Measuring Humidity with Hair

 

Before modern meteorological measurements, humidity was measured using hair. In 1783 Swiss scientist H.B. Saussure invented the hair hygrometer. It’s similar to the image above. As the relative humidity increases, hair becomes longer, and as the humidity drops it becomes shorter. On very humid days, your hair actually becomes longer and this extra length causes the frizziness that gives us bad hair days. This instrument uses strands of human or horse hair with the oils removed attached to levers that magnify a small change in hair length. Red hair works best. An ink pen and rotating cylinder, known as a hygrograph, can provide a record of how relative humidity varies throughout the day. The disadvantages of the hair hygrometer and hygrograph are that they are not as accurate as other kinds of hygrometers such as the sling psychrometer. Also, a hair hygrometer needs frequent adjustment and calibration. Hair hygrometers also tends to have large errors at very high and very low relative humidities. You can get your “haircast” forecast at: www.justweather.com

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