A hygrometer is a device for measuring of air humidity. Depending on the principle of the device distinguish between weight hygrometer, which allows to determine the amount of water vapor in grams per 1 m3 of air; condensation hygrometer, based on the cooling air to the dew point and condensation of water vapor; psychrometer (see) and the hair hygrometer, based on the property of a human hair shortened at reduction of relative humidity and extended.
Different types of hygrometers are widely used in the determination of relative and absolute humidity in the field, at the meteorological stations. The weight and condensation hygrometer is usually used only in the laboratory to determine the absolute air humidity.
the hair hygrometerIn winter the only device for determination of ambient air humidity is the hair hygrometer (Fig. 1), as the observations by the psychrometer terminated when the air temperature is below -10 degrees. The main part of the hair hygrometer is fat-free human hair, stretched on the frame so that the upper end of it is secured with a rolling screws and lower connects to the unit and lift small weights attached to the unit. With the same unit linked easy arrow-pointer. When the relative humidity of the air changes the length of the hair and the pointer moves along the scale, which caused division, directly indicates the percentage of humidity.
hygrographFor continuous registration of changes in the relative humidity is recording hygrometer - hygrograph (Fig. 2). It consists of perceiving part (beam fatless human hair), systems of transfer of arms, ending with an arrow with a feather, and the registration part (drum with tape, which rotates clockwork). There are gigography weekly and daily plant.