356 THE PHYSICAL CONDITION OF THE OCEAN. 



fear that discomfort is the prevailing feeling that many carry away. 

 The height to which storm waves may arise has never been very satis- 

 factorily determined. Apart from the difficulty of the task and the 

 small number of people who will address themselves to it when they 

 have the chance, it isbutrarely that any individual sees really abnormal 

 waves, even though he may be at sea all his life. Different heights 

 for what are called maximum waves have been recorded, and they vary 

 from 40 to 00 feet from crest to hollow. All we can say is that the 

 most probable ligure is about 50 or GO feet. These great storm waves 

 travel very far. In some cases they convey a warning, as their velocity 

 always far exceeds that at which the storm is traveling. In others 

 they intimate that a gale of which no more is seen has occurred some- 

 where — it may be many miles distant. When they have traveled 

 bej^ond the limits of the wind which raised them they lose the steep- 

 ness of slope which characterizes them when under its influence and 

 become an undulation which is scarcely noticed when in deep water. 

 On approaching shallow water, however, they are again apparent, and 

 the "rollers" that occur unperiodically at various jilaces in latitudes 

 where gales never occur would seem to be caused by such waves, origi- 

 nating in areas many thousands of miles distant. Such appears to be 

 the origin of the well-known rollers at Ascension and St. Helena, where 

 the rocky and ex])osed nature of the landing has caused this phenom- 

 enon to be especially noticed. 



Other rollers are, however, undoubtedly due to earthquakes or vol- 

 canic eruptions occurring in the bed of the sea. INIany of the great 

 and sudden waves which have caused devastation and great loss of life 

 on the shores of western South America are referable to this cause. 

 Observations to enable the focus of such a disturbance to be traced 

 have generally been lacking, but it is probable that where the wave has 

 been large the point of origin has not been far distant. • In one nota- 

 ble instance the conditions were reversed. The point of origin was 

 known, and the distance to which the resulting wave traveled could be 

 fairly satisfactorily traced. This was the great eruption in the Straits 

 of Sunda, in August, 1883, which locally resulted in the disappearance 

 of the major part of the island of Krakatoa, and the loss of nearly 

 40,000 lives on the neigboring shores of Java and Sumatra by the huge 

 wave which devastated them. The records of automatic tide gauges 

 and the observations of individuals enabled the waves emanating from 

 this disturbance to be followed to great distances. These waves were 

 of great length, the crests, arriving at intervals of about an hour, and 

 moving with a velocity of about 350 miles an hour, were about that dis- 

 tance apart. The waves recorded at Cape Horn were apparently 

 undoubtedly due to the erui)tion and traveled distances of 7,500 miles 

 and 7,800 miles in their course on either side of the south polar land. 

 They were only 5 inches in height above mean level of the sea, while 

 the waves recorded at places on the southern part of Africa, at a dis- 

 tance of about 5,000 miles from the sceue of the erui)tion, were from 



