HYDROGRAPHY. 



IO7 



The ascent of the isotherms and the isohalines towards the shore, cannot therefore, in so far 

 as regards the deeper strata, be the direct consequence of the influence of the water from the rivers. 

 It must be accounted for in this way, that the water in the depth has a component of motion in a 

 northerly direction, which is larger than the corresponding component in the case of the surface strata. 

 Such a state can arise thereby, that the water coming from the rivers in Iceland, produces a current 

 of reaction in the depth against its own direction. If we only take into consideration the relative 

 motion of the water in a northerly and southerly direction, the case will be, that in the depth we 

 shall have a current running north towards the coast, while at the surface there will 

 be a current setting south, a state of matters which will give rise to an eddy with an 

 approximatively horizontal axis, so that the water at the bottom gets an upgoing motion near the 

 coast, while the water at some distance from this latter has a downward going motion. Even if in 

 reality no eddy is formed, the forces that act on the single particles of water are of such a nature, 

 that they would cause an eddy to appear, if the specific gravity of the water was the same in all 

 depths, that is to say, that the particles of water near the bottom at the coast are acted upon by a 

 power working upwards, while the particles of water, at some distance from the land, are subject to 

 the action of a power that is working downwards. These powers manifest themselves by a rising of 

 isotherms and isohalines along the bottom towards the coast, and by a descent farther away from this 

 latter. Owing to the vague determination of the position of the isohalines, it will in this case be ad- 

 visable only to take the isotherms into consideration. We see that there is really such a descent in 

 these latter in the sections II, III, IV, V. 



It is a matter of course that a correct representation of the currents in the sea, cannot be 

 given by an experiment in a laboratory, but as it seems to me that the following is a good elucidation 

 of the subject, I shall say a few words about it. 

 A vessel 14 centimetres long and o - 8 centimetres 

 broad, with parallel glass-plates as lateral sur- 

 faces, is filled with water. By means of a pi- 

 pette, a strong, and in consequence of this heavy 

 solution of chloride of calcium, is brought down 

 to the bottom in so large a quantity, that this 

 solution, which is coloured by permanganate 

 of potassium, reaches to about 1 centimeter 

 from the upper edge of the vessel. The boundary- 

 plane between the solution and the pure water 

 will remain distinctly visible for a long time, so 

 that a little deviation from the horizontal plan 

 can be seen immediately. A slow and uniform 



flush of water is through the tube A (see the illustration) made to run along the surface. It will be 

 seen then that the boundary-plane adopts the shape of the curve B, which is drawn on the figure, 

 when the motion in the vessel has become stationary. The curve appears in this shape, as in 1 mi- 

 nute 5-4 cubic centimetres of water have run out of the tube, the eduction orifice of which has a diameter 



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