Mr. S. Rowley on a New Theory of Vision. 203 



than that of the convergence of the ax^s are not apprehended in 

 their true visible positions in the surfaces of vision. 



Why, then, does consciousness mistake, precisely as we find 

 it doing, the true place of the visible image of any object, lying 

 not at the point of intersection of the axes, nor at any point 

 equally distant with this from the base of vision* ? 



My answer is, that under tendencies resulting from experi- 

 ence, consciousness apprehends erroneously the distances really 

 presented for its action according to the laws of vision, and with 

 respect to each lateral image apprehends the distance of the sur- 

 face of vision from the base of vision, and the distance in the 

 surface from the image at the centre, for the distances that would 

 exist between these surfaces and these images if the given 

 image now laterally and obscurely seen were, with its corre- 

 sponding image of the other eye, directly and distinctly exa- 

 mined at the centre. 



Hence the place in which such an image seems to be seen. 



For example, let the axes be turned to the images of an ob- 

 ject at B (fig. 2) . They will be seen at B, the left eye's 2 T % 

 inches to the left from its image at a! of the object at A, and the 

 right eye's 2 T 4 - inches to the right from its image at a of the 

 object at A, each in a surface of vision measuring, from the apex, 

 18 inches from the base of vision. 



Let, now, the axes be turned to the images of the object at A 

 (fig. 1). These will now be seen at A, that of the left eye's -f w 

 inch to the right from its image at b of the object at B, and 

 the right eye's y 8 -^ inch to the left from its image at b' of the ob- 

 ject at B, each in a surface measuring, from the apex, 6 inches 

 from the base of vision. 



At first, then, the left eye's image of an object atB, when par- 

 ticularly examined, will always be apprehended at the distance 

 of 2 T 4 ir inches to the left from the image at a 1 of an object at A 

 in the surface of vision 18 inches from the base. Hence, after 

 due experience, will arise a tendency of mind to apprehend this 

 image at a distance of 2 T % inches to the left from the image of 

 the object at A in the surface of vision 18 inches from the base. 

 Therefore, when the axes are turned toward the images of the 

 object at A, the mind will be influenced by this tendency, with 

 respect to the left eye's image at b of the object at B, to appre- 

 hend 6 inches, the distance of the surface of vision from the 

 base, as 18 inches, and -— inch, the distance in the surface from 

 the image at A of the object at A, as 2 T 4 ¥ inches. 



Again, the effect of experience in regarding directly the images 



* By base of vision I mean a plane cutting perpendicularly, at the centre 

 of the interval between the eyes, a line drawn through this point and the 

 point of convergence of the optic axes. 



