130 LETTERS ON NATURAL MAGIC. 



cise part which the mind performs in perceiving them ; 

 but the philosopher considers that he has given a satisfac- 

 tory explanation of vision when he demonstrates that 

 distinct pictures of external objects are painted on the 

 retina, and that this membrane communicates with the 

 brain by means of nerves of the same substance as itself, 

 and of which it is merely an expansion. Here we reach 

 the gulf which human intelligence cannot pass ; and if 

 the presumptuous mind of man shall dare to extend its 

 speculations farther, it will do it only to evince its inca- 

 pacity and mortify its pride. 



In his admirable work on this subject, Dr. Hibbert has 

 shown that spectral apparitions are nothing more than 

 ideas or the recollected images of the mind, which in 

 certain states of bodily indisposition have been rendered 

 more vivid than actual impressions, or, to use other words, 

 that the pictures in the * mind's eye " are more vivid 

 than the pictures in the body's eye. This principle has 

 been placed by Dr. Hibbert beyond the reach of doubt ; 

 but I propose to go much farther, and to show that the 

 "mind's eye" is actually the body's eye, and that the 

 retina is the common tablet on which both classes of im- 

 pressions are painted, and by means of which they receive 

 their visual existence according to the same optical laws. 

 Nor is this true merely in the case of spectral illusions. 

 It holds good of all ideas recalled by the memory or 

 created by the imagination, and may be regarded as a 

 fundamental law in the science of pneumatology. 



It would be out of place in a work like this to adduce 

 the experimental evidence on which it rests, or even to 

 explain the manner in which the experiments themselves 

 must be conducted ; but I may state in general, that the 

 spectres conjured up by the memory or the fancy have 

 always a "local habitation," and that they appear in front 

 of the eye, and partake in its movements exactly like the 



