Topic 1: Measuring the Cold
To study the cold, you have to be able to measure temperature -- and for that you need a thermometer. There are many different kinds of thermometers but they all use some kind of material that changes if heated or cooled. The classic mercury thermometer, for example, in which silver mercury gently rises up a thin glass tube when it gets warmer, relies on the fact that liquids expand when they get hot. The hotter the area around the thermometer, the hotter the mercury gets, the more it expands, and the higher it rises up the tube.
A tube in which a liquid rises and falls will tell you that temperature is changing. To measure the exact temperature however, you need some kind of scale -- marks on the tube to tell you what the temperature is when the liquid rises to any given point.
There are three scales most commonly used today:
Developed by the German physicist Gabriel Daniel Fahrenheit in 1724, the Fahrenheit scale sets zero as the temperature of a mixture of equal amounts of water, salt, and ice. On this scale, the freezing point of water is 32 degrees, and he named the boiling point of water at 212 degrees. (Fahrenheit also invented the mercury thermometer in 1714.) The Fahrenheit scale is the scale most commonly used in the U.S.
The Celsius scale is named after the Swedish astronomer Anders Celsius who developed an early version of the scale -- originally called the centigrade scale ("centi" because the scale was divided into 100 degrees). The Celsius scale names the freezing point of water as 0 and the boiling point of water as 100. The Celsius scale is the scale most commonly used everywhere in the world except in the U.S..
The Kelvin scale was invented by Lord Kelvin, a Scottish physicist, in 1848. He set as zero on his scale the coldest any material could possibly get, a point now known as absolute zero. Nothing can ever be colder than absolute zero -- the temperature can only go up from there. That zero point corresponds to -273.15 C and -459.67 F. The Kelvin scale is the one most often used by scientists who study extremely cold temperatures.