This instrument measures what your hair already does – humidity in the air.

In fact, the materials to make this weather measuring device include – hair.

This project is more complex than the preceding three weather machines.

It integrates nicely with other weather machine activities, including barometer and cloud study.

What makes it special is that the hair hygrometer, invented in 1783 was the technology of choice to measure humidity until the 1960′s.

Hygrometer – Measure Humidity in the Air

Materials:

• corrugated cardboard 12inches long and 9 inches wide
• piece of thin cardboard
• scissors
• knife
• one pushpin or other large-diameter pin
• one straight or common pin
• strand of hair that’s 12 inches long
• hot glue gun
• dime
• hair dryer
• access to a shower

Procedure:

1. Hold the cardboard so the 9″ edge is on top.
2. Measure one inch from the left edge.
3. Cut two slits 1/4-inch apart, about 1/2-inch deep.
4. From thin cardboard, cut a banner shaped triangle.
5. The deep end should be about 2 inches and the length about 6 inches.
6. Measure one inch from the left edge of the banner.
7. Cut two slits on the bottom of the banner about 1/4-inch deep.
8. This banner is your pointer.
9. About 1/3 from the bottom of the left side of the cardboard push pin the fat end of the pointer.
10. Wind the hair strand through the top and bottom slits so it runs the length of the corrugated cardboard.
11. Glue the hair in place in both sets of slits.
12. Glue the dime 1.5 inches from the narrow end of the pointer.
13. Stick the straight pin through the hole in the pointer-you want the hair to be slightly stretched when the pointer is horizontal.

To Calibrate Your Hygrometer:
Bring it into the shower.
When you finish, mark where the pointer stops. That’s 100% humidity.
Now dry the hair on the hygrometer with a hair dryer.
Mark where the pointer stops. That’s 0% humidity.

Now try placing your hygrometer in different locations. What can you tell about the humidity in different rooms of your house?

Play with your hair for science:
What happens to a strand of your wet hair when you pull on it?
What happens to a strand of straight hair when you hold it between your thumb and forefinger and then run your fingernail across the strand? Does it break? Does it curl?
What are the qualities of hair that make this humidity indicator work?

For further study, research Chilled Mirror Hygrometer invention by David Egan, Jeffrey Hawkins and Napoleon Baeuvais.

NOTE:
I’m always looking for ways to improve projects and activities. Contact me with
your results or if anything is unclear to you.