The Thermometer is probably the one weather instrument that just about everyone has used, at one time or another. Thermometers can be as basic as one hanging on a tree in the back yard, that you can read from the kitchen window, to a very sophisticated electronic thermometer that feeds hourly temperature data into your home computer. They all serve the same purpose of telling us what the temperature is outside and plays a major role in how we dress or prepare for each day.
Galileo invented the first thermometer in the late 1600s. The exact year is not known, but historians estimate that it was in 1593. He was a famous Italian Mathematician and Scientist whose inventions and mathematical theories are still in use today. 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 invented the first reliable mercury thermometer in 1714. His scale is still used today. Anders Celsius 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 wound 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.