by Chris Woodford. Last updated: September 18, 2012. Is it going
to rain today? Is it going to stay fine? And how can you tell?
One easy way is to measure the air pressure. If it's rising and
the pressure is high, chances are it'll be a fine day; if the
pressure is falling, it's more likely to be wet, windy, and
dull. Instruments that measure air pressure are called
barometers and people have been using them for weather
forecasting and scientific research for hundreds of years. Let's
take a closer look at how they work! Photo: This traditional
aneroid barometer dates from the mid-20th century and is
calibrated (marked) as a crude weather-forecasting device, but
it's simply an instrument that measures the air pressure. The
needle turns clockwise when the pressure is rising (indicating
fair or dry weather); it turns anticlockwise when the pressure
is falling (indicating rain or stormy weather). What is air
pressure? If you've ever been scuba diving, you'll know just
what pressure feels like. Dive down beneath t