302 THE SPECIAL SENSES 



81. Long-sight, or hyperopia, is common among school-chil- 

 dren, nearly as much so as short-sight, and must not be 

 confounded with the defect known as the "far-sight" of old 

 people ; although in both affections the sight is improved by 

 the use of convex glasses. Children not infrequently discover 

 that they see much better when they chance to put on the 

 spectacles of old persons. For the relief of short-sight, con- 

 cave glasses should be employed ; as they so scatter the rays 

 of light as to bring the focus to the retina, and thus cause the 

 vision of remote objects to become at once distinct. That form 

 of " squint," in which the eyes are turned inward, is generally 

 dependent upon long-sight, while that rarer form, when they 

 turn outward, is due to short-sight. (Bead Note 10.) 



82. The Function of Accommodation. If, after looking 

 through an opera-glass at a very distant object, it is desired 

 to view another nearer at hand, it will be found impossible 

 to obtain a clear vision of the second object unless the adjust- 

 ment of the instrument be altered, which is effected by means 

 of the screw. If an object, like the end of a pencil, be held 

 near the eye, in a line with another object at the other side of 



10. On the Production of Short-Sight. "The observations of Conn 

 in the schools and University of Breslau, of Kruger in Frankfort-on-the- 

 Main, of Erismann in St. Petersburgh, of Von Hoffmann in Wiesbaden, 

 and others abroad, prove most conclusively that one of the bad effects of 

 school and college life is to produce diseases of the eyes. They have 

 shown that near-sightedness increases rapidly in frequency as you go up 

 in the scale of schools from the primaries of the rural districts to the 

 universities. The gravity of this finding may be appreciated when we 

 remember that near-sightedness is a disease, and that it very frequently 

 descends from one generation to another, marked by such organic changes 

 in the eyes as tend to the production of the worst forms of the malady, 

 and to blindness. In 1867, Cohn, of Breslau, published the results of the 

 examination of the eyes of 10,060 scholars. His examinations covered 

 the entire range of school life. He found that 1,750 of the 10,060 children 

 had defective vision about seventeen per cent. He also examined, 

 without selection, 410 of the 964 students of the Breslau University, and 

 found that not one-third had normal eyes." Dr. C. It. Agnew. 



81. Long-sight, how common ? With what must it not be confounded ? Kind of glasses 

 for short-sight ? Why ? Squint ? 



82. What is stated in connection with the opera-glass ? Experiment with pencil and dis- 

 tant object ? 



