f 
S. Rowley on Vision. 155 
their object at a distance of 1,, inch from the two images 
Aguilonius is the only author who, meeting the question in 
its full extent, undertakes to assign for each” image both the 
line of visible direction and the absolute visible distance from 
the retina on the line of visible direction. ; 
Sir David Brewster indeed gives both conditions of external 
visible position for the images falling on the vertices of the 
retin. But for every other image he merely assigns Kepler's 
line of visible direction, being silent regarding the visible dis- 
tance—the essential complement of the former in determining 
ion. 
All the component points of the total impression on the retina 
or axial ray of the pencil. 
- : . . . 4 > he 
ify the , in thi it is intended to sig: 
nify the ere in this paper the word ray is used, | 
ies 
