THE VISION OF A TROUT. 83 



section of the cone in Diagram 8, cutting the surface 

 of the water at A B. Then the rays of light from M N 

 can only be seen by the trout situated at E when they enter 

 along the dotted lines N B E, M b E, and the fish sees M N as 

 in the direction b B and also relatively reduced in size b B. 



Objects immediately over the trout will suffer least from 

 the influence of refraction, but their shape and size will suffer 

 the more as they leave the zenith, and objects on the 

 horizon will suffer most, etc. 



To the trout, the full moon as it rises will appear as a 

 small horizontal line of light 42 degrees above the real 

 horizon, and it will assume its circular shape as it approaches 

 the zenith. 



It will thus be seen that the nearer an object is to the 

 water level when outside the water, the less will be the angle 

 which it will relatively subtend to the fish ; in other words, 

 the lower the position of an object when at equal distances, 

 the smaller it will appear to the fish. 



This important fact is taken advantage of by the fisher- 

 man, who, although he may not understand the optical laws 

 of refraction, has learnt from experience that, in order to 

 avoid scaring the fish, he must crouch as much as possible 

 and thus reduce his height, and that a side cast is less likely 

 to scare the fish than an overhead one. Not that he escapes 

 being seen, but that his bulk and the bulk of his rod is then 

 generally insufficient to seriously frighten the fish. Wading 



is for this reason the best method for approaching fish. 



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