488 PKOCEEDINGS OF THE SOCIETY. 



her by touch. You would suppose that the peculiar form of a pair of 

 scissors, as suggested to the mind through the medium of touch, would 

 be recognized through the sight more readily than anything else ; and 

 yet when it was first shown to her, she utterly failed to recognize 

 it as the implement which she had been in the habit of handling. 

 This recognition of a solid form from a visual picture, then, is the 

 result of the experience we gain in very early life, from the 

 association of the mental impressions made by the retinal pictures 

 with those we obtain through the sense of touch, — by which I mean 

 not only the contact with the fingers, but the muscular action which 

 gives movement to them, — so that, in course of time, the visual picture 

 comes to suggest the solid form of the object to the mind. Our best 

 evidence of this is derived from pictures obtained by means of photo- 

 graphy ; especially those in which the relations of light and shade are 

 strongly brought out ; for these pictures suggest the idea of solidity 

 much more perfectly than any others can do. Some of you will pro- 

 bably remember the old Dioramic pictures in the Eegent's Park, with 

 their wonderful appearance of solidity, especially in the case of archi- 

 tectural designs; the impression produced being so entirely that of 

 solidity, that it was only by moving the head from side to side that 

 the illusion was detected. These pictures were based on photographs ; 

 Daguerre and others having worked out the original " daguerreotype " 

 process for the purpose of producing them most effectively. 



In ordinary drawing and painting, an artist is subject to continual 

 changes in the conditions of the light and shade, even in the course 

 of half an hour; and therefore no painting, except one by artificial 

 light, can give a true representation of light and shade at any par- 

 ticular moment. Therefore it is that photographs of many subjects 

 are most wonderfully illusive, and most especially so when they are 

 looked at ivith only one eye. The explanation of this effect is, that when 

 you look at the picture with both eyes, and it is tolerably near to you, 

 you are forced to see it as a flat surface ; but when you shut one eye 

 and keep the head still, you lose the power of measuring relative 

 distances ; and a visual conception of solid form is suggested by its 

 chiaroscuro and its perspective. If you look, for example, with one 

 eye at the photographs of relievos hanging upon the opposite wall, 

 you will, if you have not tried the experiment before, be astonished 

 at the way in which the figures seem to stand out with all the effect 

 of stereoscopic relief. This is a pure case of mental suggestion ; and 

 is due to the perfect similarity of the photograph to the retinal picture 

 produced by natural vision of the object itself upon a single eye. 

 The camera, like the eye, projects a flat picture, which is recorded by 

 photography ; and you have then permanently just the picture which 

 one eye would form of the object. You look at this with one eye, 

 and, trained by experience, you interpret what you see according to 

 your preconceived conceptions. A similar effect is obtained when 

 you look at such pictures with both eyes, at a distance great enough 

 for the axes of the eyes to be virtually parallel. 



I remember some large imitation relievos on the cornices of some 

 of the apartments in the Louvre at Paris, and some still larger pic- 



