56 Account of some Experiments 



yellow glass being afterwards interposed before one of 

 the lights^ while only one pane remained before the 

 other, the colours of the shadows immediately re- 

 turned. 



The results of these experiments having confirmed 

 my suspicions that the colours of the shadows arose 

 from the different degrees of whiteness of the two 

 lights, I now endeavoured, by bringing daylight to be 

 of the same yellow tinge with candlelight, 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 candlelight. 



In the course of these experiments, I observed that 

 different shades of yellow, given to the daylight, pro- 

 duced 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 colour, and the blue shadow 

 to a light green ; two sheets of the same glass nearly 

 destroyed the colours of both the shadows ; and three 

 sheets changed the shadow which was originally yel- 

 low to blue, and that which was blue to a purplish 

 yellow colour. 



When the beam of daylight was made to pass 

 through a sheet of blue glass, the colours of the shad- 

 ows — the yellow as well as the blue — were improved 

 and rendered in the highest degree clear and brilliant ; 

 but, when the blue glass was placed before the candle, 

 the colours of the shadows were very much impaired. 



In order to see what would be the consequence of 



