154 American Fisheries Society 



Figure 2 shows one view that a fish might get. For 

 comparison the various angles at the right of figure one 

 are indented on the margin of figure 2. In the angles I, 

 II, III the fish sees directly the bottom and the submerged 

 part of the bather. In the angle IV he sees the inverted 

 image of the submerged part and of the bottom. Within 

 the angle marked 96° in figure 1, the fish views the outer 

 world. It is as though he looked through a round win- 

 dow over his head — or as though he looked out through 

 a funnel with an angle of 96°. On all sides of this win- 

 dow the lower face of the water's surface is opaque to 

 the fish, and he sees in it only the reflected images of 

 submerged objects. Through the window he sees the 

 outer world. In this view of the outer world two things 

 are noteworthy. First, the tops of the trees and the up- 

 per part of the bather are shortened or depressed as are 

 the segments of the rod la to 6a, in figure 1. Second the 

 part of the bather just above the water and the trunks 

 of the trees are not visible at all and in their place is 

 seen a dark band. The reason for this should appear 

 from a study of figure 1 within the angle 12°. In figure 

 1 rays from points on the rod below 7 are represented as 

 penerating the water and the fish should see these points. 

 But the amount of light that penetrates the water from 

 any points on the rod depends on the angle at which that 

 light strikes the water. Since the rays from point 8 

 strike the water at a very acute angle most of them are 

 reflected and but few penetrate. More rays penetrate 

 from points higher up and fewer are reflected. Hence the 

 visibility of exterior objects to the fish depends on their 

 apparent height above the surface. Objects in the direc- 

 tion of the line Z and below it within the angle 12° are 

 practically invisible. If these objects are near the fish 

 they may be quite close to the surface of the water, if 

 on the shore they may be higher, if more distant they 

 may be very high and still all are invisible to the fish. 

 If a mirror is placed in the water at the point F in figure 

 1 and tilted at the proper angle the outer world is visible 

 to one looking down into the mirror (Von Aufsess, 1913), 



