 In 1870 he began work as a librarian at the "Universitätsbibliothek" in Freiburg, followed by professorships at the Universities of Innsbruck (1871) and Kiel (1873).In 1874 he was named "Oberbibliothekar" (head librarian) at the University of Königsberg, shortly afterwards, given the same title at the "Niedersächsische Staats- und Universitätsbibliothek" in Göttingen (1875).From 1886 to 1914 he was general director of the "Königliche Bibliothek" (Royal Library) in Berlin, where he was successor to Karl Richard Lepsius.