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A weather instrument is any type of measurement device that gives information about the weather. Meteorologists and hobbyists use many different types of weather instruments to gauge accurate information about current climate and help to predict future weather. A weather instrument may be as simple as a thermometer or as complicated as a digital handheld device that measure solar radiation.
One common type of weather instrument measures properties of wind. A weather vane is usually placed in a high, unimpeded spot, and features a stylized arrow that is weighted at the back. When wind blows, the arrow spins to a point in the direction that the wind is blowing. There are also devices that measure wind speed, usually referred to as anemometers. Some anemometers have a structure with several arms that can spin in the wind; the measurement of wind speed is divined from reading the rotational spin of the arms. The highest wind speed ever recorded by an anemometer occurred on 12 April 1934 at the Mount Washington observatory in New Hampshire. According to the anemometer and the very surprised technician sent to read it, the wind blew at a record breaking 231 miles per hour (371.75 kilometers per hour).
Thermometers are extremely vital to measuring the temperature of the air. This weather instrument uses either a Fahrenheit or Celsius scale for meteorological purposes. Most thermometers are a glass bulb that extends into a long, thin tube. The bulb is filled with mercury, which expands it heats. The expansion forces the mercury out of the bulb and into the tube, which is marked with a temperature scale. Whatever degree the mercury reaches establishes the temperature.
Humidity is a weather property that describes the amount of moisture or water vapor in the air. The weather instrument used for measuring humidity is called a hygrometer. Hygrometers come in several different types: a psychrometer measures the difference in temperature between a bulb that is damp and one that is dry, while a condensation hygrometer uses a mirror that can detect the point at which fog condenses on the mirror.
When a weatherman comments that a town has received five inches of rain, it is based on a device known as a rain gauge. One of the most simple types of rain gauges involves a ruler or measuring device suspended in a narrow container. As rain collects in the container, the amount of rain can be measured by referring to the ruler. It is important for a rain gauge to be placed in an open area; shelter given by trees or roofs will cut down on the amount of rain that reaches the container, making the reading inaccurate.