308 SCIENTIFIC AMUSEMENTS. 



the effect may be produced (fig. 149) that an observer, looking into 

 the mirror, sees his own reflection at first, but suddenly this 

 changes to a grinning skull or something equally horrifying. This 

 is effected by suddenly changing the position of the mirror (by 

 swinging it on its axis) from that directly fronting the observer, 

 AB, to the inclined position marked by the dotted line CD, 

 when the reflection, F, of the skull hidden behind the screen at E 

 is seen instead of the observer's own face. The skull should be 

 supported on a table, &c., draped with black cloth, so that nothing 

 else can be seen, and should be well illuminated, the lights being 

 so placed as not to be directly visible to the observer. 



A somewhat similar illusion was formerly largely used in their 

 calling by so-called necromancers and magicians, consisting of a 

 flat mirror swinging on a vertical axis like a door, (e.g., like the 

 mirror CD, fig. 149), so as to give the reflection of the person 

 looking into it, when placed in one position, and that of something 

 else, otherwise hidden from view, when placed in another position. 

 When the wizard was consulted and made use of the magic mirror 

 to " reveal the future," the person to be impressed was first placed 

 in front of the mirror in the ordinary position, and consequently 

 saw his or her own reflection. His attention being momentarily 

 called off by some appropriate " business " (as an actor would say) 

 or by-play, such as extinguishing the lights in the room, the mirror 

 was noiselessly placed in the second position, and the light illumin- 

 ating the picture supposed to be supernaturally revealed gradually 

 turned up; accordingly, the expectant spectator saw gradually 

 developing in the mirror a vision representing the answer to his 

 questions. By and by, when the full effect on his imagination was 

 produced, the first mirror was restored to its ordinary position 

 fronting him and the lights relit, when everything in the apart- 

 ment would resume its usual appearance. A magic lantern was 

 often employed to produce the vision, the picture being at first 

 produced out of focus and "misty," but subsequently becoming 

 clear and definite as the lenses were focussed, and finally fading 

 away again and disappearing, the light being cut off by means of a 

 dark slide. 



Expt. 343. Formation of two Images by ordinary Looking 

 Glasses. A "looking glass" or flat mirror consists of a plate of 

 glass, behind which is affixed a layer of reflecting substance, such 

 as a film of metallic silver deposited by chemical processes (Expt. 

 198) or a sheet of tinfoil and mercury amalgam (Expt. 288); 

 consequently there are two reflecting surfaces present in such a 

 mirror, whereas there is only one in the case of a polished plate of 

 metal or speculum. 



