Abstract
The following studies arose from experimental work done at the University of Surrey and were aimed at a mathematical formulation of the spectral power distribution of daylight in order that this might be compared with experimental results. There does not appear to be an accepted theoretical curve representing the spectral power distribution at the Earth' s surface at the present time. This seemed to be due to the many factors requiring consideration. The radiation emitted by the sun itself is not a constant although much work has been done to find the 'solar constant'. The earth's motion also affects the received light. The earth's atmosphere with its absorbing and scattering effects is of major importance. This implies a consideration of the scattering of light by small particles, a subject which has been treated at great length by theorists. Theories have also been formulated by experimentalists wishing to find some simple explanation for observed effects. It was necessary therefore to consider the approaches made by other people on this and related fields* A computation of the S. P. D. for direct sunlight was made involving mainly molecular scattering. The various selective absorption effects due to ozone and water vapour caused certain modifications to be made and the results were compared with experimental ones - although direct sunlight measurements have not been made for some years. Following this a study was made of the contribution due to sky scattered light. These vast computations were found to relate considerably with the experimental results even on the greatly simplified model of the atmosphere used. Following the v/ork done on molecular scattering, 'Mie' particles were considered. Owing to the complexity of the problem, the areas of work requiring further study are described in Section 9.