SPECIFIC GRAVITIES AND OCEANIC CIRCULATION. 



319 



the " Challenger " observations and a few made by the " Gazelle " near South America, 

 the Great Southern Ocean is without observations to the south of about lat. 45° S. ; and, 

 as regards this region, no other part of the ocean of equal influence and importance can 

 be named as ruling oceanic circulation. 



The following is a list of the maps * : — 



Map 1. — Mean Annual Specific Gravity of the Surface of the Ocean at Tempera- 

 ture of Observation. 

 Map 2. — Specific Gravity at Observed Temperature at depth of 100 fathoms. 



Map 3. 

 Map 4. 

 Map 5. 

 Map 6. 

 Map 7. 



Do. 

 Do. 

 Do. 

 Do. 

 Do. 



do. 

 do. 

 do. 

 do. 

 do. 



do. 



200 fathoms. 



do. 



300 fathoms. 



do. 



400 fathoms. 



do. 



800 fathoms. 



from depth of 1500 

 fathoms, to the bottom. 



60° 

 39-2 



at depth of 100 fathoms. 



depth of 1500 fathoms to 



Map 8. — Specific Gravity of the Ocean S 



Map 9.— Do. do. 



the bottom. 

 The following table shows the mean specific gravity of the ocean deduced, as above 

 described, from all available observations at the various selected depths ; first, reduced 

 to the uniform temperature of 60° ; and, second, to the observed temperatures of the 

 observations. In calculating these averages, the observations made in " closed areas " 

 were not used ; the observations are, however, entered on the maps. 





At 60°. 



At Observed 





Temperatures. 



Mean specific at surface, 



1-0262 



1-0252 



,, 100 fathoms, 



1-0260 



1-0261 



200 „ 



1-0258 



1-0268 



300 „ 



1-0257 



1-0271 



400 „ 



1-0256 



1-0273 



800 „ 



1-0256 



1-0276 



1500+ „ 



1-0258 



1-0279 



2000+ „ 



1-0258 



1-0280 



Since the first column, which shows the specific gravities reduced to the uniform 

 temperature of 60°, may be regarded as giving the approximate salinities t of the ocean 

 at the different depths, it is seen that the mean salinity of the ocean is the maximum at 

 the surface,— that it steadily diminishes from 1-0262 to T0256 from the surface to 800 



* Maps showing specific gravity at ( S— J were also constructed for depths of 200, 300, 400, and 800 fathoms, 



which are not produced with this Paper, but are referred to in the text. 



t In this paper the term salinity will, for convenience, be employed to represent the specific gravity at 60'. 



