PETTERSSON- INTRODUCTORY X — 



These conditions were already known in the main from eai^lier investigation, before 

 the beginning of the international investigations, and in not a few cases, even in 

 details. 



There remains yet to investigate, if these hydrographical conditions are con- 

 stant from year to year and from one season to another. A solution of this 

 question can only be gained by the method chosen by the international investiga- 

 tions, namely, simultaneous observations at the same oceanic stations 

 at different periods of the year and over a series of years. 



A period of two years is naturally insufficient to settle this qiiestion. If we 

 bring into consideration, however, the results of the preliminary observations made 

 over a period of lo years before the international investigations began, and also 

 the phenomena accompanjang the fluctuations in the circulation of the oceanic 

 waters, which clearly indicate an annual periodicity, the evidence for a flood- 

 period of the Atlantic water during autumn and an ebb-period during spring, 

 Anmui periods gaius greatly in weight. A brief account of these things is given in this Appendix. 

 It is shown: 



that, during the autumn months, there is regularly an inflow of warm water 

 through the deep channels in the most easterly divisions of the North Atlantic 

 water-system, in the Barents Sea as in the Kattegat and Belts, whilst cold currents 

 prevail in the spring; 



that the volume of the Atlantic Stream north-east of Shetland, as also the 

 temperature and salinity of its waters, increases from June to September; 



that the water-level in the Norwegian Sea, the North Sea and the Baltic 

 ' shows an extraordinarily well-marked annual period, the highest water-level on 



our coasts occurring in October^, the lowest in March. 

 Annual periodic Thcsc phcnomeua are related to the fact, determined previously in 1897 



ti.r chcuiTii'o'n ^"^ 1898^, that the real circulation of the Gulf Stream in the region of the trade 

 of the winds, extends only as far as the Azores during spring (March), but in the course 

 of the summer and autumn gradually spreads to the east and north-east. This 

 flow of the warm surface-water of the tropical and subtropical regions continues 

 like a wave through the North Atlantic Ocean, and is felt in the most distant 

 regions of the Atlantic Stream system as a rise in oceanic level and a quickening 

 of the warm under-currents. 

 Correspondence Invcstlgators wlU Tcquirc to pay the greatest attention in the future to the 



fluctuations of study of thc periodic and unperiodic fluctuations in the hydrographical conditions, 

 the Gulf Stream ^g j^ j^^g ^gg^ showu, that SL large group of phenomena undergo corresponding 

 phenomena varlatlous. Thc most important of these are: 



meteorological phenomena (pressure and temperature of the atmosphere), 

 plankton-biological phenomena (occurrence of various plankton-species), 

 migrations of fishes. 



1 Or rather, in October and December with a secondary minimum in November. See diagrams 

 in the Appendix. 



2 See Appendix. 



