The first modern thermometer was designed by Daniel Fahrenheit in 1714, thus perfecting the Galileo Galilei thermometer of 1592. The thermometer is the physical device used to measure heat and temperature, so it is closely linked to physics.
At the beginning of the 18th century, Fahrenheit, a Dutch glazier, invented the first mercury thermometer and the temperature scale that bears his name.
Daniel Fahrenheit
Thermometers containing alcohol or alcohol-water mixtures were previously used, but they were very imprecise. Therefore, Fahrenheit decided to use mercury, which provided greater precision.
A mercury thermometer consists of a glass reservoir that extends into a rod fitted with an empty capillary tube. Through there, mercury rises as it expands as a consequence of the absorption of heat.
On the glass rod is engraved the graduated numerical scale that will allow "reading" the degrees of temperature.
Unlike other types of thermometers, a mercury thermometer can directly visualize the physical phenomenon. That is, you can see how the mercury expands in the capillary column of the thermometer.
To achieve this, Fahrenheit had to develop a mercury purification system. It had to remove all the impurities in the mercury that made it stick to the glass walls and not be useful.
Modern thermometer background
The basis for these inventions is the physical principle according to which a liquid expands and changes density with temperature. Thus, various ancient sages tried to make rules to measure temperature using water and air.
The invention of the first apparatus to measure temperature is due to Galileo Galilei, in 1592, with the water thermometer or glass thermometer. This apparatus consisted of a large glass cylinder filled with water that had glass balls of different colors.
Each of these balls moved up or down depending on the change in temperature.
Some were located in the lower zone and others in the upper zone. To read the ambient temperature, the lowest of the balls that were in the upper zone had to be taken in the gutter.
In 1610, Galileo changed the system to wine instead of water, and this is credited with the first alcohol thermometer.
Galileo Galilei - Source: Domenico Tintoretto
A later attempt occurred in 1612, when the Italian inventor Santorio Santorio made use of the first clinical thermometer, designed to be inserted into the mouth. Santorio also became the inventor in putting a numerical scale.
But it wasn't until 1641 that the first sealed thermometer appeared. The Grand Duke of Tuscany designed a device that used alcohol and had degree markings, but it was still inaccurate and did not use a level scale.
The Fahrenheit scale
Comparison of degrees Celsius and degrees Fahrenheit. Source: 85fce
In 1709, Fahrenheit introduced its temperature scale based on the use of two fixed points. As a zero point, he used the lowest temperature he could get, adding salt to the ice.
Then he marked the normal temperature of the human body and made 96 divisions between the two points. Thus, the body temperature corresponded to 96 degrees. While the freezing temperature of pure water corresponded to 32 degrees.
With his scale, he affirmed that between the freezing point of water (0 °) and the boiling or boiling point they should pass 180 degrees.
So he modified the scale slightly so that the boiling point was 212 degrees Fahrenheit, exactly 180 more than the freezing point. With this, the normal temperature of the human body was 98.6º Fahrenheit.
Today, the Fahrenheit scale is used in Great Britain, the United States, Canada, South Africa, and New Zealand.
References
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- Redal, E. Heat and Temperature. Natural Sciences 2nd ESO. Santillana Educación, SL Recovered from vedrunav.org.
- Sandino, A. (2012). Thermodynamics as the origin of the industrial revolution of the 18th century. Unam, Mexico. Recovered from researchgate.net.
- Velazco, S. and Fernández, C. (2005). A walk through the history of thermometry. Recovered from gtfe.usal.es.