BY WAY OF INTRODUCTION 5 



entirely submerged, and the whole of it is visible 

 against the surface of the water, while the trout 

 has the large boulder as a background. 



I have now described the appearance of 

 objects both near and distant, above, on and 

 below the surface. Only one more position 

 remains to be considered, namely, when the 

 lower portion of the object is on the bottom — 

 on a level with the submerged observer — and the 

 upper portion is above the surface. This is 

 illustrated by a wading angler on the plate 

 opposite. 



y is the point of observation, x z the diameter 

 of the " window," z w the reflecting surface of 

 the water beyond the "window." How the 

 wading angler appears to the observer from the 

 point y is shown in the lower half of the plate. 

 In the foreground are the rocks on the bottom 

 of the stream, with subaquatic vegetation 

 attached to a boulder on the right, then the legs 

 of the angler encased in brogues and waders, and 

 above this a streak of light, where his thighs 

 break the surface. The remainder of the image 

 up to the arc of the circle at z 1 is merely 

 reflection. 



Above the arc of the circular " window " are 



