108 'LETTERS ON NATURAL MAGIC. 



light must appear absolutely black, however 

 brilliant be their colour in the light of day. 



As the methods now discovered of producing 

 yellow light in abundance were not known to 

 the ancient conjurors, nor even to those of later 

 times, they have never availed themselves of this 

 valuable resource. It has been long known that 

 salt thrown into the wick of a flame produces 

 Fig. 21. 



yellow light, but this light is mixed with blue 

 and green rays, and is, besides, so small in 

 quantity, that it illuminates objects only that are 

 in the immediate vicinity of the flame. A method 

 which I have found capable of producing it in 

 abundance is shown in Fig. 21, where AB is a 

 lamp, containing at A a large quantity of alcohol 

 and water, or ardent spirits, which gradually 



