xvin.] LIMITS OF THE DISCUSSION. 255 



The finest series of observations of this kind that we pos- 

 sessed in 1878, was that collected by Prof. Young near the time 

 of the last maximum of sun-spots, during his stay at Sherman, 

 at a height of 8 ; 000 feet. The result which stares us in the 

 face when we examine the work done by Young is most 

 striking ; but although his observations of the chromospheric 

 lines extend over the whole visible spectrum, the list of lines 

 in the solar spots is limited to the less refrangible region ; 

 the discussion was therefore limited to this region. 



As a basis for this discussion, the lines given in Thaleu's 

 admirable tables were taken, comparing them with those shown 

 in Angstrom's map, and indicating the intensities of the lines 

 which are given in the tables, and which particular line occurs 

 in the map only. A glance, then, shows which line is seen in 

 spots and prominences, and how it is affected. In short we 

 have in one view, for each metallic substance, exactly what 

 happens to the lines of that substance which lines are not 

 touched; those which are visibly affected both in spots and 

 storms, or those recorded in one table and not in the other. 



Taking all the lines included in the discussion, the following 

 statistics will show how they are distributed : 



Total number of lines in Thalen's list and map 



included in the discussion . ...... 345 



Number of lines affected in spots 108 



Number of lines bright in storms (prominences) 122 



Number of lines common to spots and storms . 68 



Number of lines seen in neither spots rior storms 183 



So much for the list of lines as a whole. It is also necessary 

 to show the number of lines assigned to each metal, and those 

 among them which occur in both spots and storms, or only in 

 one or the other. In order that this may be clearly shown the 

 table overleaf is appended. 



