Are there different types of thermometers?

Dateline article| David Murphy|

by David Murphy

Yes. There are several types of mechanical thermometers.

The type you're probably most familiar with is the Liquid-In-Glass Thermometer. In fact, your ancestors may have been familiar with it too, because it was developed way back in the 1600s. This is the sort that features a tube and an expanding liquid that rises along a path of marked readings as the temperature goes up. See How Does A Thermometer Work? for a more detailed explanation. A Maximum Thermometer usually contains mercury, which expands and stops at the high temperature for the day. A Minimum Thermometer often contains alcohol and a dumbbell-shaped device that sinks as the temperature drops and then remains in place as the temperature rises, marking the daily low. A Bimetal Thermometer consists of two thin metal strips that are attached to each other and have much different rates of expansion when they're heated. As the temperature rises, the strips curl. How far they curl indicates the temperature. A Thermograph continuously records temperature by drawing a line on graph paper that corresponds with the progression of temperatures throughout the day. A bimetal strip is usually attached to the thermograph to sense the changing temperature. There are also Electrical Thermometers. A common type is the Thermistor, which contains a small electronic part that resists the flow of electricity. This resistance changes a bit with a change in temperature, so that the amount of current passing through the device can be used to generate a temperature reading.

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