TEMPERATURE
Not surprisingly, over time, there have been various attempts at and proposals for, the measurement of temperature. Only the five most important, that had any degree of usage or practicality are dealt with here.
One of the earliest was that devised by Gabriel Daniel Fahrenheit (1686-1736) a German physicist. He introduced the use of mercury as the measuring fluid, which brought a higher degree of accuracy and stability to thermometers than had previously been known. He also used a mixture of salt and water, which had a lower freezing-point than pure water, to mark the zero point on his scale - by doing this he hoped to avoid having negative temperatures. He wanted the temperature of the human body to be about 100° on his scale but then adjusted things so that the difference between the freezing- and boiling-points of pure water were whole numbers and had a 'nice' value between them (180°). So these values then became 32° and 212° respectively. Body temperature was then 98.6 degrees. And that scale was adopted very quickly (about 1724) and been used ever since.
Another early attempt was by R A F de Réamur (1683-1757) a French scientist. He knew nothing of Fahrenheit's work and did not use mercury, but did produce a good working thermometer. He used the freezing-point of water as his zero mark, and put the boiling-point at 80 degrees. This scale was widely used (especially in France) for some time but is now obsolete. He has a greater claim to fame for much of the other scientific work he did.

Another well-known name in thermometry is that of Anders Celsius (1701-1744) a Swedish astronomer. In his proposal he set the boiling-point of water as his zero mark, and put the freezing-point at 100 degrees!!! It was only reversed a few years later (and it was possibly not done by him). It gained wide popularity, especially with scientists, but became known as the Centigrade scale because of its 100 divisions. Perhaps this did not matter but, unfortunately, there was also a unit called a 'grade' which was sub-divided into 'centigrades' and used for measuring angles. So, in 1947 the General Committee on Weights and Measures ruled that the word 'celsius' and °C was to be used. But these things take time - even in the year 2000, a leading manufacturer of clinical thermometers was still labelling them as 'centigrade'!
For scientists the most important name in thermometry is that of Kelvin. He was William Thomson, Baron Kelvin (1824-1907) a Scottish physicist and mathematician. He it was who discovered the principal laws governing the behaviour of matter in relation to energy and heat. And this led to the idea of an 'absolute zero', a temperature below which it was impossible to go since matter had zero energy at that point. He used the celsius degree for making his measurements so 1K=1°C. (Note the degree sign is not used with the Kelvin scale.) It is hardly likely to be used for 'ordinary' work - imagine stating a room temperature as 293K (about 20°C) or a normal body temperature as 310.15K (=37°C)!

Finally, W J M Rankine (1820-1872) a Scottish engineer created his scale, which was merely the Kelvin scale using the Fahrenheit degree instead of the Celsius.