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
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