. Fig. 37. Distribution of the anomaly of specific volume. Section off the mouth of Orange river on survey II. The probable direction of water-movement in a vertical plane, deduced from the shape of the isosteres, is also indicated. Positions of stations are shown in Fig. 2. south to north, then the upper water layer would be set in motion. Under the provisions of Ekman's theory of wind drift, and when the thickness of the upper water layer is greater than the depth of frictional resistance, the lower water layer should remain at rest, while the boundary between the two would take up a slope a
. Fig. 37. Distribution of the anomaly of specific volume. Section off the mouth of Orange river on survey II. The probable direction of water-movement in a vertical plane, deduced from the shape of the isosteres, is also indicated. Positions of stations are shown in Fig. 2. south to north, then the upper water layer would be set in motion. Under the provisions of Ekman's theory of wind drift, and when the thickness of the upper water layer is greater than the depth of frictional resistance, the lower water layer should remain at rest, while the boundary between the two would take up a slope across the canal. This slope would rise to the right (east, if one faces in the direction of flow of the surface-current) and thus the underlying heavier water would accumulate on the right-hand side of the current. At the same time a transverse circulation would form in the upper layer, which would depend on the velocity and direction of the wind. The upper layer circulation will form a left-handed screw motion. This would be strongest if the wind blew from the east, and sup- pressed if it blew from the west. Applying these deductions to the South-west African coast we can regard the coast as the canal bank on the east. The west bank is missing, but this does not matter since the wind which is being applied (the south-east trade) is of limited lateral extent. Defant thus deduced a circulation pattern as in his fig. 7. The circulation is complicated by the fact that in the sea there are not two separate well-defined density layers but a general increase of density with depth. The trade wind induces a transverse circulation similar to that in the canal, a horizontal axis being present above which the water 9-2 WOODS HOLE '
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