174 



AND ITS METEOROLOGY. 



appearance of wliirlpools, as tliougli the water were drawn into a 

 chasm below. The celebrated Maelstrom is caused by such a con- 

 flict of tidal or other streams. The late Admiral Beechey, K.N.,* 

 gave diagrams illustrative of many " rotatory streams in the Eng- 

 Esh 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 

 actmg obliquely upon each other." 



375. It is not necessary to associate with oceanic currents the 

 nS!^iikYthosr?/^ ^^^^ *^^* *^®y iii^st, of necessity, as on land, run 

 land rimofneces- from a higher to a lower level. So far fi'om this 

 lower levels. being the case, some currents of the sea actually run 

 up hill, while others run on a level. The Grulf Stream is of the 

 first class (§ 83). 



376. The currents which nm from the Atlantic into the Medi- 

 The Red Sea current, tcrrancan, and from the Indian Ocean into the Ked 

 Sea, are the reverse of this. Here the bottom of the current is 

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

 dotvii 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 reborned 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 part of this sea is said to be two 

 feet lower than it is near the mouth. t 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 gomg 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 evaporation from this sea and the Persian Gulf 

 is probably greater than it is from any other arms of the ocean. 

 We know that the waste from canals by evaporation, in the summer- 

 time, is an element which the engineer, when taking the capacity 



* See an interesting paper by liim on Tidal Streams^ of tlie North Sea and 

 Englisii Channel, p. -703; Phil. Transactions, Part ii„ 1851. 

 t Johnston's Physical Atlas. 



