Built at the order of Peter Leopold of Lorraine on the highest floor of Palazzo Torrigiani between 1780 and 1789, the Astronomical Observatory of the Specola was annexed to the Imperial and Royal Museum of Physics and Natural History (today's "La Specola" Museum). In the intentions of the Grand Duke, the little tower was to become the most important astronomical observatory in Tuscany, rivaling the great centers of Greenwich and Paris. In 1784, in a room called the "Hall of Storks", the astronomer Giuseppe Slop (1740-1808) built a "camera obscura" sundial with a metal wire stretched a few centimeters above the floor which served the function of measuring the passing of the Sun over the local meridian with maximum precision. The gnomic pinhole was drilled in the frame of a small window, a fact which, along with a set of blocks placed at regular intervals along the sides of the meridian line, suggests the presence of another singular instrument, the quarantale, which made the sundial usable even by night. It consisted of a small telescope sliding on tracks anchored to the blocks, which sighted a star passing over the meridian through the open window and projected its image onto the meridian line.