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 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?
Steps to be taken
1. Using the ruler, draw an arrow about 12 centimetres by 2 centimetres on the thin card. Cut out the card arrow. 2. Stick one end of the strand of hair to the top of the cliff card. 3. Using drawing pins, attach the stiff card to the long edge of the piece of wood 4. Attach the free end of the hair to the back of the arrow head. 5. Place the arrow against the card and move it until the hair is stretched out fully. Then attach the other end of the arrow to the card with a drawing pin 6. Stand the hygrometer outside. Make sure that it can't fall over. When the Sun is shining, mark on the card 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 card. 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.