96 



VERTICAL PLANE OF SIGHT 



mouth of which subtends over its head an arc of 

 about half that in which these objects really exist, 

 and consequently, the comparative size of these objects 

 must be relatively smaller in view of their being 

 cramped into the smaller field of vision. 



e - 



a c b d, A B C D, surface of water ; 



E, the eye of trout ; 



E A, E B, E C, E D, the upward cone within which is 

 confined the trout's sight of all objects above the 

 surface of the water within the range of the trout's 

 vision. 



In order to make this perfectly clear to my readers, 

 I have shown two diagrams. 



In Diagram 8, E is the eye of the fish, from which 

 rises a vertical cone E A, E C, E B, E D, the sides of 

 which cut the surface of the water, as shown at 

 A BCD. 



All rays of light from objects above the water which 

 reach the trout at E must enter the water within the 

 circle A C B D. Let A E B (see Diagram 9) be a 

 vertical section of the cone in Diagram 8, cutting the 



