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Experiential Science 10—Terrestrial Systems
Activity 9
4 field activity
4 lab activity
library activity
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classroom activity
4 chapter project
research team activity
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Making a Hygrometer
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Purpose
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To build a hair hygrometer to measure moisture in the air.
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Background Information
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Invented in 1783, the hair hygrometer was so reliable that it
was not replaced by an electrical instrument until the 1960s.
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Materials and Equipment
Procedure
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0
cm
• a scrap piece of wood or piece of Styrofoam
approximately 10 cm by 20 cm
• a thin piece of plastic approximately 7 cm in length,
thin enough to cut with scissors
• 2 small nails
• 3 long strands of human hair (approx. 20 cm in length)
• a dime
•glue
•tape
•hammer
• scissors (to cut the plastic)
• metric ruler
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A simple hygrometer made with strands of human hair. When
humidity is higher, the hair cells expand and the weight of the
dime moves the pointer lower. When humidity is lower, the
hair cells contract and pull the pointer higher.
7. Pull the hair strands straight and tight so that the pointer
points parallel to the ground, and glue the hair around
the nail at the top of the wood or Styrofoam. Be sure that
the hair strands are perpendicular to the pointer, so that
the pointer is pointing horizontally and the hair is hanging
straight down.
1. Cut the piece of plastic into a triangular shape.
8. Tape a ruler vertically near the pointer to use as a scale.
2. Tape the dime onto the plastic, near the point.
9. Take daily observations of the hygrometer, marking in your
notebook where the pointer is.
3. Poke one of the nails through the plastic pointer, near the
base of the triangle. Make the hole large enough that the
nail turns freely.
4. Between the nail and the dime, glue the end of the hair
strands to the plastic.
5. Position the pointer on the wood or Styrofoam base about
three-quarters of the way down the side. Attach the nail to
the base. Again, be sure that the pointer can move freely
around the nail.
6. Attach the other nail to the top of the wood or Styrofoam
near the top, directly above the spot on the pointer where
the hair is glued.
Conclusions
1. What did you observe over the course of a week? Was
there a pattern?
2. How does recording humidity patterns help you forecast
the weather?
3. How do your readings compare with those from your
community weather monitoring station?
SCIENTIFIC TERMS
hygrometer: an instrument used to measure humidity.