A PHOTOGRAPHIC STUDY OF ARC SPECTRA. II.' 



By Caroline Willard Baldwin. 



II. 



Metallic Spectra. 



CERTAIN metals when introduced into the arc tend to obscure 

 the band spectrum, e.g. Na, Li, K, Sr, Ba, Ca ; while others, 

 as Zn, Cd, Cu, Ag, give the band spectra with equal or increased 

 brilliancy. In no case was the band spectrum entirely invisible, 

 but it was so much weakened by the alkalies that it is not strange 

 that in their presence the carbon bands were not detected by the 

 bolometric measurements of Professor Snow. 



In the ensuing paragraphs the results obtained by photograph- 

 ing: the arc when cores of the carbons were filled with various 

 alkalies are briefly described and tables of the lines are given. 



LitJiimji Carbonate. 



Lithium gives an almost homogeneous carmine-colored arc. 

 The spectrum has much the same general appearance as the 

 spectra from the outer sheaths of the arc, with the addition of 

 the lithium lines, and at a very short distance from the center of 

 the arc the band spectrum is entirely invisible. However, the 

 bright groups are faintly visible in the photographs taken from the 

 center of the arc. 



Lithium does not materially affect the other metallic lines 

 present in the ordinary arc spectrum. The lines which are most 

 brilliant in the outer sheaths of the original arc are, with but few 

 exceptions, the strong lines present when lithium is introduced. 

 The carbon lines 3585.99, 3586.04, and 3590.52 are much fainter 

 than in the yellow of the ordinary arc, and are not visible at 

 1 Concluded from the Physical Rev'iew, March-April, 1S96. 



