Hygrometer

HYGROMETER, an instrument for determining the humid ity of the atmosphere (Gr. i ypen, wet, js pov, a measure), an instrument which determines the humidity changes only is termed a "hygroscope." The earlier instruments generally depended for their action on the alterations in the length of substances when exposed to varying degrees of moisture; catgut, twisted cords and wooden laths, all of which contract with an increase in the humid ity, being the most frequently employed.

Many of the early forms are described in C. Hutton,

Math. and Phil. Dictionary (1815) . Modern instruments, which utilize other principles, are described in METEOROLOGY.