THE TIDES 149 



to earn a dividend for their shareholders, must have 

 dispatch, their daily working expenses being so high. 

 Therefore, in a port like Cardiff, for instance, with 

 a great rise and fall of tide, docks are an absolute 

 necessity. And it is most interesting to a thoughtful 

 observer to see an entire fleet of mighty ships reposing 

 in the deep waters of the docks there, while the work 

 of loading them is going on with the utmost expe- 

 dition, and at the same time the sea-bed outside the 

 dock gates is bare for miles, just a great expanse of 

 mud and ooze. Then, at the appointed time, the 

 sparkling flood comes gliding in. Gradually it 

 obliterates all the uglinesses of the muddy flats 

 with their stale smells, replacing these unpleasant- 

 nesses by a bright flood of clean sea water. The 

 tide rises higher and higher, being carefully watched 

 by those in charge of the docks until the smaller 

 vessels begin to be "locked" out, for the basin of 

 the dock is a lock which may be worked without 

 losing much water from the area of the dock proper. 

 And all the time the water outside is rising until the 

 great gates may all be thrown open, and the largest 

 ships the dock will accommodate may enter and leave, 

 steaming away serenely over what was only a few 

 hours before a foul expanse of evil-smelling mud. 

 This regular flooding of an almost level foreshore 

 with pure sea water, a natural deodorizer and dis- 

 infectant, is by no means the least of the services that 

 the tide renders to man, but as the subject impinges 

 upon the function of the ocean as a health-breeder for 

 the whole world, I can do no more than make passing 

 allusion to it here. 



The work of the navigator is, of course, immensely 



