266 



Mr. J. N. Lockyer. 



[June 19, 



XXVII. " On a New Method of Studying Metallic Vapours." 

 By J. Norman Lockyer, F..R.S. Received June 19, 1879. 



On May 29 I read a note before the Royal Society, stating that I 

 had lately been engaged in studying the spectrum of sodium under 

 new experimental conditions, and I pointed out that the vapour given 

 off from the metal after slow distillation in a vacuum for some time 

 shows the red and green lines without any trace whatever of the 

 yellow one. 



No detailed account of the method employed in the experiments 

 was given, as the most convenient form of apparatus had not then been 

 determined. 



The novelty of the method consists in the use of the luminous 

 electric current as an explorer and not as agent for the supply of the 

 vapours under examination ; that is to say, the vapours are first pro- 

 duced by an external source of heat, and are then rendered luminous 

 by the passage of the current. The length and bore of the tube there- 

 fore control the phenomena to a certain extent. 



A form of apparatus which I have found to answer very well is 

 shown in the accompanying photograph. 



