We explain what a thermometer is, what it is for and who invented it. Also, the types of thermometers and how they work.
What is a thermometer?
A thermometer is called an instrument used to measure temperature through various mechanisms and scales. The most common of these mechanisms was expansion, the property of certain materials to expand in the presence of heat, common among metals and other substances, such as alcohols.
The invention of the thermometer and its incorporation into daily life was an important success in the technological development of medicine (clinical thermometer), since it allowed the measurement of the temperature of the human body and accurately measure symptoms such as fever.
What is recorded by the thermometers is marked based on a specific temperature scale:
- Celsius (°C). In honor of the Swedish physicist Andreas Celsius, also known as degrees Celsius.
- Fahrenheit (°F). Proposed by the German physicist Daniel Fahrenheit in 1724, preferably used in the Anglo-Saxon world.
- Kelvin (°K) The scale of the absolute temperatureis used in the International System of Units. It coincides with the Celsius scale, but 0 has been set at the so-called “absolute zero”, that is, the lowest temperature that exists: -273.15 °C.
- Reaumur (°R) Disused today, due to René-Antoine Ferchault de Réaumur, French physicist.
Who invented the thermometer?
The thermometer is a long-standing artifact in human history, whose first version was called 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 immersed face down in a mixture of alcohol and water, leaving the sphere on top. As the liquid heated, it rose up the tube.
To said invention A numerical scale was added between 1611 and 1613 (attributed to Francesco Sagredo and Santorio Santorio), thus giving rise to the first thermometers and also thermoscopes, devices that measure environmental temperature.
Types of thermometer
There are the following types of thermometer:
- Mercury thermometer. Taking advantage of the enormous expansion capacity of the only liquid metal, these thermometers were 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 has expired, becomes an environmental contaminant.
- Pyrometers Used in foundries and factories, where 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 Subjected to a constant pressure and volume, certain gases are used based on their capacity to expand when heated. This gives very accurate results and is therefore used to calibrate other thermometers.
- Bimetallic sheet thermometer It is made up of two metal sheets that have different expansion coefficients, folded so that the one with the highest coefficient is inside. This is how the temperature sensor operates in a thermohygrograph.
- Digital thermometers They operate based on electronic circuits and specialized sensors, capable of measuring small variations in voltage and translating them into digits within one of the temperature scales (or several).
- Clinical thermometers This is the name given to thermometers especially used in medicine to measure body temperature. They are usually made of glass (mercury ones) or plastic (digital ones).
How does a thermometer work?
The principle that governs the thermometer is simple: the device It has a sensitive end, where the sensors are located (in the case of a digital thermometer) or the expandable substance (in the case of mercury or alcohol thermometers), and which must be introduced into the body or substance whose temperature you wish to measure.
After waiting a few minutes, the heat of the body or substance will cause the mercury to rise or alcohol to a point equivalent, on the scale recorded on the device, to the degree of heat measured.
