36 F. L. Ekman, 



If an ocean-stream move forward in a mass of water, either at 

 rest or having a slower motion in the same or any other direction, the 

 mass of the former will during its progress continually increase, while 

 that of the latter diminishes; for the more rapid stream will communicate 

 its motion to the water-molecules of the latter. Hence arises the sharp de- 

 finition of the streams, apparent even in the free ocean, which has so 

 often been an object of wonder to travellers. The mixture of the waters 

 of the different streams, which is formed at the place of contact, is in 

 fact carried off in the more rapid stream, in which is it absorbed. In 

 most cases the more rapid stream is a surface-current of lighter water. 

 The water of it, that mixes with the surrounding heavier water, does not 

 therefore continue to run as an intermediate stratum between the streams, 

 but it sinks into the lighter stream, though not beneath it, as being- 

 lighter than the slower stream's water. The sinking mixture is replaced 

 by other water, flowing from the middle towards the sides of the stream, 

 and thus arises within the constant^ advancing stream an inner circula- 

 tion in the place of its section. By this inner circulation an on the 

 whole perpetual, though ever less and less marked difference is main- 

 tained between this stream and the more slowly flowing heavier water, 

 the properties of which remain almost unchanged; for, though it parts 

 with some of its water, it receives none. This circulation, which is also 

 reinforced by the difference of pressure between the two streams, is 

 also probably the cause of the tendency, which free ocean-currents (e. 

 g. the Gulfstreem) display, to split longitudinally into new streams. 



In some places, as e. g. along the Swedish coast of the Ska- 

 gerack, it happens, that of two streams, running beside eachother, that 

 with the heavier water is the more rapid. In these cases the circula- 

 tion just described takes another course, in that the mixture of lighter 

 water, which the heavier current continually acquires, flows upward. It 

 then happens, that for a moderate wind the undulations will be more 

 feeble on those parts of the heavier stream, which are contiguous to the 

 lighter water; for new masses of water, hitherto unaffected by the wind, 

 are there constantly rising to the surface. 



Surface-currents of lighter water have a tendency to diffuse them- 

 selves, partly in consequence of the new water that they acquire, as 

 also in consequence of the greater lateral pressure due to their higher 

 level; this will be the greater the lighter the water is in comparison 

 with that around. An ocean-current of warm but salt water, such as the 



