Kater's pendulum minutes per day slower than at Paris, or equivalently the length of a pendulum with a swing of one second there was 1¼ Paris "lines", or 2.6 mm, shorter than at Paris. It was realized by the scientists of the day, and proven by Isaac Newton in 1687, that this was due to the fact that the Earth was not a perfect sphere but slightly oblate; it was thicker at the equator because of the Earth's rotation. Since the surface was farther from the Earth's center at Cayenne than at Paris, gravity was weaker there. Since that time pendulums began
Foucault pendulum vector diagrams is still the same force acting on the bob that causes it to rotate (turn) with the Earth. The point of significance is that the same forces imparting an angular velocity to the pre-released bob are still acting on the swinging bob. At the Equator, the relative motion of the Earth is not observable because there is no change in the force imparting an angular velocity to the bob. This is because the central axis of the pendulum is perpendicular with the axis of rotation of the Earth. At intermediate latitudes: The rotation of the Earth is observable in relation