The time and space variability of global radiation have been studied using data collected from a mesoscale network of integrating pyranometers established in Wisconsin, for the period December 1966 through June 1967. The data have been normalized so that they are expressed as a percent of the clear day global radiation. The atmospheric transmission coefficient over the State changes from about 0.75 in winter to 0.60 in summer. For a typical month, the standard deviations of the State daily mean varied from a few percent up to 50 percent of the State mean. Mean day-to-day changes of approximately ± 18 percent-radiation were recorded. From use of records for any one site in the State, the global radiation elsewhere in the State can be estimated with an approximate standard error of ±25 percent or less of the clear day radiation on a daily basis, ± 15 percent or less on a 5-day basis, and ± 10 percent or less on a monthly basis. Alternatively, if the network data from the sites surrounding the unknown point can be used for interpolation, the global radiation anywhere in the State can be estimated with an approximate standard error of ± 20 percent or less of the clear day radiation on a daily basis, ± 10 percent or less on a 5-day basis, and ± 6 percent or less on a monthly basis.