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Scientific American Supplement, No. 620, November 19,1887 by Various
page 92 of 138 (66%)
curved surface which, commencing at low water, passes over the summit
of the tide down to the next low water--this is a wave of the first
order. In waves of the second order, the force raising them acts only
on the surface, and there the effect is greatest (as in the wind
waves)--where one assists in giving to the water oscillating motion
which maintains the next, and gradually puts the whole surface in
commotion; but at a short distance down that effect entirely
disappears.

If the earth presented a uniform globe, with a belt of sea of great
and uniform depth encircling it round the equator, the tide wave would
be perfectly regular and uniform. Its velocity, where the water was
deep and free to follow the two luminaries, would be 1,000 miles an
hour, and the height of tide inconsiderable. But even the Atlantic is
not broad enough for the formation of a powerful tide wave. The
continents, the variation in the direction of the coast line, the
different depths of the ocean, the narrowness of channels, all
interfere to modify it. At first it is affected with only a slight
current motion toward the west--a motion which only acquires strength
when the wave is heaped up, as it were, by obstacles to its progress,
as happens to it over the shallow parts of the sea, on the coasts, in
gulfs, and in the mouths of rivers. Thus the first wave advancing
meets in its course with resistance on the two sides of a narrow
channel, it is forced to rise by the pressure of the following waves,
whose motion is not at all retarded, or certainly less so than that of
the first wave. Thus an actual current of water is produced in straits
and narrow channels; and it is always important to distinguish between
the tide wave, as bringing high water, and the tidal stream--between
the rise and fall of the tide and the flow and ebb.

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