- a block of wood, or heavy cardboard, about 10'' x 4''
- a thin piece of thin plastic, about 3'' x 3''
- 2 small nails
- 3 strands of human hair, about 8'' long (I donated a few gray ones).
- a dime
- a hammer
- heavy scissors
- and, since we used light colored hair, we added a piece of black construction paper, to place behind the hair, so it would show up.
We glued the construction paper to the wood.
Then, we nailed the triangle, low on the block of wood, with the small nail, through the large hole. The large hole allows the plastic to spin freely on the small nail.
We hammered in the second nail, about two inches above the middle of the triangle, on the block of wood.
Finally, we wrapped the hair around the top nail, and stretched it down to the middle of the triangle, using a spot of hot glue to secure it to the nail, and triangle, so when we stood the block up, the triangle would hang perpendicular to the hair.
When there is more moisture in the air, the hair will expand, and lengthen, and the triangle will tip down. When, the air is dry, the hair will contract, and pull the tip back up.
We marked our hygrometer, and then tested it, by placing it in the bathroom, while one of the children showered with the fan off. The tip of the triangle didn't move a lot, but it did move down enough to be noticeable. And, when we removed the hygrometer from the steamy bathroom, the pointer returned to it's original spot. So, it seems to be working.
Oh, and just as a by the way - relative humidity is the difference between the amount of moisture in the air, and the total amount of moisture the air can hold at that temperature. It would take a slightly more complicated device to measure that difference, but ours will be good enough for tracking changes in the humidity level throughout the day.
It's great to be a homeschooler.