S. Rowley on Vision. 159 
luminous point at A should be seen at T’ in a surface cutting 
the axis FB at right angles in B (and the plane of the axes in 
the line EG) and the right eye’s image at T, 
But if the left eye’s image of the point at A is seen at T’ 
then by the same proposition the right eye’s image of the 
point at E’ opposite A in a line between F’ and e, a position 
in IK, directly beyond T’, should be seen in the same line of 
no variation a little beyond T’ at e. If the experiment be 
made it will be found that the right eye’s visible image of an 
object placed as a point at E’, nearly 1,°, inch from A, will 
be seen a little behind the place where the left eye’s image of 
an object placed as a point at A is seen, 
the two middle images of the pins placed as a test of 
ance in the first of these experiments are seen united at 
the intersection of the surfaces of vision. 
faces immediately begins very gradually to recede from that of 
the vertical planes of the axes, and the longitudinal axes of 
pin i 
le 
; e whose image is seen by 1 : 
little to the left and the other duly to the right. Should this 
Would be sec 
ihe approximate result may be obtained if two rulers® ot 
legs of a pair of compassest be so placed that their longi- 
dinal axes shall lie in the vertical planes of the optical 
> eg evident that for the two objects in the a sgt 
‘these es, a may put a single object at - az 
See Wells, p36, Smith's Optics, Art. ort. ¢ Well 
