Physics and Chemistry. 273 



Ann. xxj 73). The Atlantic system of rivers drains by far the greater 

 portion of the continents and has the same position in latitude ; thus 

 " ; greater than in any other part 



the evapoi 

 of the Oc( 



The Atlantic is divided into five regions, viz i 



Reg. Ill, Arctic region, mean of 16 analyses, -f 156 

 " II, North temperate, " " 24 " -j-lGs 

 I, " tropical, " "14 " -\-2l1 

 X, South " " " 6 " -t-24Y 



" XI, " temperate, " « 6 " +104 

 " XVI, Antarctic Ocean, « " 1 '•■ -544 



Thus the tropical part of the Atlantic is the saltest, and the amount 

 of salt regularly decreases toward the poles ; yet the northern Atlantic 

 is more salt than the southern (an influence of the Gulf Stream).* 



The first great circulation of terrestrial water is represented in these 

 numbers : only a part of the water evaporated between the tropics di- 

 rectly returns to land and sea in form of rain ; another part is carried 

 to the polar regions, here condensed to snow and ice, returning toward 

 the equatorial belt either in great fresh-water currents or in veritable 

 ice-streams, thus re-establishing the equilibrium. 



(2.) Saitness of Oceanic Currents.— The equatorial current has in the 

 % of Benin a saitness of +38; crossing the equator between long. 

 25° and 35° W., this successively increases by evaporation to +173 and 

 4-208. On the same longitude, at lat. 15° S. the saitness is +3 Is, 

 lat. 12-14'^ N, +2l9 and 194; thus the current is less salt than the 

 ocean near it— indicating the freshening influence of the great rivers of 

 Guinea. Near St. Thomas, West Indies, the saitness is only +17— the 

 enormous amount of fresh water from the Amazon and Orinoco reach- 

 ing thus far— since a few degrees north of the current the saitness of 

 the ocean is again +27. At the Bermuda Islands 

 --the evaporation in the Gulf has been counter^-'- 

 the Mississippi. Northward the Gulf stream i 

 238 ; but at lat. 43° 26', long. 44" 19' W. where the St. Lawrence e 

 ties, the saitness abruptly sinks to +l5 (a diminution of 2| iuuu- 

 sandths!). From this minimum it slowly rises to +189 and at last 

 diminishes again iti the higher latitudes. These regular oscillations m 

 <^e saitness of the great Atlantic current show tlie fresh water supply 

 '^Jainedfrom the gredt African and American rivers, ""'j^^^f^f^^^' F£ 

 ih^ current It^parHcuLl dwIcFion. Forchhammer represents these num- 

 t»ers by a proportional breadth of the current (dotted for negative values) 

 --thus showing at a glance this most important law. . , „ ^ , 



. The mean saitness 5f the polar current of Baffin's Bay is +82, but 

 iiicreasing towards north. 



Latitudes, 5%" 5Z' 64° 69° 



Saitness, +158 +103 +4 



stowing how the water of the Arctic sea is freshened by the northern 

 'ivers, Greenland glaciers, and the Hudson's Bay rivers. 



I*rt of th^AtlanS, oppositJthe dry'coLts'of Sahara, whence hot, dry wi 

 tto fresh water may be obtained, lat. 24° 13' N., long. 23° U' W. 



r.— SeCOXD SEHIMf 



XSXIV, No. 101.— Sept., 1863. 



