AND ITS RELATION TO SOLAR SPECTRA. < 59 



"Apart from the interference of other lines, the intensities correspond closely with those 

 of the terrestrial spectrum. 



This result is in good accordance with the work of LOCKYEK on eclipse spectra, 

 which has shown that enhanced lines in general are specially developed in the 

 chromosphere. , My own observations* have further shown that enhanced lines 

 appear as " high-level " lines in the chromosphere, while arc lines are mostly restricted 

 to the region near the photosphere. In the case of scandium, the enhanced line 5527 

 is certainly a high-level line, and 5240, according to my recent observations, is of the 

 same type. That the same is true of other enhanced lines in the blue, notably 4247, 

 is indicated by the lengths of the corresponding arcs in photographs of eclipses taken 

 with the prismatic camera. In YOUNG'S catalogue high frequency may often be taken 

 as an indication of high level, since lines of the latter class are brought into view by 

 comparatively feeble disturbances, and the lines 5031, 5G58, and 5G84 may be regarded 

 as of the high-level class from this evidence. 



It may therefore be concluded that scandium exists in the higher reaches of the 

 chromosphere, under conditions specially favourable to the production of enhanced 

 lines, while there is no evidence of its presence at lower levels except that afforded by 

 the feebly developed arc lines in the Fraunhofer spectrum. 



Summary of Results. 



1. The arc spectrum of scandium consists of two distinct sets of lines, which behave 

 very differently in solar spectra. Each set includes both strong and faint lines. 



2. Lines belonging to one set correspond with the enhanced lines of other elements, 

 notwithstanding that they appear strongly in the ordinary arc spectrum. 



(ft) These lines are very feeble or missing from the arc-flame spectrum, and are 

 strengthened in passing to the arc, the arc in hydrogen, or the spark. 



(b) They occur as relatively strong lines in the Fraunhofer spectrum. 



(c) They are weakened in the sun-spot spectrum. 



(d) They occur as high-level lines in the chromosphere. 



3. The remaining lines show a great contrast when compared with the first group. 



(a) They are relatively strong lines in the arc-flame. 



(&) They are very feebly represented in the Fraunhofer spectrum. 



(c) The stronger lines are prominent in sun-spot spectra. 



(d) They have not been recorded in the spectrum of the chromosphere. 



4. The special development of the enhanced lines in the Fraunhofer spectrum, 

 together with their presence in the upper chromosphere, indicates that the greater 



* ' Monthly Not. R.A.S.,' vol. 66, p. 362 (1906). 

 I 2 



