Eight Offprints on Extreme Ultraviolet Spectroscopy

Millikan received the Nobel Prize in Physics in 1923 for his measurement of the elementary electric charge and his work on the photoelectric effect, but the papers offered here belong to the sustained research program he conducted with Ira Sprague Bowen at the Norman Bridge Laboratory of Physics at Caltech in the years immediately following; a program that produced some of the most precise and significant experimental confirmations of the Bohr atomic model ever obtained. Working in the extreme ultraviolet, a spectral region below 2000 Å then almost entirely unexplored, Millikan and Bowen developed the vacuum spark and grating techniques that made systematic measurement possible, and then applied them to a systematic stripping of successive electrons from light elements, producing hydrogen-like and helium-like ions of carbon, nitrogen, oxygen, fluorine, and the second-row elements through chlorine, whose spectra they measured with sufficient precision to test the predictions of Bohr theory term by term. The sequence of papers offered here runs from the 1921 methodological foundation, establishing the grating and wavelength measurement procedures the program required, through the 1924 primary survey of over 800 lines across twenty elements, to the progressive stripped-atom series analyses of boron, nitrogen, oxygen, fluorine, phosphorus, sulphur, and chlorine, culminating in the confirmation that the Moseley law and the x-ray doublet laws govern the entire optical region of the periodic table; a unification of optical and x-ray atomic structure formalisms that laid the direct observational foundation for Bowen's identification, the following year, of the long-mysterious nebulium lines as forbidden transitions of doubly ionized oxygen and nitrogen, one of the landmark results of twentieth-century astrophysics. The unified understanding of atomic electronic structure Millikan and Bowen established underlies the design of the fluorescent lamps, LED lighting, and display screens in everyday use today. (1) [with] R.A. Sawyer. The Vacuum-Spark Spectra in the Extreme Ultra-Violet of Carbon, Iron, and Nickel; from The Astrophysical Journal, Vol. LIII, No. 2, pp. 150-160. Chicago: The University of Illinois, 1921. Offprint, 8vo (241 x 172mm), pp. 11, [1]. (2) Extreme Ultra-Violet Spectra; from Physical Review, No. 1, pp. 1-34. Ithaca, NY: American Physical Society, 1924. Offprint, 8vo (254 x 178mm), pp. 34. (3) The Series Spectra of the Stripped Boron Atom (BIII); from the Proceedings of the National Academy of Sciences, Vol. 10, No. 5, pp 199-203. Washington, D.C.: National Academy of Sciences, 1924. Offprint, (256 x 175mm), pp. 7, [3]. (4) The Fine Structure of the Nitrogen, Oxygen, and Fluorine Lines in the Extreme Ultra-Violet; from the Philosophical Magazine, vol, xlviii, pp 259-264. London: Taylor & Francis, 1924. Offprint, 8vo (221 x 143mm), pp. 6, plus 1 inserted plate. (5a) The Series Spectra of Two Valence-Electron Atoms of Phosphorus, Sulphur and Chlorin; from Physical Review, Vol. 25, No. 5, pp. 591-599. [and] (5b) The Series Spectra of Three Valence-Electron Atoms of Phosphorus, Sulphur and Chlorin; from Physical Review, Vol. 25, No. 5, pp. 600-605. Ithaca, NY: American Physical Society, 1925. Offprints, 8vo (254 x 178mm), pp. 9, [3]; [1], 6. (6) The Series Spectra of the Stripped Atoms of Phosphorus, Sulphur and Chlorine; from the Physical Review, No. 3, pp. 295-305. Ithaca, NY: American Physical Society, 1925. Offprint, 8vo (255 x 177mm), pp. 11, [1]. (7) Stripped Oxygen, OVI, the PP' Group in OV, and New Aluminum Lines in the Extreme Ultra-Violet; from Physical Review, Vol. 27, No. 2, pp. 144-149. Ithaca, NY: American Physical Society, 1925. Offprint, 8vo (255 x 177mm), pp. [1], 6, [1]. Individual papers fully described HERE.…