"The Compton generator is a beautiful demonstration of the Coriolis force due to the earth's rotation,.... A narrow glass tube in the shape of a torus or ring (radius R of the ring >> radius of the tube) is filled with water, plus some dust particles to let one see any motion of the water. The ring and water are initially stationary and horizontal, but the ring is then spun through 180 degrees about its east--west diameter. After this rotation the water has acquired a velocity in the tube due to the Coriolis force. Derive the Coriolis force on a small element of water at position [theta]. In which direction will the water move? Now derive the speed of the water in the tube after it has rotated 180 degrees and show that it is v=2wRsin[lambda] (the water is initially at rest). Where R is the radius of the circle that the tube forms, [lambda] is the latitude on the earth and w is the earth's angular speed.