SECRETS OF THE SALMON 



is as three to two and is called the index of re- 

 fraction; it is 1.5 to 1. in the case of water. It will 

 be found, if we lay off the line BE on the surface 

 of the water and the line DF below the water in 

 the same way, that the angle between DB and the 

 surface becomes forty-eight and one-half degrees 

 and the angle DBF, forty-one and one-half de- 

 grees. As light coming from the water into the 

 air follows the same path as that from air into 

 water, it is evident that light from below striking 

 the surface at an angle of forty-eight and one-half 

 degrees or more, being bent at that angle, can- 

 not get out to the air as it is parallel to the sur- 

 face of the water and must, therefore, be totally 

 reflected. This means that the fish can only 

 see out of the water at an angle of forty-eight 

 and one-half degrees or more to the surface, and 

 beyond that angle he sees only the reflection of 

 objects below the surface, reflected back from the 

 surface as from mirrors. If the water is not too 

 deep he will see the bottom reflected against the 

 surface, beyond the angle of forty-eight and one- 

 half degrees. From forty-eight and one-half de- 

 grees to vertical he can see out. He therefore 

 sees out through a circular window; the angle 

 from his eye is twice forty-one and one-half, or 



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