hygrometric balance

An instrument for indicating the relative density of the air, and consequent changes of rain or dry weather. It consists of a balance, from one arm of which is suspended a bra weight, and from the other a large, thin, hollow cylinder, closed at each end. The two are arranged so as to be in equilibrium at a given density of the atmosphere, and it is evident that if the air become heavier, the large cylinder, displacing more air than the solid weight, will become more buoyant and ascend. If, on the contrary, the air become lighter, it will sink. A rod descending from the scale-beam serves to indicate, on the graduated arc below, the comparative density of the air at the time of making the observation. If the air be heavy, fine weather may be expected; but if the cylinder sink, rain usually follows. hygrometric-plants, s. pl. Bot.: Plants so sensitive to changes in the atmosphere that they will indicate a change in its Peru) shuts after 7 A. M., rain is near at hand. hy-grom-ě-try, s . [HYGROMETER.] The me as urement of the amount of aqueous vapor in the air at any time. This may be effected by absorbing the moisture from a given quantity of air; by finding the dew point, that is the point at which dew is deposited, or by a psychrometer (q.v.). ( Ro iter .) hy-groph-a-nous, a . [Pref. hygro- ; Gr. phaino = to cause to appear, and Eng. suff. -ous.] Bot .: Having such a structure that it is transparent when moist and opaque when dry.