

HORIZONTAL PLANE OF SIGHT 



95 



trout, as regards all objects external to the water, is 

 confined to the interior of a hollow cone, the apex 

 of which cone is situated at the eye of the trout, and 

 the sides of which rise upward at an angle of 42 degrees 



A B C D, horizontal plane of trout's vision ; 



E T, trout ; 

 D A C B, horizontal zone of trout's sight. 



to the surface of the water. So far as the fish is con- 

 cerned, within this hollow cone which, therefore, 

 subtends an angle of 96 degrees in every upward 

 direction is confined the view of all objects within 

 the 180 degrees vertically above the water. In other 

 words, the trout sees, as it were, all objects above the 

 surface of the water from the bottom of a well, the 



