Flies and Fly-fishing. 321 



the surface of the water an object must be at a given 

 distance, to render it visible within the circle ; or in 

 other words, to determine the limits within which refrac- 

 tion would produce this result. For this purpose a red 

 rag was used. It was placed on the water-level at the 

 extreme end of the tank, thus being five feet (accurately 

 four feet ten and a half inches) from the observer. It 

 was then slowly raised, as nearly as possible perpendicu- 

 larly, till it began to appear within the edge of the trans- 

 parent circle. This took place at an elevation of five 

 inches from the surface; whence I conclude that anything 

 over ten inches above the surface for every ten feet of 

 distance, will be visible. 



Herein we find the reason why experience has shown 

 the advantage of wading over fishing from the bank ; 

 or when fishing from a boat, that it is better to cast sit- 

 ting rather than standing. 



Though theoretically we all know that an object seen 

 within this circle cannot appear in its true position, still 

 perhaps it is not generally realized how extensive this 

 . apparent displacement really is. 



In the preceding illustration E represents the actual 

 position, and F the position of the red rag as it ap- 

 peared to me during the preceding experiment. As 

 the body seen approaches more and more nearly to a 

 position immediately above the trout, this apparent dis- 

 placement uniformly diminishes in extent, until, when 

 on the perpendicular, it ceases altogether and the body 

 appears in its true position, since there is then no refrac- 

 tion at all. 



We have all cast in vain upon unruffled waters, and 

 prayed for a ripple, and we have all noticed the marked 

 change of luck which followed its advent. The reason 



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