DENSITY OP SEA- WATER. 25 



The water of enclosed basins into which large rivers 

 flow, as would naturally be expected, is much less salt 

 than that of the open sea. Thus the Baltic and Black 

 seas, both of which receive the drainage of large dis- 

 tricts, are much less salt than the Atlantic Ocean. The 

 Mediterranean, on the contrary, owing to its great 

 depth, and to the few great rivers that flow into it, in 

 proportion to its surface, but perhaps chiefly owing 

 to its southern latitude, favourable to an enormous 

 evaporation, is of greater density than similar parallels 

 of the Atlantic. 



Experiments have been made on samples of sea- water 

 collected in various latitudes, from which it appears 

 that in the open sea the density is greater in the south- 

 ern than in the northern Ocean, whilst at the equator 

 it is nearly intermediate between the two. According 

 to Dr. Marcet the mean specific gravity in the southern 

 ocean, rain-water being 1-00000, is 1-02919, and in the 

 northern, 1-02757, and at the equator 1-02777. The 

 greater amount of land in the northern hemisphere, 

 furnishing a greater influx of fresh water than the at- 

 tenuated southern continents and small islands supply, 

 is perhaps the cause of the observed difference ; and 

 possibly a part may be owing to insufficient experiments. 

 It appears, however, to be well established that the sea 

 always contains a greater proportion of salt where it is 

 deepest and furthest removed from land. The differ- 

 ences observed in the densities of sea-water in different 

 latitudes seem trifling when we compare with the waters 

 of the Ocean, those of the Dead Sea, which, according 

 to Dr. Marcet, have a specific gravity of 1-211. 



