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Observations of solar radiation in the wavelength range from one centimetre to four metres are studied in relation to expected thermal radiation. The data are derived partly from published and partly from unpublished observations. It is found that a relatively constant component can be identified throughout the whole of this wavelength range despite the complication introduced on the longer wavelengths by the presence of highly variable components. This steady component has the properties expected of thermal radiation and it is concluded that it is, in fact, thermal radiation from the ionized gases of the outer atmosphere of the sun. The intensity of radiation is found to increase fairly uniformly from that corresponding to black-body radiation at about 104 �K . at 1.25 cm. to about 106 �K. at 1.5 m. The results yield direct confirmation of the hypothesis that the corona has a kinetic temperature of about a million degrees.