Fahrenheit:

Daniel Gabriel Fahrenheit developed this temperature scale in 1724. His temperature scale was based on the earlier work of Ole Rømer, the Danish astronomer. In Rømer’s scale brine freezes at zero, water freezes and melts at 7.5 degrees, body temperature is 22.5 degrees, and water boils at 60 degrees. Fahrenheit began his new scale by multiplying each of the values by four in order to eliminate fractions. This meant that the freezing point of water would be 30 and body temperature would be 90. He then re-calibrated the scale so that the melting point of ice would be 32 and body temperature would be 96. This new calibration meant that there would be 64 intervals between the melting point of ice and body temperature. This allowed him to mark degree lines on his instruments by simply bisecting the interval six times.

Ole Rømer is shown above.

Fahrenheit is shown above.

In experimenting with his scale, Fahrenheit observed that water boils at about 212 degrees. Other scientists would later slightly redefine the scale so that there would be 180 degrees between the freezing and boiling points of water. With this revised scale, body temperature is about 98 degrees.

The zero point on the Fahrenheit scale was determined by placing the thermometer in brine: a 1:1:1 mixture of ice, water, and ammonium chloride.

Celsius:

Unlike the United States, most countries in the world use a temperature scale based on a simple proposition: water freezes at zero and boils at 100. Since there are 100 degrees between freezing and boiling, this scale has often been called centigrade. After 1948 this name of this scale changed to Celsius after the Swedish astronomer Anders Celsius.

Celsius was the first scientist to conduct and publish careful experiments regarding temperature. His goal was to establish the definition for an international temperature scale on scientific grounds. With his experiments he found that the boiling point of water is dependent on atmospheric pressure. He initially proposed in 1742 that the freezing point of water should be designated as 100 and the boiling point as zero. In 1745, a year after his death, this scale was reversed by Carl Linnaeus.

Anders Celsius is shown above.

Two Scales:

In English-speaking countries, Fahrenheit was the primary temperature standard until the 1960s. As a part of the metrification process of the late 1960s and 1970s, the Celsius scale replaced Fahrenheit. The United States, with its metric phobia, resisted this change and has continued to use Fahrenheit.

A comparison of Celsius and Fahrenheit is shown above.