1. Air temperature is measured with a mercury thermometer, which uses the principle of contraction and expansion. As the temperature rises, the mercury expands and rises in the thermometer tube. Cold weather causes mercury to contract and therefore fall.

2. The Celsius (or centigrade) scale is used in most countries. On this scale, water freezes at 0° and boils at 100°. 

3. On the Fahrenheit scale, adopted in the United States, 32º is the point at which water freezes and 212º is the extent to which it boils.

4. To convert degrees on the Fahrenheit scale to Celsius, subtract 32 from them and divide the result by 1.8. To make a quick and approximate calculation, divide Fahrenheit degrees by 2 and subtract 15 from the result. To do the reverse operation (Celsius to Fahrenheit), multiply by 1.8 and add 32 to the result.

5. The only temperature scale that does not have negative values ​​is the Kelvin.

6. Unlike Celsius and Fahrenheit, temperatures described in Kelvin are not accompanied by “degrees” before. 0°C, for example, is the same as 273 K.

7. The lowest possible temperature is 0 K, also known as “absolute zero”.

8. It is possible to find a temperature in Kelvin from the correlated Celsius temperature by simply adding 273. Therefore, 100°C is the same as 373K, 101°C is the same as 374K, and so on.

9. Gabriel Daniel Fahrenheit was born in the city of Danzig, Germany. As a young man, he went to live in Holland and became a meteorological instrument maker. In 1714, Fahrenheit created the first mercury thermometer. At the time, thermometers were made with alcohol, which made it difficult to measure high temperatures because the boiling point of the liquid is so low. Scientists used to mix water to compensate for this problem, but the swelling of the material was not uniform. This prevented the thermometer scale from having small subdivisions. But it was still necessary to establish fixed values ​​to measure the temperature variation. As the marks were made randomly, according to the reference material, it was difficult to find two thermometers that marked the same temperature.

10. In the previous decade, the physicist Isaac Newton had suggested the use of two temperatures as a reference for the construction of a thermometric scale: that of the human body and that of the solidification of water. He also proposed that the scale interval between these two points be subdivided into twelve units. Fahrenheit mixed salt in water to obtain a lower freezing point, and assigned the value zero to this point. As a second reference, it assigned a maximum value for the temperature of the human body. To obtain the exact value of the solidification of pure water, he adapted these two measurements. Fahrenheit's research with thermometers confirmed that every liquid has a fixed boiling point and also that the boiling point varies with pressure. The thermometer made of mercury revolutionized the system of thermometric measurements and the Fahrenheit scale is still used in English-speaking countries today.