THE PERCEPTION OF SIGHT. 265 



not lead to any contradiction is that of the Empirical Theory, 

 which regards all our perceptions of space as depending upon 

 experience, and not only the qualities, but even the local signs 

 of the sense of sight as nothing more than signs, the meaning 

 of which we have to learn by experience. 



We become acquainted with their meaning by comparing 

 them with the result of our own movements, with the changes 

 which we thus produce in the outer world. The infant first begins 

 to play with its hands. There is a time when it does not know 

 how to turn its eyes or its hands to an object which attracts its 

 attention by its brightness or colour. When a little older, a 

 child seizes whatever is presented to it, turns it over and over 

 again, looks at it, touches it, and puts it in his mouth. The 

 simplest objects are what a child likes best, and he always 

 prefers the most primitive toy to the elaborate inventions of 

 modern ingenuity. After he has looked at such a toy every 

 day for weeks together, he learns at last all the perspective 

 images which it presents ; then he throws it away and wants a 

 fresh toy to handle like the first. By this means the child 

 learns to recognise the different views which the same object 

 can afford in connection with the movements which he is con- 

 stantly giving it. The conception of the shape of any object, 

 gained in this manner, is the result of associating all these 

 visual images. When we have obtained an accurate conception 

 of the form of any object, we are then able to imagine what 

 appearance it would present if we looked at it from some other 

 point of view. All these different views are combined in the 

 judgment we form as to the dimensions and shape of an object. 

 And, consequently, when we are once acquainted with this, we 

 can deduce from it the various images it would present to the 

 sight when seen from different points of view, and the various 

 movements which we should have to impress upon it in order 

 to obtain these successive images. 



I have often noticed a striking instance of what I have been 

 saying in looking at stereoscopic pictures. If, for example, we 

 look at elaborate outlines of complicated crystalline forms, it is 

 often at first difficult to see what they mean. When this is the 



