Refractor at Dorpat he discovered a great number of double stars, and published in 1827 a list of all the known objects of this kind (Catalogus novus stellarum duplicium).
His micrometric measurements of 2714 double stars were made from 1824 to 1837, and are contained in his principal work, Stellarum duplicium et multiplicium mensurae micrometricae (St Petersburg, 1837 seq.; a convenient summary of the results is given in vol.
The places of the objects were at the same time determined with the Dorpat meridian circle (Stellarum fixarum imprimis duplicium et multiplicium positiones mediae, St Petersburg, 1852 seq.).
His principal works are Catalogus stellarum australium (London, 1679), the substance of which was embodied in vol.
His principal work, De Motu Stellarum, was published at Nuremberg in 1537 by Melanchthon, in a blundering Latin translation by Plato Tiburtinus (fl.