to a far greater public, and the Marquise wrote a celebratory review in the Journal des savants. Voltaire's work was instrumental in bringing about general acceptance of Newton's optical and gravitational theories in France, in contrast to the theories of Descartes. Voltaire and the Marquise also studied history, particularly the great contributors to civilization. Voltaire's second essay in English had been "Essay upon the Civil Wars in France". It was followed by La Henriade, an epic poem on the French King Henri IV, glorifying his attempt to end the Catholic-Protestant massacres with the Edict of Nantes, which established religious toleration. There followed a historical novel on King Charles XII of Sweden. These, along with his Letters on the English, mark the beginning of Voltaire's open criticism of intolerance and established religions. Voltaire and the Marquise also explored philosophy, particularly metaphysical questions concerning the existence of God and the soul. Voltaire and the Marquise analyzed the Bible and concluded that much of its content was dubious. Voltaire's critical views on religion led to his belief in separation of church and state and religious freedom, ideas that he had formed after his stay in England. In August 1736, Frederick the Great, then Crown Prince of Prussia and a great admirer of Voltaire, initiated a correspondence with him. That December, Voltaire moved to Holland for two months and became acquainted with the scientists Herman Boerhaave and Willem 's Gravesande. From mid-1739 to mid-1740 Voltaire lived largely in Brussels, at first with the Marquise, who was unsuccessfully attempting to pursue a 60-year-old family legal case regarding the ownership of two estates in Limburg. In July 1740, he traveled to the Hague on behalf of Frederick in an attempt to dissuade a dubious publisher, van Duren, from printing without permission Frederick's Anti-Machiavel. In September Voltaire and Frederick (now King) met for the first time in Moyland Castle near Cleves and in November Voltaire was Frederick's guest in Berlin for two weeks, followed by a meeting in September 1742 at Aix-la-Chapelle. Voltaire was sent to Frederick's court in 1743 by the French government as an envoy and spy to gauge Frederick's military intentions in the War of the Austrian Succession. Though deeply committed to the Marquise, Voltaire by 1744 found life at her château confining. On a visit to Paris that year, he found a new love—his niece. At first, his attraction to Marie Louise Mignot