170 BREAKER DIRECTION AND HEIGHT 



high, should break at angles of about 16° to 35° with the part of the 

 shore that was at right angles with their crests offshore, assuming that 

 they did so where the depth was equal to 1.3 times their own heights 

 at breaking, while their heights would be reduced by a little more 

 than one-half there accordingly, as compared with the most exposed 

 part of the island. Observations suggest that the reduction in height 

 might actually be of about this general order of magnitude. Theoreti- 

 cally, too, the inshore ends of the waves should lose still more in 

 height by the time they reach the more sheltered side of the island. 

 However, landing is not apt to be as much easier there as this might 

 suggest, especially if the island is small, for the following reasons : 



a. Since the inshore ends of the waves are still at a considerable 

 angle with the coastline when they break, and since the coasts of 

 round islands are usually rocky, bouldery, or strewn with coral heads, 

 landing is much more difficult for practical reasons, than it would be 

 if waves of equal height were breaking parallel with the shore, and 

 if the latter were sandy or pebbly. 



b. Although the reduction, by refraction, in the heights of the 

 waves around a small circular island is greatest on the most protected 

 side, the surf may be made very confused there because of the inter- 

 ference that often develops between the two trains of waves that meet, 

 as they are refracted around from the two sides. We ourselves have 

 vivid memories of attempts to land on rocky islets that were unsuccess- 

 ful for this very reason. 



In short, the chance is not very good of landing anywhere around 

 the shore lines of a small rocky island that is circular in form, if the 

 sea is too heavy to allow this on one or other of its two lateral quad- 

 rants, and if the submarine contour is such that the waves are re- 

 fracted right around it. But there may be a shadow zone of quiet 

 water in the lee of an islet, if its shores rise abruptly from water so 

 deep that the waves then running are refracted but little, as they 

 approach it. just as there may be in the lee of a promontory of similar 

 character, and for the same reason (p. 166). But anyone who takes 

 advantage of this to land will be well advised to keep a sharp eye on 

 the state of the sea, and be prepared to put off again at once if the 

 latter rises, for a troublesome surf may develop with astonishing 

 suddenness, as we have often seen. 



The more irregular the coast of an island is, and the more abruptly 

 it alters from place to place, the more likely it is that one can find a 

 place in some cove, or in the lee of some headland that will be sheltered 

 from the surf, under conditions of sea that would prevent landing 

 on the more exposed parts of the shore. One or the other of two 

 shallow bights, for example, marked A and B on figure 54, that flank 

 a short promontory on the northern side of No Man's Land, off 



