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Light and the Eye 



I. Vision 



In many aspects of human life, vision is far more important than any 

 other sensation. History, legal agreements, and knowledge of the uni- 

 verse are all recorded in a written form. Without vision these would be 

 of little value. In most measurements in physics, it is customary to base 

 sensitive, precise observations on visual data. In mechanics, the 

 position of a pointer on a balance, length on a meter stick, and pressure 

 are all measured visually. Even in acoustics, precise data are usually 

 based on the readings of electrical meters. This latter is the direct 

 result of the prominent role played by electronics in acoustics. (Similar 

 statements can be made about all other branches of physics.) In 

 chemistry and in the biological sciences, electronic tools have also come 

 to be widely used measuring devices. Today, in almost all of natural 

 science, the reading of electrical meters is an important means of gathering 

 data. However, even before the advent of electronics, the data of the 

 biologist and the chemist, just as those of the physicist, were based 

 primarily on what he could measure by visual means. 



Vision plays other roles in life besides data gathering. Many of our 

 aesthetic pleasures come from objects which are viewed. The pre- 



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