1645 - entered the University of Leiden to study mathematics and law. 1655 - visited Paris for the first time. 1654 - De Circuli Magnitudine Inventa, published. 1655 - discovered a satellite of Saturn. 1658 - Horologium, published. 1659 - discovered the true shape of the rings of Saturn. 1666 - became one of the founding members of the French Academy of Sciences. 1673 - Horologium Oscillatorium, published. 1689 - visited London and met Sir Isaac Newton. 1690 - published his own Theory of gravity in Discours de la cause de la pesanteur.