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A Search for the Extreme Infra-Red Spectrum of the Sun



THE solar spectrum in the infra-red has been thoroughly investigated throughout the range of wavelengths up to about 11µ. Radiation of longer wavelength is practically completely absorbed, chiefly by the water vapour present in the atmosphere. According to E. von Bahr1, there are reasons to expect, from theoretical considerations, that for wavelengths greater than ca. 400µ, water vapour will be again transparent. In 1914 Rubens and Schwarzschild2 made an attempt at the Astrophysical Observatory at Potsdam to measure the intensity of solar radiation in this region of the spectrum by using the quartz lens method for isolating it, but the intensity proved too small to be detected even by means of the very sensitive instrument they used.

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  1. 1

    E. von Bahr, Verh. Deutsch. Phys. Ges., 710; 1913.

  2. 2

    Rubens und Schwarzschild, Sitzungsberichte Preus.Akad. Wissensch., 702; 1914.

  3. 3

    L. Bergmann, Phys. Z., 32, 688; 1931.

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