336 OBSEKVATIONS ON THE CUKRENTS. 



Major Rennell says : — It has been observed that the waters of thd 

 Atlantic have a greater tendency toward the middle of the Ocean than 

 otherwise, and this seems to indicate a reduced level, forming a kind of 

 hollow space or depressed surface. It is certain that the setting of the 

 Currents is such as might be expected to take place if such a hollow existed; 

 for the Currents do really set into the Sargasso Sea from the North and 

 from the South ; whilst in the middle part, although within the region of 

 the Trade "Wind, the Currents are not regular, but indicate a kind of 

 vortex.* 



By others it is considered as an immense eddy or whirlpool, formed by 

 the inclination of the water to the "Westward, caused by the influence of 

 the Trade "W^inds and the Gulf Stream. 



Others, again, argue that it is a raised surface, maintained in a quiescent 

 condition by the surrounding currents, and retaining all floating matter 

 that is poured into it by the surrounding influences. 



It is also considered as the grand receptacle of the Gulf Stream, which, 

 recurving at the Azores, here turns into this space all that it has trans- 

 ported through its long course. 



All these theories have some facts to bear them up in some degree, but 

 others can be adduced to show their futility. 



(291.) It is here urged that a simple explanation can be given of this 

 curious region, in the analogous condition of the atmosphere, so powerful 

 an agent in the production or alteration of Ocean Drifts and Currents. 



By referring to Maury's Trade Wind Charts, cited on page 128 (48), it 

 will be seen that there is an uncertainty about meeting with the Northern 

 sdge of the N.B. Trade Winds through an extent of at least 10° of latitude; 

 add to this the vibration of this zone of Trade Winds consequent on the 

 motion of the sun in the Ecliptic, which amounts to from 5° to 8*^ in 

 latitude, as exemplified in the diagram of the Hmits of the Trade Winds at 

 page 125, and we have a range of 15° to 18° of latitude over which, during 

 some portion of the year, and over a large section of it throughout the 

 year, there is nothing but light airs and variable winds, being, in fact, the 

 "Horse Latitudes," see page 168 (96 to 100). 



Under this zone, therefore, the sea is subject to no continued or regular 

 drift, and, consequently, whatever is thrown on to its surface will remain 

 for a long time, and the Sargasso, or gulf- weed, being one of the few marine 

 plants which lives when broken from its rocky bed, may exist here for a 

 very long period, and thus accumulate by the fresh additions constantly 

 brought by the outer or Eastern edge of the Gulf Stream, as well as that 

 drifted around the Northern part of the Atlantic, and passing with the S.E. 

 current by the Azores (262) into this quiescent zone. That the Gulf Stream 

 is the primary feeder to this weedy sea will be shown presently. 



(292.) There is another condition, also, which favours the maintenance 

 and growth of this pecuhar plant. The temperature of this water is very 

 equable, less warm than that under the more vertical sun, and not varying 

 more than 6° or 7° Fahr. throui^hout the year in the Eastern part, or Q' or 

 9° in the Western part. This temperature is, as said, lower than that of 



• Renuell's "Investigation," page 72. 



