Instrument identical to the hygrometer described by Horace-Bénédict de Saussure c. 1780. It consists of a brass frame on which is stretched a bundle of hair (originally, a single hair was called for) secured by small jaws and passing over a pulley with a pointer. A counterweight, connected to the pulley, kept the bundle taut. The hair, which functions as a hygroscopic substance, varies in length with air humidity. The changes can be read on a semicircular silvered scale registering the positions of the pointer. This instrument, attributed to the maker Jaques Paul, is similar to item inv. 3708.