THE SPECIAL SENSES 



269 



short and the retina lies too near the lens. In order to 

 see near objects the little ciliary muscle must be put to 

 a severe strain to make 

 the lens convex enough. 

 Thus it happens that the 

 eye of a long-sighted per- 

 son is usually under a 

 strain when working. 



U 



This leads to headache 

 and fatigue. In child- 



FIG. 1 68. Diagram illustrating the 

 Nearsighted Eye. 



hood this Strain may paSS The image P' of a distant point P falls in front 

 , . . . " i of the retina even without accommodation. 



unnoticed for a time, but 



By means of a concave lens (Z,) the image may 

 be made to fall on the retina (dotted lines). To 

 save space P is placed much too near the eye. 



sooner or later it shows 

 itself by a sense of 

 fatigue, dizziness, and blurred and indistinct vision. 



370. How the Eyes may be abused in Reading. The 

 habit of reading the daily papers, with their blurred and 

 indistinct type, in a steam or electric car or in a carriage, 

 is a severe strain on the eyes. The small type, poor paper, 



and presswork of the 

 many cheap editions of 

 popular books are very 

 frequent causes of weak 

 and diseased eyes. It is 

 a dangerous practice to 



FIG. 169. Diagram illustrating the 

 Farsighted Eye. 



The image /"of a point P falls behind the retina read in bed at night, Or 

 in the unaccommodated eye. By means of a while j f 



convex lens (L) it may be focused on the retina < 



without accommodation (dotted lines). To Or lounge in a darkened 

 save space P is placed much too near the eye. 



cles of the eyeball are put to a great deal of strain. 



371. Proper Light and Good Eyesight. The direction from 

 which the light comes is an important matter. The worst 



