Temperature
Three scales of temperature, each of which permits a precise measurement, are in concurrent use: the Fahrenheit, Celsius, and Kelvin scales. These three different temperature scales were each developed by different people and have come to be used in different situations.
The scale that is most widely used by the general public in the United States is the Fahrenheit scale. In 1714, Daniel Gabriel Fahrenheit, a German physicist who was living in Holland and operating an instrument business, developed a mercury-in-glass thermometer and the temperature scale that still carries his name.
His original scale had two
fixed points: 0° was the lowest temperature that he could achieve in a solution of ice, water, and salt, and 96° was what he believed was the normal temperature of the human body (though this was later determined to be 98.6°). Based on this scale, he calculated that the freezing point (or ice point) of water was 32°; in later studies,
it was determined that the boiling point of water (the steam point) was 212°. The Fahrenheit scale came to be accepted as the standard measure of temperature in a number of countries, including Great Britain, and from there it was spread to British colonies throughout the world. Today, however, the United States is the only major country in the world that still uses the Fahrenheit scale.
The scale that is in use in
many other countries is the Celsius scale. Anders Celsius (1701-1744), a Swedish astronomer, developed a thermometer in 1741 that based temperatures on the freezing and boiling temperatures of water. On the thermometer that Celsius developed, however, 0° was used to indicate the boiling temperature of water, and 100° was used to indicate the freezing temperature of water. After his death, the scale was
reversed by a friend, the biologist Carl yon Linne(1707-1748), who achieved acclaim for his development of the Linnean classification system for plants and animals. On the new scale after the reversal by yon Linne, 0° indicated the freezing temperature of water, and 100° indicated the boiling temperature of water.

At around the same time that Celsius and yon Linne were working on their thermometer in Sweden, a similar thermometer was being developed in France.

After the French Revolution, the scale developed in France was
adopted as part of the metric system in that country under the name centigrade, which means "a hundred units" and from there it spread worldwide.
In 1948, an international agreement was made to rename the centigrade scale the Celsius scale in honor of the scientist who was first known to use a 100-degree scale, though it should be remembered that the scale that Celsius actually used himself was the reverse of today's scale.