- qaandd. Thus the pictures of the two lines would make theit 
184 W. B. Rogers on Binocular Vision. 
the two eyes L and R, fig. 85, and let us assume that while the 
optical centres of the eyes are fixed in a horizontal position the 
ines a,d,.. .of fig. 85 are adjusted to paralellism with this- 
85. 86. i ae 
bi 
gi 
direetion. Further let us assume that in converging the axes by 
cross vision to bring a and d together, there is an entire absence 
of vertical rotation. In this case if the axis of the eye R be di- 
rected to the line d which is on a higher level than a, the axis of 
will pass above a. Thus the picture of d will fall cenérally. 
on the retina of R, and that of a above the retinal centre of L. 
If again we suppose both axes to range in a horizontal line mid- 
way in height between a and d, fig. 86, the pictures of @ an 
will fall at equal distances respectively above and below the cen- 
tres mand x. In all these cases the vertical distance between @ 
and d on the two retinas will be the same. Under these condi- 
ment, it is easy to see that the images a and d may be made to 
cover the centres or other corresponding parts of the retinas above 
or below. In the case of fig. 85, we may suppose the left eye to 
revolve so as to carry the centre m up to a, while the other cen- 
re n, is kept fixed in its coincidence with d. In the case of fig. 
36, we may imagine the left eye to rotate upwards and the right 
lownwards, until mm and n are brought severally to coincide with 
t 
g 
. 
: 
impressions centrally on the two retinas, and might be expected 
2 
ht is midway between the upper and lower components, SUP” 
g these to have been brought by ordinary convergence to be 
one above the other. According to this view the law 
f binocular direction would apply to the vertical as well as the 
horizontal inclination of the optic axes, so that when in the above 
experiments the two lines are made to appear as one by the com> 
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