History of thermometers

A thermometer is a device that measures the temperature of an object. There are several types of thermometers available today but they all have “a measurable property that changes continuously with changes in temperature” this is called a thermometric property.

In 1592, Galileo Galilei invented the first thermometer.
It was simply a round bottom flask with a glass tube coming out the top, which was placed upside down in a container of water or wine. When you place your hand on the round part of the flask the air expands and the water level drops when the hand is removed the flash cools and the air contracts causing the water to rise. Galileo attached a scale to his thermometer and marked it in degrees but he did not mark any particular point (e.g. boiling point of water) to his scale. The thermometric property of this type of thermometer was the expansion of air.

Galileo’s thermometer was not very accurate and vary with air pressure as well as temperature. In 1641, Ferdinand II Grand Duke of Tuscany invented the first closed thermometer. This thermometer had a small amount of coloured alcohol in a sealed glass tube, when it was place into something hot the alcohol would expand and temperature read off a scale on the thermometer.

Then in 1741 Gabriel Fahrenheit created the first thermometer to use mercury. Mercury expands more per degree than air or alcohol making this type of thermometer very accurate. Mercury thermometer became the standard until recently when they stopped being used due to safety concerns.

In the 1821 the thermocouple was invented and in the 19th century the bimetallic strip was introduced.