PREFACE 



Anything that disturbs the equilibrium of the water will start a 

 system of undulations; that is, it will produce waves. This will hap- 

 pen, for example, if one drops a stone in the water. A ship as she 

 steams along starts a system of waves; and so does a submarine earth- 

 quake, a volcanic eruption, or a rapid change in the barometric pres- 

 sure of the atmosphere. The gravitational forces that cause the tides 

 also produce waves. Other events that do this, commonly falling 

 under the eyes of seafarers, are a porpoise leaping and dropping back 

 again, or the tail of a flying fish cutting a pattern on the surface in 

 calm weather. But the most familiar cause of waves that furrow the 

 sea is the wind ; and jt is of these wind waves that this book treats. 



Waves force themselves on the attention of everyone who follows 

 the sea. No seafarer can ignore them, whether fisherman, merchant 

 sailor, yachtsman, or member of the naval establishment; nor can the 

 seaside dweller ignore the breakers as they thunder on the beach. It is 

 no wonder, then, that the waves of the sea have attracted attention 

 since time immemorial, or that more or less extended accounts of waves 

 are to be found in many of the texts that have appeared in recent years 

 on seamanship, on oceanography, on meteorology, on shore line proc- 

 esses, on the construction of breakwaters, and on the protection of 

 beaches from erosion. Waves also have been the subject of many 

 theoretical studies. Yet, no simple, comprehensive account of wind 

 waves from the standpoint of the man at sea has yet appeared in the 

 English language. And it is in the hope of filling this gap that the 

 following description is offered. 



Most of the information here presented has been drawn from pub- 

 lished sources. We also owe a debt of gratitude to many persons for 

 assistance, especially to Dr. H. U. Sverdrup for his kindness in re- 

 viewing some of the theoretical discussions and to Capt. Fenner A. 

 Chase, Jr., AUS, of the Hydrographic Office, Navy Department, who 

 has aided in the editing of the manuscript. We wish it expressly un- 

 derstood that we have made no contributions to the theory of waves. 

 But we would not have dared to undertake the task, if we had not ob- 

 served the behavior of waves at sea, from large craft and from small, 

 in various parts of the world, under various conditions of wind and 

 weather ; or if we had not had many an opportunity to watch the de- 

 velopment of breaker*; — and to cope with the smaller sizes — off beaches 

 of various shapes, off rocky coastlines, and over submerged ledges. 



