from the Falkland Islands to Monte Video. 633 



depths in the Atlantic, the higher specific gravity of the surface-water in 

 the Atlantic to the north than to the south of the equator), it is probable 

 that the general circulation is kept up chiefly by an excess of evaporation 

 in the region of the North Atlantic, balancing a corresponding excess 

 of precipitation over evaporation in the water hemisphere. 



Determinations of the specific gravity of the surface-water have been 

 made daily. The mean of these for the section between [Stations 323 and 

 335, the temperature reduced to 15°*56 C, is 1-02620. Of the eighteen 

 days occupied in running the section nine were dry and fine, and on 

 nine rain fell either continuously or in showers. The mean for the nine 

 dry days is 1-02639, and for the nine wet days 1*02591. The maximum 

 surface specific gravity for the section (1-02680) was at Station 323, at 

 the point where probably the Brazil current has most effect on the surface, 

 and the minimum (1*02494) was at Station 326 after a heavy fall of rain. 

 The mean specific gravity of the surface-water at the temperature at 

 which it was procured was 1-02502. 



The specific gravity of the bottom-water was determined at ten 

 stations on the section. Reduced to a temperature of 15°'56 C, the 

 mean was 1-02601 ; the maximum, 1*02650, was at Station 323 at a 

 depth of 1900 fathoms ; and the minimum, 1*02580, was at Station 326 at 

 2775 fathoms. The mean specific gravity of the bottom- water at the 

 depth at which it was procured was 1-02811, showing a difference be- 

 tween the two means of 0*00210, due to difference of temperature aloue. 



It seems from these observations that the differences of surface spe- 

 cific gravity due to differences of salinity along the section are very small, 

 and that, with the exception possibly of station 323, which is abnormal 

 in many respects, they depend mainly on the rainfall. 



The difference between the mean surface specific gravity, the tempe- 

 rature reduced to 15°-56 C, and the mean bottom specific gravity under 

 the same conditions is also very slight ; the actual specific gravity at every 

 point is practically determined by the temperature * and consequently 

 the bands of equal density are, like the bands of equal temperature, 

 virtually continuous with those of the Southern Sea. 



There seems to be little doubt that the specific gravity of the surface- 

 water is considerably higher in the North Atlantic than it is on the 

 present section. On one section between Teneriffe and Sombrero, in 

 1873, Mr. Buchanan found the mean specific gravity at the surface (the 

 temperature reduced to 15°*56 C.) to be nearly 1*02760 ; from the 

 surface it fell rapidly to 1*0260, at a depth of about 600 fathoms, after 

 which it remained nearly the same to the bottom. 



Throughout the whole of this section the trawling-operations have 

 been singularly unsuccessful. Out of ten trials in depths over 1000 

 fathoms only four produced any thing like satisfactory results • and this 

 was the more unaccountable, as the comparatively moderate depths of 

 most of them were such as usually to make the process almost certain. 



