522 THE SENSORIAL FUNCTIONS. 



It is not until long after this association has 

 been established that we learn, by deduction 

 from scientific principles, that the part of the 

 retina, on which the impression causing this 

 appearance is made, is on the side opposite to 

 that of the object itself; and also that the image 

 of a straight object is curved, as well as inverted. 

 But this subsequent information can never in- 

 terfere with our habitual, and perhaps instinc- 

 tive reference of the appearance, resulting from 

 an impression made upon the upper part of 

 the retina, to an object situated below us ; and 

 vice versa. Hence we at once refer impressions 

 made on any particular part of the retina to a 

 cause proceeding from the opposite side. Thus 

 if we press the eye-ball with the finger applied 

 at the outer corner of the orbit, the luminous 

 appearance excited by the pressure is imme- 

 diately referred to the opposite or inner side of 

 the eye. 



If we place a card perpendicularly between 

 the two eyes, and close to the face, the card will 

 appear double, because, although each surface is 

 seen by the eye which is adjacent to it, in the 

 direction in which it really is with regard to that 

 eye, yet, being out of the limits of distinct vision, 

 it is referred to a much greater distance than 

 its real situation ; and consequently, the two sides 

 of the object appear separated by a wide interval, 

 and as if they belonged to two different objects. 



