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 an instrument whose utility is to measure temperature, through various mechanisms and scales. The most common of these mechanisms was dilation, the property of certain materials to expand in the presence of heat, common among metals and others substances, Like the alcohols.
The invention of the thermometer and its incorporation into everyday 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 registered by the thermometers is marked based on a certain 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 theabsolute temperature, is 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.
- Réaumur (° 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, the first version of which was calledthermoscope 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 the sphere up. As the liquid heated up, it moved up the tube.
To this 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 to thermoscopes, devices that measure ambient temperature.
Thermometer types
There are the following types of thermometer:
- 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, where it is required to measure the exact (very high) temperature, they operate based on various mechanisms: the capture of infrared radiation, the distribution of thermal radiation (based on the color), and even the photoelectric effect.
- Gas thermometer. Subjected to a Pressure Y volume constant, 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 remains 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 thermometers especially used in medicine to measure body temperature. They are usually made of glass (those made of mercury) or plastic (the digital ones).
How does a thermometer work?
The principle that governs the thermometer is simple: the device has a sensitive end, where the sensors (in the case of a digital thermometer) or the expandable substance (in the case of mercury or alcohol thermometers) are located, and that it must be introduced into the body or substance whose temperature is to be measured.
After waiting a few minutes, the heat of the body or the substance will cause the mercury or alcohol to rise to a point equivalent, on the scale registered on the device, to the degree of heat measured.