376 PHILOSOPHICAL TRANSACTIONS. [aNNO 1794. 



ably bright the rays of the sun are, when compared to the light of any of 

 our artificial illuminators, may be gathered from the result of this experi- 

 ment. 



It appearing very probable, that the difference in the whiteness of the 2 kinds 

 of light, which were the subjects of the foregoing experiments, might be the 

 occasion of the different colours of the shadows, I attempted to produce the 

 same effects by employing 2 artificial lights of different colours; and in this I 

 succeeded completely. In a room previously darkened, the light from 1 burning 

 wax candles being made to fall on the white paper at a proper angle, in order to 

 form 2 distinct shadows of the cylinder, these shadows were found not to be in 

 the least coloured; but on interposing a pane of yellow glass, approaching to a 

 faint orange colour, before one of the candles, one of the shadows immediately 

 became yellow, and the other blue. When 2 Argand's lamps were used, instead 

 of the candles, the result was the same; the shadows were constantly and very 

 deeply coloured, the one yellow approaching to orange, and the other blue ap- 

 proaching to green. I imagined that the greenish cast of this blue colour was 

 owing either to the want of whiteness of the one light, or to the orange hue of 

 the other, which it acquired from the glass. When equal panes of the same 

 yellow glass were interposed before both the lights, the white paper took an 

 orange hue, but the shadows were to all appearance without the least tinge of 

 colour; but 2 panes of the yellow glass being afterwards interposed before one of 

 the lights, while only 1 pane remained before the other, the colours of the 

 shadows immediately returned. 



The result of these experiments having confirmed my suspicions, that the 

 colours of the shadows arose from the different degrees of whiteness of the 2 

 lights, I now endeavoured, by bringing day light to be of the same yellow tinge 

 with candle light, by the interposition of sheets of coloured glass, to prevent 

 the shadows being coloured when day light and candle light were together the 

 subjects of the experiment; and in this I succeeded. I was even able to reverse 

 the colours of the shadows, by causing the day light to be of a deeper yellow 

 than the candle light. In the course of these experiments I observed, that dif- 

 ferent shades of yellow given to the day light produced very different and often 

 quite unexpected effects: thus one sheet of the yellow glass interposed before 

 the beam of day light, changed the yellow shadow to a lively violet colour, and 

 the blue shadow to a light green; 2 sheets of the same glass nearly destroyed 

 the colours of both the shadows; and 3 sheets changed the shadow which was 

 originally yellow to blue, and that which was blue to a purplish yellow colour. 

 When the beam of day light was made to pass through a sheet of blue glass, 

 the colours of the shadows, the yellow as well as the blue, were improved and 



