An ANEMOMETER A THERMOMETER measures the air temperature. Most measures wind speed. The cups catch the wind, turning thermometers are closed a dial attached to the glass tubes containing liquids instrument. The dial shows such as alcohol or mercury. the wind speed. There are When air around the tube different types of heats the liquid, the liquid anemometers, but the expands and moves up the most common type is tube. Some thermometers measure temperatures in both called a cup anemometer. Celsius and Fahrenheit scales. A WEATHER VANE is an A BAROMETER measures air pressure. It tells you instrument that determines the direction from which the whether or not the air pressure is rising or falling. wind is blowing. They are also called a wind vane. They are A rising barometer means often mounted on a pole or sunny and dry conditions, tower that is in turn mounted while a falling barometer on the roof of a tall building. means stormy and wet When the wind blows, an conditions. Big changes in arrow indicates the wind the barometric pressure mean a storm is coming. direction. A RAIN GAUGE measures the amount of rain that has fallen over a specific time period. After the rainfall is measured, meteorologists will look at the other weather instruments to see what the conditions were like right before the rain. This helps them make weather predictions. A HYGROMETER measures the water vapor content of air or the humidity. The amount of water in the air compared to the amount that it could hold is the “relative humidity”. If air holds all of the water vapor it can, it is at 100% relative humidity and is “saturated”. .