§ 140-142. THE GULF STREAM. 47 



west. This sargasso is directly south of the Georgian Islands, 

 and is, perhaps, less abundantly supplied with, drift matter, less 

 distinct in outline, and less permanent in position than any one 

 of the others. 



1-iO. There is no warm current, or if one, a very feeble one. 

 One in the South Aowiug out of the South Atkutic. Most of the 

 Atlantic. jj.[f(^ matter borne upon the ice-bearing current into 



that sea finds its way to the equator, and then into the veins 

 which give volume to the Gulf Stream and supply the sargasso 

 of the North Atlantic with extra quantities of drift. The sar- 

 gasso of the South Atlantic is therefore small. The formations 

 and physical relations of sargassos will be again alluded to in 

 Chapter XVIII. 



141. Let us return (§ 129) to this great expanse of warm water 



The large volume of w^hich, comiug from the torrid zone on the south- 

 warm water outside , ^ „ . ., .,.p , .,1 ^ 



of the Gulf Stream, wcstcm Side 01 the Atlantic, driits along to the north 

 on the outside of the Gulf Stream. Its velocity is slow, not suffi- 

 cient to give it the name of current ; it is a drift, or what sailors 

 call a " set." By the time this water reaches the parallel of 85° or 

 40° it has parted with a good deal of its intertropical heat; con- 

 sequent upon this change in temperature is a change in specific 

 gravity also, and by reason of this change as well as by the diffi- 

 culties of crossing the Gulf Stream, its progress to the north is ar- 

 rested. It now turns to the east with the Gulf Stream, and, yield- 

 ing to the force of the westerly winds of this latitude, is by them 

 slowly drifted along ; losing temperature by the way, these waters 

 reach the southwardly flow on the east side with their specific 

 gravity so altered that, disregarding the gentle forces of the wind, 

 they heed the voice of the sea, and proceed to unite with this 

 cool flow, and to set south in obedience to those dynamical laws 

 that derive their force in the sea from differing specific gravity. 



142. The Thermal Charts of the North Atlantic afford for these 

 The resemblance be- vicws othcr illustratious which, wben compared 

 in the North Atian- with the charts of thc North Pacific now in the 



tic and the North . • -n i jmi i. ^^ 



Pacific process of construction, will make still more striK 



ing the resemblance of the two oceans in the general features o 

 their systems of circulation. We see how, in accordance with 

 this principle (§ 132), the currents necessary for the formation 

 of thickly-set sargassos are generally wanting in southern oceans. 



^ 



