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 necessary, because in
the extreme cold or arctic regions man cannot live, and in the dark
places where the light never penetrates man sickens and dies. Both
heat and light are essential 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 rainbow. We do not always realize that light
is beneficial, because sometimes it fades our clothing and our
carpets, and 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.