PICTURES ON THE RETINA. 49 



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 impression, 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 reaeh of doubt ; but I propose to go mucli 

 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 impres- 

 sions 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 funda- 

 mental 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 con- 

 jured 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 impressions of luminous objects, 

 after the objects themselves are withdrawn. 



In the healthy state of the mind and body, the 

 relative intensity of these two classes of im- 

 pressions on the retina is nicely adjusted. The 

 mental pictures are transient and comparatively 

 feeble, and in ordinary temperaments are never 

 capable of disturbing or effacing the direct 

 images of visible objects. The affairs of life 



