Hygrometer

View of a hygrometer, here referred to as a notiometra, in an outdoor, mountainous setting. Hygrometers are used to measure the amount of humidity and water vapour in the atmosphere. A dial is visible on the left leg [as viewed] showing a nonlinear scale, and a piece of string is suspended in between the legs.

Plate 27 from a German translation of Joachim d’Alence’s Tractatus de barometris… (Ludwig Bourgeat, Mainz, 1688), an early account of meteorological instruments including barometers, thermometers and hygrometers.

Joachim d’Alence (1640-1707) French astronomer and physician.