SINGLE VISION. 41 



in reality possesses ; and the yellow string, in- 

 stead of appearing single in the common axis, 

 and perpendicular to the visual base, will now 

 be seen as two, each inclined to the base ; that 

 seen by the right eye, apparently occupying the 

 place in reality possessed by the green string, 

 and that seen by the left eye, the place of the 

 red string. 



PROPOSITION III. 



Objects, situated in any Line drawn through the mutual 

 Intersection of the Optic Axes to the Visual Base, do 

 not appear to be in that Line, but in another, drawn 

 through the same Intersection, to a Point in the Visual 

 Base distant half this Base from the similar Extremity 

 of the former Line, towards the left, if the Objects be 

 seen by the Right Eye, but towards the right, if seen 

 by the Left Eye. 



Two cases of this proposition have already 

 been proved. For it has been shown by the 

 first proposition, that objects, placed in the axis 

 of either eye, appear to it to be situated in the 

 common axis. But the common axis is a line 

 drawn through the mutual intersection of the 

 optic axes to the visual base, and its termina- 

 tion there is distant, by construction, half that 

 base, from the similar terminations of the axes 



