Ole Rømer (1644-1710)
Eclipsareon, ca. 1680-1681
Paris, Bibliothèque Nationale de France, inv. GA 281

A twin of the planetarium, this instrument allowed its user to forecast eclipses of the Sun and Moon by turning the small key on the rear quadrant until the mobile index reached the discs of the Sun and the Moon. At that point, he would take note of the year and day by means of two indices situated on the rear quadrant, on which a small mobile hand indicates the month.