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there was no appearance of any such in the sky, which was 
cloudless, or of any colour except the blue of the empyrean. 
Its resemblance to a bow I found to be an optical illusion, 
which was caused by the fact that the eye, being naturally 
focussed to the most brilliant part, which was at the greatest 
distance, followed the line of light downwards with the same 
adjustment of focus, so that the nearest light seemed at the 
same distance from the eye as the farthest, as is thus shown 
in section. (See sketch, B.) The light, as I afterwards 
found, was reflected from the sun by a medium floating on 
the surface of the lake. 
The fog had almost disappeared, but a thin haze stilJ 
seemed to intervene between me and the base of the distant 
mountains, without, however, obstructing the view of the 
spectrum line, as 
“ There, low flashing on the flood, it spread 
Its floor of flashing light.” 
I called out my friends to view the scene, and their astonish- 
ment was equal to mine. I could not hear that it had 
ever been seen before. We took out the boat and rowed 
towards the middle of the lake, anxious to understand the 
phenomenon before its light, from any cause, should fade. 
When there, a double or bifurcated band of light was seen 
on our left hand, it being also most brilliant near the shore, 
at its termination. The sun was behind us, so that we had 
three distinct spectra — the original or first one on our right 
hand, looking towards Low Wood; and turning our heads 
in the other direction towards Wray Castle, we had the 
