98 W. B. Rogers on Binocular Vision. 
It thus appears that in the positions above chosen for the dra 
ings, the combination of the two smaller circles into one in the — 
indeed is the condition under which we see — 
tive resultant not included in the vertical — 
in-w ich the images of the drawings — 
ifr \venti reflecting — 
oked 
overlo 
the eye to distinct vison at different distances are presumed 
This statement as we have just seen is true only of those parts of 
the resultant which lie in the vertical plane of HK, but in rega? 
to the rest and by far the greatest part of the perspective fig 
the “ordinary relations” mentioned by Prof. Wheatstone are 
preserved. 
I would remark in conclusion, that this necessity of depar 
from the usual adjustment of the eyes is no doubt one of the 
sons that so large a number of persons having sound and equa! 
balanced eyes, are unable on first looking into a stereoscope, © 
perceive the resultant figure clearly and steadily, and that € 
experienced observers are obliged in the case of certain figures 
ot considerable effort in order to effect the binocular combr 
IOTE, Yo ot, 
