vanishing tide—In a predominantly mixed tide with a very large diurnal inequality, the lower high water and higher low water become indistinct (or vanish) at times of extreme declinations.

variation (of compass)—Difference between true north as determined by the Earth's axis of rotation and magnetic north as determined by the Earth's magnetism. Variation is designated as east or positive when the magnetic needle is deflected to the east of true north and as west or negative when the deflection is to the west of true north. The variation changes with time. Also called magnetic declination.

variational inequality—An inequality in the Moon's motion due mainly to the tangential component of the Sun's attraction.

velocity (of current)—Speed and set of the current.

vernal equinox—See equinoxes.

vulgar establishment—Same as establishment of the port.