The instrument, made by Felice Gori, consists of an optical tube that rotates and tilts by means of an arc. The tube rests on a disk whose angle with the base plate can be adjusted by means of a second arc. The disk is tilted to match the local latitude and the optical tube is pointed at the Sun so that the Sun's image is projected on the center of a small tilted ivory plate inserted in the tube. When the tube is oriented in this way, a window in the rotating disk shows the hour, while a mobile pointer displays the minutes on a circular scale. Provenance: Lorraine collections.