16 " F. L. Ekman,. 



form a closed whirl-pool. Local circumstances must determine, wich of 

 these motions, the under-current or the lateral eddies, form the chief 

 channel, whereby the artificial water carried off by the wind finds its 

 way back. 



In lakes, where in consequence of their small extent the wind 

 covers almost the whole surface, the vertical circulation, which is so in- 

 dispensable a condition for the freshness of the water, is in a very 

 great measure maintained by the wind'). In the ocean on the contrary, 

 the surface of which can only be partially covered by any particular 

 wind, the superficial stream produced must also be accompanied by side- 

 eddies. The difterence of level between two opposite coasts, which a 

 wind of great extent can there cause, may, in consequence of the great 

 length of the surface, on which the wind acts, be considerable, even 

 though the force of the wind be but moderate: how vast the differences 

 of level, which violent winds can produce, is sufficiently evidenced by 

 the so-called storm-floods. That the trade-winds, which collect the water 

 towards the equator from N. E. and S. E. and drive it towards the 

 east, are the cause of the so-called equatorial currents, is now j^erhaps 

 doubted Ijy nobod}^ It seams also clear that an elevation of level, 

 caused by these winds on the eastern coasts of the continents, has a 

 material effect in the formation of the Gulf-stream, and that this in con- 

 junction with a corresponding sinking on the western coasts causes the 

 whirling motions with sargassos in their centre, which in the northern 

 hemisphere in consequence of the form of the continents are so clearly 

 developed. 



V:o Streams caused hij (he mechanical effect of a mass of ?vater, 



alreadi/ in motion, on the neighbouring particles of nater : 



Reaction Streams. 



If a stream is produced by any cause in the ocean, it must of 

 course set in motion the particles before it, in order to be able to 



') The folfowiDg example from the lake Avstaviken at Stockholm here deser- 

 ves perliaps to be noticed. The lake has an arrow communication with the «Mälaren», 

 the water of which contains a little salt. As long as Arstaviken is frozen, the deeper 

 water also there is found to be slightly Salter, e. g. 0.0.5 p. m. chlornatrium at the 

 .surface, 0.08 at 3'/.^ fathoms depth. But as soon as the ice is melted and the wind 

 can fveely operate on the surface, the saltness of all depths is uniform, and conti- 

 nues so all the summer. The undulation in that little lake is of course very iuconsi- 

 deiable, so that no other cause can be assigned for the fact mentioned, then the ge- 

 neral circulation caused by the winds. 



