24 THE EYE 



habit which makes the matter so easy that we become 

 wholly unconscious of the efforts of the mind. A child 

 who has not had this practice often construes falsely, grasps 

 at the stars, as at the shining buttons on his father's 

 coat ; tries to blow out the moon, as he would the light 

 upon the table. And we find that the same phenomena 

 are observed in those born blind, who have been operated 

 on ; one remarkable case of this kind, is, in particular, 

 recorded in the annals of opthalmic surgery, where a man 

 born blind obtained his sight in his later years, when he 

 was capable of giving an account of his experiences, and 

 who was able fully to report how he gradually learned to 

 collocate the different sensations of light and colour into 

 orderly vision. But the most distinct proof of the correct- 

 ness of the assertion advanced lies in the fact, that we, 

 when the conditions are misleading, construe falsely, when 

 the picture on the retina has given no cause. For instance, 

 the moon appears larger when it rises, than when it is 

 sailing over us in the dark ocean of the sky. But measure- 

 ments show that the size is actually the same in both cases, 

 and that its picture on the retina is always of the same 

 diameter. The reason of the false construction is this ; 

 when the moon rises above the horizon, between hills, trees 

 or houses we are familiar with, we judge of its distance 

 from the objects surrounding it, the real distance of which 

 we know. But when the moon is above in the vault of 

 heaven, we fancy it nearer because there are no objects 

 between it and ourselves, by which we can estimate its 

 distance. Thus in the act of judging, deceived by the 

 distance, we construe differently one and the same retina- 

 picture ; therefore, under any circumstances once falsely. 



These investigations, which I have rather sketched out 

 and indicated, than given a complete picture of, lead to 



