Along the south coast from
Land's End to Beachy Head the average velocity is 40 miles per
hour, the rate reducing as the wave approaches Dover, in the
vicinity of which the tidal waves from the two different
directions meet, one arriving approximately twelve hours later
than the other, thus forming tides which are a result of the
amalgamation of the two waves. On the ebb tide the direction of
the waves is reversed.
The mobility of the water around the earth causes it to be very
sensitive to the varying attraction of the sun and moon, due to
the alterations from time to time in the relative positions of
the three bodies. Fig. [Footnote: Plate I] shows
diagrammatically the condition of the water in the Southern
Ocean when the sun and moon are in the positions occupied at
the time of new moon. The tide at A is due to the sum of the
attractions of the sun and moon less the effect due to the
excess of the centripetal force over centrifugal force. The
tide at C is due to the excess of the centrifugal force over
the centripetal force. These tides are known as "spring" tides.
Fig. 2 [Footnote: Plate I] shows the positions occupied at the
time of full moon. The tide at A is due to the attraction of
the sun plus the effect due to the excess of the centrifugal
force over the centripetal force.
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