CURRENTS OF THE SEA. 173 



371. The faima and the flora of the sea are as much the crea- 

 The fauna and flora tiu'es of cHmate (§ 161), and are as dependent for 

 of the sea. j^]^q[j^ woll-being upon temjDeratm^e, as are the fauna 

 and the flora of the dry land. Were it not so we should find 

 the fish and the algas, the marine insect and the coral, distributed 

 equally and ahke in all parts of the ocean. The arctic ^Yhale 

 ^YOuld delight in the torrid zone, and the habitat of the pearl oyster 

 ^yould be also under the iceberg, or in the frigid waters of polar 

 seas. 



372. Nevertheless, though the constituents of sea water be the same 

 Those of southern in kind, WO must uot infer that they are the same 



unlike those of north- . ■, ,, iJii inn'' on 



ern seas. m degree throughout all parts oi the ocean, for there 



is a peculiarity, perhaps of temperatm^e, perhaps of transparency, 

 which marks the inliabitants of trans-equatorial seas. MM. Peron 

 and Le Sueur, who haye turned their attention to the subject, 

 assert that out of many thousand examples they did not find a 

 single one in which the inhabitants of trans- equatorial were not 

 distinguishable from those of their species in cis-equatorial seas. 



373. Water, while its capacities for heat are scarcely exceeded 

 The capacity of by thoso of any other substance, is one of the most 

 Avater to convey heat. comiDloto of nou-conductors. Heat docs uot per- 

 meate water as it does iron, for instance, or other good conductors. 

 Heat the top of an iron plate, and the bottom becomes warm ; but 

 heat the top of a sheet of water, as in a pool or basin, and that at 

 the bottom remains cool. The heat passes through iron by con- 

 duction, but to get through water it requires to be conyeyed by a 

 motion, which in fluids we caU currents. Therefore the study of 

 the climates of the sea inyolyes a knowledge of its currents, both 

 cold and warm. They are the channels through which the waters 

 circulate, and by means of which the harmonies of old ocean are 

 preserved. 



374. Hence, in studying the system of oceanic circulation, we 

 Currents of the spa get out With, the vory simplo assumption, \dz., that 



to be considered lu ^ , i '^ n n ^ ^ , ■ n ^ 



pairs. n'om wnatever part oi the ocean a current is lounci 



to run, to the same part a cmTent of equal volume is bound to 

 retm^n ; for upon this principle is based the whole system of cm-rents 

 and counter-cmTcnts of the air as well as of the water. Hence, 

 the advantage of considering them as the anatomist does the nerves 

 of the human system — in pairs. Currents of water, like currents 

 of ah^, meeting fi'om various directions, create gyrations, which 

 in some parts of the sea, as on the coast of Norway, assume the 



