PoLLOK — The Vacuum Tube Spectra of some Metals. 263 



Principal Lines of Cobalt — continued. 



Calcium. 



Calcium chloride does not readily yield a spectrum in the vacuum tube, 

 and as a rule only tliree lines show in photographs, A 4226"9, X 3968" I, and 

 X 3933-8, these lines being also the ultimate lines of the spark spectrum of 



2s2 



