Hair Hygrometer

Ever notice that when it‘s humid you have a Bad Hair Day? Hair increases its length when humidity increases. So curly hair frizzes and straight hair goes limp. From dry to humid, hair length can change by 3 percent. In this activity, we‘ll hook up a hair to a lever system and create a hair hygrometer to measure changes in humidity. Invented in 1783, the hair hygrometer was so reliable that it was not replaced by an electrical instrument until the 1960s!!!!!!



  • Empty milk carton
  • Large sewing needle
  • Broom straw,
  • 2" long Scotch or masking tape
  • A Cent 9" human hair, wiped clean of oil
  • 4 thumbtacks
  • Paper clip
  • Dishpan



  • Cut the carton so as to make a small horizontal slit near the top; insert the paper clip. (Fig.1).
  • Cut a vertical slit near the bottom. Then cut horizontal slits perpendicular to this cut at its end points - like an H on its side. (Fig.1)
  • Pry out the flaps thus made and bend them to an upright position. Insert the needle through these flaps. (Fig.2)
  • Tie the hair to the paper clip, wind it around the needle, tape the cent to the other end of the hair, and let the penny hang over the end of the box, which should be lying on its side.
  • Put a card with a scale on the side of the carton under the straw which has been pushed through the eye of the needle. (Fig.3)
  • Place the hygrometer on a wet towel in a dishpan and cover with a damp cloth. After 15 minutes remove it from the cloth and set the straw at numeral 10 on the scale.
  • Watch to see whether the straw moves. Since humid air causes the hair to stretch and dry air causes it to shrink, the straw should move toward the dry end of the scale as the hair dries.