12 GENERAL SCIENCE 



enabling persons to see more distinctly, are quite as often 

 prescribed to relieve eyestrain. Changes in the eyeball it- 

 self naturally occur as a person grows older, making necessary 

 the wearing and the refitting of glasses from time to time. 

 That objects at different distances may be seen distinctly, 

 changes in the form of the crystalline lens are continuously 



FIG. 4. The workers here are not likely to have impaired eyesight. 



taking place. This adjustment in form is known as the power 

 of " accommodation, " and it is more or less completely lost 

 in old age. 



A whole train of bodily ailments often attend upon or are 

 caused by eyestrain. Headaches, nervous exhaustion, and 

 impaired digestion are often directly traceable to it. Im- 

 patience and ill-temper may arise from it. No one should 

 be ignorant of what constitutes right conditions for continu- 

 ous use of the eyes, especially any close application of them. 



