The Sense of Sight. 259 



Color Blindness. It is found that some persons cannot distinguish 

 certain colors. Blindness to red and green are most common. This 

 is a matter of importance among railroad men and sailors, where it is 

 necessary to distinguish red and green signals. 



THE CARE OF THE EYES. 



1. Objectionable Light. In reading we wish light from 

 the printed page. Hence we should avoid light entering 

 the eye from any other source at this time. While reading, 

 then, do not face a window, another light, a mirror, or white 

 wall. White walls are likely to injure the eyes. Choose 

 a dark cover for a reading table. Sewing with a white 

 apron on has injured the eyes. Direct sunshine very near 

 the book oV table is likely to do harm. 



2. Position in Reference to Light. Preferably have the 

 light from behind and above. Sitting under and a little 

 forward of a hanging lamp will allow the light to fall on 

 the book and keep it away from the face. In reading by 

 daylight avoid cross-lights so far as possible. 



3. Electric Light. The incandescent electric light has 

 advantages in throwing the light downward and in giving 

 out little heat ; but owing to its irregular illumination (due 

 to the shadow cast by the wire or filament), it is not well 

 suited for study or other near work. For this purpose an 

 Argand gas or kerosene burner is much to be preferred, 

 since it throws a soft, uniform, and agreeable light upon 

 the work. 



4. Reading Outdoors. Reading out of doors is likely to 

 injure the eyes, especially when lying down. To read 

 while lying in a hammock is bad. Too much light directly 

 enters the eye, and too little falls upon the printed page. 



