Type of hygrometer invented by Francesco Folli c. 1660. A brass frame, in the shape of a finely decorated balustrade, carries a small roll at each end, on which is wrapped the end of a paper (now missing) ribbon serving as a hygroscopic substance. The center of the frame holds a decorated brass dial fitted with a circular graduated scale. The dial is integral with a pointer that, by means of a simple mechanical system, indicates the changes in ribbon length due to the variations in atmospheric humidity.