ERRORS OF REFRACTION AND ACCOMMODATION. 157 



becomes smaller than before. This is the image from the 

 anterior surface of the lens. It is large and dim in the un- 

 accommodated eye because the surface which forms it is fairly 

 flat. During accommodation when the surface becomes more 

 curved the image becomes smaller and appears to move forward 

 because of the movement of the reflecting surface. 

 Experiment 62. Schemer's Experiment. The course of rays 

 which enter the eye, from objects at distances for which the 

 eye is not accommodated, can be traced by blocking all but 

 two pencils of them and finding out which regions of the retina 

 are affected by the two pencils of light. In a piece of heavy 

 paper prick two holes less than the diameter of the pupil apart. 

 Stick two needles upright in a strip of wood, one 30 cms. and 

 one 60 cms. from the end. Hold the screen with the holes 

 horizontal in front of one pupil and, closing the other eye, 

 look along the stick and accommodate for the far pin. Note 

 that the image of the near pin is double. Cover one hole in 

 the screen and see which image disappears. Repeat, with the 

 eye accommodated for the near pin. From your results draw 

 diagrams of the course of rays entering the eye (a) from an 

 object at the distance for which the eye is accommodated, 

 (b) from one at a greater distance, (c) from one at a less. Com- 

 pare with the diagrams from the results of Exp. 48 and explain 

 the differences. 



