Weather Instruments

Thermometer What does it do? What does it do? It measures the air temperature It measures the air temperature

How do they work? Most thermometers are closed glass tubes containing liquids such as alcohol or mercury. Most thermometers are closed glass tubes containing liquids such as alcohol or mercury. When air around the tube heats the liquid, the liquid expands and moves up the tube. When air around the tube heats the liquid, the liquid expands and moves up the tube.

Barometer What does it do? What does it do? It measures air pressure It measures air pressure

How does it work? It tells you whether or not the air pressure is rising or falling. It tells you whether or not the air pressure is rising or falling. When a barometer reading is rising, it means sunny and dry. When a barometer reading is rising, it means sunny and dry. When a barometer reading is falling, it means stormy weather is coming! When a barometer reading is falling, it means stormy weather is coming!

The first barometer was built in 1643 by an Italian scientist named Torricelli. The first barometer was built in 1643 by an Italian scientist named Torricelli. It works by balancing the weight of mercury in the glass tube inside against the atmospheric pressure, just like a set of scales. It works by balancing the weight of mercury in the glass tube inside against the atmospheric pressure, just like a set of scales.

If the weight of mercury is less than the atmospheric pressure, the mercury level in the glass tube rises. If the weight of mercury is less than the atmospheric pressure, the mercury level in the glass tube rises. If the weight of mercury is more than the atmospheric pressure, the mercury level falls. If the weight of mercury is more than the atmospheric pressure, the mercury level falls.

Sling Psychrometer What does it do? What does it do? It measures relative humidity, using the cooling effect of evaporation. It measures relative humidity, using the cooling effect of evaporation.

How does it work? Two thermometers are used. Two thermometers are used. A wet cloth is placed on one of the two thermometers in the psychrometer. The psychrometer is swung around a few times. A wet cloth is placed on one of the two thermometers in the psychrometer. The psychrometer is swung around a few times. Water evaporates from the cloth, causing the temperature on that thermometer to be lower than the other. Then you can calculate the relative humidity – comparing one thermometer to the other. Water evaporates from the cloth, causing the temperature on that thermometer to be lower than the other. Then you can calculate the relative humidity – comparing one thermometer to the other.

Rain Gauge Measures the amount of rain that has fallen over a specific period of time. Measures the amount of rain that has fallen over a specific period of time.

Wind Vane Determines the direction from which the wind is blowing. Determines the direction from which the wind is blowing.

Anemometer Measures wind speed. Measures wind speed.

Hygrometer Measures the water vapor content of the air, or the humidity. Measures the water vapor content of the air, or the humidity.

Weather Balloon A WEATHER BALLOON measures weather conditions higher up in the atmosphere. A WEATHER BALLOON measures weather conditions higher up in the atmosphere.

Weather Satellites Used to track and photograph large weather systems.