Jacques Cassini (Cassini II, February 18, 1677 - April 16, 1756) Together with his father, he was involved in the great degree measurement to improve the geographic knowledge of France. After the death of his father in 1712, he succeeded him as the director of the Paris Observatory. His astronomical activities include observations of Saturn and studies of the proper motion of stars, detecting that Arcturus (Alpha Bootis) had changed its latitude by 5' in 159 years, while neighboring Eta Bootis remained unchanged. In 1740, he published Elements of Astronomy.