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The Spokesman-Review Newspaper
Spokane, Washington  Est. May 19, 1883

Calculating temperature goes back centuries

Michelle Boss Correspondent

The need to know the temperature of something confronts us every day. The oven, the thermostat in our house, our hamburger patty on the grill, and even our own bodies, measure the temperature. In meteorology, we are mainly concerned with the temperature of the air, and how it changes in the vertical, the horizontal and over time. Of course, all of these measurements are made possible by some type of thermometer.

The most basic instrument to measure temperature was invented back in 1593 by Galileo Galilei, a well-known Italian mathematician and philosopher. In his library, Galileo kept a glass bulb, about the size of a chicken egg, filled with a clear liquid that had a thin tube sticking out of the top. He and his friends watched the liquid inside the tube rise and fall as the temperature changed. Galileo correctly calculated that the volume of the liquid would expand as it warmed and shrink as it cooled. There was no scale associated with Galileo’s device, called a thermoscope.

In later years, other inventors would add a scale to the thermoscope. None really caught on until German physicist Gabriel Daniel Fahrenheit came along more than 120 years later in 1724. In his thermoscope with a scale – a thermometer – he used mercury rather than water or alcohol for the liquid. This gave his instrument higher precision. His scale was such that water boiled at 212 degrees “Fahrenheit” and froze at 32 degrees. A couple of decades later, Anders Celsius proposed a scale using 100 degrees “Celsius” and 0 degrees, respectively. These mercury-in-glass type thermometers are widely used today using both the Fahrenheit and the Celsius scales.

There are other ways to measure temperature, however, besides using the expanding and contracting properties of a liquid. These same properties in a solid are used to make a bimetallic strip thermometer. Strips of two differing metals (usually steel and copper) are joined together. The two metals expand/contract at different rates when heated/cooled, causing the strip to bend. A scale can be applied to the degree of bending, and temperature can be measured. This type of thermometer is commonly used in thermostats to regulate heating and cooling, and also in the everyday backyard dial thermometer.

Electrical resistance and voltage output are also properties that are temperature dependent. This knowledge has been used to invent temperature sensors called thermistors and thermocouples, which are used for ovens and water heaters.

Infrared thermometers measure temperature by using the infrared radiation emitted by an object. This type of thermometer can be used to measure the temperature of an object that is far away, such as a cloud. It is also the technology used in those handy ear thermometers that make taking a child’s temperature much easier.

In meteorology, many of these different types of thermometers are used. The mercury in glass thermometer is the most common way to measure air temperature at the surface, and is what most people are familiar with. Weather balloons launched twice daily at upper air stations across the U.S. utilize the thermistor to chart the temperature of the air from the ground to altitudes of tens of thousands of feet. Infrared thermometers on satellites provide cloud top temperatures, which help computer programs paint images of the clouds on an infrared satellite image.

No matter what type of thermometer you use, one thing is for sure. Temperatures are on their way down. With recent snow in the mountains, and cool highs in the 40s in the valley locations, wintry weather will be upon us before we know it.