( 45 1 ) 
cne Retina that communicates with the Right or Left part of 
the other, of the fame hignefs and at the f ame time as in tlfi 
ether ; hecauje in whatever Pofition the Object is, it muft be 
nearer to one Eye than to the other , except it be juft in a Line 
from the Nofe betwixt the two Eyes freight forward. 
Hence it is that if there be two Candles fet before any 
one, the Firflat theDiftanceof one Foot, and the Second 
at the Diflance of two Feet, from the Eyes ; he that looks 
at the fecond Candle at B will fee it Tingle, but fee the firffc 
Candle or the Candle A double $ one Appearance being 
in the Line AD y, the other in o A E, becaufe it paints it 
felf upon oo in the Retina of each Eye, which Points are 
not the middle Points, but farther from the Nofe than the 
middles m m. 
So if B be the firft Candle, and C the fecond, he that 
looks at B will fee C double, becaufe it is painted in the 
Retina at the Points n n nearer the Nofe than m m ; and fo 
will appear to be in the fame Pofition as p r. in Fig - 
If y p be two Candles fo difpofed. Fig . 30, that by the 
Interpofition of a perforated Board F F, y can paint it felf 
only in the Eye R, and p in the Eye L. Upon making the 
Optic Axes meet at B and to tend towards p and y, p and y 
will each paint an Image on the Middle of the Retina o£ 
each Eye, by crofling their Rays at B : and thus the two 
Candles will appear to be but One, or rather to be in one 
Place, upon the account of the Communication of the 
Middle of each Retina. But if inftead of the Candles, 
p be a piece of red Silk, and ^apiece of green Silk, the 
fame Pofition of the Eyes will make an Image at B, ap- 
pearing like a red and green Spot together without a 
Mixture of the Colours. If p be a red hot Iron, and y a 
Candle of Sulphur, the Phenomenon will be more diftindt. 
If die Optic Axes be turn’d diredily towards y and p, as if 
there was no Board F Fin the way, there will appear two 
A a a a a Holes 
