[7] SCIENTIFIC EXAMINATION OF THE GERMAN SEAS. 531 



density at a temperature of + 2°, whilst water containing 1£ per cent, 

 salt wonkl reach its greatest density at a temperature of about zero. 

 Water containing 2 per cent, salt would be heaviest at a temperature of 

 — l°.l ; water containing £ per cent, salt freezes at a temperature of 

 about — 0°.G, and 1£ per cent, at — IP, and 2 per cent, at — 1°.2. 



From these figures the following rules may be deduced as regards the 

 water of the Baltic : In the eastern part, where the saltness of the deep 

 water is not very considerable, the temperature will always be above 

 zero, whilst in the western part it may happen that the water with a 

 high degree of saltness and a low temperature of the atmosphere shows 

 a temperature considerably below zero. 



From this quality of the water many phenomena may be explained. 

 If, for instance, the western part of the Baltic in some year, through the 

 influx of a considerable quantity of North Sea water, receives a large 

 number of animal germs from the North Sea, these may develop and 

 flourish for a time, until the unfavorable temperature of a single winter 

 destroys them ; so that such animals cannot be permanently acclima- 

 tized in the Baltic. On the other hand, the above-mentioned quality of 

 the water will explain the circumstance that in the northern and eastern 

 parts of the Baltic, on account of the more favorable temperature of the 

 deep water containing but little salt, the spring spawning season, and 

 the migration of the fish connected with it, begin much earlier than in 

 the western and southern parts. 



B. The North Sea. — The conditions of saltness, temperature, and 

 currents are entirely different from those of tbe Baltic. In the North 

 Sea three parts may be distinguished by their different depth : First, 

 the southern and shallowest part, with a depth of about 35 meters, con- 

 nected with the ocean by the narrow British Channel. To this part 

 belong the Doggerbank and the coast waters of the Schleswig-Holstein 

 and Jutland coasts. Second, the central part, extending northward as 

 far as a line drawn from Peterhead, in Scotland, to Cape Skagen (Jut- 

 land), with a depth of about 100 meters. Third, the northern part, with 

 much greater depths. This last-mentioned part has free communica- 

 tion with the Northern Atlantic. All three parts meet in the Skagerack, 

 and through its waters are connected with the Baltic. 



The North Sea, therefore, freely mingles its waters with those of the 

 Atlantic, but the manner in which this is done differs in its different 

 parts. The mingling of the waters takes place most freely in the northern 

 part, but on account of its connection with the Baltic, the North Sea 

 receives from the former some of its water containing less salt. Several 

 large rivers also tend to decrease its saltness, which is therefore less 

 than that of the Atlantic. 



As regards the saltness of the North Sea, we therefore arrive at the 

 following result: that it is less near the German and Danish coasts 

 where the influence of the Baltic and the rivers is strongest, than in 

 the central and northern parts, although the strong tide of the North 



