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, it 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 kicking 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 single. 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 f he retina, or were truncated previous to their con- 

 vergence *.jto a focus. The images which they formed, 

 were therefore ill defined. When one of the lateral holes 



* Annals of Philosophy, i. p. 171. 



