In the 17th century, scientists became fascinated with ways of measuring the amount of moisture in the air. Horace Benedict de Saussare, a Swiss scientist, remarked that hair responds to humidity levels and incorporated hair into his hygrometer design. Hair makes an ideal substance for this weather instrument because it expands and contracts in response to changing humidity levels. When humidity levels rise, hair lengthens. Conversely, when humidity levels fall, hair shortens.