# How to make a Hygrometer?

## How to make a Hygrometer?

When you’re planning a picnic with your friends, you need to know that the weather will be fine so that you can enjoy yourselves.
Many people need to know what the weather will be like so that they can plan their work or other outdoor activities.
Scientists who study the weather are called meteorologists.
They use many different instruments to collect information about temperature, air pressure, wind speed and direction. They also study the amount of moisture in the air.
Meteorologists measure the speed of the wind with an anemometer, and the amount of moisture with a hygrometer.
These instruments are used in weather stations on the ground, or in aircraft, ships and weather balloons. Meteorologists use the information from these instruments to forecast what the weather is going to be like.

You will need:

• a pencil a ruler
• a piece of thin  card board,
• 6 inches x 1.5 inches
• (15 centimeters x 4 centimeters)
• a piece of stiff cardboard,
• 8.5 inches x 11 inches
• (21 centimeters x 27.5 centimeters)
• a pair of scissors
• tape
• a strand of hair, about
• 8 inches (20 centimeters) long
• apiece of wood,
• 11 inches x 2 inches x 2 inches
• (27.5 centimeters x 5 centimeters x 5 centimeters)
• six thumb tacks
• a colored pen with a fine point

You can make your own hygrometer.
Keep a chart of your results every day for three weeks.
Can you forecast whether it will be wet or dry during the fourth week?
1. Using the ruler, draw an arrow about 5 inches by 1 inch (12.5 centimeters x 2.5 centimeters) on the thin cardboard. Cut out the arrow.

2. Tape one end of the strand of hair to the center-top of the stiff cardboard.

3. Using thumb tacks, attach the stiff cardboard to the long edge of the piece of wood.

4. Attach the free end of the hair to the middle of the back of the arrow.

5. Place the arrow against the cardboard and move it until the hair is stretched out fully and also parallel to the long side of the cardboard. Then attach the end of the arrow (opposite the arrowhead) to the cardboard with a thumb tack.
6. Stand the hygrometer outside. Make sure that it can’t fall over. When the sun is shining, mark on the cardboard where the arrow is pointing. Write “dry” by the side of this mark. When the weather is damp, the arrow will point lower. Mark its new position and write “damp” on the cardboard.

## How does your hygrometer work?

On a damp day, the strand of hair will absorb moisture from the air. This will make the hair stretch and so the arrow points lower. On dry, sunny days the hair dries out and becomes shorter.