LOOKING UPWARD 39 



but only sees the bottom of the tank reflected on the 

 surface. Thus a fly floating on the surface outside the 

 angle of 48 degrees from the perpendicular to the eye of 

 the observer is unseen, unless it or a part of it penetrates 

 the surface, or makes some impression on it breaking up 

 its mirror-like smoothness. If some impression only is 

 made, it may, and no doubt does, afford the fish some 

 indication that something, which may be fly-food, is ap- 

 proaching. If it, or any part of it, breaks through the 

 surface, then that part only which breaks through the 

 surface becomes visible outside the angle of 48 degrees, 

 and it is reflected against the underside of the surface. 

 This was well illustrated by the effect produced by the 

 gardener's birch broom being thrust into the water to sweep 

 aside some discarded shucks which had fallen from budding 

 trees into the water. Only that part of the broom which 

 was put through the surface was visible, and that was 

 duplicated by reflection. The rest, for all that could be 

 seen of it, might as well not have existed. 



But inside the semi-circle, within the angle of 48 degrees, 

 everything floating on the surface was not only visible, 

 it was extremely clearly visible, and was surrounded by a 

 prismatic radiance which was more specially in evidence 

 the nearer the fly was to the outer edge of the semi-circle. 

 There was no difficulty about distinguishing the colours of 

 flies on the underside or on the sides. Indeed, the effects 

 produced were all much what I have suggested above may 

 be the light effects where the light is behind, or at any 

 rate not directly shining into the eye of the trout. 



I blame myself for not having ascertained and recorded 

 precisely the position of the pond and the observation 

 chamber in relation to the points of the compass, and the 

 relative position of the sun at the time of observation, so 

 that I might be able to deduce with more certainty the 



