( 45 ° ) 
Eye, falls upon the Middle of the Retina, as a a or A a 
Fig. 28. 
II. Definition. 
To look at any Point, is to turn both Eyes towards it 
in fuch manner, that the Optic Axes making an Angle at 
the faid Point as a, the Rays from a may have the Optic 
Axii for their Axis, and (by their Convergence upon the 
Retina after Refradion in the Eye ) may paint the Image of 
the faid Point upon the Middle of the Retina of each Eye, 
where the Optic Axis in each Eye falls. 
III. Definition. 
To fee without looking , is to dire# the Optic Axes to 
fome other place than to the Point which is then feen ; 
and in fuch a cafe, the Image of the Point feen will be 
proje&ed upon a part of the Retina of each Eye, where 
the Optic Axis does not fall, namely either nearer to the 
Nofe N as in {Fig. 2 6.) at the Points of the Retina mark’d 
nn \ or farther from the Nofe than the Middle of th e Retina, 
as at co'mFig. 29. 
Whatever is Jeen, by being look’d at with both Eyes, 
always appears fingle, by reafon of the Communication 
between the Middle of the Retina in one Eye, and the 
Middle of the Retina of the other : there being no fuch 
Communication between any other part of the Retina in 
one Eye, and the Correfpondent part of the Retina in the 
other, when thefe correfpondent parts are equally diftant 
from the Nofe, 
There is indeed a Communication between the Nervous Fibres 
on the Right -fide of the Retina of one Eye , and the nervous 
Fibres on the Right-fide of the Retina of the other Eye , and 
fo of thofe on the Left : but no fingle Objetf can be fo painted 
in each Eye, as to have its Image on the Right or Left Part of 
one 
