The Pressure's On

Evangelista Torricelli, one of Galileo's students, invented the barometer in 1644. A barometer measures atmospheric pressure. It's a quick and easy forecasting tool. When the barometer reports high (or rising) pressure, expect improving or mostly sunny weather. If the barometer reading is low (or falling), you better bring along an umbrella. Low pressure means stormy weather. The faster and lower the pressure falls, the more severe the storm's likely to be.

Twists and Turns

Why does wind spiral clockwise around a high and counterclockwise around a low? Shouldn't it just flow from one to the other in a straight line? The Coriolis effect is the answer to this riddle.

The Coriolis effect is named after French mathematician Gaspard Coriolis, who observed and explained this process in around 1835. The Coriolis effect is an apparent deflection in the motion of wind or water currents (or anything else that moves), caused by the Earth's rotation. Wind appears to curve to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. For more about the Coriolis effect, read Tying Down the Wind, pages 29 to 32