Weather Eye: the story of how the temperature was measured
Paul Simons, The Times Online 12 Jan 09;
Three hundred years ago Daniel Gabriel Fahrenheit made his first thermometer in his home town of Danzig (now Gdansk in Poland). The thermometer was filled with alcohol and completely sealed, but it was not much use without some sort of scale to measure the temperature.
One story goes that, during the winter of 1708-09, Fahrenheit took a measurement of 0 degrees as the coldest temperature outdoors — which would now read as minus 17.8C. Five years later he used mercury instead of alcohol for his thermometers, and made a top reference point by measuring his own body temperature as 90 degrees. Soon afterwards he became a glassblower, which allowed him to make thinly blown glass tubes that could be marked up with more points on the scale and so increase accuracy.
Eventually he took the lowest point of his temperature scale from a reading made in ice, water and salt, and a top point made from the boiling point of water. The scale was recalibrated using 180 degrees between these two points and Fahrenheit was able to make much more accurate and more consistent measurements of temperature.
But in 1742 a rival challenged the Fahrenheit scale and eventually superseded it. Anders Celsius, in Sweden, invented a scale of 100 degrees between the freezing and boiling points of water and gradually won over many countries. However, the British remained wedded to Fahrenheit until well into the 20th century.