This instrument, similar to the hygrometer described by Horace-Bénédict de Saussure c. 1780, consists of a brass frame with leveling screws holding a circular crown with a scale. The frame carries the mobile clamp for holding the single hair used as a hygroscopic substance. The changes in atmospheric humidity lengthen and shorten the hair, causing the pointer to move. The instrument, made by Jaques Paul, is incomplete: the axle with the pulley and the pointer are missing.