 Upon request of Duke Johann Friedrich of Hanover, Pope Innocent XI made him Vicar Apostolic for the Nordic Missions on 21 August 1677.He was consecrated titular bishop of Titiopolis on 19 September by Cardinal Barbarigo and moved to the Lutheran North.In the year after he was made bishop, he was probably involved in the banning of publications by Spinoza, There he had talks with Gottfried Leibniz, the librarian; the two argued about Spinoza and his letter to Albert Burgh, then Steno's pupil.