166 



Scientific Proceedings, Royal Dublin Society, 



strongly as an impurity in most of the spectra of the alkalis and alkaline 

 earths ; if more is present, the lines X 2802-8 and A 2795-6 also show, so these 

 three lines may be accepted as the ultimate lines of the vacuum tube spectra 

 of magnesium. If any appreciable quantity of the substance is present, 

 practically all the lines of the spark spectrum of the element come out, and 

 there is little change on the introduction of a condenser. When much 

 vapour is present, some strong bands show from X 3880 to X 3680. 



Principal Lines of Magnesium. 



PoTASSiUM. 



The specimen of potassium cliloride examined gave a brilliant lumi- 

 nescence in the tube, but the photograph consisted of the lines of the spectra 

 of sodium and lithium, together with the banded spectrum of water-vapour, 

 and the lines of chlorine, together with one or two other lines, not yet 



