190 



Sir Norman Lockyer. 



coronal rings; but, as I pointed out in the preliminary report on the 

 observations, at Viziadrug, the arcs and rings are readily distin- 

 guished."^ 



The coronal rings which have been noted on the photographs may 

 be divided into three groups, defined by the position-angles in which 

 they have their greatest brightness. The typical rings are (1) the 

 green ring at X 5303'7 ; (2) a violet ring at A. 3987, near He ; and (3) 

 a blue ring at X 4359*5, near Hy. The structure and brightness of 

 these are shown in the accompanying diagram, but it may be remarked 

 that the fainter members of the three groups do not exhibit the differ- 

 ences of structure so clearly. 



Fia. 1. — Diagram showing the Forms of Three Typical Coronal Eings, and the 

 Positions of the Prominences photographed at the same time. 



The tables which follow show the wave-lengths of the rings which 

 are believed to belong to each of the three groups, and indicate also 

 the average brightness of each ring. 



* * Koy. Soc. Proc./ toI. 64, p. 38. 



