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Part III. — Fifteenth Annual Report 



may bo greatly increased by northerly winds, and, no doubt, diminished 

 by winds from the opposite quarter. It also appears that the speed is, as 

 a rule, greatest at some distance from the coast of Scotland and the north 

 of England ; that it diminishes quite near the coast, and likewise at a 

 considerable distance, say 50 or CO miles, from it. The rate at which 

 the reversed movement took place in December 1896 and January 1897 

 was much the same as the southerly movement under northerly winds. 

 The meteorological conditions as we have seen were strong southerly and 

 south-easterly winds in December, and north-easterly winds in January. 

 One bottle travelled very rapidly from off Kincardineshire to Orkney, a 

 distance of 135 miles in 16 days, or over 8 miles a day. Further south 

 the rate was about 4 to 6 miles, off the Yorkshire coast (in January with 

 east and north-east winds) it was about 5 miles a day, and between the 

 Dutch coast and Norfolk the same. 



The rate at which the movement of the surface water takes place across 

 the southern part of the North Sea is not so easy to define owing to the 

 uncertainty of the curve taken by the drifter. But from an examination 

 of the cases where some members of the same group or of allied groups 

 were stranded on the English coast and others on the Continent, it would 

 appear that the rate, as a rule, is a little over 2 miles per day. The 

 northerly movement on the eastern side of the North Sea appears to be 

 somewhat faster, especially on the west coast of Norway. The particulars 

 given in the tables shows this to be the case. 



With respect to the depth to which the movement extends, the experi- 

 ments do not give much information, but such as it is it supports the 

 view that the bottom layers, at least in the southern part of the North 

 Sea, move in the same direction. One of the bottom drifters put away 

 on the Dogger Bank in October was found 50 days later 35 miles to the 

 southward, having been brought up in a trawl-net. The temperature 

 observations made by Dr Murray on some of the west coast lochs and by 

 Dr H. E. Mill in the Firth of Clyde, show that a strong wind blowing 

 for a day or two may affect the water clown to very considerable depths ; 

 and it can scarcely be doubted that a fairly constant circulation 

 of the surface water in the North Sea, as described in this paper, is 

 associated with movement in the same direction of the intermediate or 

 bottom layers, at all events where the depth is not great. For the special 

 purpose I had in view in beginning these experiments, namely, the 

 transport of floating fish eggs, it is sufficient if the surface layers — down 

 say to 6 or 7 fathoms — move in the direction indicated. At the same 

 time it appears to me that experiments made with floats of a special and 

 superior kind, designed to remain suspended at different depths, would 

 throw a great deal of light on the movement of the deeper strata. The 

 method of tracing such movements by differences of physical property in 

 the water (salinity and temperature) is comparatively simple where these 

 differences are strongly marked, as in the areas so systematically investi- 

 gated by Professor Pettersson. But in the greater part of the North Sea 

 the differences are comparatively slight, and it will be a matter of 

 difficulty to satisfactorily elucidate the movement of the deeper layers by 

 the method named. It will, at all events, involve a very great number 

 of simultaneous observations over a wide area, and their frequent repeti- 

 tion for a number of years. On the other hand, very large floats, arranged 

 so as to sink very slowly, and connected by silk cord with a small surface 

 float just large enough to buoy the large float at a given depth, would, I 

 th ink, furnish valuable information at comparatively small expense. 



