title SUMMARY /title The Istituto e Museo di Storia della Scienza of Florence preserves some ancient Chinese scientific instruments, very interesting for historians. These instruments are: one compass for navigation, one geomantic compass, one compass with agricultural calendar, two sound spheres, two balances. Only the first of them has been studied, the others are not known yet. The present paper begins a close cooperation between the Institute of Florence and the Istituto Universitario Orientale of Naples (Group of Research on History of Sciences and Technologies of Eastern Asia, direct by A. Tamburello); here, I will attend to the second instrument over mentioned, the geomantic compass. The geomantic compasses are very important for the history of sciences because they bear witness to enormous complexity of the Chinese thought and, in the technical and scientific field, they represent the instrument for the ancient studies on feng shui. After a panoramic description of the divining system of feng shui, I give a deep explication of the geomantic compass preserved in Florence that seems particularly important because it presents some characters rarely used in this kind of instruments.