H: Torricelli, Celsius, & Fahrenheit

What do the these three famous names have in common?  You guessed it, the thermometer.  Galileo’s student, Evangelista Torricelli (top right), invented the first thermometer in the late 1600s. The exact year is not known, but historians estimate that it was in 1593. The basic principle behind a thermometer, the expansion of air by heat and contraction by cold, was know many hundreds of years earlier. As far back as 300 B.C. experiments of Philo of Byzantium illustrated this principle. Along with Galileo, several other scientists developed better and more accurate thermometers. They were Marin Mersenne, Otto Von Guericke, Robert Boyle, Christian Huygens and Sir Isaac Newton. 

Gabriel Fahrenheit (middle right) invented the first reliable mercury thermometer in 1714 (see below). His scale is still used today. Anders Celsius (bottom right) had a major role in developing another popular scale for thermometers. In 1742 he proposed that the boiling point of water be represented by 0 degrees and the melting point of ice be 100 degrees. This scale was widely accepted and it still used today for scientific work. Today’s Celsius scale is reversed with boiling water equal to 100 and melting ice 0 degrees. Jean Pierre Christin proposed this change in 1743. 

Today’s thermometers are made in different ways. The most common is the alcohol or mercury thermometer. These are the most accurate and measure the air temperature by the expansion of the fluid in a thin, enclosed glass tube. Another way of measuring air temperature is by measuring the expansion of different metals. These are called Expansion Thermometers. These are made of two different metals that expand and contract at different rates when the air temperature changes. The metals are fused together and wind like a spring. When the temperature changes, the spring either unwinds or winds up. A needle is connected to the spring and points to the indicated air temperature.