ORGANS OF PERCEPTION. 189 
three pin-holes, so disposed, that the interval between the 
most distant of them shall not exceed the diameter of the 
pupil, the object will be seen single; but if the object be 
brought either within or beyond the limits of distinct vision, 
it will be seen multiplied as many times as there are holes 
in the card, and each of the three images will be as perfect 
as the single one*.” If the statements here made be cor- 
rect, 1t must follow, that objects may be seen distinctly by 
rays which do not accurately converge on the retina. These 
three images are formed from three pencils of rays, which, 
as they possess different degrees of divergence when they 
strike the eye, must converge at unequal distances behind 
it, and be intersected by the retina under different circum- 
stances. But upon repeating the experiment, I obtained 
very different results. Upon looking through three pin- 
holes, placed on a line, the distance of the lateral ones from 
each other, not exceeding the diameter of the pupil, at a small 
dot made upon white paper, lying six inches distant from the 
eye, the dot appeared smgle. But when I brought the dot 
within three inches of the eye, and viewed it through the 
perforated card, keeping the central hole opposite the opti- 
cal axis, the images of three dots appeared ; differing, how- 
ever, in their distinctness, the central image being clear, 
the lateral ones obscure. It is obvious, in this case, that 
the cone of rays which entered the middle pin-hole, posses- 
sed least divergence, and, consequently, converged nearly 
at the focus of parallel rays, the ordinary station of the re- 
tina. But the cones of rays which entered the lateral holes 
possessed greater divergence, and consequently met in points 
beyond the retina, or were truncated previous to their con- 
vergence into a focus. The images which they formed, 
were therefore ill defined. When one of the lateral holes 

* Annals of Philosophy, i. p. 171. 
