In skies with scattered predominantly cumulus cloud cover the global irradiance is very close to that which would occur for a clear sky due to scattering and reflection from the sides of clouds. Several examples of this effect are shown. Limited data on the insolation indicate that the reduction in insolation due to scattered cumulus type clouds cannot be represented adequately by the traditional linear relationship (Angstr¿m, 1924) for cloud covers less than 0.5.