"In all sciences depending on observation, we must 

 reckon with errors due to imperfections of our 

 senses." Henri Poincare, Science and Method 



The Visual World 



Ihese ducks of the Delta Marsh use their en- 

 vironment in an orderly fashion; there is a pattern to their travels. They 

 learn to follow the arrangements of land and water, reeds and willows, that 

 make every corner of this marshland different from any other part of the 

 world. The duck accommodates itself to the environment that meets the 

 eye; it learns the places in its world by seeing them; its local orientation 

 depends upon eyesight. A clue to the importance of sight is to be found in 

 the size of the avian eye. One is misled by outward appearances, for the 

 cornea is enclosed in a relatively small lid-opening. When the skin is re- 

 moved, the eye structure is found to occupy a very large part of the head, 

 and the two eyes of a Mallard weigh nearly as much as its brain ( Figure 2 ) . 



In examining the world of waterfowl, it must not be assumed that earth, 

 sky, and all things between appear the same to man and bird. Indeed, the 

 true nature of the world has been the study of philosophers since the be- 

 ginning of civilization; earlier than the year 400 B.C., Protagoras exclaimed 

 that "what seems to me is to me, what seems to you is to you" (Jeans, 

 1943 : 32 ) . Leibnitz believed that he was "able to prove that not only light, 

 color, heat and the like, but motion, shape, and extension too were mere 

 apparent qualities," and Berkeley claimed that "all the choir of heaven and 

 furniture of earth, in a word all those bodies which compose the mighty 

 frame of the world, have not any substance without the mind" (Barnett, 

 1948:306). We become aware of the poorly defined boundaries between 

 science and philosophy when speaking to a color-blind friend about the 

 things we perceive. There is no science to aid in the hopeless attempt to 

 define the color red to such a companion. He simply does not perceive red as 

 we do, nor do we see it as he does. Thus the visible world for him is not 



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