CHAPTER X 



LIGHT 



98. 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 flickered, where the shadows never stole across 

 the floor, and where the soft twilight could not tell us that the 

 day was 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, because 

 sometimes it fades our clothing and our carpets, arid burns 

 our skin and makes it sore. But we shall see that even these 

 apparently harmful effects of light are in reality of great 

 value in man's constant battle against disease. 



99. The Candle. Natural heat and light are furnished by 

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

 makes artificial light necessary, and even during the day 



104 



