Hygrometer of the type invented or perfected by Vincenzo Viviani. The instruments are incomplete: the hygroscopic substance—a paper ribbon—and the pointer are missing. The iron frame bears a small plate to which a paper scale is glued. A small strip of hygroscopic paper was fitted with an indicator and held by the frame. It lengthened or shortened with the changes in atmospheric humidity. This instrument is identical, even in size, to item inv. 2, 2438.