Pendulum the pendulum could be used to measure the force of gravity. During his expedition to Cayenne, French Guiana in 1671, Jean Richer found that a pendulum clock was minutes per day slower at Cayenne than at Paris. From this he deduced that the force of gravity was lower at Cayenne. In 1687, Isaac Newton in "Principia Mathematica" showed that this was because the Earth was not a true sphere but slightly oblate (flattened at the poles) from the effect of centrifugal force due to its rotation, causing gravity to increase with latitude. Portable pendulums began to be taken on voyages
Foucault pendulum vector diagrams vectors on opposite sides of the pendulum. The evaluation is to identify whether the vectors on each side of the pendulum swing are 1) balanced in the same direction, 2) acting in the same plane, or 3) unbalanced or in opposing directions. If the vector components on opposite sides of the pendulum swing are balanced in the same direction or act in the same plane of the pendulum then the rotation of the Earth will not be observable in relation to the swing of the pendulum. If the plane of the pendulum swing establishes the "x"-"y" plane then the z-component