ix.] PROMINENCES ON DISC. 117 



thus be seen on the disc of the sun itself, 1 as this was not in 

 accordance with Kirchhoff s hypothesis. Subsequent observa- 

 tions, however, soon showed that this is quite possible. 2 



The first observations of this nature were made by Father 

 Secchi and myself almost simultaneously. My observation was 

 made on the llth of April, 1869, and Secchi's letter to the Paris 

 Academy announcing the same appearance is dated the 13th. 



FIG. 48. Edge of chromosphere (billowy). 



This reversal of the hydrogen lines on the sun's disc was also 

 observed by Captain Herschel on June 10th, 1869, and by Pro- 

 fessor Young, who in a communication to the Franklin Institute, 

 dated October 3rd, 1870, 3 thus describes the reversal of the c 

 and F lines in a group of spots then visible : 



" At 4.05 P.M. the brilliance of the p line increased so greatly 

 that it occurred to me to widen the slit, and to my great delight I 



FIG. 49. Edge of chromosphere (pointed). 



saw upon the disc of the sun itself a brilliant cloud, in all its 

 structure and detail identical with the protuberances around the 

 limb. Indeed, there were two of them, and there was no difficulty 

 in tracing out and delineating their form. Fig. 50 represents them 



1 Proc. Roy. Soc. No. 110, 1869. See also Secchi, Comptes Rcndus, vol. Ixviii. 

 p. 237. 



'- Proc, Roy. Soc. vol. xvii. p. 415. 3 Nature, vol. iii. p. 113. 



