Facts About Hair Hygrometers
Measuring humidity is an important aspect of tracking and predicting weather conditions. It also is valuable for keeping people and animals comfortable, since very high or low humidity levels can inhibit the ability to sweat and cool, or can cause problems such as dry, cracked skin. Scientists have come up with many ways to measure humidity, but the main instrument used is the hygrometer. Some modern hygrometers are quite sophisticated, but a simple hygrometer still can be made using human hair.
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Definition
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A hair hygrometer is an instrument that measures relative humidity levels using human hair, which expands and contracts. Hair hygrometers may show the relative humidity with a simple scale, or it can be recorded on a hygrograph.
How They Work
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Hair hygrometers work under the principle that human hair expands as humidity rises and contracts as humidity lowers. This is made possible by hair's physical structure. Human hair is hooked to a lever (gauge). As the hair expands and contracts with the changes of humidity, the lever moves. When placed next to a simple graph or other scale that can show percentages, an individual can measure both the current humidity level and monitor how the humidity level is changing. Sometimes the lever system of the hygrometer is hooked up to a writing utensil and scroll of paper that can rotate (a hygrograph) so that humidity changes can be recorded.
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History
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The hair hygrometer was invented in 1783 by Horace Benedict de Saussure. The hair hygrometer was seen as such a simplistic, effective method of humidity measuring that it wasn't replaced by electrical devices until the 1960s. Today, hair hygrometers have been replaced for the most part, but they still are occasionally used and are often constructed as teaching projects in schools.
Benefits
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One of the main benefits of the hair hygrometer is that it does not require electricity to operate. Additionally, a hair hygrometer is cheap to make---it can be constructed with a bit of metal, cardboard, a few push pins, and of course, a few strands of hair.
Drawbacks
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Hair hygrometers have two main drawbacks. The first is that, because hair can expand and contract only a certain amount, the errors at very low or very high relative humidity levels tend to be large. Furthermore, hair hygrometers have to be adjusted and calibrated often or readings will be inaccurate.
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