Why do meteorologists
humidity is the ratio of water vapor in the air at a given temperature
to the maximum amount that could exist at that temperature. On hot summer
days, the higher the relative humidity, the greater the discomfort. It
is harder to sweat and stay cool as perspiration evaporates less readily
and the body feels more hot and sticky. If the humidity is high there
is more moisture in the air and so more chance of clouds forming and rain
falling if the temperature drops.
The forecaster bases
the possibility of rain on current weather patterns, including wind and
humidity, as well as the effect of terrain and long-term weather statistics.
How can we make a humidity meter?
We used human
hair to make our hygrometer. Hair is composed of many millions of
cells. The cell walls are sensitive to moisture and will change
shape and size as the moisture content in the air changes. Hair
can therefore indicate the level of moisture in the air by expanding
Our meter was
made by simply attaching one end of a long strand of hair (15cm, or about 6 inches)
to the base (bottom left hand corner but invisible in the picture)
and the other end to the end of a stick pointer which was pivoted
near to this point. To make the meter perform correctly a weight
was attached just the other side of this pivot (string and nut).
When the air is moist, the hair will expand and lengthen, making
the pointer pivot down. When the air is dry, the hair will contract
and shorten, making the pointer pivot up. When we made our regular
hygrometer observations, we made a mark to indicate where the pointer
rested. Over time, you'll be able to see the humidity patterns that
will help you forecast the weather.