On the general Causes of the Ocean-Currents. 37 



Gulf Stream, can therefore by no means have the same tendency to 

 diffuse itself which a fresh-water-stream from a river has. It can there- 

 fore long proceed in the form of a free-flowing ocean-current, and so 

 much the more as its tendency to diffusion is counteracted by its vis 

 inertiae in the same proportion as its velocity is great. It must for this, 

 like fresh-water streame in a lake, jiroduce reaction-streams on both 

 sides as well as beneath itself. Undoubtedly the Gulf-Stream thus 

 contribute greatly towards producing the circumstance, that the Polar- 

 water along the Eastern coast of America penetrates in the form of a 

 superficial current so far to the South, and also the under-current, which 

 proceeds towards the Gulf of Mexico, must in a great measure be pro- 

 duced by it. 



C. THE VARIOUS CAUSES OF THE OCEAN-CURRENTS, WORKING 



IN COMBINATION WITH EACHOTHER ON THE WATERS 



OF THE FREE OCEAN. 



I have in the preceeding pages endeavoured as far as possible to 

 illustrate separately each of the different causes, which give rise to 

 ocean-currents, as well as the various kinds of streams thus originating. 

 But it is self-evident, that the Ocean-currents, such as they in nature 

 present themselves, must, both as regards their force and their course, be 

 determined by many or all of these causes contemporaneousl}', and this 

 the more so, the more extensive the currents are. The original prime- 

 movers, heat, evaporation, rainfall and wind, act in reality with very 

 different average force and in a very different manner in different parts 

 of the current's course, to say nothing of their variation with seasons of 

 the year etc., and of the irregularity of the winds and atmospheri« pres- 

 sure; this obtains especially as regards the oceanic surface-currents, which 

 in their long course are exposed to all the vast differences of meteoro- 

 logical circumstances, which take place on the surface of the earth. 

 Every stream outside the region, in which its driving-force is especially 

 active, must associate itself with some other movement of the ocean, 

 and its course will therefore be materially influenced by the circumstan- 

 ces, which render such a combination with 'other streams possible. The 

 reaction-currents, which it causes, may again give rise to other similar 

 streams, and besides the reaction-streams can sometimes affect both the 

 form and direction of the original current, which is moreover so essen- 

 tially influenced by the contours of the bottom and the shores. 



