Type of hygrometer invented by Francesco Folli c. 1660. A square-sectioned wooden rod carries a small roll at each end. One of the rolls holds the end of a paper ribbon, while the other end passes over the second roller. It originally supported a small (missing) weight that kept the ribbon in tension. The center of the rod holds a vertical support for a decorated brass dial fitted with a circular graduated scale. On the dial a pointer is pivoted with a pulley: the ribbon passes over the pulley and its length variations, in response to change in atmospheric humidity, are indicated by the pointer.