34 PITYSICAL GEOGRAPITY OF 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 foreto!d 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 storm-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 
