Temperature Classification of Gadolinium Lines.

Wave-length measures and temperature classifications are given for 5775 lines of gadolinium from X 2135 to X 10677. The classification, including a segregation of the lines of Gd `and Gd ii, was obtained by comparing the spectra of the carbon-tube furnace at three temperatures with those of the arc and spark. Features of these spectra in successive wave-length regions are described. The absorption furnace was used to obtain low-level lines of Gd I in the ultraviolet to X 2700. At shorter wave lengths, rich spectra of the arc and spark were photographed with a quartz spectrograph, the spark spectrum in this region giving many lines probably belonging to Gd In. These are usually absent from the arc; but some, evidently from low levels, appeared at the arc pole. A comparison with the solar spectrum showed that approximately 60 lines of Gd ii are probably present, though sometimes masked, in the sun. These lines are very strong in the arc spectrum and as a rule have considerable strength in the furnace. About half of them are known from preliminary term analysis to arise from low atomic levels