The Open Door Web Site
Facts and Figures Index
Types of Thermometer
Some interesting temperatures
FACTS AND FIGURES
Temperature is a measure of the hotness or coldness of an object.
How can we measure temperature?
Your body is a temperature measuring instrument. By simply touching an object, you can tell if it is hot or cold. However, this does not tell you how hot or cold it is.
Using a thermometer
Scientists are always interested in measuring things, so it is not surprising that a devise was invented to measure temperature. It is called a thermometer.
The inventor of the first thermometer is thought to have been a very famous Italian scientist called Galileo Galilei. Galileo was born in 1564. His first thermometer was a very simple one. Like most of the thermometers in use today, it worked on the idea that as things get hot they expand and as they cool down they contract.
Galileo's thermometer was "open" at one end which made it sensitive to air pressure changes. The first "closed" thermometer was invented by Ferdinand II Grand Duke of Tuscany in 1641. He invented the alcohol thermometer. His invention started a thermometer making tradition in Florence. The thermometers made in Florence in the 17th century were so good that some of them were still being used 200 years later.
Alcohol is a good liquid to use in a thermometer because it remains a liquid over most of the normal temperatures found on the Earth's surface. You will sometimes use alcohol thermometers in school. The alcohol is often coloured red or green in these thermometers so that the liquid can be seen more easily. However, alcohol is not much use at hot temperatures because it boils at about 80°C, which is quite a low temperature.
For higher temperatures a different liquid is needed. The Florentines experimented with mercury which boils at a much higher temperature than alcohol, at 357°C. The main problem with mercury thermometers is that they need a very fine tube, so it is difficult to see the level of the liquid inside them.
Now that accurate thermometers had been made to measure the temperature, scientists discussed what units they should use to measure temperature in. It is not surprising that everyone had their own particular ideas about this. By the 18th century as many as 35 different temperature scales had been developed. Fortunately, scientists like to standardise their measurements and use only one type of unit to measure things by. All we have left today are two scales of temperature in everyday use, (Fahrenheit and Celcius), and one scale used by many scientists, especially physicists, who deal with really low temperatures (Kelvin).
The Fahrenheit scale
The Fahrenheit scale is named after Gabriel Daniel Fahrenheit, a Dutch instrument maker who was famous for the quality of his thermometers. In 1714 he put forward a temperature scale which was based on the human body temperature. Originally, human body temperature was 100 on the Fahrenheit scale, but it has since been adjusted to 99°F.
Fahrenheit temperatures are written like this: 32°F
The Fahrenheit scale is still used in a few countries, such as the USA, but scientists all over the world usually use the other two scales.
The Centigrade scale
In 1740, Anders Celcius, a Swedish astronomer, proposed a temperature scale which was based upon the freezing point of pure water (which he set at 0 degrees) and the boiling point of pure water (which he set at 100 degrees). He divided the temperatures in between 0 and 100 degrees into 100 equal units. This explains why the Celcius scale is also called the Centigrade scale (centi - grade = 100 parts). Celcius temperatures are written like this: 37°C.
The two scales, Fahrenheit and Celcius naturally give different numerical results for the same measurement:
To convert Fahrenheit to Celcius:
or X minus 32, multiplied by five and then divided by nine.
To convert Celcius to Fahrenheit:
or X multiplied by nine, then divided by five, then add 32 to the result.
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