On the general Causes of the Ocean-Currents. 17 



move forward, and also other particles must flow to the place, whence 

 the stream set out; or in other words: the motion of the stream must be 

 propagated to other localities than that, where the forces, that originally 

 produced it, operate. But a stream may throughout its whole course by 

 mechanical action give rise to secondary motions in the surrounding- 

 water, and it is to streams (if this kind that wo shall now for a while 

 turn our attention. 



Wherever a stream flows in contact with a tpiiet or more quiescent 

 mass of water, the molecules of the former will by friction communicate 

 a part of their motion to those of the latter. The quantity of the flowing- 

 water is thus increased, while the velocity is diminished. Without at 

 first occupying ourselves with the question, in what relation the velocity 

 of the thus increasing stream stands to its mass, we may nevertheless 

 conclude, that a diminution of the mass in the surrounding- water must take 

 place at every spot, where the stream communicates its motion to the 

 particles of that water, and carries them away in its own direction. This 

 diminution, like that caused by evaporation or by wind, must produce a 

 change of level, whereby the equilibrium is disturbed down to the bottom, 

 and this disturbance again must produce an afflux of water to the place 

 in (piestion, whereby the water carried oft" is replaced. The said dimi- 

 nution cannot evidently be compensated by the original stream itself, for 

 this would require an increase of the streams velocity, in consequence 

 whereof the quantity of water-particles, carried of by the stream, would 

 even be increased; or in other words, the level would be continually 

 sinking in the part of the stream behind that, where the new molecules 

 are set in motion. To suppose again that the void can be filled up by 

 new molecules of the increased stream, woidd be evidently tantamount 

 to supposing that the motion, which had caused the void, had not taken 

 place. On the other hand an afflux from the more quiescent water, out- 

 side the stream itself, both can and must take place, which motion will 

 be similar to that generally brought about b_v the disturbance to an un- 

 limited depth of hj-drostatic equilibrium. 



The velocity of the increased stream i*' another point of importance 

 for the question. If we designate with W the velocity and with m the mass 

 of water of the original stream, which passes by in a unit of time, and 

 with V and 31 velocity and mass of a following- part, where it has taken 

 up into itself new molecules, supposing the velocity to decrease in the 



Nova Acta Reg. Soc. Sc. Ups. Ser. III. 3 



