

 from the screen PQ, which remained fixed, and 

 at the same time keeping the image upon the 

 screen distinct, by increasing the distance of the 

 lens D from the sliders in E F. When the lan- 

 tern approached to P Q, the circle of light P Q, 

 or the section of the cone of rays PDQ, gra- 

 dually diminished, and resembled a small bright 

 cloud, when D was close to the screen. At this 

 time a new figure was put in, so that when the 

 lantern receded from the screen, the old figure 

 seemed to have been transformed into the new 

 one. Although the figure was always at the 

 same distance from the spectators, yet, owing to 

 its gradual diminution in size, it necessarily ap- 

 peared to be retiring to a distance. When the 

 magic lantern was withdrawn from PQ, and the 

 lens D at the same time brought nearer to EF, 

 the image in PQ gradually increased in size, 

 and therefore seemed in the same proportion to 

 be approaching the spectators. 



Superior as this exhibition was to any repre- 



