x.] HYDROGEN EJECTIONS. 131 



lines are bright indicates that the hydrogen which produces 

 them is more intensely heated than usual, and we may assume, 

 therefore, that it comes from below the region of higher tem- 

 perature. We can therefore regard them as enormous ejections, 

 or uprushes of hydrogen, so intensely hot that it radiates 

 much more light than it absorbs. This gradually replaces 

 the absorbing hydrogen, which is driven down again with such 

 a considerable velocity that it commonly suffers a displacement 

 towards the red, while the hot ascending hydrogen undergoes a 

 similar alteration in the direction of the violet. 



In the great width of some of these bright patches we find a 

 parallel phenomenon to the widening of the bases of the chro- 

 mospheric lines and of the lines in spots, and this resemblance 

 naturally leads to the suspicion that all these phenomena may 

 be due to some common cause, that cause, as we have seen in 

 the case of spots and chromospheric lines, being increased 

 pressure or quantity of any particular vapour. 



2. The Simplification of Spectra. 



We have already seen that the spectrum of the chromosphere 

 is far simpler than the general solar spectrum, and that the 

 lower regions of the chromosphere are more complex than the 

 upper reaches. It was next observed that the spectrum of 

 the same substance varied at different distances from the 

 sun. Of the hydrogen lines, F was found to be the longest, 1 

 so that at a certain elevation all the other lines were left 

 behind, and we had a stratum in which hydrogen was repre- 

 sented by a single line only. Further observation disclosed the 

 same fact in the case of magnesium. Its lines & 1 , & 2 , were of 

 nearly equal height, while 5 4 was much shorter. 



To explain these facts Dr. Frankland and I continued our 

 researches on gaseous spectra, and found that under certain 



1 See letter to Mr. Warren De La Rue, Oct. 23rd, 1868, printed in Proc. Roy. 

 Soc. No. 105, 1868. 



K 2 



