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 is observable as directly related to the magnitude of the Coriolis effect. The examples show that the Earth turns underneath the plane of the pendulum swing and how this change in relationship can be interpreted at different latitudes by evaluating the surface velocity components underneath the swing of the pendulum. For a pendulum swing at the North Pole it is shown that the surface velocity vectors of the Earth underneath one side of the pendulum swing are directed in opposition to the velocity vectors underneath the other side of the swing (see Figure 1). The Earth's rotation can then be