oa South African Medical Journal - Some aspects on the effect of solar radiation and other factors of fhe climatic environment on human beings (Continued) : B : solar radiation in South Africa and Europe and its effect on the human body (1,039)



The factors determining the radiation climate in South Africa and Europe can be summarized as follows: - 1. The angle of incidence of the solar rays during a large part of the day is greater in South Africa than in Europe. This results in a steeper incidence of the rays on a horizontal surface and also on sunbathers lying flat on the ground. 2. Length of the days. In South Africa the days are, on an average, two hours shorter in summer and two hours longer in winter. Consequently the hours with comparatively great intensities are, on clear days, in summer less numerous in South Africa than in Europe. The reverse is the case during winter. 3. The cloudiness is relatively small in South Africa and hours with bright sunshine much more numerous than in Europe. 4. The total amount of solar radiation obtained is greater, particularly during winter, in South Africa than in Europe. The greater number of hours with bright sunshine is the predominant cause of this, although the altitude of the sun also plays a role. 5. The intensity of the direct solar radiation at noon on clear days is practically equal at Davos and Johannesburg, bu t lower at Kew than at Durban. The altitude of the sun is, however, responsible for a difference in the effect on the human body during exposure in a lying position. 6. During a sunbath of 10 minutes' duration in summer, an adult person would be exposed to comparatively great intensities in Europe as well as in South Africa. In winter, however, the irradiation in Europe would be much less.


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