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
Griffith Observatory the Foucault pendulum, which was designed to demonstrate the rotation of the Earth. The exhibits also included a 12-inch (305mm) Zeiss refracting telescope in the east dome, a triple-beam coelostat (solar telescope) in the west dome, and a thirty-eight foot relief model of the moon's north polar region. Col. Griffith requested that the observatory include a display on evolution which was accomplished with the Cosmochron exhibit which included a narration from Caltech Professor Chester Stock and an accompanying slide show. The evolution exhibit existed from 1937 to the mid-1960s. Also included in the original design was a planetarium under the