CHAPTER XXVI 

 LIGHT 



What light does for us. Heat keeps us warm, cooks our 

 food, drives our engines, and in a thousand ways makes life 

 comfortable and pleasant, but what should we do without 

 light ? How many of us could be happy even though warm 

 and well fed if we were forced to live in the dark where the 

 sunbeams never flicker, where the shadows never steal across 

 the floor, and where the soft twilight cannot tell us that the 

 day is done ? Heat and light are the two most important 

 physical factors in life; we cannot say which is the more nec- 

 essary, because in the extreme cold or arctic regions man 

 cannot live, and in the dark places where the light never pene- 

 trates man sickens and dies. Both heat and light are essen- 

 tial to life, and each has its own part to play in the varied 

 existence of man and plant and animal. 



Light enables us to see the world around us, makes the 

 beautiful colors of the trees and flowers, enables us to read, 

 is essential to the taking of photographs, gives us our moving 

 pictures and our magic lanterns, produces the exquisite tints 

 of stained-glass windows, and brings us the joy of the rain- 

 bow. We do not always realize that light is beneficial. Light 

 energy sometimes causes sunburn. Our clothing and carpets 

 fade in sunlight. But in spite of these apparently harmful 

 effects, light energy is in reality of great value in man's constant 

 battle against disease. 



The candle. Natural heat and light are furnished by 

 the sun, but the absence of the sun during the evening makes 



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