168 J. LeConte on Binocular Vision. 
visual line of the other eye is turned from the direction Ib to 
the direction Ia. 
of the pupil ; and it is well known that under the circum 
stances represented by the figure, the pupil of the eye II 
would contract also, although the direction of the visual line 
is unchanged. ( 
Il. The Horopter. 
If we look intently at’ any point the visual lines converge 
and meet at that point. Its image is therefore impressed on 
exactly corresponding points of the two retinee, viz: on the 
of view which coalesce at that moment, constitute the Horop- — 
ter. Of course the image of all points lying in the Horoptet 
fall on corresponding points of the retina, : 
Is the Horopter a surface or is it a line ? In either case 
the ir 
if the position of identical points of the retinee under all cl — 
is that a true theory of the Horopter can be 
nstructed ; and yet the experimental apveatigstion as usually 
from the point of sight 
