41 'J Sir Norman Lot-kyn ;uid Dr. W. .1. S. I...ckyer. 



Since the year 1879, the selective absorption in spots has been <>!.- 

 served for every spot that was large enough to be spectroscopically 

 examined, the method adopted being as follows : 



The regions of the spectrum investigated lie between F b and b D, 

 and an observation consists in ol>serving the six most widened lines in 

 each of these regions. These lines are then identified on the best solar 

 spectrum maps available and their wave-lengths determined. 



An examination of many years' records of these widened lines has 

 shown that at some periods they are easily traceable to known elements, 

 while at others their origins have not been discovered, so the latter 

 have been classed as " unknown " lines. If we compare these two 

 periods with the sunspot curve as constructed from the measurements 

 of the mean spotted area for each year, it is found that when the 

 spotted area is greatest the widened lines belong to the " unknown " 

 class, while when the spotted area is least they belong to the " known " 

 class. 



The majority of the lines traced to some terrestrial origin belong to 

 iron, but the lines of other elements, such as titanium, nickel, vanadium, 

 scandium, manganese, chromium, cobalt, &c., are also represented in a 

 less degree. 



It is quite likely that some of the " unknown " lines are higher 

 temperature (enhanced) lines of known chemical elements. 



In our laboratories we have means of differentiating between three 

 stages of temperature, namely, the temperature of the flame, the 

 electric arc, and the electric spark of the highest tension. At the 

 lowest temperature, that of the flame, we get a certain set of lines ; a 

 new set is seen as the temperature of the electric arc is reached. At 

 the temperature of the high tension spark we again have man}* new 

 lines, called enhanced lines, added, while many of the arc lines wane in 

 intensity. 



It is found that at sunspot minimum, when the " known " lines are 

 most numerous, the lines are almost invariably those seen most promi- 

 nent in the arc. Passing from the sunspot minimum towards the 

 maximum the " unknown " lines gradually obtain the predominance. 

 As said before, they may be possibly " enhanced lines " that is, lines 

 indicating the action of a much higher temperature on /.//"// sul>- 

 stances. 



Unfortunately the records of enhanced lines at South Kensington, 

 having been obtained from photographs, are chiefly confined to a region 

 of the spectrum not covered by the visual observations of widened 

 lines in sunspot spectra. 



We can only point to the evidence acquired in the case of one metal 

 iron, for which photographs of the enhanced lines, in the green and 

 yellow parts of the spectrum, have been obtained. 



This evidence quite justifies the above suggestion, for the enhanced 



