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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 The data are derived partly from published and partly from unpublished observations.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.

Radio-frequency power received from the sun at a wavelength of 50 cm. was measured at three well-separated places during the solar eclipse of November 1, 1948. Abrupt changes in slope on the records of received flux density were interpreted as being the result of the covering and uncovering on the sun of small areas of great radio brightness. These areas were found to be associated with some visible sunspots, with positions previously occupied by sunspots, and with one prominence. The average effective temperature of the bright areas was about 5 X 106 �K., and the are= contributed a total power of roughly one-fifth of that from the entire sun. After the effects of active areas had been taken into account, the remaining four- fifths of the power received from the sun was found to originate from a source larger than the visible disk. About 40 per cent. of the power from this source originated outside the edge of the visible disk. The results were consistent with a theoretical distribution of brightness on the source, which involved limb-brightening. The relative magnitudes of the two circularly-polarized components of the solar radiation showed small differences as the bright areas were eclipsed. No predominance of one component was seen when one hemisphere of the sun was eclipsed ; hence no effects of any general magnetic field on the sun were detected.

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Daily observations of solar radiation at frequencies of 1200 Mc/s., 600 Mc/s., and 200 Mc/s. taken between August 18 and November 30, 1947, are described. The characteristics of the radiation at 200 Mc/s. were in general agreement with those observed by earlier workers. At 600 Mc/s. and 1200 Mc/s., the received intensity was normally steady on any one day but underwent long-period variations over a range of about two to one. The radiation received when the sun was almost free of sunspots corresponded to an effective black-body temperature of 0.5 million �K. at 600 Mc/s. and 0.1 million �K. at 1200 Mc/s. As sunspots appeared, the temperature rose and showed marked oar- relation with sunspot area. It is considered that radiation at these frequencies is entirely thermal in origin and that the long-period variations are at least partly due to the influence of the magnetic field of sunspots on the mechanism of thermal emission from a magneto-ionic medium. On a few occasions, isolated disturbances were observed on 600 Mc/s. and 1200 Mc/s. some of which were associated with chromospheric flares and radio fade-outs. The difficulties arising in the calibration of the apparatus and the steps taken to overcome them are discussed in detail.