118 



THE CHEMISTRY OF THE SUN. 



[CHAP. 



as they were from 4.05 to 4.10 ; Fig. 51 gives the form at 4.15 4.20. 

 They were then considerably fainter than at first. During the 

 intervening ten minutes I examined the other lines of the spectrum, 

 and found that the form could be distinctly made out in all the 



FIG. 50. The prominence at 4.05. 



hydrogen lines, even in h ; but that the reversal of the other lines, 

 including D 3 , was confined to the region immediately over the spot- 

 nucleus, where the smaller but brighter cloud terminated abruptly, 

 or, I might better say, originated. The larger one faded out at 

 both ends. When the clockwork of the equatorial was stopped, 



FIG. 51. The prominence at 4.20. 



the luminous cloud took 16*7 seconds of time to traverse the slit 

 which was placed parallel to the hour-circle. This indicates a 

 length of at least 130,000 miles, without allowing anything for the 

 foreshortening resulting from the nearness to the sun's limb. 



2. Contortions of Spectral Lines. 



In my first observations of the chromospheric lines by the 

 new method, 1 I was greatly puzzled to account for the occasional 



1 Phil Tram. 1869, p. 425. 



