THE SPECIFIC GRAVITY OF THE SEA, ETC. 225 



born tide of the ocean. B3^ Fig. 1 the south Pacific also outweighs 

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

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

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

 winter, and spring; those south, during the fall and first winter 

 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 ah, have pointed 

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

 as compared with that contained in sea water north. 



447. Testimony of the hydrometer in favour of the air crossings at 

 the calm belts. — These indications, as far as they go, and this view 

 of the subject, whatever future investigations may show to be its 

 true worth, seem to lean in support of the idea advanced and 

 maintained by facts and arguments in Chapter IV., viz., that the 

 southern seas are the boiler and the northern hemisphere the con- 

 denser 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 sup 

 ply our fountains with rain for the great American lakes, and 

 with rains for the majestic w?ier-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 temperature for temperature, than the waters of cis- 

 equatorial seas. We begin to find that the hydrometer is bearing 

 testimony in support of the evidence adduced in Chapters IV. and 

 VII., to show that when the trade-wdnds meet and rise up in the 

 equatorial calm belt, the atmosphere which came there as south- 

 east trade-winds passes with its vapour over into the northern 

 hemisphere. AVe had not anticipated that this little instrument 

 could throw any light upon this subject ; but if, as it indicates, the 

 sea water of the other hemisphere be Salter and heavier than the 

 sea water of this, what makes it so but evaporation, and what pre- 

 vents cuiTents from restoring its equilibrium but the winds, which 

 are continually sucking up from the brine of trans-equatorial seas 

 and pouring it down as fresh water upon cis-equatorial seas and 



* According to Dr. IMarcet, the southern ocean containa more salt than tho 

 northern in the proportion of 1.02919 to 1.02757. 



Q 



