152 American Fisheries Society 



except as indicated above, appear as they would in air. 

 In the angles IV and V the fish sees the rest of the wa- 

 ter's surface, except that lying within the angle marked 

 96°. The lower face of the water's surface in the angles 

 III, IV, V, is a reflecting surface — like that of a mirror. 

 A ray of light from the point near D on the staff is indi- 

 cated by the dotted line and its direction is shown by 

 the arrow heads. When such a ray strikes the lower 

 face of the water's surface at any angle greater than 48° 

 with the vertical it does not emerge into air, but is re- 

 flected back into the water. Thus the ray from D is re- 

 flected and reaches the fish's eye at F and the fish sees 

 an image of D in the surface of the water as in a mirror. 

 In whatever direction the fish looks within the angles III, 

 IV and V, it does not see out into the air, but sees rather 

 this mirror like opaque surface of the water with the 

 inverted images of submerged objects visible in it. In 

 the angle IV the fish therefore sees an inverted image 

 of the submerged part of the rod. Whatever the fish 

 sees in the water within the angles III, IV, V it may also 

 see duplicated by an inverted reflected image. These 

 images are like those we see when we look from air at 

 the surface of still water, especially in the morning or 

 evening. 



Since light penetrates into the water from air the fish 

 is able to see objects above the surface. When a ray of 

 light penetrates still water obliquely it is bent or refract- 

 ed toward a perpendicular extending downward from the 

 water's surface. As shown in figure 1, vertical ray T is 

 not refracted and passes directly to the eye of the fish 

 at F. The rays U, V, W, X, Y and Z are refracted in 

 varying degrees depending on the obliquity with which 

 they strike the water. Even a ray which comes from a 

 point near 9, just above the surface of the water, and is 

 therefore nearly parallel to that surface, penetrates. It 

 is refracted at an angle of 48°. As appears from the 

 figure light reaches the eye of the fish from all visible 

 objects above the surface — that is from all objects be- 

 tween the horizon on all sides and the zenith. But the 



