Solar radiation measurements in the region from 50 micrometers to one millimeter wavelength were conducted during April, 1965, at Kitt Peak National Observatory near Tucson, Arizona. The manner in which these tests were conducted and the results obtained are described in this paper. It was found that when the total precipitable water-vapor content in the atmospheric path from the sun to the telescope was less than about 0.2 centimeter, the solar radiation was observable at several atmospheric windows having wavelengths greater than 300 µ, with the maximum transmission through the window at 345 µ, wavelength estimated to be on the order of two percent. The spectral data obtained under a variety of total water-vapor columns and path lengths are presented in a series of charts contained within this paper.