How Humid's That Air? Ask Your Hair.
Wx and the City
By Ann Posegate, Guest Contributor
D.C.'s tropical rainforest-like summer weather has begun, and I know I'm not the only one out there with a frizzy hair problem as a result. Not sure how a bad hair day is related to weather? Believe it or not, human (and horse) hair is a great indicator for relative humidity.
Keep reading for more on the connection between hair and humidity. Will today's humid air lead to afternoon and evening storms? See our full forecast, and NatCast for tonight's game at Nationals Park.
Humans have been using hair to test humidity since 1783, when Horace Benedict Saussure discovered that the length of human and animal hair changes according to humidity levels and invented the hair hygrometer. Before that, inventors thought that wool, sponge and even rat bladders could accurately measure moisture in the air and predict rain. I don't know about you, but I'd rather pluck a few hairs from my head than watch the expansion and contraction of a rat bladder filled with mercury.
Why hair? Relative humidity measures the saturation of the air, or how much water vapor air "holds" depending on temperature; the higher the moisture, the higher the humidity. (Check out USA Today for a thorough guide to understanding humidity). In a hair hygrometer, several strands of human or horse hair are stretched out and held at a constant pressure. When hair is exposed to water (i.e., high humidity), the hydrogen bonds in keratin -- a protein found in hair -- break, and the hair lengthens. When the air becomes drier, the bonds form again and the hair shortens.
Spending much of my childhood in Arizona and years of my adult life in northern New England, I didn't have to worry much about humid summers until moving to D.C. Now I have a deeper understanding for the subject. And as an informal weather observer, I can now appreciate a bad hair day.
Want to make your own hair hygrometer? Check out these fun experiments.
Capital Weather Gang
| July 9, 2008; 10:45 AM ET
Categories: Education, Posegate, Wx and the City
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