Born: 1630 in France - Died: 1696 in Paris, France
Richer was an astronomer who is famed for two
pieces of work.
In 1871 Richer was sent on an expedition to Cayenne, French Guyana
by the Frence Government.
His first task there was to measure the parallax of Mars and the
observations were to be compared with that taken at other sites to compute the
distance to the planet. This data enabled the scale of the solar system to be
computed, the first reasonably accurate results to be found.
Richer's second important work was to examine the periods of
pendulums at different points on the Earth. He examined the period of a pendulum
while on the expedition to Cayenne, French Guyana and found that the pendulum
beat more slowly than in Paris. From this Richer deduced that gravity was weaker
at Cayenne, so it was further from the centre of the Earth than was Paris.
Newton and Huygens used Richer's gravity data to show that the Earth is an oblate sphere.