It is
asserted, however, as an explanation of the phenomenon which
occurs, that the centripetal force acting at any point on the
surface of the earth varies inversely as the square of the
distance from that point to the moon, so that the centripetal
force acting on the water at the side of the earth furthest
removed from the moon is less effective than that on the side
nearest to the moon, to the extent due to the length of the
diameter of the earth. The result of this is that the
centrifugal force overbalances the centripetal force, and the
water tends to fly off, forming an anti-lunar wave crest at
that point approximately equal, and opposite, to the wave crest
at the point nearest to the moon. As the earth revolves, the
crest of high water of the lunar tide remains opposite the
centre of attraction of the sun and moon, so that a point on
the surface will be carried from high water towards and past
the trough of the wave, or low water, then past the crest of
the anti-lunar tide, or high water again, and back to its
original position under the moon. But while the earth is
revolving the moon has traveled 13 degrees along the elliptical
orbit in which she revolves around the earth, from west to
east, once in 27 days 7 hr. 43 min, so that the earth has to
make a fraction over a complete revolution before the same
point is brought under the centre of attraction again This
occupies on an average 52 min, so that, although we are taught
that the tide regularly ebbs and flows twice in twenty-four
hours, it will be seen that the tidal day averages 24 hr.
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