Tests Which Scientists Use to Show Why We Can 



The eye is a kind of pho- 

 tographic camera. You don't 

 always want a bright light 

 when you photograph, and 

 neither does the eye when it 

 sees. A camera has a dia- 

 phragm which can be opened 

 more or less to regulate the 

 amount of light admitted; 

 the eye has an iris which does 

 the same automatically. But 

 the eye can be fooled. In the 

 picture the observer is look- 

 ing through a lens at an 

 object. When the object is 

 moved farther away and the 

 lens removed the iris opens 

 to see better, and yet the 

 intensity of the light has 

 not changed and the widen- 

 ing of the iris is unnecessary 



Photos by Jacques Boye 



The "olfactometer" which de- 

 termines the density of vapor at 

 which the first perception of 

 smell is possible. By its use 

 we learn that there are many 

 odors which we do not perceive 



At left: An interesting test to 

 prove to the human brain that 

 the muscles can lift a greater 

 load than seems possible. The 

 load is increased very gradually 



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