32 NATURAL SCIENCE. j AN „ 



areas is accordingly liable to become, at least in its lower layers, 

 deficient in oxygen ; and fresh supplies must be obtained by mixture 

 with water from the ocean, if animal life is to remain healthy and 

 abundant. 



Having found that, in the cases referred to, the Swedish fisheries 

 depended on the influx of ocean water, rich in oxygen, at the entrance 

 to the Baltic, Professor Pettersson was naturally anxious that the 

 oceanic streams should be explored beyond Swedish waters, and his 

 representations in this country led the Fishery Board for Scotland to 

 undertake the survey of the region to the north and east of Scotland 

 and round the northern and western borders of the continental 

 plateau. During the whole of August, 1893, H.M.S. "Jackal" was 

 engaged upon this work, and further expeditions were made in 

 November, 1893, an( ^ * n February and May, 1894. The results of 

 the investigations, which were made under the scientific direction of 

 the present writer, are published in the Twelfth Report of the Fishery 

 Board (part iii.). Observations were made by Swedish, German, 

 Danish, and Norwegian vessels simultaneously with those of the 

 "Jackal," in different parts of the North Sea, and a joint report on 

 part of the work is at present in preparation. 



The work of the " Jackal " was unfortunately restricted to a study 

 of the water circulation by means of observations of temperature and 

 salinity. Gas analyses and observations with the'tow net were beyond 

 the resources at our disposal, and it is chiefly by assuming that 

 Professor Pettersson's results hold good, to a greater or less extent, in 

 the open sea, that the circulation of water disclosed by our observa- 

 tions gains marked significance in relation to fisheries. It will be 

 seen, however, that the presumptive evidence in favour of such an 

 assumption is so strong as to make complete investigations of urgent 

 importance. 



Our attention was first directed to the narrow, deep channel 

 between the Faeroe and Shetland groups, which forms a submarine 

 gulf opening from the basin of the Norwegian sea, and is cut off from 

 the Atlantic basin at its southern end by a barrier rising to within 

 300 fathoms of the surface— the Wyville Thomson ridge. It has long 

 been known that the lower strata of this channel consist of water 

 from the Norwegian Sea, recognisable by its low temperatures (31 

 to 33 F.), and also that Atlantic water flows over the ridge, north- 

 wards along the channel, with considerable velocity ; but it seemed 

 necessary to ascertain whether the relations of the Atlantic stream to 

 the underlying cold water varied from year to year. On comparing 

 our observations with those of the " Porcupine" and " Knight Errant " 

 it was found that in 1893 cold water rose nearer to the surface at the 

 southern end of the channel, and warm water descended nearer to the 

 bottom at the northern end than had been the case during the earlier 

 expeditions; a result indicating that the Atlantic stream was stronger 

 than usual, and the " reaction current " or undertow in the cold 



