Under pressure

Barometers and altimeters have saved thousands of lives since their invention, although their occasionally inaccurate predictions have caused tempers to flare

-  Charles Harris

SIR WILLIAM EDEN, father of Anthony and an irritable watercolourist, once flung his barometer into the garden when it indicated sunshine during a shower. ‘Look for yourself, you fool,’ he cried. Barometers, once tapped reflexively when setting off on a walk, are largely unacknowledged instruments, yet their predictions have saved countless lives at sea and, after morphing into altimeters, made modern flying possible.

Aristotle thought that air had no weight. In 1645, however, Italian scientist Evangelista Torricelli invented the first barometer, which demonstrated how atmospheric pressure (weight of air) supported a column of mercury in a glass tube. Increases in column height mean that air pressure has risen, usually indicating fair weather; if it falls, then wind and storms are on the way. This is because air moves, as wind, from areas of high pressure to low, sometimes extremely fast.