( 0(>r> ) 



tlie lioalod calciiun vapour forniod a in ucli more extended atmosphere 

 aroinid the i)ole8 tliaii witli a weaker eurrent. 



Kayskk ') asserts, llioiijili. tlial it lias liitlierto remained unknown, 

 \\ hat are the exact conchtions upon wliicli the phenomenon dej)ends. 



Ill coiiiiectioii witli the jireeedinj^ eonsiderations, 1 hohl it possible 

 thai ill those experiments the metallic vai)oui' has, dui-ing tiie (short) 

 exposures, formed a kind of flame of tul)ular structure, which hajipened to 

 be in the exact direction of the spectroscope. This view seems reasonable 

 if ^^(' bear in mind the well-known "blowing" which is of frequent 

 Oi-ciirrence in a |)0werful arc loaded with much vapour. The I'adiations, 

 pioceediiig t'nnn the core of the arc, which caused the wide emission 

 baud, underwent anomalous dispersiiui in the enveloping vapour and 

 travei'sed the tiame-shaped streamer, following sinuous paths. 



A simple expei'iment convinced me that the j)eculiar light-distribution 

 observed in all strongly widened Fraunhofer lines'), iiii\V be strikingly 

 imitated in the absorptioii-öi»ectrum of sodium vapour. The only 

 thing necessary was to force the absorbing vapour into a more or 

 le ;s tubular structure, such as we presumed it to exist in the corona. 



A slightly converging beam of electric light was throwji on to 

 the slit of a grating-spectroscope. At a distance of rathei- more than 

 100 ('.III. b-om the slit, and about 1,5 cm. below the axis of 

 the beam was the opening of a specially constructed bunsen-burner, 

 from which a sodium-tlame emerged. This opening was slit-shaped 

 (30 c.m. long, 0,2 cm. wide) and adjusted in a jiosition exactly 

 jiarallel with the axis of the incident beam. 'J'lie j)ressure of the 

 gas wa>^ somewhat varialile, and a good regulator unfortunately not 

 at hand. Tn oi-der to su|»|)ly the long llame with sodium, the con- 

 struction of the burner included a kind of narrow gutter on either 

 ^ide, into which had been j)oui'ed a solution of a sodium-salt. This 

 ascended into the llame by stri|)s of asbestos jiaper. When viewing 

 this flame lengthwise, it was as if one were looking through a com- 

 |»ressed tube, the sides of which consisted of sodium- vapour. The 

 density of the va|>our diminished gradually towards the centre as well 

 as towards the outside. 



The sodium-lines were observed in the spectrum of the third order. 

 In s|>itc of the great length of the llame the real absorption lines 

 were narrow: they stood out from a |n'etty dark softly shaded 

 background, ilie width of which amounted to several Angstrom 

 units. The di>tributioii of the light entirely corres|)oiKled to Jkwkll's 



1) 1. c. p. 354. 



2) Jewell, Aslrupli. Jouru. HI, p. lOl ; Hale, Aylropli. Jouin. Ill, p. 150 — IGl. 



