248 THE CHEMISTRY OF THE SUN. [CHAP. 



spectrum to the other. Note also that the least refrangible 

 line shown on the diagram is coincident with h in the violet 

 part of the solar spectrum, and that the next line is coincident 

 with the line H, to which reference has been made in the notes 

 I have quoted. Note also the relative intensities of the lines H 

 and K in the sun, in which their intensities are about equal, 

 and in t) Ursse Majoris, in which K is altogether 'absent. These 

 are the first points in this diagram to which attention must be 

 drawn. There will be other points as we proceed further. 



In descending from the general to the particular Dr. 

 Huggins writes : 1 " The spectrum of Vega may be taken con- 

 veniently as typical of the whole class of white stars, so that 

 the distinctive features of the other stars of this class may be 

 regarded as modifications or departures from this common 

 typical form." He then adds : " There are principally three 

 directions in which changes take place ; " one of these consists 

 " in the presence or absence of K, and if present, in its breadth 

 and ntensity relative to H." He goes on, " One of these modi- 

 fications, which possess great suggestiveness, consists of the 

 absence, or difference of character presented by the line K. In 

 all the stars of this class this line is either absent or is very thin 

 as compared with its appearance in the solar spectrum, at the 

 same time that H remains very broad and intense. In the 

 spectrum of Arcturus, a star which belongs to another class 

 which includes our sun, this line K has passed beyond the 

 condition in which it occurs in the solar spectrum, and even 

 exceeds the solar K in breadth and intensity." Arcturus is 

 given in the lower part of the diagram, and it will be seen that 

 there K is relatively thicker than H ; and also that with this 

 relative increase in the thickness of K we get a considerable 

 complexity of spectrum, very much more approaching the solar 

 spectrum in the number of lines that we have to contend with. 

 But at the same time I should point out that the positions of 



1 Phil. Trans. 1880. 



