( mo j 



very accnmte (leleniiiiiatioiis of waveleuotlis. AikI these ai'e for the 

 firealer part the most })roiniiieiit lines of tlie speetruni, especially the 

 shaded -ones *). 



Jkwell emphasizes the fad that all distijuMly shaded lines iji the 

 solar spectrum show to a greater or less degree the following' typical 

 feature '). 



Within a Itroad, shaded, moderately dark hackgroniid a much 

 darker central al)soi-ptioii hne contrasts rather sharj)ly (Fig. 2). 



Fc 



'S 



u 



%3. 



Besides, the ahsoi-ptioii cui-nc often shows dippings close to the central 

 line, as in Fig. 3, sometimes symmetricah sometimes dissymmetrical. 

 jK\\KLr> aflii-ms that this is not aji optical delusion, due to contrast, 

 but a real |>henomenou. lie assumes, therefoi'e, that the broad absorp- 

 tion ban<l is |)ro(biced in the h)wer jtorlious (»f tiie solar atmos|)here 

 and under a gi-eal range of pressure ; that in higher levels radiation 

 pre\ails again, prtxhiciug a raliiei- w ide emission line ; and that linally 

 in the highest parts, w here the jtressure is vei-y mucli less, tlie sharp 

 absor[)tion line is [)rotluced. The position of this eentral absorption 

 line with respect to tlie emission line is usually unsymmetrical, which 

 is conspicuous iu the case (»f // and A'. The central line itself also 

 \ai-ies somewhat in width uj>on dilferem j)lates and its maximum of 

 ijitensitv is not always in the middle of the line. The displacement 

 of this eentral line in // and A^ varies in magjiitude, but, so far as 

 has been observed, always toward the red with i-espect to the emis- 

 sion line and the corresponding metallic line (in the arc). 



.Ikwf.ll concludes that the absorbing calcium vapour descends all 

 over the solar surface with a velocity sometimes amounting to about 

 75 miles per minute. 



Upon the same plates showing strong dissymmetry in H and K, 

 the shaded lines of other elements {Fe, A/, My, Si) have been 

 examined. The strongest iron lines and one aluminium line showed 

 displacements of the same character as that observed iji the case of 



1) Astroph. Journ. XI, p. 23G, 1900. 



~) Jewell, "Certain peculiarities in the appearance of lines in the solar spectrum 

 and their intcrprelalion". Astroph. Jouru. 111. p. 'J9, 1890. 



