11 ^ Count Rumford's Account of some 
wax candles were coloured, the one blue, and the other yellow, 
by interposing a sheet of yellow glass before one of them , I 
now tried what the effect would be when blue glass was made 
use of instead of yellow, and I found it to be the same ; the 
shadows were still coloured, the one blue, and the other yellow, 
with the difference, however, that the colours of the shadows 
were reversed, that which, with the yellow glass, was before 
yellow being now blue, and that which was blue being yellow. 
I afterwards tried a glass of a bright amethyst colour, and 
was surprised to find that the shadows still continued to be 
coloured blue and yellow. The yellow, it is true, had a dirty 
purple cast ; but the blue, though a little inclining to green, 
was nevertheless a clean, bright, decided colour. 
Having no other coloured glass at hand to push these par- 
ticular inquiries farther, I now removed the candles, and open- 
ing two holes in the upper parts of the window -shutters of two 
neighbouring windows, I let into the room from above two 
beams of light from different parts of the heavens, and placing 
the instrument in such a manner that two distinct shadows 
were projected by the cylinder upon the paper, I was enter- 
tained by a succession of very amusing appearances. The 
shadows were tinged with an infinite variety of the most un- 
expected, and often most beautiful colours, which continually 
varying, sometimes slowly, and sometimes with inconceivable 
rapidity, absolutely fascinated the eyes, and commanding the 
most eager attention, afforded an enjoyment as new as it was 
bewitching. It was a windy day, with flying clouds, and it 
seemed as if every cloud that passed brought with it another 
complete succession of varying hues, and most harmonious tints. 
If any colours could be said to predominate it was purples; but 
