Ever notice how hair (especially long hair) seems different on humid days than on dry days? That’s because it is. One property of human hair is that it is measurably and reliably longer in humid conditions. A human hair at 100% humidity is about 2.5% longer than at 0%. While that isn’t very much, it can be directly observed. Horace Bénédict de Saussure is credited with creating the first human hair hygrometer in 1783.

One simple way to make a hygrometer only requires a long hair, a small weight, a tack, a small ring, a marker, and something to use as a backboard:

  • For best results wash the strand of hair in alcohol to remove any oils.
  • Tie the hair to the weight.
  • Loop it between the ring and the weight a few times.
  • Tie it off and attach to the backboard by the ring with the tack.
  • The weight should hang from the hair attached to the tack.

To calibrate a “dry” mark, use a hairdryer to dry the hair thoroughly, mark the board in line with the weight. This should be the shortest the hair contracts to. As the hair is exposed to humidity, it will lengthen, and the weight will drop slightly, indicating more moisture.

While this style is simple and easy to make, since the hair doesn’t change much it would be easier to read if the movements were exaggerated.

For an easier to read version, collect a paper plate, a tack, a bamboo skewer, some tape, a marker, a small washer, and another long beard (or head) hair.

First, attach one end of the hair to the bamboo skewer a couple of inches from the blunt end with tape.
Then push the tack through the wrong side of the paper plate an inch or so from one edge.

Impale the bamboo skewer near the blunt end on the tack. The skewer should swing along the face of the plate using the tack as a pivot. Make a nick in the paper plate near the top. Draw the free end of the hair up and though the nick. Pulling on the hair should raise and lower the free end of the bamboo skewer. Attach the washer to the skewer so it pulls the hair taught. Pull the hair until it raises the skewer across the face of the plate, and tape the end of the hair to the back.

The bamboo skewer acts as a pointer, and its movement is magnified by the attachment point being close to the pivot. The basic principle is the same as the first example; in high humidity, the hair gets longer and the end of the pointer drops, in low humidity the hair dries and gets shorter, raising the pointer. Lines can be drawn to indicate humidity levels. These reference marks can even be calibrated by comparing the results to a store bought hygrometer.

More advanced versions of this same principle are possible. Folksy wooden swinging hygrometers called “weather houses” were once not uncommon. They have a pair of figures in a house shaped frame that is balanced on a board suspended by a hidden wrapping of hair (or similar acting material). Which figure swings out is dependent on the humidity.

Beard Hair and Homemade Hygrometers was last modified: by

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