278 



DEPTHS OF THE OCEAN 



60 metres near the coast, the water naturally having become 

 lighter and its tendency to spread westwards having overcome 

 the effect of rotation acting eastwards. When the coast-water 

 is cooled down in autumn it becomes heavier again, is not then 

 so much lighter than the Atlantic water, and has consequently 

 not such a great tendency to spread westwards over the surface 

 as in summer ; it is then forced towards the land (to the right) 

 again by the rotation of the earth. Thus there are in the 

 course of the year periodic lateral movements of the coast- water, 

 which are of importance, for instance, in their effect on the 

 distribution of the young fish. 



The water-layers, then, slant differently according to the 

 strength of the surface-current and the vertical distribution of 

 density. Supposing the surface-current to run sometimes fast 

 and sometimes slow, the layers will respectively be lowered or 

 raised. Again, regarding Fig. 186, the layers that in I. are 

 comparatively deep at Station A, by an increase of the surface- 

 current (as in II.) will rise considerably higher. Thus vertical 

 oscillations are set up as a consequence of the fluctuations of 

 the current ; at a certain fixed point the movement will be like 

 that of a submarine wave. Such vertical oscillations may be 

 imagined to arise in other ways. It is, for instance, highly 

 probable that there exist in the sea standing waves with one or 

 more nodes, similar to the undulations of a violin string. Forel, 

 Chrystal, and others have found these standing waves in 

 lakes, the Japanese have shown them to be present in their 

 seas, and we have several indications of their existence in the 

 Norwegian Sea. 



We cannot dwell any longer upon this question, but will 

 now examine some observations made during the "Michael 

 Sars " Expedition, which show marked vertical oscillations of 

 one kind or another. We made a number of careful measure- 

 ments in the course of twenty-four hours at Station 115, in the 

 eastern part of the Faroe-Shetland Channel, near the slope west 

 of Shetland, in 570 metres of water. Here we anchored a buoy, 

 near which the steamer kept as long as the observations lasted. 

 We made continuous observations of temperature and salinity 

 at the same depths, and were thus able to see whether or not 

 the conditions at a certain depth varied. At the same time 

 similar measurements were made by the Scottish research 

 steamer, the "Gold-Seeker," on the Faroe side of the channel. 

 By these simultaneous investigations we hoped to determine 



