Temperature Measuring Scales

Galileo is credited with inventing the thermometer, but it had no scale. Many thermometers has since then be conceived, but none of them was universally recognized. We know today about 10 different scales, five of them pretty well known (Fahrenheit, Celsius, Kelvin, Rankine and Reamur); but only three of them are widely used today.

Fahrenheit

The earliest scale using Mercury was invented in the 1700’s by Dutch instrument maker Gabriel Fahrenheit. He used a mixture of Ice water and salt and labeled it “zero degrees”. For the high end of his scales he chose the human blood temperature and called it 96 degrees.

Celsius

Around 1742, Anders Celsius proposed that the melting point of ice and the boiling point of water be used for the two benchmarks.

Kelvin

In the early 1800’s, Lord Kelvin developed a universal thermodynamic scale based upon the coefficient of expansion of an ideal gas. His scale remains the standard for modern thermometry.

 This is a comparison of the different scales:

 

°C

°Réaumur

°F

K

°Rankine

Boiling point of water
(at 1 atm = 101325 Pa)

100

80

212

373.15

671.67

Freezing point of water
(at 1 atm = 101325 Pa)

0

0

32

273.15

491.67