IX.] 



BRIGHT LI$TES ON DIS 



the slit was just on one edge of the prominence, the central 

 figure gives its appearance when it was entirely included in 

 the slit, and the right-hand figure when the slit was on the 

 opposite edge. 



There was another important fact connected with this : when 

 the phenomena were observed close to the limb it was very 

 often seen that the dark line on the surface of the sun was 

 broken ; in fact we got a doubling of the dark F line in 

 exactly the same way as we got this doubling of the bright line 

 in the prominence itself. 



FIG. 55. Contortions of the hydrogen lines. The right-hand side of each 

 diagram is the most refrangible. 



The next point observed was (and this was an observation 

 very difficult indeed to make near the limb) that whenever 

 we got any very considerable activity we got a new order of 

 phenomena altogether, indicated in the two diagrams (Figs- 

 56 and 57). 



It was found that the absorption of the hydrogen, or of the 

 magnesium, or of the sodium, as the case might be, was 

 enormously reduced; that for that part of the sun there was 

 practically no absorption; but instead of absorption an ex- 

 cessive brilliance in that part of the spectrum where the dark 

 line would otherwise have been. In the brighter portion 

 between the two small spots (Fig. 57) the absorption was 



