186 W. B. Rogers on Binocular Vision. 
a height intermediate between that of the two figures seen later- 
ally at the same time, in other words, between the left and right 
pictures of the diagram. This conclusion, it will be observed, 
corresponds, so far as vertical effect is concerned, with the o 
servations of Prof. Wheatstone, cited on a previous page. 
34. Limited range of the vertical compared with the horizontal 
power of combination. 
The details which have been presented indicate the narrow 
limits within which the power of vertical adjustment and com 
bination is restricted as compared with those of binocular com- 
bination by ordinary convergence. Hence in combining figures 
which differ to the same extent in the horizontal and vertical di- 
rections, we generally find that while the coincidence on the right 
and left sides of the resultant is perfect and apparently simulta- 
neous, the union at the top and bottom is but partial and is obvi- 
ously successive. Indeed it is only when the disparity of heights 
ts very inconsiderable that the combination appears to be equally 
complete in all parts of the resultant. 
As an example of this, in attempting to unite the two squares 
of fig. 89, with the precautions as to spnmaarie before described, 
I find that while the ver- 
tical sides of the resultant Reman. 
ure appear each as a per- 
fectly clear and distinct 
single line, the lower side 
appears double until the , 
view has been fixed upon : 
it fora sensible time and 
that on carrying the eyes to the top of the resultant this side also 
seems for a moment to be double. When however, the disparity 
between the heights is reduced to half the amount in the figure 
the upper an lower sides of the resultant present themselves in 
7 the shape of single lines as immediately and to all appearance as 
Bea tencously 9 the vertical sides, and of course the resultant 
e appears of a height intermediate between that of the right 
and the left hand figures. Like effeets are exhibited by unequal 
Circles and other pairs of figures geometrically similar. 
35. Perspective position and usually warped figure of the re- 
sultant. 
e have seen in the preceding section that when figures of 
a breadth are united binocularly they form a re- 
st , 
Thus when by cross vision I combine the squares © 
vag 89 I see the left hand side of the resultant figure nearer t0 
"nig 
