Baroscope

BAROSCOPE (from Greek baros-weight and scopeo-I look), a name, mainly, for instruments that determine barometric pressure based on the density of atmospheric air. The instruments are based on the principle that when weighing any body in air, the scales do not indicate the true weight of the body, but only the difference between the true weight and the weight of the volume of air displaced by the body. Thus, if a large hollow sphere is suspended to the beam of very sensitive scales, and on the other side of the beam it is balanced with a small heavy weight, then such a system will be in equilibrium only at a certain barometric pressure; but if this pressure changes, then due to the change in air density, the equilibrium of the beam will be disrupted, since the difference in the weight of the displaced air will be different than before. In the Heller baroscope, the movements of the instrument's beam are read by means of a mirror; in the Galileo baroscope, the oscillations of the beam are transmitted to a pointer moving along a scale with divisions. The readings of the instruments are strongly influenced by temperature and air movement. Some authors by the word baroscope mean specially constructed shortened mercury barometers. The term baroscope is also often applied to all sorts of simple instruments by means of which one can demonstrate changes in barometric pressure in one way or another.