No. 6.] 



STUDY OF ARC SPECTRA. 



449 



all when the slit is at a little distance from the center of the image, 

 while a line at 3583 is very sharp in all the photographs. The 

 calcium lines 4299.14, 4302.68, 4318.80, 4425.61, 4435.86, and 

 4456.81 are stronger than in the yellow of the arc, being nearly 

 as strong as 4307.91 ; but Ca 4527.17 is fainter in comparison to 

 surrounding lines. Line 4527.17 is in fact hardly visible. 



Lithium lines photographed. ^ 



Sodium Nitrate. 



When sodium is in the arc the flame is homogeneous and quite 

 dense ; the band spectrum is not so faint as when lithium is 

 present, still it is much reduced in brilliancy. All of the calcium 

 lines are strengthened. Calcium seems to have been present as 

 an impurity in a number of the salts used. The /?-lines were re- 

 versed both when the nitrate and chloride were used. 



Sodium lines photographed. 



' The wave lengths of the metallic lines are taken from Kayser and Runge, Ueber 

 die Spectrum der Elemente, with whose measurements the scale readings agreed quite 

 accurately. These tables are not given to establish wave lengths, but to show which of 

 the lines already catalogued were found in these photographs. 



