There are several theories about the origin of the scale. On one of them, Fahrenheit originally took as 0 ° F melting point (freezing) of a mixture of ice and salt in equal quantities, and for 100 ° F - normal body temperature (Fahrenheit, but wrong in the last measurement: Normal human body temperature is 97 9 ° F). There is a theory according to which over 100 degrees Fahrenheit temperature scale adopted his wife's body temperature, which at the time of measurement was not well - it is this and caused the displacement of a point on the centigrade 2,1 ° F, rather than an error of the measurement. Fahrenheit himself believed that the temperature (according to its scale) is never negative.

On the Fahrenheit melting point of ice is equal to +32 ° F, and the boiling point of water +212 ° F (at normal atmospheric pressure). In this case, one degree Fahrenheit is equal to 1 / 180 the difference between these temperatures. Range 0 ° ... +100 ° Fahrenheit is roughly equivalent range -18 ° ... +38 ° Celsius.

One degree Fahrenheit is 5 / 9 degrees Celsius and the temperature on the Fahrenheit scale related to the temperature on the Celsius scale by the following formulas.

From 38.2 Celsius to Fahrenheit:
F = C * 9 / 5 32

Of the Fahrenheit scale in Celsius:
C = (F-32) * 5 / 9
38.2 Celsius to Fahrenheit=100.76
In addition, the temperature measured in degrees Celsius, Reaumur, Rankine, Delila, as well as in Kelvin.

Degree Reaumur (° R) - now unimproved temperature unit. 1 ° R is equal to 1 / 80 of the temperature range between the melting point of ice (0 ° R) and boiling water (80 ° R), ie 1 ° R = 1,25 ° C. Proposed in 1730, RA Reaumur.

Rankin scale (measured in degrees Rankine - ° Ra) - now rarely used the absolute temperature scale, named after the Scottish physicist William Rankine (1820-1872).

Rankin scale starts at absolute zero temperature, the freezing point of water corresponds to 491,67 ° Ra, the boiling point of water 671,67 ° Ra. The number of degrees between freezing and boiling of water in Fahrenheit and Rankine are same and equal to 180.

Relation between degrees Kelvin and Rankin: 1 K = 1,8 ° Ra, Fahrenheit converted to degrees Rankine formula ° R = ° F + 459,7.

Degrees Delila (symbol: ° W or ° De) - now unimproved temperature unit. Was invented by the French astronomer Joseph Nicolas Delila (1688-1768). Delila scale is similar to the temperature scale Reaumur.

In 1732, Delisle has created a thermometer using mercury as a working fluid. As a zero was choused temperature of boiling water. For one-degree made such a change in temperature, which let to a decrease in the volume of mercury per one hundred thousandth.

One degree Delisle is -2 / 3 degrees Celsius (or Kelvin) and absolute zero corresponds to 559,725 degrees Delisle.

Kelvin (symbol: K) - temperature unit in the SI was proposed in 1848.
One kelvin is equal to 1 / 273, 16 of the thermodynamic temperature of the triple point of water. Start of scale (0) coincides with the absolute zero. Kelvin size coincides with degrees Celsius. Prior is to 1968, officially called Kelvin degrees Kelvin.

Degree Celsius (symbol: ° C).