barometer
The thermometer was developed a short time after the barometer made it possible to study pressure in a quantitative manner. Although crude thermometers had been available for quite some time, Daniel Fahrenheit constructed a more accurate thermometer in 1724 using mercury in glass. Because the height of the mercury in the thermometer was a relative measure, certain fixed points needed to be defined. Originally, Fahrenheit defined a 1:1:1 mixture of ice, salt, and ammonium chloride as 0F, and the freezing/melting point of ice as 32F. On this scale, the normal temperature of the human body is 96F, and the boiling point of water is 212C. The modern Fahrenheit scale is defined in terms of the normal freezing and boiling points of water.