182 LETTERS ON NATURAL MAGIC. 



producing it in abundance is shown in Fig. 21, where A B 

 is a lamp containing at A a large quantity of alcohol and 

 water or ardent spirits, which gradually descends into a 

 platina or metallic cup D. This cup is strongly heated 

 by a spirit-lamp L, inclosed in a dark lantern ; and when 

 the diluted alcohol in D is inflamed, it will burn with a 

 fierce and powerful yellow flame : if the flame should 

 not be perfectly yellow, owing to an excess of alcohol, a 



Fi~ 21. 



proportion of salt thrown into the cup will answer the 

 same purpose as a further dilution of the alcohol.* 



A monochromatic lamp for producing yellow light may 

 be constructed most effectually by employing a portable 

 gas lamp containing compressed oil gas. If we allow the 

 gas to escape in a copious stream, and set it on fire, it will 

 form an explosive mixture with the atmospheric air, and 

 will no longer burn with a white flame, but will emit a 

 bluish and reddish light. The force of the issuing gas, 

 * See Edinburgh Transactions, vol. ix. p. 435. 



