166 * J. LeConte on Binocular Vision. 
line A E, the objects a and a’ combine at A, while the median 
line and the object M are doubled and the images of the 
* 
latter are seen at m and m’. 
shutting one eye, but the two eyes do not. Each eye sees its 
own object in the true direction, but the binocular observer sees 
their combination in a wrong direction. e law of direction 
is true in all cases in monocular vision, but is not always true 
in binocular vision. In the case of the double images m and m’ 
of the object M, it is still more difficult to explain their 
apparent position by the law of direction. 
ose, however, that in all cases of ocular convergence it 
may be possible by an ingenious device to save the law of 
direction; but in the case of ocular divergence it is impossible 
by any device to explain the position of double images by that 
law. ‘The position of images in this case is in direct violation 
of that law ; the laws of direction and of corresponding points 
are in contradiction to each other and the law of corresponding 
points prevails, is we now proceed to show. 
We have seen, p. 160 and figs. 1 and 2, that in drowsiness the 
optic axes may diverge 20°, and that in such cases the double 
images of an object in /ront are seen right and left 10° from 
the real position of the object which they represent; and oD 
the iter ha ual 
in making the double images of an object 
directly in front separate 50°, and those of objects 50° ee 
combine directly in front. There can be no doubt that 1! we 
could turn our eyes directly outward, or if our eyes, retaining 
* By comparing these figures with those of my previous paper, it will be see? 
that I have g the 
the face itself in the rotation, as well as in the shifting, of the field of view of each 
eye. In convergence this bri the two images of the nose nearer together 1» 
front and thus narrows the common field, which is exactly what actually happens. 
In divergence, on the contrary, the double images of the nose separate and the 
common field is widened. 
a aE a ae RS 
aie sey tna eee 
