Mr. S. Rowley on a New Theory of Vision. 201 



distance of A, the axes be fixed upon the images of the pin at B, 

 then the image of the pin at A seen by the left eye, and that of 

 a pin placed "nearly \{\ s inch directly to the right of A seen by 

 the right eye, will be found lying in the same perpendicular of 

 no variation, the latter beyond the former, the distance between 

 the two images being less than in the first case. 



In experimenting with this instrument, the position of the 

 image of the pin at B seen by the left eye in a surface at right 

 angles to the optic axis of that eye is visibly realized. For when 

 the axes are fixed toward A (as in the first instance), the image 

 of the transverse piece seen from the left eye visibly has a posi- 

 tion at right angles to the axis of that eye, and intersects the 

 corresponding image of the right eye, in a line of common inter- 

 section crossing each image where that image, whether referred 

 back to the retina or to the distance of the transverse piece itself, 

 would be pierced by the optic axis. 



In making these experiments, care should be taken not to 

 turn the axes into the oblique directions, to do which there is 

 always a strong inclination ; for then the images which were 

 seen in those directions as described, the one before or behind 

 the other, would be seen coincident. 



I will now proceed to answer an apparent objection. In the 

 first demonstration under my proposition, I undertake to show 

 that the impression on the left eye from B becomes visible and 

 is seen at b, by showing that it is seen a little behind where the 

 impression on the right eye from an object placed at D is seen 

 by the right eye, arguing that nothing else than a projection in 

 the manner described can account for the local relationship in 

 which these impressions are seen. The evidence of conscious- 

 ness, then, that these impressions are seen in a certain local 

 relationship, is made the groundwork of my argument. Now it 

 may be urged that the evidence of consciousness is equally 

 strong that the impression from the object at B on the left eye, 

 when seen, lies in the axis of the right eye at the actual distance 

 of the object itself at B*. 



In the first place, let us determine whether consciousness, 

 when carefully examined, does really continue to find this im- 

 pression elsewhere than at b. To reveal in consciousness the 

 true distance in a lateral direction of the visible image at b of an 

 object at B (fig. 1), employing the pins and board, place a pin 

 at b. The left eye's image of the pin at B will not be recognized 

 to the left of the left eye's image of it. 



Again, take three equal small rings of pasteboard. Attach to 

 each, in the direction of a radius produced, a pin, by cementing 

 with a dropof sealing-waxthe head of the pintotheedgeof the ring. 

 * See Wells, pp. 38 & 27. 



