The idea of progress : an inquiry into its origin and growth /A gondolatszabadság története /Storia della libertà di pensiero /Duitschland en slavonische beschaving. In het Nederlandsch overgezet door W. de Veer.A history of freedom of thought.Sedjarah kemerdekaan berfikir. Terdjemahan [dari bahasa Inggris oleh] L.M. Sitorus.A history of freedom of thought.Dějiny svobody myšlení /