216 PHYSICAL GEOGRAPHY OF THE SEA, AKD ITS aiETEOROLOGY, 



than the waters of the north Atlantic ; but this difference may be' 

 more apparent than real ; for the observations were made in the 

 northern smnmer on this side, and in the southern fall and winter 

 on the other side of the equator. Had we a series of observations 

 the converse of this, viz., winter in the north Atlantic, summer in 

 the south, perhaps the latter would then appear to be specifically 

 the lighter ; at any rate, the mean summer temperature of each 

 Atlantic, north and south, is higher than its mean mnter tempera- 

 ture, and consequently the specific gra\dty of the waters of each 

 must change with the seasons. A diagram — had we the data foi- 

 such a one — to show these changes, would be very instructive ; it 

 would show beautifully, by its marks, the ebb and flow of this new- 

 born tide of the ocean. By Fig. 1 the south Pacific also outweighs 

 the north in specific gravity ; but here again the true difference, 

 whatever it be, is somewhat masked by the time of year when the 

 observations were made. Those north were made dming the fall,, 

 winter, and spring ; those south, dm'ing the fall and fii'st v^inter 

 months of that hemisphere. Nevertheless, the weight of the 

 observations presented on Plate X. does, as far as they go, indicate- 

 that the seas of the southern do outweigh in specific gravity the 

 seas of the northern hemisphere in the proportion of 1.0272 to- 

 1.0262 of specific gravity.* Daubeny, Dove, et al., have pointed 

 out an excess of salt contained in sea water south of the equator, as- 

 compared mth that contained in sea water north. 



447. These indications, as far as they go, and this view of the 

 restimonyofthe subjcct, whatcver future investigations may show to 

 ofTheSfcros^'sing's"' ^^ i^s truo worth, scom to lean in support of the idea 

 at the calm belts, advauccd and maintained by facts and arguments in 

 Chapter lY., -vdz., that the southern seas are the boiler and the- 

 northern hemisphere the condenser for the grand atmospherical 

 engine, which sucks up vapour from the south to feed the northern 

 hemisphere with rains. If it be true, — and Dove also thinks it is 

 — that the clouds which supply oiu: fountains with rains for the 

 great American lakes, and vdth. rains for the majestic water-courses 

 of Europe and Asia, Northern Africa and America, are replenished 

 from seas beyond the equator, then the waters of the ocean south 

 should be a little Salter, and therefore specifically a little heavier, 

 parallel for parallel, and temperatm^e for temperatm'e, than the 

 waters of cis-equatorial seas. We begin to find that the hydrometer 



* According to Dr. Marcet, tlie southern ocean contains more salt than the 

 northern in the proportion of 1 .02919 to 1 .02757. 



