Solar radiation and the duration of sunshine

Records of solar radiation ( Q ) and of duration of sunshine ( n ) on a monthly basis have been collected for 32 stations and regression equations relating the data calculated in the form Q = Q A ( a + bn/N ) where QA is the maximum possible radiation in the absence of an atmosphere, and N is the maximum possible duration of bright sunshine. For five of these stations records for long series of individual months have been examined and for all stations mean monthly values. In the overall regression equation a = 0.23 and b = 0.48.