Experiments upon coloured Shadows. 1 1 r 
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 con- 
stantly 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 yellow glass being afterwards in- 
terposed before one of the lights, while only one pane remained 
before the other, the colours of the shadows immediately re- 
turned. 
The result of these experiments having confirmed my sus- 
picions, that the colours of the shadows arose from the diffe- 
rent degrees of whiteness of the two lights, I now endeavoured, 
by bringing daylight 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 daylight 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 daylight to be of a deeper yellow 
than the candle light. In the course of these experiments I 
observed, that different shades of yellow given to the daylight 
produced very different and often quite unexpected effects : 
thus one sheet of the yellow glass interposed before the beam 
of daylight, changed the yellow shadow to a lively violet 
eolour, and the blue shadow to a light green ; two sheets of 
