Chapter 2 OBSERVING WEATHER AIR PRESSURE: BAROMETER: An area of higher air pressure than that of the surrounding air. LOW PRESSURE AREAS: A device used to measure air pressure. HIGH PRESSURE AREAS: The push of the air in all directions against its surroundings. An area of lower air pressure than that of the surrounding air. WIND VANE: A device, often shaped like an arrow, used to show the direction of the wind. WINDSOCK: ANEMOMETER: The amount of water vapor in the air. RELATIVE HUMIDITY: A device used to measure the speed of the wind. HUMIDITY: A device used to show wind direction, consisting of a cloth bag that is open at both ends and hung on a pole. The amount of water vapor present in the air at a given temperature compared to the maximum amount that the air could hold at that temperature. EVAPORATE: To change from liquid to a gas. CONDENSES: CLOUD: A mass of tiny droplets of water that condensed from the air. PRECIPITATION: To change from a gas to a liquid. Any form of water that falls from clouds to Earth’s surface. RAIN GAUGE: A device for measuring precipitation.