III. The spectrum of scandium, and its relation to solar spectra

The present investigation of the spectrum of scandium was undertaken in connection with the work on the spectra of sunspots and solar prominences with which I have been occupied during the past few years. The presence of scandium in spots and prominences was already well known, but all the desired information with respect to the positions and characteristics of the various lines could not be gathered from published tables. Thalén's observations of the spark spectrum extend from 4247 to 6305, but though his intensities give a useful term of comparison in some cases, the wave-lengths lack the precision necessary for use with modern solar tables, and a considerable part of the red is omitted. A few of the Fraunhofer lines were identified with scandium by Rowland, but, probably for want of suitable material for the production of the scandium spectrum, the comparison was far from complete. More extensive observations of the arc and spark spectra have been made by Exner and Haschek, but, as they extend no further into the visible spectrum than 4744, they scarcely enter the region in which the spectra of spots and prominences are best known. The arc spectrum has been further studied by Lockyer and Baxandall, but here again the region from 5718 to the red end was not included, and but little attempt was made to classify the lines.