Measurements of iron arc spectra have been made with Pachen-Runge spectrographs and a specially designed photoelectric photometer of the ac ratio type allowing continuous scanning and recording. The temperature and self-absorption present in different parts of the arc, and in the arc under different operating conditions, have been determined, and are presented for use in determining which lines are self-absorbed under given conditions. Some unexplained mechanism in the arc causes deviation from equilibrium values of the intensities of all lines within multiplet 68. This mechanism does not operate in the furnace. Corrected values are given for some ƒ values given in the literature. Additional measurements of the arc are now under way for the calculation of high-excitation ƒ values.
RAY HEFFERLIN, "Behavior of the dc Iron Arc and Its Usefulness in the Determination of ƒ Values," J. Opt. Soc. Am. 49, 680-685 (1959)