34 PHYSICAL GEOGRAPHY OP THE SEA. 



neap-tides are only twelve feet high, while the ordinary spring- 

 tides rise to more than twenty feet. 



The highest tides take place during the equinoxes; and 

 eclipses of the sun and moon are also invariably accompanied 

 by considerable floods, a circumstance which cannot fail to add 

 to the terror of the ignorant and superstitious when a mysterious 

 obscurity suddenly veils the great luminaries of the sky. It 

 has also been remarked that the tides are stronger or weaker, 

 according as the moon is at a greater or smaller distance from 

 the earth. 



Thus as the height of the floods is always regulated by the 

 relative position of the sun and moon, and the movements of 

 these heavenly bodies can be calculated a long time beforehand, 

 our nautical calendars are able to tell us the days when the 

 highest spring-tides may be expected. 



This however can only be foretold to a certain extent, as the 

 tidal height not only depends upon the attraction of the heavenly 

 bodies, but also upon . the casual influences of the wind, which 

 defies all calculation, and of the pressure of the air. Thus Mr. 

 Walker observed on the coasts of Cornwall and Devonshire that 

 when the barometer falls an inch, the level of the sea rises 

 sixteen inches higher than would otherwise have been the case. 



When a strong and continuous wind blows in an opposite 

 direction to the tide-wave, and at the same time the barometer 

 is high, the curious spectators will therefore be deceived in their 

 expectations, however promising the position of the attracting 

 luminaries may be ; while an ordinary spring-tide, favoured by 

 a low state of the barometer and chased by a violent storm 

 against, the coast, may attain more than double the usual 

 height. When all favourable circumstances combine, an event 

 which fortunately but rarely occurs, those dreadful storvrv-tides 

 take place, as menacing to the flat coasts of the Netherlands as 

 an eruption of Etna to the towns and hamlets scattered along 

 its base, for here also a vast elementary power is let loose 

 which bids defiance to human weakness. It is then that the 

 rebel sea affords a spectacle of appalling magnificence. The 

 whole surface seethes and boils .in endless confusion. Gigantic 

 waves rear their monstrous heads like mighty Titans, and hurl 

 their whole colossal power against the dunes and dykes, as if, 

 impelled by a wild lust of conquest, they were burning to devour 



