German Physicist 

Born in Poland, this German scientist spent most of his life in the Netherlands. There he devoted himself to studying physics and manufacturing precision meteorological instruments. 

Fahrenheit discovered that water can remain liquid below its freezing point and that the boiling temperature of liquids varies with atmospheric pressure. His invention of the alcohol thermometer emerged from these discoveries. He developed a scale, called the Fahrenheit thermometric scale, which is still used in the United States and Canada. In developing the scale and thus the thermometer, Fahrenheit used an equal ice-salt mixture for his zero point and 98½ for body temperature. Body temperature was later revised to 98.6½. He is also credited with inventing the first mercury thermometer.

Swedish Astronomer 

Known for his invention of the Celsius thermometer (also called Centigrade), Celsius was actually an astronomer. He served as Professor of Astronomy at the University of Uppsala in Sweden. 

He was an advocate of the measurement of an arc of a meridian in Lapland, and participated in an expedition there to accomplish it. This work confirmed Newton’s theory of almost a hundred years earlier that Earth’s poles are somewhat flattened. 

His development of the Celsius scale took 0° as the freezing point of water and 100° for the boiling point. The scale has been called centigrade because of the 100-degree interval used between the two points. It is the centigrade scale which is most commonly used throughout the world.