Hygrometer attributed to Vincenzo Viviani, fully resembling the model invented by Santorio Santorio. On a wooden board, to be hung on a wall, a horizontally stretched rope of twisted gut is used as hygroscopic substance, weighted at the center by a boxwood ball. The changes in air humidity cause the gut to lengthen or shorten, modifying the ball's vertical position. This is measured by means of a graduated brass plate attached to the board. The brass plate is probably the only original part.