156 THE WAY OF A TROUT WITH A FLY 



water, and in a later stage for the spent spinner floating 

 down helpless or dead. Trout rise at spent gnats and fallen 

 spinner in a quiet, deliberate way, differing greatly from 

 the fierce rushing motions with which they bulge at the 

 ascending nymphs which they fear may escape them by 

 hatching and transfer to the air. 



So far we have only dealt with the fly in the surface, and 

 not the fly under it, nor the fly over it, the wholly wet 

 and the wholly dry. On the subject of these, as well as 

 on the subject of the semi-submerged, the experiments 

 conducted by means of Dr. Francis Ward's under-water 

 observation chambers (of which experiments an account 

 appeared in the Field of May 4, 1912, and are recorded 

 at pp. 38 to 43 of this book) may shed a little needed 

 light. They show that the under-side of the surface 

 film outside a certain angle to the perpendicular above 

 the observer's eye acts as a mirror, and is impenetrable to 

 vision. That angle is 48 J degrees for the human observer, 

 but may, for all I know, be different for trout, and, again, 

 for other fish. But whatever that angle may be, outside 

 it the trout can only see those parts of the fly which 

 penetrate the surface film. Thus a sunk fly is visible to 

 a trout at any distance, a semi-submerged fly at quite a 

 considerable distance; a line floating and not breaking or 

 denting the surface, and a perfectly dry and floating fly 

 are not visible at all, except within the circle of which the 

 place where the perpendicular above the trout's head meets 

 the surface is the centre, and the angle of reflection indi- 

 cates the circumference. Within that circle a floating fly 

 looks remarkably clear, bright, and attractive, but if the 

 hook comes through the film it looks particularly gross 

 and obnoxious. 



The deductions which may be drawn from these facts 

 are as follows: 



