The History Of The Thermometer

November 2, 2021

The Thermometer is an instrument capable of measuring temperature, either body or environment. At the beginning, they were manufactured taking advantage of the phenomenon of expansion, making the stretching of the material easily detectable at high temperatures. The most widely used substance at that time was mercury, enclosed in a glass tube with a built-in graduated scale.

It dates back to human history, the first version of which was called a  thermoscope and invented by the Renaissance scientist Galileo Galilei: it consisted of a glass container that culminated in a closed sphere, which had to be submerged upside down in a mixture of alcohol and water, leaving above the sphere. As the liquid heated up, it moved up the tube.


The passage of the years and technological improvements have given rise to  different thermometers that  currently exist . The best known are:

  • Mercury thermometer. Taking advantage of the enormous expansion capacity of the unique liquid metal, these thermometers have been manufactured for centuries since their invention in 1714 by the physicist Fahrenheit. They are extremely practical and accurate. They are still widely used, although in certain countries their manufacture was prohibited because mercury, once the useful life of the thermometer, becomes an environmental pollutant.
  • Pyrometers.  Used in foundries and factories, in which it is required to measure the exact temperature (very high), they operate based on various mechanisms: the capture of infrared radiation, the distribution of thermal radiation (based on color), and even the photoelectric effect.
  • Gas thermometer.  Under constant pressure and volume, certain gases are used based on their ability to expand when heated. This gives very accurate results and is therefore used to calibrate other thermometers.
  • Bimetallic foil thermometer.  It is made up of two metal sheets with different coefficients of expansion, bent so that the one with the highest coefficient is inside. This is how the temperature sensor in a thermohygrograph works.
  • Digital thermometers.  They operate on the basis of specialized electronic circuits and sensors, capable of measuring small voltage variations and translating them into digits within one of the temperature scales (or several).
  • Clinical thermometers.  This is the name given to the thermometers especially used in medicine to measure body temperature. They are usually made of glass (the mercury ones) or plastic (the digital ones).


Prior to the use of mercury, alcohol was used, and it was Galileo Galilei, who in 1610 created a thermometer made up of a glass tube that ends in a closed sphere. The open end was submerged upside down in a mixture of alcohol and water and when the liquid was heated, it went up the tube until it reached the sphere depending on the temperature.

In 1612, Santorio assigned a numerical scale to the first clinical thermometer that took the patient’s temperature by putting it in the mouth.

The first sealed thermometer was designed for the Grand Duke of Tuscany in 1641, which used alcohol and had degree markings, but did not use a standardized mark. It was not until 1714 that the first modern thermometer arrived at the hands of the physicist Fahrenheit, who was commissioned to create the mercury thermometer and introduce the standard temperature scale that bears his name today. This scale divides the freezing and boiling points of water into 180 degrees. Initially, the human body temperature was 100º F, but since now it has been adjusted to 98.6º F.

The first practical medical thermometer used to take a person’s temperature appeared in the hands of the English physician, Sir Thomas Allbutt in 1867. This thermometer was 6 inches long and took 5 minutes to record a patient’s temperature. .

The latest advancement is the ear thermometer, invented by Theodore Hannes Benzinger during World War II. David Philips made a number of improvements to this latest version, turning it into an infrared ear thermometer in 1984.


These thermometers are used to measure both body temperature and a different material. The mercury inside them expands and contracts with changes in temperature.

This thermometer is capable of measuring air temperature, without the result being affected by any object around it.

In 2007, these models of thermometers were banned from use in several countries due to mercury poisoning that could result if the object were accidentally broken.

Mercury is a toxic material that can cause serious problems if large amounts are inhaled. Breathing this material can cause neurological and behavioral disorders, such as insomnia, memory loss, or headaches.

If you still have a mercury thermometer and it accidentally breaks, you should keep in mind that to clean it, you have to use rubber or latex gloves and carefully pick up the pieces of broken glass. When you visualize the mercury droplets, use an eyedropper to pick them up and place them on damp kitchen paper. Later, store the kitchen paper in a ziplock bag and close it. Go back to the area where the thermometer has been broken, and with a brush with shaving cream on top, clean the affected area to collect those drops that are not seen but are there. Once finished, put the brush in the same ziplock bag and label it correctly specifying “Contains Mercury”.

Above all, avoid having direct contact with the mercury! Do not touch it with bare hands!

Dr. Loony Davis5
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Born and raised in Brussels in an English family, I have always lived in a multicultural environment. After several work experiences in marketing and communication, I came to Smart Water Magazine, which I describe as the most exciting challenge of my career.
I am a person with great restlessness and curiosity to learn, discover what I do not know, as well as reinvent myself daily, someone who is curious about life and wants to know. I enjoy sharing knowledge.
This is my personal project but I also collaborate in other blogs, it is the case, the most important web on water currently exists in the US, if you are interested you can read my articles here.

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