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I. § 5.] MOTION OF SEA- WAVES.
whole, at rest during its passage, and a slight yielding of their separate parts is all that their constitution generally admits of. In fluids, or in the air, a continuous forward motion is equally out of the question. The movement of the particles composing the Sound-conveying medium will be found to be of a kind examples of which are constantly presenting themselves, but without attracting an amount of attention at all commensurate with their interest and importance.
5. An observer who looks down upon the sea from a moderate elevation, on a day when the wind, after blowing strongly, has suddenly dropped, sees long lines of waves advancing towards the shore at a uniform pace and at equal distances from each other. The effect to the eye is that of a vast army marching up in column, or of a ploughed field moving along horizontally in a direction perpendicular to the lines of its ridges and hollows. The actual motion of the water is, however, very different from its apparent motion, as may be ascertained by noticing the behaviour of a cork or other body floating on the surface of the sea, and therefore sharing its movement. The floating body does not advance with the waves, but rides over their crests and sinks into their troughs as though it were a buoy at anchor. Hence, while the waves travel