REFLECTION BY UNSILVERED GLASS. 437 



glass gg, in the interior of a decanter. Fig. 247 A 

 shows the phenomenon itself, while B gives a plan of 

 the arrangement. 



It is in this manner that ghosts and other spectral 

 phenomena are produced on the stage. A large sheet 

 of plate glass is placed in front of the stage so that its 

 edges are hidden by a framework of scenery ; and the 

 actors on the stage are thus seen, but not the glass 

 itself. In front of the glass, below the proscenium, 

 and thus hidden from the audience, is a space where the 

 objects or persons to be reflected are arranged ; a strong 

 light is thrown upon them when they are to make 

 their appearance, and, the glass plate being inclined to 

 the audience, the reflected images appear behind the 

 glass as if they were upon the stage opposite to the 

 spectator. 



For the experiment shown in fig, 247 a pane of window-glass 

 should be fixed in a suitable manner in the retort-stand, and a piece 

 of cardboard, having a rectangular aperture, is arranged so as to 

 hide the edges of the glass and also the flame itself. The illusion 

 will be specially perfect if the experiment is made in the evening, 

 and care is taken that no other objects, upon which the light of the 

 candle may fall, are reflected by the glass. The dotted line I c d e 

 indicates the edge of the cardboard, the line hikl that of the 

 aperture. 



Reflecting surfaces which are not plane give rise 

 in general to distorted images, as may be easily seen 

 on observing the reflection of the face in a bottle of 

 dark glass, by a bright button, a soap-bubble, or any 

 similar surface. Images which correctly conform to an 

 object placed at a definite distance from the reflecting 

 surface can only be produced by such curved surfaces 

 as form a portion of a sphere, and have only a 



