Museo Galileo
Virtual Museum
Folli's paper-ribbon hygrometer
    • Setting:
      Room IX
    • Inventor:
      Francesco Folli
    • Maker:
    • Date:
      second half 17th cent.
    • Materials:
      wood, brass
    • Dimensions:
      length 711 mm, height 238 mm
    • Inventory:
    • Folli's paper-ribbon hygrometer (Inv. 2434)

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.