CURRENTS OF THE SEA. 181 



thoiigli the water were drawn into a chasm below. The cele- 

 brated Maelstrom is caused by such a conflict of tidal or other 

 .streams. The late Admiral Beechey, E.N.,* gave diagrams 

 illustrative of many " rotatory streams in the English Channel, a 

 number of which occur between the outer extremities of the 

 channel tide and the stream of the oceanic or parent wave." 

 " They are clearly to be accounted for," says he, " by the streams 

 acting obliquely upon each other." 



375. Marine currents do not, like those on land, run of necessity 

 from higher to loicer levels. — It is not necessary to associate with 

 oceanic currents the idea that they must, of necessity, as on 

 land, run from a higher to a lower level. So far from this 

 being the case, some currents of the sea actually run up hill, 

 while others run on a level. The Gulf Stream is of the first 

 class (§ 83). 



376. The Bed Sea current. — The cun-ents which run from the 

 Atlantic into the Mediterranean, and from the Indian Ocean into 

 the Eed Sea, are the reverse of this. Here the bottom of the 

 current is probably a water-level, and the top an inclined plane, 

 running doicn hill. Take the Eed Sea current as an illustration. 

 That sea lies, for the most part, within a rainless and riverless 

 district. It may be compared to a long and narrow trough. 

 Being in a rainless district, the evaporation of it is immense ; 

 none of the water thus taken up is returned to it either by rivers 

 or rains. It is about one thousand miles long; it lies nearly 

 north and south, and extends from latitude 13° to the parallel of 

 30° north. From May to October, the water in the upper pai-t 

 of this sea is said to be two feet lower than it is near the mouth. f 

 This change or difference of level is ascribed to the effect of the 

 wind, which, prevailing from the north at that season, is supposed 

 to blow the water out. But from May to October is also the hot 

 season ; it is the season when evaporation is going on most 

 rapidly : and when we consider how dry and how hot the winds 

 are which blow upon this sea at this season of the year ; that it is 

 a narrow sea ; that they blow across it and are not saturated, we 

 may suppose the daily evaporation to be immense. The evapo- 

 lation from this sea and the Persian Gulf is probably greater 

 than it is from any other arms of the ocean. AVe know that the 



* See an interesting paper by him on Tidal Streams of the North Sea and 

 English Channel, p. 708 ; Phil. Transactions, Part ii., 1851. 

 t Johnston's Phj'sical Atlas. 



