In 1816 he refused an extraordinary professorship at Heidelberg in order to accompany BG Niebuhr to Italy as secretary to the Prussian embassy. Subsequently he assisted Immanuel Bekker in the preparation of his edition of Aristotle. In 1821 he became professor of philosophy in the newly founded University of Bonn, and in 1823 published his Aristotelius et Theophrasti Metaphysica. With Böckh and Niebuhr he edited the Rheinisches Museum, to which he contributed important articles on Socrates (1827, 1829). From 1836 to 1839 he was tutor to the young King Otho of Greece.
His great work, the Handbuch der Geschichte der Griechisch-Römischen Philosophie (1835-1866); republished in a smaller and more systematic form, Geschichte der Entwicklungen der griechischen Philosophie und ihrer Nachwirkungen im römischen Reiche, 1862-1866), is characterized by sound criticism.