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Published online by Cambridge University Press: 25 April 2016
The origin of the high degree of linear or circular polarization frequently observed in the 18 cm radiation of hydroxyl molecules has proved to be a formidable theoretical problem for which no adequate solution appears to exist at present. It is usually supposed that the radiation arises from some form of maser action and so it is possible that the polarization may arise from an interaction of radiation with the various frequencies and polarizations, through the coupling agency of the populations of the energy levels of the molecule.