Daniel Gabriel Fahrenheit

Daniel Gabriel Fahrenheit (1686-1736) was a German physicist who worked in the Netherlands. He became known for the precise instruments he made. The degree Fahrenheit is named after him. He was the first to be able to determine the temperature with precision. His thermometers used Ethyl alcohol at first. When he read an article by Guillaume Amontons about using mercury in barometers, he got the idea of using that substance for his thermometers. He calibrated his mercury thermometers to a cold temperature he could produce easily, the freezing point of salt water. 
In 1724 he discovered that water can be supercooled below its freezing point without turning into ice. 
Fahrenheit also developed a hydrometer, a pycnometer and a hypsobarometer