There have been five main temperature scales,
each one being named after the person who invented it.
G D FAHRENHEIT (1686-1736)
a German physicist, in about 1714 proposed the first practical
scale. He called the freezing-point of water 32 degrees
(so as to avoid negative temperatures) and the boiling-point
R A F de REAUMUR
(1673-1757) A French entomologist, proposed a
similar scale in 1730, but set the freezing-point at 0 degrees
and the boiling-point at 80 degrees. This was used quite
a bit but is now obsolete.
Anders CELSIUS (1701-1744)
a Swedish astronomer, proposed the 100-degree scale (from
0 to 100) in 1742. This was widely adopted as the centigrade
scale. But since grades and centigrades were also measures
of angle, in 1948 it officially became the Celsius scale.
Also, the S I system of units gives preference to naming
units after people where possible.
1st Lord KELVIN (1824-1907) a Scottish mathematician
and physicist, worked with J P Joule - about 1862 - to produce
an absolute scale of temperature based on laws of heat rather
than the freezing/boiling-points of water. This work produced
the idea of 'absolute zero', a temperature below which it
was not possible to go. Its value is -273.15 degrees on
the Celsius scale.
William J M RANKINE
(1820-1872) a Scottish engineer and scientist,
promoted the Kelvin scale in its Fahrenheit form, when the
equivalent value of absolute zero is -459.67 degrees Fahrenheit.
Nowadays, while scientists use the KELVIN scale, the CELSIUS
scale is the preferred scale in our everyday lives. However,
the Fahrenheit scale is still widely used and there is frequently
a need to be able to change from one to the other.