58 Account of some Experiments 



board for that purpose. A small stand, capable of 

 being made higher or lower, as the occasion requires, 

 should likewise be provided for supporting the candle ; 

 and, if the board with the paper fastened upon it be 

 surrounded with a broad black frame, the experiments 

 will be so much the more striking and beautiful. For 

 still greater convenience, I have added two other 

 stands, for holding the coloured glass through which 

 the light is occasionally made to pass, in its way to the 

 white surface upon which the shadows are projected. 

 It will be hardly necessary to add that, in order to the 

 experiments appearing to the greatest advantage, all 

 light which is not absolutely necessary to the experi- 

 ment must be carefully excluded. 



Having fitted up a little apparatus according to the 

 above directions, merely for the purpose of prosecuting 

 these inquiries respecting the coloured shadows, I pro- 

 ceeded to make a great variety of experiments, some 

 with pointed views, and others quite at random, and 

 merely in hopes of making some accidental discovery 

 that might lead to a knowledge of the causes of appear- 

 ances, which still seemed to me to be enveloped in 

 much obscurity and uncertainty. 



Having found that the shadows corresponding to 

 two like wax candles were coloured, the one blue and 

 the other yellow, by interposing a sheet of yellow glass 

 before one of them, I now tried what the effect would 

 be when blue glass was made use of instead of yellow, 

 and I found it to be the same : the shadows were still 

 coloured, the one blue and the other yellow, with this 

 difference however, that the colours of the shadows 

 were reversed ; that which, with the yellow glass, was 

 before yellow, being now blue, and that which was blue 

 being yellow. 



