In this paper were investigated experimentally the relations between the rate of evaporation from several sorts of soils and the quantity of water hold in the soils. In order, to be free from the complex meteorological influences, we adopted the ratio of the evaporation from soils to that from free water as the representation of the rate of evaporation. Soils used were divided into 4 classes according as the magnitude of their grains; (1) 2.0_??_0.55mm., (2) 0.55_??_0.145mm., (3) 0.145_??_0.075mm., (4)<0.075mm.
Results of experiments, are as follows:-
(1) When every kind of soils holds equal quantity of water near its surface, the rate of evaporation is as the first approximation independent of the magnitude of the soil grains.
(2) But by more precise measurements it was found that:
(a) Soils of large grains (soil (1)) are permeated by water very quickly but cannot suck it up till high place. Therefore the rate of evaporation from them is in the beginning pretty fast, but the surfaces of them dry up soon and evaporation becomes faint before long.
(b) The rate of evaporation from grains of moderate magnitude (soil (2) & (3)) is largest.
(c) With regard to soils of small grains (soil (4)) water penetrates most slowly, but can go up highest by their strong capillary action, so that the rate of evaporation is moderate but does not decrease till the quantity of water in them falls to scanty.
(3) After the sruface of soil dries up the rate of evaporation decreases very quickly and it is nearly inversely proportional to the depth of the dried portion of the soil.
(4) Except the effect of solar radiation most meteorological influences were same on the evaporation from soils and that from free water. As to the effect of solar radiation it was found that the above mentioned ratio is about 20% larger when the sun is shining (during day-time) than when there is no sun-shine (during night). But the effect of the sunshine is not so serious if we consider the daily mean value.
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