158 J. LeConte on Binocular Vision. 
by about 1° 20’ (fig. 7). On bringing the circles together I 
found that at a certain distance of the diagram—but only ata 
ages 
+ 
———— a 
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| 
certain distance depending upon the interval between the 
circles—the verticals coalesced perfectly; the horizontals, 
however, as might be expected, still crossed at a small angle, 
and in the same direction as before, viz: the whites or right 
eye image thus _— and the blacks or left eye image thus 
“—, Indicating in this case also rotation of each eye out 
ward. Beyond the proper distance the verticals approach but 
do not attain parallelism; within the proper divans 
2 
cross in a direction contrary to that in the diagram. e 
the circles are ten inches apart, the proper distance is nearly 
three feet and the image therefore about seven inches from the 
eyes, 
Helmholtz has a diagram similar in all respects to my 0W2 
except turned upside down, in which, he states. both verticals 
and horizontals coincide perfectly when the circles are comM- 
bined ur own figure (tig. '7) turned upside down will a)- 
swer for Prof. Helmholtz’s. We quote his own words: “The 
horizontal lines are parts of the same straight line ; the vertl- 
cal lines are not perfectly vertical. The upper end of those of 
the right figure are inclined to the right and those of the lett 
figure to the left by about 1:1 degrees.” But bis experience 
differs from our own in a most unaccountable manner. H 
says : " Now combine the two sides stereoscopically, either by 
squinting or by a stereoscope, and you will sce that the while 
lines of the one coincide with the black lines of the other, 4 
both figures coincide, although the ver 
© figures are not parallel to each othe? 
He accounts for this, not by rotation of the eyes but by the 
. 
