OCULAR ILLUSIONS. 97 



objects are painted on the retina, and in a way of which 

 we are ignorant, it conveys the impression of them to the 

 brain. 



Fig. 1. 



This wonderful organ may be considered as the sentinel 

 which guards the pass between the worlds of matter and 

 of spirit, and through which all their communications are 

 interchanged. The optic nerve is the channel by which 

 the mind peruses the handwriting of Nature on the retina, 

 and through which it transfers to that material tablet its 

 decisions and its creations. The eye is consequently the 

 principal seat of the supernatural. When the indications 

 of the marvellous are addressed to us through the ear, the 

 mind may be startled without being deceived, and reason 

 may succeed in suggesting some probable source of the 

 illusion by which we have been alarmed : but when the 

 eye in solitude sees before it the forms of life, fresh 

 in their colours and vivid in their outline ; when 

 distant or departed friends are suddenly presented to 

 its view; when visible bodies disappear and reappear 

 without any intelligible cause ; and when it beholds 

 objects, whether real or imaginary, for whose presence 

 no cause can be assigned, the conviction of super- 



