276 



DEPTHS OF THE OCEAN 



seen in the direction of the trade-winds, monsoons, etc. The 

 rivers of Siberia flowing northwards to the Polar Sea, eat into 

 their eastern beaches as an effect of the rotation of the earth. 

 It is the same influence which directs the course of the great 

 ocean-currents. In the North Atlantic the warm currents from 

 the south bend in general to the right, that is to the east, and 

 the cold currents from the north likewise bend to the right, that 

 is to the west ; thus the Gulf Stream flows across to Europe, 

 and the polar currents to Greenland and Labrador. Let us 

 now suppose that we take observations at a couple of stations 

 right across a current. This may be represented roughly by a 

 vertical section, as in Fig. 186 ; we must here imagine that the 

 motion takes place in the direction from the eye through the 

 paper, that the motion is swiftest at the top, and that we are in 

 the northern hemisphere. The rotation imparts to the water 



A ^ 3 A _^ B 



'^ — "^^r 



--^ t 



M 



Fig. 186. 



(represented by the horizontal arrows) the water-layers 

 acquire a slanting position, determined by the difference of 

 velocity and density in the different layers. 



mass a tendency to 

 move to the right ; 

 J there will be a pressure 

 in that direction (indi- 

 cated by the arrows), 

 forcing the layers down 

 at Station B, raising 

 them nearer to the 

 surface at Station A. 



By reason of the deflecting influence of the earth's rotation "FU.'c rr\\Te'c tVio K/->iir>.-1 



i^^r^^^^^^tc^A K„ ^^r.^ i,„,-w„„toi ovK,^,.,e\ ti.a ,.,oto,- io„^.-c ^ ^ib ^ives loe UOUnQ" 



ary-layers a slanting 

 position, as shown by 

 the broken lines, the incline being slight if the surface- 

 current is slow (I.), and strong if the current is rapid 

 (II.). Consequently the light water will go deep at B, the 

 station situated to the right in the current, while at Station A, 

 on the left, the heavy water from below will come nearer to the 

 surface. Wherever there is a strong current in the upper 

 water-layers the following rule will apply in the northern 

 hemisphere : on the right-hand side the water is comparatively 

 light, on the left-hand side comparatively heavy ; the conditions 

 are reversed in the southern hemisphere. There are many 

 examples illustrating this. Off the west coast of Norway the 

 current runs north, and the water to the right, near the coast, is 

 light, while that to the left, in the middle of the Norwegian 

 Sea, is heavy. In the Gulf Stream off the east coast of North 

 America the water is light (warm) on the right side of the 

 current, and cold (heavy) on the left. The southern hemisphere 



