TIDES AND WAVES 69 



than the lower parts and curl over in ad- 

 vance. Waves, in mid-ocean, may reach an 

 enormous size and some have been measured 

 which were thirty or forty feet in height. Such 

 waves, should they reach the shore, would 

 pile up to still greater heights and would pos- 

 sess enormous destructive force, but as a 

 rule the size of waves is greatly overestimated 

 and waves ten or twelve feet in height are 

 unusually large. It often happens that one 

 wave overtakes another and combines with 

 it to form a wave much larger than its fel- 

 lows and this great wave may overtake and 

 combine with still others until a gigantic 

 wave is formed which towers far above 

 all the surrounding seas. Such waves are 

 called "cumulative waves" and when such a 

 cumulative wave meets a ship it ifrequently 

 causes a vast amount of damage. A short 

 time ago the Clyde West Indian liner Semi- 

 nole was struck by such a wave, thrown 

 upon her beam ends and seemed about 

 to capsize, when a second cumulative wave 

 struck the ship on the opposite side, righted 

 her and saved her from capsizing, although 



