5(5 MR. A. FOWLER ON THE SPECTRUM OF SCANDIUM, 



lines, both of scandium and iron, occur in the upper chromosphere (see p. 59), it seems 

 to follow that the greater part of the scandium absorption is produced at a relatively 

 hifh level, where the conditions are such as to bring about the comparative isolation 

 of the enhanced lines. The same is probably true of strontium and barium, where the 

 enhanced lines are strong in the Fraunhofer spectrum, and in the upper chromosphere, 

 while the arc lines are feeble or missing. 



It results that Avhile in the case of some elements solar identifications are to be 

 based chiefly 011 arc lines, in others it is the enhanced lines which may be expected to 

 show the most important coincidences. 



Comparixini with the Simspot Spectrum. 



The previous work of HALE"" and myself t has shown that in the spectra of sunspots 

 there is a general tendency for Fraunhofer lines of enhanced metallic origins to be 

 weakened, while flame lines are specially selected for strengthening. This difference 

 of behaviour is well marked in the case of scandium, as will be seen from Tables IV. 

 and V. The data for spots given under " HALE" are derived from the Mount Wilson 

 preliminary catalogue, of spot lines, extending from 5009 to 5853,| and from the 

 recent more detailed list covering the region 4000 to 4500. The intensities under 

 my own name have been derived either from the Mount Wilson photographic map of 

 the spot spectrum (4GOO to 7200), or from photographs in the region 3930 to 5800 

 which have been kindly placed at my disposal by Mr. MiCHlE SMITH, Director of the 

 Kodaikanal Observatory, India. Several lines which have escaped record in the 

 published catalogues of spot lines are clearly seen to be affected when special attention 

 is directed to them. Some of the lines have also been noted in my own visual 

 observations, and in those of CoilTlK and MlTOHELL. 



lleferring first to the enhanced lines of scandium (Table V.), it is evident that in 

 the less refrangible parts of the spectrum there is a distinct weakening of these lines 

 in spots, while in the region more refrangible than F the evidence as to actual 

 weakening is very slight. For the most part there is no definite change of intensity 

 of the enhanced lines in the blue end of the spectrum, but it has already been 

 recognised that, on account of photospheric light diffused over the spot, or from still 

 undetermined causes, the sunspot spectrum as a whole tends to lose its characteristic 

 features in the blue and violet, in so far as it has yet been photographically registered. II 

 If the difference in the two parts of the spectrum be real, and independent of the 

 conditions of observation, it may be that the "phenomenon is related to that found in 



* ' Astrophys. Jour.,' vol. 24, p. 202 (1906). 



t ' Trans. Int. Sol. Union,' vol. 1, p. 228 (1906). 



| ' Astrophys. Jour.,' vol. 23, p. 15 (1906). 



' Astrophys. Jour.,' vol. 27, p. 45 (1908). 



|| HALE, ' Astrophys. Jour.,' vol. 25, p. 90 (1907). 



