altered 



THE TIDES 151 



in force and direction by atmospheric con- 

 ditions obtaining hundreds of miles away, this renders 

 the work of the pilot more involved than ever. And 

 nowhere in the world are there to be found more 

 varieties and vagaries of tide than there are around 

 these favoured islands of ours, the home of the greatest 

 oversea carrying trade in the whole world. From the 

 raging torrents of the Pentland Firth or the Race 

 of Portland, to the gentle tidal waters of the east coast 

 and the almost unimaginable inrush of the flood found 

 in the Severn and Solway, all the ways in which the 

 moon's influence upon the sea can affect the naviga- 

 tion of waters near the land may be tested in Great 

 Britain. 



But as if to prove how dependent the tides are 

 upon the configuration of the land, there is the striking 

 lesson afforded by the great land-locked Mediterranean 

 Sea, and more especially the Black Sea, really an 

 off-shoot of the former. The narrow entrance to the 

 Middle Sea from the Atlantic effectually precludes 

 the inrush of the vast tidal waves of the ocean in 

 sufficient volume to cause such vicissitudes as occur 

 elsewhere. Not that the Mediterranean is, as it has 

 so often been called, a tideless sea. On the contrary, 

 the tide does make itself felt more or less all round the 

 Mediterranean shores, attaining its maximum on the 

 coast of Africa, about Tunis, of an amplitude of about 

 ten feet. On the average, however, the rise and 

 fall is only about a foot or two. Still, the circula- 

 tion of this great body of water is maintained by 

 currents both surface and lower, in some places attain- 

 ing such a velocity that they have become a part 

 of classic lore. We need only mention Scylla and 



