1630-1696

French Physicist

Jean Richer is remembered for having determined that pendulums beat more slowly at the equator than at higher latitudes, a discovery that initiated the famous controversy between Newtonians and Cartesians over Earth's shape. Also, his observations of Mars were used by Giovanni Domenico Cassini (1625-1712) to make the first accurate estimate of the size of the solar system.

The details of Richer's early life have been lost, but when the Académie des Sciences was organized in 1666, he was admitted as an élève astronome (assistant astronomer). In March of 1670 he was selected to carry out astronomical measurements in the East Indies in conjunction with measurements to be made simultaneously in Paris. During this trip he was also responsible for testing Christiaan Huygens's (1629-1695) marine clocks constructed for the purpose of determining longitude at sea.

Last minute changes resulted in the expedition being...