52 Account of some Experiments 



This appearance, which was not only unexpected, but 

 was really in itself in the highest degree striking and 

 beautiful, I found, upon repeated trials and after vary- 

 ing the experiment in every way I could think of, to be 

 so perfectly permanent that it is absolutely impossible 

 to produce two shadows at the same time from the 

 same body, the one answering to a beam of daylight 

 and the other to the light of a candle or lamp, without 

 these shadows being coloured, the one yellow and the 

 other blue. 



The experiment may very easily be made at any 

 time by day, and almost in any place, and even by a 

 person not in the least degree versed in experimental 

 researches. Nothing more is necessary for that pur- 

 pose than to take a burning candle into a darkened 

 room in the daytime, and open one of the. window- 

 shutters a little, about half or three quarters of an inch, 

 for instance ; when, the candle being placed upon a 

 table or stand, or given to an assistant to hold, in such 

 a situation that the rays from the candle may meet 

 those of daylight from without at an angle of about 

 40°, at the surface of a sheet of white paper, held in 

 a proper position to receive them, any solid opaque 

 body, a cylinder, or even a finger held before the 

 paper at the distance of two or three inches, will pro- 

 ject two shadows upon the paper, the one blue and 

 the other yellow. 



If the candle be brought nearer to the paper, the 

 blue shadow will become of a deeper hue, and the 

 yellow shadow will gradually grow fainter ; but, if it be 

 removed farther off, the yellow shadow will become 

 of a deeper colour, and the blue shadow will become 

 fainter; and, the candle remaining stationary in the 



