Temperature and Humidity

• Perhaps the most familiar instrument is the thermometer, which measures the temperature either in Fahrenheit or in Celsius. Early thermometers used a column of mercury in a tube to gauge the temperature; today's thermometers are electronic. Less familiar is the hygrometer, an instrument that measures the amount of moisture in the air, or humidity.
  
  

Atmospheric Pressure

• A barometer measures atmospheric --- or air --- pressure. When the air pressure rises, it means good weather is coming; when it falls, it means bad weather is on the way. A microbarograph measures and records the air pressure on a piece of paper continuously. As with other weather instruments, modern ones use electronic sensors.
  
  

Precipitation

• The simplest instrument is the rain gauge, which measures rainfall and other precipitation in millimeters. It is a long cylinder that collects this precipitation. To measure the amount, insert a measuring stick and record the level. A weighing bucket rain gauge works a little differently than the standard rain gauge by weighing the amount of precipitation and converting that inches.
  
  

Wind

• An anemometer measures wind speed and direction. Anemometers resemble windmills that have three metal cups that spin when the wind blows. They may also have a tail that points in the direction of the wind. They spin faster when the wind is stronger. A common sight around airport runways and in people's yards is the wind sock. It looks like a conical tube with two open ends. Wind enters one end, lifting it in the air and pointing it in the direction of the wind.