(b Schweinfurt, 22 May 1836; d Adelboden, 4 Sept 1899). German writer on ancient Greek music. After studying at Erlangen, Göttingen, and Berlin, where he taught for a time, he held posts in Gymnasien at Landsberg, Saargemünd and Strasbourg. He was outstandingly well equipped both as classical scholar and as musician, and between 1859 and 1899 he published numerous articles on fundamental aspects of his subject; many of these articles are still valuable. A major contribution was his admirable Musici scriptores graeci (1895), which remains the standard text for many of the technical theoretical treatises (see Greece, §I); this volume also included a summary list of manuscripts, now superseded by RISM, B/XI (1988). In 1899 Jan published as a supplement a collection of editions and transcriptions of the then-known fragments of ancient Greek music, which was not superseded until the appearance of Egert Pöhlmann's Denkmäler in 1970.