434 
Proceedings of the Royal Society 
direct images wliich fall nearly upon the retinal extremities of the 
visual axes are mentally referred close to the middle line in obedience 
to Bering’s law (quoted and supported hy Helmholtz), that points 
looked at in space are referred to a line drawn from the root of the 
nose to the junction of the visual lines. Thus the hole A may 
be referred to c, and the hole B to d. The two indirect images 
are referred to the outer side of the hole which gives rise to them. 
Thus the image of the left hole A, upon the retina of the right 
t 
Fig. 1. 
eye, is mentally referred to e, and the image of B to /. Heglecting 
for the present the lateral false images, it is easy to make the 
holes at such a distance that the two central false images c and d 
either coincide as in fig. 3, or appear in the same vertical line as in 
fig. 4, in which case a slight obliquity is given to the paper, though 
it remains in the same plane. Each hole is now exactly in the 
visual axis of its corresponding eye, and were these axes parallel, 
this would he a simple method of obtaining what Bonders has called 
