266 EXPERIMENTAL PHYSIOLOGY. 



(d) At a distance of six inches from the eyes, hold a 

 veil or thin gauze in front of some printed matter placed at 

 a distance of two feet or thereby. Close one eye, and with 

 the other, one soon sees either the letters distinctly or the 

 tine threads of the veil, but one cannot see both equally 

 distinct at the same time. The eye, therefore, can form a 

 distinct image of a near or distant object, but not of both 

 at the same time, hence the necessity for accommodation. 



HP 



Fig. 121. Schemer's Experiment. 



6. Schemer's Experiment. 



(a.) Prick two smooth holes in a card at a distance from 

 each other less than the diameter of the pupil. Fix two long 

 fine needles or straws in two pieces of wood or cork. Fix 

 the cardboard in a piece of wood with a groove made in it 

 with a tine saw, and see that the holes are horizontal. Place 

 the needles in line with the holes, the one about eight 

 inches and the other about eighteen inches from the card. 



