Notes on the measurement of natural illumination II. Daylight and skylight at Pretoria; The luminous efficiency of daylight

In this paper is presented an analysis of the natural illumination data assembled at Pretoria (Union of South Africa) during 1955. The results are the first available for the Southern Hemisphere regarding the intensities of the total luminous flux, through a horizontal surface, and also of its component due to skylight. The basic instrumentation and the record standardization procedures have been discussed in a previous contribution. The main results are compared with those derived at Kew (England), Tashkent (U. S. S. R.), Vienna (Austria), and Washington (U. S. A.).