The vacuum wavelengths of 27 lines of Hg198 and 6 lines of Kr86 have been measured relative to the international standard of length, the Kr86 line at 6057.80211 Å, by photographic Fabry–Perot interferometry. These measurements were made with Hg198 electrodeless lamps containing argon at pressures of , 3, and 10 mm Hg and a Kr86 hot-cathode lamp operated according to the conditions prescribed by the International Conference on Weights and Measures in 1960. Energy-level values have been derived from the wavelengths of each of the Hg198 sources, and on the basis of these values, the energy level and wavelength shifts per unit pressure of argon have been calculated. The suitability of the Hg198 electrodeless lamp as a source of wavelength standards for interferometric measurement of length and wavelength is discussed.
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