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A short history of thermometers

Last Updated: 29.11.21

A thermometer is a tool which measures both the temperature and the temperature gradient. It consists of a temperature sensor usually made of mercury that changes when the temperature changes too. It also has a numeric scale, so you can see how big the change of the temperature is. The value scale can be both printed and digital. Thermometers are indispensable in areas such as medicine, industry, meteorology or for personal use.

Its history is a long one, and the idea of thermometer dates back to the Ancient Greeks. The modern-day thermometer slowly evolved from the thermoscope, and it has transformed into the compact and incredibly useful standardized device we all utilize today.

The early days

In the early stages of development, a thermometer was called a thermoscope. Several inventors actually came up with the idea at the same time. It is a well-known fact that the Italian genius Galileo Galilei invented the thermoscope among other things, but at the same, time he laid the foundations of the first water thermometer in 1593, which was very inaccurate.

The first record that speaks of a thermometer dates back to the 16th century, and it says it was created by Santorio Santorio, an Italian from Venice. But that doesn’t mean he invented it alone. He just took something that already existed in the scientific community and gave it a shape and a name, and, ultimately, helped the tool evolve as many other great people did with their work.

What he did was that he applied a scale to a preexisting air thermoscope in 1612, by thus creating the image we all associate with this device today. It was an air thermometer, and it wasn’t very accurate because there were laws of physics that were acting on the air and on the machine, which were poorly understood at that time so they couldn’t be stopped from changing the thermometer’s results.


Things never stay the same

Then it was time for a change, and the more familiar sealed liquid-in-glass thermometer was created. In 1654, it was produced by Ferdinand II, The Duke of Tuscany and it had an alcohol filling. But even his thermometer was inaccurate, and it didn’t have any standardized scale.

It took almost one hundred years for the first mercury thermometer to make its debut. Gabriel Fahrenheit was the one who designed it, and it was a breakthrough because mercury has a more predictable expansion rate and thus it made the device much more accurate.

And with the first mercury filling came the first standardized scale. Fahrenheit decided to divide water into 180 degrees between its freezing and boiling points. This often criticized scale is still used today in most parts of America and some laboratories, unlike Europe which prefers the Celsius scale because it seems more straightforward.

Another scale that appeared soon after the Fahrenheit one was the Réamur Scale, which was implemented by the French René Antoine Ferchault de Réamur, who decided that the freezing point of water should be 0 degrees. On the other hand, he thought the point of boiling should be at 80 degrees, which is why the scale is not in use as of today.

Celsius comes to change the status quo

The most famous scale came to shake things up. In 1742, a young Swedish whose name was Anders Celsius designed a thermometer scale where he practically and efficiently divided the boiling and the freezing points of water in 100 degrees. 100 was the point of freezing and 0 the point of boiling.

Soon later, Jean Pierre Cristin inverted the already famous scale and transformed it into the Centigrade scale we still use today. The name was kept as the Celsius scale because the Frenchman didn’t do anything else to it, except making the freezing point 0 and the boiling point 100.

Now, a thermometer is a tool that should not miss from our kitchen drawers or our medical cabinets. They can help us when we have a cold, when we are cooking something delicious or when an unexpected situation needs to be taken care of. It is important to compare digital thermometers for adults before buying one, to make sure you find the one that is going to give you the best value for its money.



Ioana Moldovan

Ioana’s professional experience in the optics field has helped her understand the value of passing her knowledge forward. Her curious personality helps her gather useful information for her readers and her goal is to make technical information fun and accessible to everyone.

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