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



197 



seen across (or lie in the axes exactly fixed upon) the near end 

 of the rule, that distance for eyes 2j% inches apart will be accu- 

 rately found. Now fix the axes of the eyes on the near end. 

 The images of the remote end will appear as two at the sides, 

 that of the left eye at some unknown distance on the left, and 

 that of the right eye in like manner on the right. Holding the 

 rule in the left hand in the same position with respect to the 

 plane of the horizon as the other, apply its remote end on the 

 window-bar to the left of the remote end of the rule in the right 

 hand, so that the right eye's image of the former will cover the 

 left eye's image of the latter. Now measure the distance between 

 the far ends on the bar. If all the conditions of the experiment 

 shall have been exactly complied with, the distance found will be 

 4 t 9 q inches, as predetermined in the diagram. 



The experiment, then, 

 shows that the geome- 

 trical consequence of the 

 principles of the propo- 

 sition, as illustrated in 

 the diagram, holds good 

 in actual practice, and 

 that when the axes are 

 fixed upon the images of 

 an object placed as a lu- 

 minous point at A, the 

 left eye's visible image 

 of an object placed as a 

 point at B in the line 

 F B, is seen a little be- 

 yond where the right 

 eye's visible image of an 

 object placed as a point 

 at D in the line drawn 

 through F and d is seen, 

 both in the same line of 

 no variation. It is ob- 

 vious by the proposition 

 that it ought not to affect 

 the "conjunction" of the 

 images, wheresoever in 



the line passing through F' and d the object might be placed 

 and this will be found to be the fact. It was placed opposite B 

 at J) merely for convenience of applying the diagram in actual 

 experiment, and to procure a correct appreciation of the interval 

 between the images. 



Suppose, in the second place, the axes represented by C B, 



