HYDROGRAPHY. j, x 



The deep curve of the 35 - oo isohaline at station 59, can, as shown below, be accounted for 

 by the fact of the upper-layer or ice-water in the East Icelandic Polar Current 

 flowing with a greater velocity at this place than the under-layer. If we make the 

 assumption that currents in the sea, upon the whole, are due to powers acting on the surface, such a 

 ratio as the above mentioned, between the velocity of the under-layer and that of the upper-layer, 

 must inevitably arise in consequence of the exceedingly small internal friction in the water, of which 

 has been spoken on page 125. 



As the southerly flowing surface-layer of the Polar Current meets the Atlantic -water that is 

 moving in an easterly or north-easterly direction, the motion of the surface-layer is stopped in its 

 original direction, and it will try to move towards the bottom and towards the south-east and east. Of these 

 two motions, the one towards the bottom will cease, when the power that is resulting from the kinetic 

 energy in the upper-layer, has become equal to the hydrostatic counteracting power that arises when 

 water of little specific gravity is brought down to large depths. The result will be, however, that a 

 thick layer of ice-water will accumulate at the top on account of the upper-layer coming in contact 

 with the Atlantic-water. 



That the state of matters must be such as represented here, where two currents are meeting 

 one another, or where a current is flowing towards the main land, is a conclusion we have come to 

 by reasoning. We can easily prove the correctness of this assumption by a new experiment, which is 

 performed in the following manner. 



The bottom of a large glass vessel is covered with a liquid which is heavier than water, for 

 inst with a coloured solution of salt or — still better — bisulphide of carbon. The vessel is filled 

 with water, and a stream of water is led into it through a glass-tube, the lower end of which, at a 

 place a little above the under-layer (the liquid on the bottom of the vessel), is bent to give the stream 

 a horizontal direction. 



At the place where the stream meets the side of the glass, a depression will appear in the 

 under-layer, and large enough to be seen, even if the water be flowing very slowly. If we make two 

 similar currents in the vessel, and make them run against one another, a similar depression will arise 

 in the under-layer at the place, where the said currents meet, and this will be the case whether the 

 two currents are flowing straight against one another or their directions are forming an angle less 

 than 180 . In the last case, it will be seen that the two currents unite into one single current, and 

 that in the under-layer — close behind the depression that has been formed in this latter, and in the 

 direction in which the aforesaid united current is flowing — a little elevation will arise, the greatest 

 height of which above the original boundary plane between the liquids, will be smaller than the 

 greatest depth of the depression under the same plane. If the two currents are flowing straight 

 against one another, the depression will adopt the shape of a spherical segment; and in case of the 

 courses of the currents forming an angle with one another, less than 180° the form of the depression 

 will be elongated, and with its greatest length in that direction in which the united currents 

 are flowing. 



As now in section XXI, at station 59, we have found a corresponding depression in the under- 

 layer of the Polar Current, or rather in the 35-00 isohaline, this must of course be indicative of our 



17* 



b 



