190 



Our Surroundings 



HAVE You ASTIGMATISM? 



With one eye closed look at this 



figure. If the lines seem blurred, 



there is astigmatism. 



2. Do not read in twilight. Unconsciously the eyes are 

 strained as the light becomes dimmer. 



3. When reading, sit so that light comes from behind over 

 the shoulder and strikes the page perpendicularly. When writing, 

 sit so that the light over the shoulder causes no shadow to be cast 

 on the line that is being written. 



4. Do not read on moving trains 

 or automobiles as it is difficult for the 

 eyes to adjust themselves to the con- 

 stant changes of position, and eyestrain 

 results. 



5. Do not read while lying down, 

 for too much light enters directly into 

 the eyes and not enough falls on the 

 printed page. 



6. Do not read books with very 

 small type or with pages having a 

 glossy surface. 



7. Rest the eyes frequently. Like other organs of the body, 

 the eyes tire and require relaxation. 



8. If the eyes are defective, consult an oculist at once. 

 Motion Pictures. A motion picture camera takes a series of 



small photographs on long strips of film, each picture including 

 slightly different successive positions of all moving objects. When 

 these films are run through a motion picture projector, the pic- 

 tures are thrown in rapid succession on a screen. As the retina 

 of the eye retains each picture until the next has taken its place, 

 the slight changes of position blend, and an impression of con- 

 tinuous motion is produced. 



Artificial Lights. We have already discussed the fact that 

 heat waves seem to differ from light waves only in that they are 

 a little longer. The higher the temperature, the shorter the heat 

 waves. If the temperature becomes high enough, light will result. 



Man has searched for a long time to find a source of light 

 without heat, but up to the present he has not been able to 

 produce such a light. Back in the distant past man had no 

 artificial light. He first learned to kindle a fire. Then he gathered 



