The shape of the earth
The problem of the shape of the earth was solved already by Pythagoras as early as in the 6th century BC. The first estimate of the size of the earth was made by Erastothenes who lived in the 3rd century BC.
The Frenchman Jean Richter (d. 1696) found out that his pendulum clock was two minutes slow at the Equator compared to Paris time. Isaac Newton (1642 1727) then proceeded to claim in his Principia (Philosophiae naturalis principia mathematica, 1687) that the earth is flattened by its poles i.e. a rotating ellipsoid. According to Newton this conclusion is also supported by the force caused by the rotation of the earth
The exact shape of the earth was finally settled at the end of the
17th century by measuring of degrees. Jacques Cassini (1677-1756) made
experimental triangular measurements between Colliour and Dunkerque
in France. According to his measurements the length of a degree was
56 950 toise (1,949 metres) at the northern end and 57 097 toise at
the southern end. This experiment showed that the earth is an ellipsoid,
i.e. flattened by its poles. There developed a scientific dispute between
the scientific academies of London and Paris about this issue. It was
discussed whether the earth is of the shape of a lemon or of that of
an orange. To settle the dispute Pierre Louis Moreau de Maupertuis,
member of the French Academy and supporter of Newtons theory,
succeeded in persuading King Louis XV to send expeditions both to the
Equator in Peru and to the arctic circle in Northern Sweden.