on Coloured Shadows. 55 



Argand's lamp, burning with its greatest brilliancy, 

 appears in the form of a dead yellow semi-transparent 

 smoke. How transcendently pure and inconceivably 

 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 experiment! 



It appearing to me very probable that the difference 

 in the whiteness of the two kinds of light which were 

 the subjects of the foregoing experiments might, some- 

 how or other, be the occasion of the differerit colours of 

 the shadows, I attempted to produce the same effects 

 by employing two artificial lights of different colours ; 

 and in this I succeeded completely. 



In a room previously darkened, the light from two 

 burning wax candles being made to fall upon the white 

 paper at a proper angle in order to form two distinct 

 shadows of the cylinder, these shadows were found not 

 to be in the least coloured ; but upon 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 two Argand's lamps were made use of 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 

 approaching 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 two panes of the 



