The value of the solar constant indicated by 30 years of observation by the Smithsonian Institution is revised in the light of the scale correction announced in 1952 and new solar spectral-irradiance data for outside the earth's atmosphere obtained by the Naval Research Laboratory. The ultraviolet and infrared corrections applied by the Smithsonian Institution in solar-constant determinations are examined and reevaluated. The accuracy of their measurement of total irradiance in the spectral range 0.346 to 2.4 microns is in general supported, only a 0.3 per cent increase being indicated owing to revision of a correction applied in reaching their value. The corrections for radiation outside this spectral range are found to be larger than those used by the Smithsonian Institution. The new value of the solar constant is 2.00 calories per square centimeter per minute, with a probable error of two percent, and the solar-illuminance constant is 13.67 lumens per square centimeter (12,700 foot-candles).

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