Abstract
A distillation instrument for the integration of radiation, described by Bellani in 1836, rebuilt in modern materials by Gunn, Kirk and Waterhouse (1945), has a thermal efficiency of over 75 per cent. The improved instrument, mounted at ground level in East Africa, with the condenser underground in constant cool conditions, had a performance that justified manufacture. Comparisons of the manufactured instruments with a Kipp solarimeter gave high linear correlations. These results show the distillation instruments, when so calibrated, to be useful for field estimations of solar radiation. Their cost is low and the daily estimate of total radiation is quickly obtained from a simple burette reading.
Ten years' data for these GunnβBellani integrators are compared with those from 4 ft diameter open water pans. A mounting is described for these pans in shallow revetted pits where their sides are shielded from the sun and are insulated from the soil by an air space. A linear correlation based on 164 tenβday means accounts for 85 per cent of the variability. It appears that in the highβaltitude tropics this radiation integrator by itself can give the basic data for adequate estimate of water use by vegetation, and for control of irrigation.