LIGHT 127 



distant object to one near at hand. They readjust the 

 lens of the eye according to the distance of the objects 

 viewed. 



One should consult a trained oculist before wearing glasses. 

 There is great danger of serious injury to the sight in using 

 glasses which are not suited to the eye. Glasses which one 

 person has found in every way beneficial may be quite the 

 reverse for another. Traveling peddlers of eye glasses 

 should not be patronized any more than street venders of 

 medicines which "cure everything." 



EXERCISES 



1. What heavenly bodies are sources of light? 



2. What heavenly bodies shine by reflected light? 



3. Is the earth a source of light? 



4. Light travels through space with a velocity of 186,000 miles per 

 second. How many times would it pass around the earth in one second? 



6. Why, considering the statement in Ex. 4, do we use " instantane- 

 ous" in speaking of the passage of light from one place to another on 

 the earth? 



6. Arrange the names of twelve substances in tables headed trans- 

 parent, translucent, opaque. 



7. What weather conditions are necessary in order that we may see 

 a rainbow? 



8. What is your position with relation to the sun when you see a 

 rainbow? Why must it be so? t 



9. If a rainbow is visible at 5 p. m., in what part of the sky must 

 it be? Why? 



10. What important differences are there in the operation of the 

 camera and the eye? 



