THE RELATIVE POSITIONS OF THE ARC AND SPARK 



LINES OF THE SPECTRA OF TITANIUM, ZINC, 



AND IRON. 



By Norton A. Kent. 



Presented April 12, 1905. Received June 12, 1905. 



Historical Survey and Statement of the Object of the 

 Investigation. 



In 1901 Haschek * stated that the lines of the spark spectrum of 

 titanium exhibit considerable shift as compared with the same lines in 

 the arc, a shift in one instance as great as 0.13 t.-m. 



In 1903 the writer of the preseut paper made a careful experimental 

 investigation of the subject, f No such large shifts were discovered ; but 

 it was shown that in all probability the wave-lengths of certain lines of 

 the titanium spark spectrum are sensitive to various conditions of the 

 electric circuit, such, for instance, as the amount of capacity, self-induction, 

 and ohmic resistance employed, and the presence or absence of an 

 auxiliary spark-gap in series with that under investigation. 



The instrument used was a ten-foot Rowland grating. It seemed 

 advisable to use greater dispersion. Hence the present work was under- 

 taken with a twenty-one-foot grating. During its progress, Eder and 

 Valenta { (using a fifteen-foot instrument) have published a paper in 

 which they state that neither in the case of "pure zinc nor brass wire do 

 the lines studied by Haschek show any shift. They attribute the results 

 of these investigators to a photographic displacement of the centre of 

 gravity of the lines due to over-exposure — the lines in question being 

 those which exhibit very strongly the phenomenon of unsymmetrical 

 broadening ; and they suggest also the possibility of a pseudo-shift due 

 to poor focus. The conclusion drawn by Eder and Valenta is that, at 

 minimum photographic exposure, the coincidence of arc and spark line 

 is perfect. Moreover, Middlekauff § has lately studied the iron spectrum 



* Astrophysical Journal, 14, 181 (1901). t Ibid., 17, 28(5 (1003). 



t Ibid., 19, 251 (1904). § Ibid., 21, 116 (1905). 



