提示：为了帮助大家轻松阅读和复习，我们特别提供了黄源深教授主编的English Book5（高级英语，即网络和函授课程中综合英语）的部分课文文稿，您可以打开金山词霸，利用其鼠标取词功能，将鼠标指向难词即可速查词义，方便快捷。本部分内容由外国语学院毛浩然老师整理，严禁转载。

What makes waves
By Rachel L. Carson

As long as there has been an earth, the moving masses of air that we call winds have swept back and forth across its surface. And as long as there has been an ocean, its waters have stirred to the passing of the winds. Waves result from the action of wind on water. There are exceptions, such as the so-called tidal waves produced by earthquakes under the sea, but the waves we know best are wind waves.

It is a confused pattern that the waves make in the open sea—a mixture of countless different wave trains, intermingling, overtaking, passing, or sometimes engulfing one another; each group differing from the others in the place and manner of its origin, in its speed, its direction of movement; some destined never to reach any shore, others destined to roll across half an ocean before they dissolve in thunder on a distant beach.

Out of such seemingly hopeless confusion the patient study of many men over many years has brought a surprising amount of order. While there is still much to be learned about waves, and much to be done to apply what is known to man’s advantage, there is a solid basis of fact on which to reconstruct the life history of a wave, predict its behavior under all the changing circumstances of its life, and calculate its effect on human affairs.

Before constructing an imaginary life history of a typical wave, we need to become familiar with some of its physical characteristics. A wave has height, from trough to crest. It has length, the distance from its crest to that of the following wave. The period of the wave refers to the time required for succeeding crests to pass a fixed point. None of these dimensions are static, all changes, but bear definite relations to changes in the wind, the depth of the water, and many other matters. Furthermore, the water that composes a wave does not advance with it across the sea; each water particle describes a circular or elliptical orbit with the passage of a wave, returning very nearly to its original position. It is fortunate for mankind that this is so, for if the huge masses of water that constitute a wave actually moved with it, navigation would be impossible. Those who deal professionally with waves make frequent use of a picturesque expression—the “length of fetch.” The “fetch” is the distance the waves have run, without obstruction, under the drive of a wind blowing in a constant direction. Generally speaking, the greater the fetch, the higher the waves. Really high waves cannot be generated within the confined space of a bay or a small, landlocked sea. A fetch of perhaps six hundred to eight hundred miles, with winds of gale velocity, is required to generate the highest ocean waves.

Now let us suppose that, after a period of calm, a storm develops out in the Atlantic, a thousand miles from the New Jersey coast, where we are spending a summer holiday. Its winds come in sudden, irregular gusts, shifting direction but in general blowing shoreward. The sheet of water under the winds responds to the changing pressures. It is no longer a level surface; it becomes furrowed with alternating troughs and ridges. The waves move toward the shore, and the wind that created them controls their destiny. As the storm continues, the waves, as they roll on, receive energy from the wind, and increase in height. Up to a certain point, they will continue to do this, but when a wave becomes about a seventh as high as it is long, it will topple in foaming whitecaps. Winds of hurricane force often blow the tops off the waves by their very violence; in such a storm, the highest waves may develop after the wind has begun to subside.

But to return to our typical wave, born of wind and water far out in the Atlantic, grown to their full height through the energy of the winds—form a confused, irregular pattern known as a "sea." As the waves pass out of the storm area, their height diminishes, their length increases, and the "sea" becomes a "swell," moving at an average speed of fifteen miles an hour. Near the coast, a pattern of long, regular swells is substituted for the turbulence of the open ocean. But as these swells enter shallow water, a startling transformation takes place in each wave. For the first time in its existence, the wave feels the drag of shoaling bottom. Its speed slackens, crests of following waves crowd in behind it, and abruptly its height increases and its form steepens. Then, with a spilling, tumbling rush of water into its trough, it dissolves in a seething confusion of foam.

An observer sitting on a beach can make at least an intelligent guess as to whether the surf crashing down onto the sand before him has been produced by a gale just offshore or by a distant storm. Young waves, only recently shaped by the wind, have a steep, peaked shape long before they reach shore. Far out on the horizon we can see them forming whitecaps as they come in; bits of foam are tumbling and boiling and bubbling down their fronts, and the final breaking of the wave is a prolonged and deliberate process. But if a wave, upon coming into the surf zone, rears high, as though gathering all its strength for the final act of its life, if the crest forms all along its advancing front and then begins to curl forward, if the whole mass of water plunges suddenly forward with a booming roar, then we may take it that these waves are visitors from some very distant part of the ocean—that they have travelled far before their dissolution at our feet.

What is true of the Atlantic wave we have followed is true, in general, of wind waves the world over. The incidents in the life of a wave are many. How long it will live, how far it will travel, to what manner of end it will come are determined, in large measure, by the conditions it meets in its progress across the face of the sea. The essential quality of a wave is that it moves; anything that retards or stops its motion dooms it to dissolution and death.