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C. Hydrographical Section 



by 

 Martin Knudsen and Johan Gehrke. 



The Baltic described by R. Witting. 



The numerous and extensive hydrographical investigations which were 

 carried out during the latter half of the previous century were not so systema- 

 tically arranged as to furnish detailed information regarding the changes 

 which take place in course of time in the ocean currents an in the chemical 

 and physical conditions of the sea. Only for certain parts of the ocean had 

 systematic hydrographie investigations been commenced before the close of the last 

 century; but the variations of the hydrographie elements were known to be so con- 

 siderable that it might be presumed they exercised an important influence on many 

 factors which concern the world of industry. Through the International Investi- 

 gation of the Sea such systematic investigations were extended over the whole 

 of the Baltic, including the Gulf of Finland, the Gulf of Bothnia, the Kattegat 

 and Skagerak, also over the North Sea, the English Channel, the Arctic Ocean, 

 the Norwegian Sea and the North Eastern part of the Atlantic Ocean. By 

 the co-operation of the United States, it is expected that the western part of 

 the Atlantic will now also be included in the area of investigation. 



"The hydrographical researches have for their object — according to the 

 Stockholm and Christiania programme, — the demarcation of the different water- 

 strata according to their geographical distribution, their depths, their tempera- 

 ture, salinity, gas-contents, plankton and currents, in order to discover the 

 fundamental principles that govern the distribution of the marine animals 

 useful to man, and also for weather-forecasts over extended periods in the 

 interests of agriculture. 



As the hydrographical conditions are subject to seasonal changes and 

 as these strongly influence the distribution and life-conditions of marine animals, 

 and also affect the state of the weather and other general meteorological con- 

 ditions, it is desirable that the observations should be made as far as possible 

 simultaneously in the four typical months, February, May, August and Novem- 

 ber, at definite points along the same determined lines." 



The investigations in the four typical months above mentioned have 

 now been carried out very regularly for a number of years, though not without 

 some considerable changes in the localities of investigation. The temperature 

 and salinity have been measured at different depths; as a rule: 0, 5, 10, 20, 

 30, 40, 50, 75, 100, 150, 200, 250, 300, 400, etc. metres down to the bottom. 



