Salmon-fishing Catching the Fish. 135 



the same reason facilitate the switch-cast as well, but it 

 cooperates with the angler in imparting an attractive 

 motion to the fly, while the wrinkled surface interposes a 

 curtain opaque to fish-vision between the angler and the 

 sharp eyes of the salmon. 



Both theory and experiment were invoked in "Fly- 

 Rods and Fly-Tackle," to show under what conditions and 

 to what extent fish can discern objects above the water. 



It will be sufficient here merely to recapitulate these 

 results. 



1st. Objects situate above the surface of the water are 

 only visible to the fish when that surface is smooth. 



2d. They are only so visible within a circular area, the 

 centre of which lies directly over the fish, and the diam- 

 eter of which is to the depth of water above the fish as 

 20 is to 13. 



3d. Every object ten inches above the water for every 

 ten feet from the centre of this circle, is visible within it 

 by refraction. 



4th. When the surface of the water is disturbed the 

 transparent area is blotted out, and the entire surface be- 

 comes opaque to fish-vision. 



We all know enough about fish to know that we know 

 comparatively little about them. That they all breathe 

 by taking water in at the mouth and discharging it 

 through their gills, and that they all wag their tails when 

 they swim, we know. But of the causes which induce 

 the many peculiarities of conduct which continually sur- 

 prise and confound the angler, and which we are apt self- 

 sufiiciently to characterize as mere caprice, we know 

 hardly more than did the builders of the Great Pyramid 



