INVESTIGATION OF BALTIC SEA AND GERMAN OCEAN. 285 



tained in the water, and also between this and the organic life. The 

 salt determinations are made with the hydrometer kept at the stations. 

 It may be objectionable that the method used is not absolutely exact on 

 account of the miequai composition of the salt in different parts of the 

 sea. It is not necessary, however, to take this into consideration here, 

 stace the currents mainly depend npon the density of the water, which 

 is indicated to a great degree of exactness by the hydrometer. At the 

 stations there is no method sim^Dle enough for a trustworthy determina- 

 tion of the air contained in the water; the air collected from the water 

 on expeditious, however, has been subjected to a chemical analysis. 



The formula adopted by the Commission was well founded, being the 

 result of the observation that an increase of the specific gravity of 0.0001 

 corresponded to an increase of 0.0131 per cent, of salt. The results thus 

 far obtained are the following : 



The specific gravity increases with the depth. In consequence of the 

 German Ocean containing less salt than the Atlantic, and again the 

 Baltic Sea less than the German Ocean, an under-current of heavier 

 water can be traced flowing from west to east, and a lighter upper cur- 

 rent flowing from east to west. This is shown by the current-meter as 

 well as by the densities of the water and the difference in temperature. 

 In very narrow straits, however, as, for instance, in the "Little Belt" 

 and the "Alsensund," the ditferent currents become turbulent and more 

 or less mixed. 



The intensity of the currents is variously changed by climatic influ- 

 ences, of which the wind is the most powerful. Prevailing westerly and 

 southwesterly winds drive heavy currents from the Atlantic into the 

 German Ocean and thence to the Baltic, at the same time retarding the 

 light upper current. Easterly and northeasterly winds act reversely, 

 diminishing the heavier under-current and increasing the lighter cur- 

 rent on the surface. In accordance with the climatic conditions is the 

 fact that the most salty water enters the Baltic in fall and winter, and 

 the least in spring and summer. The amount of salt in the sirring is 

 reduced by the melting of the ice in the north and east; plentiful rains 

 produce a like effect in summer. As the height of the water depends 

 much upon the strength and direction of the wind, the r>ercentage of salt 

 will show a certain relation to the height. This relation, however, is 

 not a simple one. Continuous west winds will not only increase the 

 whole bulk of water in the Baltic, but also produce local differences be- 

 tween the height of the water on the eastern and western coasts, as above 

 mentioned. We have then in the eastern part of the Baltic an increase 

 of the mean level and a decrease of salt, while in the western part, the 

 height of the water decreases and the amount of salt becomes greater. 



Taking into consideration certain climatic relations, especially the wind, 

 and the change of these relations in different years, it is clear that not 

 only every stratum of water of a certain locality wiU show a difference 

 in the amount of salt, but also that there will be deviations in differ- 



