ELECTRIC-FURNACE SPECTRA.—An important study of the spectra of calcium, strontium, barium, and magnesium, as produced in the electric furnace at temperatures of 1650°, 2000°, and 2350° C., has been made by Dr. A. S. King at the Mount Wilson laboratory (Astrophys. Journ., vol. xlviii., p. 13). The extension of the observations into the ultra-violet has shown that there is a limit beyond which no lines are emitted at a given temperature, and that the limit advances towards shorter wave-lengths with increase of temperature, as in the case of the continuous spectrum of an incandescent solid. The observations bring out very clearly the characteristics of the various lines, and permit their classification in relation to temperature. The line at λ 6573 is unique among the calcium lines, being faint in the arc and much weaker at high than at low temperatures in the furnace; it is much strengthened in the spectra of sun-spots, and may be used with confidence as a low-temperature indicator. In agreement with previous work, the magnesium line λ 4571 was also found to be a low-temperature line of extreme type. In the case of barium, there is not merely a sharpening of the lines as compared with the arc, but in several cases there is also a resolution of diffuse arc lines into two or three components; the resolved lines possibly occur among the faint absorption lines of the solar spectrum, suggesting that the solar conditions in the region where these lines aire produced involve a moderately high temperature combined with low pressure.
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Our Astronomical Column . Nature 102, 114 (1918). https://doi.org/10.1038/102114a0