THE PERCEPTION OF SIGHT. 303 



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 olject can afford, in 

 connection with the movements which he is constantly 

 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 case, I look out two points 



