 Initially the ring is horizontal and the water is stationary.Second the ring is then quickly rotated by 180° around its East-West diameter and stopped, such that it again lies flat on the table surface, which is horizontal.At this time, the velocity formula_4 of the water in the tube is given by
formula_5

Note that a rotation from the vertical to the vertical position produces the velocity formula_6 of the water in the tube is given by
formula_7

Compton used this measured drift velocity to determine his latitude to within 3% accuracy.