THE ARC SPECTRUM OF HYDROGEN. 

 By O. H. Basquix. 



Presented by C. R. Cross. Received June 8, 1901. 



The Problem. 



The arc spectra of those elements which are gases at ordinary tem- 

 peratures and pressures have not been extensively studied. Their spark 

 spectra, however, are easily obtained, and were among the first to be in- 

 vestigated. The general impression prevails, therefore, that these ele- 

 ments do not possess arc spectra. On the other hand practically all the 

 so-called "hot stars" and all the "new stars" possess the more impor- 

 tant lines of the hydrogen spectrum. Although our knowledge of what 

 is going on in the arc and in the spark is very crude and unsatisfactory, 

 yet it is, to the average mind, much easier to imagine a star as being in 

 a condition similiar to that of the arc, rather than in one similar to that 

 of the electric spark. It has seemed worth while, therefore, to search for 

 the more important lines of hydrogen in the arc spectrum. This is the 

 problem of the following investigation. 



Historical. 



Liveing and Dewar* examined the carbon arc in an atmosphere of 

 hydrogen and saw "the fairly bright" C line of hydrogen, also "a faiut 

 diffuse band " at the position of the F line of hydrogen. They obtained 

 these two lines also by allowing small drops of water to fall into the arc 

 in air.f They found the F line usually obscured by continuous spectrum, 

 becoming visible at intervals only, when, from some variation in the work- 

 ing of the arc, the continuous spectrum was less brilliant. Crew and 

 Basquin t incidentally noticed these two lines of hydrogen while work- 

 ing with the rotating metallic arc in an atmosphere of this gas. 



* Proc. Roy. Society, 30, 156 (1880). t Ibid., 35, 75 (1883). 



t Proc. Amer. Acad., 33, 18 (1898). 



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