October 17, 2010 in Idaho Voices

Weather watch: Just how does that thermometer work?

Michelle Boss
 

One of the main reasons people watch the weather forecast is to get an idea just how hot or cold it is supposed to be at some time in the future.

Many of us have some type of thermometer either inside or outside the house, and being the weather geek that I am, I check the temperatures numerous times a day. There are many ways of measuring temperature, and also several different scales with which to measure. The simplest technique for measuring temperature, is to take some kind of liquid which expands or contracts in response to heat and cold, and to measure the change in volume of the liquid.

Your standard mercury thermometer uses this principle. Another common way to measure temperature consists of two pieces of metal, like steel and copper, welded together. Since the metals expand/contract at different rates in response to temperature, the strip of two metals will bend one way or another due to those changes in temperature. These kinds of thermometers are called bi-metallic strips, and they are commonly used in things like meat and patio thermometers. Resistance thermometers use the fact that the electrical resistance of a substance is temperature related, and similarly a thermocouple measures temperature by taking two different alloys joined together and measuring the electrical potential between the two, a factor also related to temperature. Thermocouples are some of the most widely used types of thermometers, seen everywhere from the steel industry to the inside of the weather station I use.

Two out of the three scales used to measure temperature are probably familiar to you. They are the Fahrenheit and Celsius temperature scales. On the Fahrenheit scale – devised by Gabriel Fahrenheit who lived from 1686 to 1736 – water freezes at 32 degrees F and boils at 212 degrees F. A little later, Anders Celsius (1701-1744) came up with another scale we now call the Celsius scale or Centigrade. It is the temperature scale used by most of the world.

On this scale, the difference between the freezing temperature (0) and boiling temperature (100) is 100 degrees. Less well known, and used mostly by scientists, is the Kelvin scale, devised by physicist and engineer William Thomson, 1st Baron Kelvin (1824-1907). Zero Kelvin (0 K), also called “absolute zero” is the temperature at which there would be almost no molecular activity. Scientists have never been able to artificially bring anything down to this temperature (though they have come very close). Absolute zero is equal to -273.15 C or -459.67 F.

Whatever thermometer type you have, and whatever scale you use, it looks like we’ll be measuring some warmer than normal temperatures for the upcoming week. It will also be drier than normal, as a ridge of high pressure once again dominates the western U.S. This is not your typical October weather pattern, so enjoy it while you can!

Michelle Boss can be reached at weatherboss@comcast.net


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