Dipleidoscope designed by Giovanni Battista Amici to determine true noon. It consists of a small telescope mounted on a cylindrical stone pedestal with a prism system in front of the objective. The prisms double the solar image when the Sun is not on the optical axis of the telescope. The observer will see the images positioned symmetrically to the center of the field of view. When the Sun approaches the center of the field of view, the two images converge. When the Sun is on the instrument's optical axis, they will coincide. If the axis has been placed beforehand on the north-south vertical plane (the meridian plane), the instant when the images overlap is the locality's true noon. If correctly placed on the meridian, the instrument determines true noon to within 5-10 seconds.