58 MR. A. FOWLER ON THE SPECTRUM OF SCANDIUM, 



comparison with terrestrial spectra: namely, eclipse photographs, and visual obser- 

 vations made at ordinary times, the former being especially valuable for the blue end, 

 and the latter for the less refrangible parts of the spectrum. Eclipse records are now 

 numerous, but completely satisfactory discussions of the lines are not yet possible, 

 owing to discordances in the wave-lengths given by different observers, and the 

 inadequate resolving powers of most of the instruments which have been employed. 

 Nevertheless, since identifications usually depend upon apparent agreement in wave- 

 lengths and intensities of several lines of the same substance, there is reasonable 

 certainty as to the origins of many of the lines. 



YOUNG'S well-known catalogue of chromospheric lines,* observed without eclipse, 

 remains the principal source of information with regard to the less refrangible parts of 

 the spectrum, though supplementary observations have been made by MITCHELL,! 

 NAGARAJA,^ and myself. Further determinations of the wave-lengths and characters 

 of many of the chromospheric lines, however, are urgently needed. YOUNG'S obser- 

 vations were mostly made before liowLANo's photographic map of the solar spectrum 

 became available, and his subsequent revision was only fragmentary, so that many of 

 the wave-lengths cannot be regarded as final. A more complete distinction between 

 " high-level" and " low-level" lines is also greatly to be desired. 



A few lines of scandium have been noted by LOCKYER and others in eclipse spectra, 

 and a greater number by DYSON, j| who pointed out that the intensities agree well 

 with those of the spark. Making due allowance for the lack of highly precise data, 

 the general result of the more complete comparison which is now possible is to show 

 that it is only the enhanced lines of this element which can be regarded as 

 contributing to the chromospheric spectrum. Of the four strongest lines of the arc- 

 flame spectrum, G305'88, 5G72D5, 4023'83, and 4020'55, there is no suggestion of a 

 chromospheric coincidence except in the case of the last ; DYSON gives a line at 

 4020 '50 in his eclipse list, but, as there is no indication of the adjacent similar line at 

 4023, the coincidence may be considered accidental, especially as the wave-length 

 given by EVERSHED^! is 4020 '3. 



A complete list of the enhanced lines of scandium is given in Table V., which also 

 shows the corresponding solar and chromospheric lines. For the region more 

 refrangible than 4670, the latter have been taken from DYSON'S tables, Avhile the less 

 refrangible lines, with their " frequencies" and brightnesses, are from YOUNG'S 

 catalogue. All the brighter enhanced lines are obviously present in the chromo- 

 sphere, but the fainter ones, as might be expected, have not yet been recorded. 



* SCHEINEK'S ' Astronomical Speetroscopy,' FROST'S translation, pp. 184 and 423. 



t ' Astrophys. Jour.,' vol. 24, p. 82 (1906). 



t ' Astrophys. Jour.,' vol. 26, p. 150 (1907). 



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



|| ' Phil. Trans.,' A, vol. 206, p. 440 (1906). 



H ' Phil. Trans.,' A, vol. 201, p. 487 (1903). 



