the Italian astronomer and mathematician Giovanni Domenico Cassini ( 1625 – 1712 ), and his French – born son Jacques Cassini ( 1677 – 1756) , measured an arc of longitude extending from Dunkirk to Perpignan, and obtained a result that seemed to support the Cartesian contention that the earth is elongated at the poles. The measurement made in Lapland unquestionably confirmed the Newton – Huygens belief, and earned Maupertuis the title of “earth flattener.” In 1743, after his return to France, Clairaut published his definitive work, Theorie de la figure de la Terre. In 1752 he won a prize from the St. Petersburg Academy for his paper Theorie de la Lune, a mathematical study of lunar motion which cleared up some, to then, unanswered questions He applied the process of differentiation to the differential equation