During the Revolution of 1848 he was mainly collecting material for books on the oldest Slavic history. In 1848 he was made head of the University Library of Prague and a masterful professor of Slavonic philology in the University of Prague, but resigned to the latter in 1849 and remained head of the university library only. The reason for this resignation was that during the Revolution of 1848–49 he participated at the Slavic Congress in Prague in June 1848 and thus became suspicious for Austrian authorities. During the absolutistic period following the defeat of the revolution, he lived a secluded life and studied especially older Czech literature and Old Church Slavonic texts and culture.