8 THE WORLD OF THE SEA. 
of celestial bodies which are thousands of miles away the tides pre- 
serve, in their periodical return, as strict a mathematical regularity 
as the movements of those bodies themselves. The enormous 
volume of water which they raise, and which could sweep down 
the mightiest barriers, gently subsides at the appointed moment, 
without passing its prescribed limits. 
A HOLLOW WAVE. 
Foremost among the beauties of the sea are the waves, with 
their constant and regular progression, their everlasting and mo- 
notonous roar, their dancing, flying foam which rises and falls, 
and rises again only to disappear upon the shore. Sometimes the 
billow lashes itself against the cliffs; but on low shores it sweeps 
back again to its bed, forming a thousand cascades, a thousand 
rivulets, a thousand sinuous rills. The volume and the height of the 
waves increase with the depth of the water; it is possible indeed, 
from a knowledge of their size and velocity at any place, to calcu- 
late the depth of the sea which gives them birth. The height of 
ordinary waves may reach twelve yards ; their force wears down the 
hardest rocks, rounds off the edges of the débris, tosses about the 
