Why everyone’s talking about... Wind chill factor
It’s been bitingly cold, with the wind chill factor making it even more severe. But what is the ‘wind chill factor’?
You know it when you feel it! We’re all surrounded by a snug layer of air from our body heat. But when that’s blown away by the wind, we feel the chill more acutely. This heat loss was first measured in scientific terms by American researchers in Antarctica in 1945. Then the military started expressing it in terms of the temperature it ‘felt like’, which was easier to understand and widely adopted.
How’s it calculated?
By a complex formula based on wind speed. But although it gives an exact number, it’s also imprecise because everyone loses heat at different rates. The official figure is based on a 5ft 6in, heavy-set person walking at 3mph directly into the wind with no face covering. The formula also ignores sunlight, which can add 15 degrees Fahrenheit to the ‘feels like’ temperature.
Speaking of which, where does Fahrenheit come from?
Gdansk- born Daniel Fahrenheit, whose parents both died of mushroom poisoning in 1701, invented the mercury thermometer, which needed a standardised temperature scale. He chose zero to be as cold as he could make a mix of ice and salt water, and 96 as the temperature of a healthy man (rather than a woman, who was thought to have a lower body temperature). In fact, he was slightly out as it’s 98.2F.
And Celsius?
Fahrenheit wasn’t alone in drawing up temperature scales. Isaac Newton wanted one based on zero for freezing air and 34 for boiling water. In 1742, Swedish astronomer Anders Celsius proposed a more logical 100-degree scale, and initially had 100 degrees for freezing water and zero for boiling. It didn’t take long for the numbers to be flipped to what we know now. Originally called centigrade, scientists renamed it Celsius in 1948 to avoid confusion with another ‘centigrade’ which measures angles.
To the irritation of many, BBC staff are told to ‘always use Celsius’ in reports – even though it sounds much more impressive to say ‘the temperature hit 100’, rather than ‘37.8 degrees Celsius’.