Description

This instrument consists of a brass cylinder covered with recording paper and a stylus that is resting near the paper on one end, and attached to a bracket with a bundle of hairs (now removed and bagged separately) on the other end. The recording paper on the cylinder is marked in red ink with the days of the week and percent humidity. The instrument is housed in a metal case and protected with a hinged cover that has a glass viewing window in the front. A metal plaque on the base of the instrument has "Cat. No.580, Chart No. 58B, Pen no. 1BT, Ink No. 10” inscribed on it. A paper label found with the object reads “Recording Hair Hygrometer / Used in instrument shelters. / Manufactured by Julien P. Friez, Baltimore."

Hair hygrometers are devices that measure the humidity of the atmosphere by measuring the variation in the length of a human hair in various environmental conditions. Since hair is hygroscopic (that is, it tends to hold onto moisture), it lengthens as the air around it becomes more humid. In hair hygrometers, hair (usually human) is attached to a spring, which in turn is attached to a dial. As the hair lengthens and contracts, the dial reads the relative humidity.