100 The American Salmon- fisherman. 



colors so pronounced that the conditions of light and water 

 enable the salmon to so analyze its structure at a glance 

 as to preclude the exercise of its imagination, then it 

 seems reasonable to suppose they would recognize that 

 the fly was nothing which concerned them, and that they 

 would ignore its presence. 



If we now compare what ought to follow from this as- 

 sumption of fact with what we know actually does take 

 place, it seems to me we shall find the results in accord. 



Experience has taught us that in the early season and 

 in turbid water, or in dark and windy weather, larger flies 

 and those of a more striking hue are successful. The 

 greater depth of water, and its diminished transparency, 

 or the feeble illumination of the fly, would lead us to ex- 

 pect this, since the details of construction are then ob- 

 scured by a comparatively thin stratum of water, leaving 

 full play to the imagination of the fish. 



We also know that when the water is low and clear, 

 and untouched by wind, while the light is strong, that 

 then smaller flies of less obtrusive character alone will 

 move the fish, if indeed even they will do it. This, too, 

 should result from our theory. 



If we also take into consideration the marked degree 

 in which the visibility of the fly, and consequently the 

 power to analyze it, depends upon the direction of the 

 sun with relation to the fish, we will find, it seems to me, 

 at least a probable explanation of many other facts of 

 the same kind. We have proved experimentally that 

 when the sun is at the back of the observer, the make-up 

 of the fly is plain for a comparatively long distance; 

 while when the sun shines in the observer's face the fly 

 speedily becomes obscured. 



