78 The Life Story of the Fish 



reflected by the surface of the water toward your eye at 

 E that the object at F (or F', its apparent position) is oblit- 

 erated. This is what often happens in nature, and under these 

 circumstances a fish at F might be invisible to you on ac- 

 count of the light on the water while at the same time you 

 were visible to the fish. The compensating factor is that 

 when a ray of light approaches the water in a direction almost 

 parallel to the surface, as for instance the light traveling 



Diagram K 



from you to the fish along the line EX, most of it is reflected 

 back into the air by the surface at X, and only a very small 

 amount reaches the fish at F. To all intents and purposes, 

 you at E are invisible to the fish. It is only when light ap- 

 proaches the water at a steeper angle, as from E' in Diagram 

 K, that enough of it enters the water to be visible at F. 

 There is, then, a limiting angle E'XF which constitutes 

 under natural conditions a kind of "blind spot" for the fish. 

 Anything below the line E'X is invisible, and that is why 

 you try to keep as low as possible when fishing. In the dia- 

 gram, the whole upper half of the standing man is con- 

 spicuous, while only the top of the head of the kneeling man 

 is visible to the fish, although in neither case is there any 

 obstacle between man and fish. 



The state of the water has also a very important bearing 

 on the situation. If the surface is smooth and flat, you seem 

 when you come out on the bank, to loom suddenly over 



