112 LETTERS ON NATURAL MAGIC. 



Columbine on the other, so that by twirling round the 

 card the two are seen at the same time in their usual 

 mode of combination. The body of a Turk is drawn on 

 one side, and his head on the reverse, and by the rotation of 

 the card the head is replaced upon his shoulders. The 

 principle of this illusion may be extended to many other 

 contrivances. Part of a sentence may be written on one 

 side of a card and the rest on the reverse. Particular 

 letters may be given on one side, and others upon the 

 other, or even halves or parts of each letter may be put 

 upon each side, or all these contrivances may be com- 

 bined, so that the sentiment which they express can be 

 understood only when all the scattered parts are united 

 by the revolution of the card. 



As the revolving card is virtually transparent, so that 

 bodies beyond it can be seen through it, the power of 

 the illusion might be greatly extended by introducing 

 into the picture other figures, either animate or inanimate. 

 The setting sun, for example, might be introduced into a 

 landscape : part of the flame of a fire might be seen to 

 issue from the crater of a volcano, and cattle grazing in a 

 field might make part of the revolutionary landscape. 

 For such purposes, however, the form of the instrument 

 would require to be completely changed, and the rotation 

 should be effected round a standing axis by wheels and 

 pinions, and a screen placed in front of the revolving 

 plane with open compartments or apertures, through 

 which the principal figures would appear. Had the 

 principle of this instrument been known to the ancients, 

 it would doubtless have formed a powerful engine of 

 delusion in their temples, and might have been more 

 effective than the optical means which they seem to have 

 employed for producing the apparitions of their gods. 



In certain diseased conditions of the eye effects of a 

 very remarkable kind are produced. The faculty of seeing 



