Air thermometers measure atmospheric temperature using a long tube filled with mercury or colored alcohol that expands as the temperature rises. They use Fahrenheit, Celsius, or Kelvin scales. Galileo invented the first thermometer, and early versions used water. Spring-loaded and digital thermometers are also available.
An air thermometer is a device that measures the temperature of the inside or outside atmosphere. The most common type is a long tube that contains mercury or colored alcohol at its base, although there are other types as well, such as spring-loaded and digital thermometers. As the atmospheric temperature rises, it causes the material inside the air thermometer to expand. Conversely, as the air gets colder, the material contracts and moves back. Thermometers use temperature scales, Fahrenheit, Celsius or Kelvin, to provide a measurement of heat in degrees.
One of the first thermometers was invented by Galileo about 400 years ago to measure the temperature of water, but devices for measuring the temperature of air were not developed until much later. In general, the idea of an air thermometer is based on the fact that liquids and gases expand when heated and contract when cooled. Early air thermometers used the same basic mechanics as many of the instruments used today: a glass tube filled at the end with mercury or colored alcohol that rises through the tube as it is heated. Early thermometers held water, but later versions switched to alcohol or mercury because their freezing points are lower.
The tube of a thermometer usually has a scale printed on it that gives a measurement of temperature, and the liquid inside rises to a certain point on that scale depending on how hot it is. In the United States, the Fahrenheit scale is most commonly used, which starts at a freezing point of 32 degrees. The Celsius scale is used in Europe and most of the world outside the United States and starts with zero degrees as the freezing point. The Kelvin scale is a third type of measurement that is based on the theoretical concept of absolute zero, a point at which molecules stop moving completely and cannot cool down. It is mainly used in scientific applications.
Another type of air thermometer uses a heat-sensing metal coil attached to a dial or gauge to measure air temperature. As the air gets hotter, the spring expands, causing the hand to move higher. A spring-loaded thermometer may not be as accurate as one that uses liquids. A digital thermometer contains heat-sensitive material and displays the temperature measurement on an electronic screen rather than a printed scale. Digital thermometers can often operate faster than other types.
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