The Fahrenheit scale was developed by Daniel Gabriel Fahrenheit, a German physicist, in the early 18th century. He established the scale in 1724, using a mixture of ice, water, and ammonium chloride to define zero degrees Fahrenheit (the freezing point of this mixture) and 96 degrees Fahrenheit as the temperature of the human body.
The Celsius scale, previously known as the centigrade scale, was developed by Anders Celsius, a Swedish astronomer, in 1742. Originally, Celsius defined 0 degrees Celsius as the boiling point and 100 degrees Celsius as the freezing point of water, which was later reversed to its current convention.
The Kelvin scale, named after the British physicist and engineer William Thomson, 1st Baron Kelvin, who proposed it in the 19th century, originated from the need for an absolute temperature scale. Lord Kelvin envisioned a scale where zero represents the point at which all molecular motion ceases, known as absolute zero.
Kelvin recognized that such a scale would be more scientifically fundamental and universally applicable than the Celsius or Fahrenheit scales, which are based on arbitrary reference points. In 1848, he introduced the concept of an absolute temperature scale in a paper titled "On an Absolute Thermometric Scale." He defined the Kelvin scale in terms of the thermodynamic properties of gases, particularly the ideal gas law.
In the Kelvin scale, absolute zero is defined as 0 Kelvin (0 K), corresponding to -273.15 degrees Celsius or -459.67 degrees Fahrenheit. The Kelvin scale is widely used in scientific research, engineering, and other fields where precise temperature measurements are required, especially in contexts involving thermodynamics and quantum mechanics.