The Mediterranean Sea 225 



In the body of the sea the rise and fall are much less than at 

 any of the places in the above table. At Algiers a self-recording 

 tide gauge was set up by Aime in 1848, and from its records 

 he deduced a rise and fall of 88 millim. (say 3j in.) at springs 

 ami half that amount at neaps, a fluctuation which would 

 pe ordinary observation, as it would be masked by the 

 effects of atmospheric disturbances. At Venice and in tin- 

 upper reaches of the Adriatic, the true lunisolar tide seems to 

 be more accentuated than in other parts; but here also it- 

 effects are subordinate to those of the wind. In summer the 

 Mediterranean is within the northern limit of the north-east 

 trade wind; consequently, throughout a great part of the 

 inds are tolerably constant in direction ; and, 

 blowing as they do over large areas of water, they are instru- 

 mental in moving large masses of it from one point to another, 

 and so producing streams and currents. 



The effect of wind on a surface of water is twofold: it 

 produces the rhythmic motion of waves and the motion of 

 translation of currents. Besides the motion produced by the 

 direct action of the wind on the surface water there are currents 

 due, in the first instance, to the accumulation of water produced 

 by a wind which has been blowing constantly in one direction. 

 The phenomenon of an abnormally high tidal rise with a gale 

 of wind blowing on shore is one with which inhabitants of the 

 British Islands are familiar. It is also a matter of frequent 

 observation that, for instance, a south-west gale which exag- 

 gerates the height of high water on the western coasts of 

 Britain reduces it on the east coasts. It blows the water on 

 the west coast and off the east coast, so that the difference in 

 the hi^h-water levels on the two coasts is very pronounced. 

 ^iippo-ing free communication were quickly in. id. b<i\\<n 



coasts, a current would be the result, and it- \ i< 

 1 be much greater than would be due to the local action 

 he wind <.n : 06. In the ' mean the wind- 



blow during a great portion <>t the year very constantly ; 

 ' tion or another and .u-.-nerallv troin nrth and 



SO great that the slope produced by 



-ference of the surface n-tantly in one din < nn 



in. 15 



