HYGROMETER (Gr. hypos, moist, L Tpov, a measure)  , an instrument for measuring the absolute or relative amount of moisture in the atmosphere; an instrument which only qualitatively determines changes in the humidity is termed a " hygroscope." The earlier instruments generally depended for their action on the contraction or extension of substances when exposed to varying degrees of moisture; catgut, hair, twisted cords and wooden laths, all of which contract with an increase in the humidity and vice versa, being the most favoured materials . The familiar " weather house " exemplifies this property . This toy consists of a house provided with two doors, through which either a man or woman appears according as the weather is about to be wet or fine . This action is effected by fixing a catgut thread to the base on which the figures are mounted, in such a manner that contraction of the thread rotates the figures so that the man appears and extension so that the woman appears . Many of the early forms are described in C . Hutton, Math. and Phil . Dictionary (1815) . The modern instruments, which utilize other principles, are described in METEOROLOGY : H . Methods and Apparatus .