SPECIFIC GRAVITIES AND OCEANIC CIRCULATION. 



531 



Hence the mean salinity of the North and the South Atlantic is the same, and these 

 two oceans have a higher salinity than any of the other oceans. The Indian Ocean 

 comes next with 1*0262 ; then the South Pacific with 1 , 0261 ; and the North Pacific is 

 much lower than any other ocean, occasioned, as above suggested, by the heavy 

 rainfall in its western division and the wide area over which these specifically light 

 waters are carried by the prevailing winds. The mean salinity of the surface of 

 all the oceans combined is 1 , 0262. 



Since observations are greatly more numerous at 100 fathoms depth than at any 

 other depth, a more detailed account will be given of the salinities, Map 8, and specific 

 gravities, Map 2, at this depth. The figures on these maps show, but in a less pro- 

 nounced manner than at the surface, the essential differences between the geographical 

 distribution of specific gravities and salinities. Since, with increasing depth, temperature 



Fig. 1.— Temperature of the Atlantic at depth of 600 fathoms. 



continues to approximate closer and closer to equality in all parts of the ocean, it follows 

 that the specific gravities and salinities, as represented by departures from their respec- 

 tive averages, also tend to equality as shown by Maps 7 and 9. 



As regards the salinities at 100 fathoms, Map 8, the areas above and below the 

 general average, and the similar areas of the surface of the ocean substantially coincide. 

 Leaving out of view the North Pacific, whose salinity is exceptionally low, the ocean 

 lying between lat. 40° N. and lat. 40° S. has a salinity exceeding the average ; whereas 

 all other parts of the ocean fall short of the average. The Red Sea and the Mediter- 

 ranean have been already dealt with. 



The Atlantic stands out as the ocean characterised by the highest salinities. This 

 holds good particularly in those parts towards and over which the prevailing winds 

 blow. The low salinity on the eastern part of the South Atlantic, whence the trade 



