Historical Perspective: Temperature Scales
In the 1600s and early 1700s, scientists devised as many as 35 different temperature scales. Two have survived to become standard: the Fahrenheit and Celsius temperature scales.
The Fahrenheit temperature scale is the standard for measuring temperature in the United States. It is based on the work of Gabriel Daniel Fahrenheit, a Polish-born Dutch scientist who lived from 1686 to 1736. In 1709, Fahrenheit invented a thermometer that used alcohol, then in 1714 invented a more accurate thermometer that used mercury encased in glass. Mercury-in-glass thermometers are still used today.
The advantage of using mercury is that it expands at a nearly constant rate. That means that you can mark a scale on a thermometer similar to the way you mark a scale on a ruler. Fahrenheit chose zero to be the temperature of the coldest mixture of ice and salt he could create, and chose 96 to be the temperature of a healthy human body. He arrived at the number 96 by taking other thermometers of the time that were measured from 0 to 12 and dividing each of the 12 marks into eighths. He then measured the temperature of freezing and boiling water, and found them to be close to (but not exactly) 32 and 212 degrees according to his scale.
The Celsius, or centigrade, temperature scale is the standard for measuring temperature in most of the world outside the United States. It is based on the work of Anders Celsius, a Swedish scientist who lived from 1701 to 1744. In 1736, Celsius was part of an expedition to the northernmost part of Sweden to determine the length of a degree of latitude close to the North Pole. Celsius found that the freezing point of water was independent of latitude and barometric pressure, a fact that had not previously been known.
In 1742, Celsius created a temperature scale, with 0 as the boiling point of water and 100 as the freezing point, and called it the centigrade scale. Centigrade, derived from Latin, means “100 steps.” It refers to dividing the interval between the freezing point and the boiling point of water into 100 equal parts. Today’s Celsius scale is reversed, with 0 as the freezing point and 100 as the boiling point. Celsius’s original scale had the advantage of rarely working with negative temperatures in practical matters, but it was counterintuitive: Nearly every other temperature scale at that time increased in value as heat increased. Soon after Celsius died, the scale was reversed and quickly came into common use. In 1948, the centigrade scale was renamed the Celsius scale in honor of its inventor.
Years after Fahrenheit’s death, some experimental errors were detected in his work. Since the centigrade scale had come into common use, Fahrenheit’s scale was adjusted so that 32 degrees Fahrenheit was the temperature of freezing water and 212 degrees Fahrenheit was the temperature of boiling water, giving this conversion formula, where C is the temperature in degrees Celsius (°C) and F is the temperature in degrees Fahrenheit (°F):