>>12466675Fahrenheit proposed his temperature scale in 1724, basing it on two reference points of temperature. In his initial scale (which is not the final Fahrenheit scale), the zero point was determined by placing the thermometer in "a mixture of ice, water, and salis Armoniaci[13] [transl. ammonium chloride] or even sea salt".[14] This combination forms a eutectic system which stabilizes its temperature automatically: 0 °F was defined to be that stable temperature. A second point, 96 degrees, was approximately the human body's temperature (sanguine hominis sani, the blood of a healthy man).[14] A third point, 32 degrees, was marked as being the temperature of ice and water "without the aforementioned salts".[14]
According to a German story, Fahrenheit actually chose the lowest air temperature measured in his hometown Danzig (Gda?sk, Poland) in winter 1708/09 as 0 °F, and only later had the need to be able to make this value reproducible using brine.[15]
According to a letter Fahrenheit wrote to his friend Herman Boerhaave,[16] his scale was built on the work of Ole Rømer, whom he had met earlier. In Rømer's scale, brine freezes at zero, water freezes and melts at 7.5 degrees, body temperature is 22.5, and water boils at 60 degrees. Fahrenheit multiplied each value by four in order to eliminate fractions and make the scale more fine-grained. He then re-calibrated his scale using the melting point of ice and normal human body temperature (which were at 30 and 90 degrees); he adjusted the scale so that the melting point of ice would be 32 degrees and body temperature 96 degrees, so that 64 intervals would separate the two, allowing him to mark degree lines on his instruments by simply bisecting the interval six times (since 64 is 2 to the sixth power).[17][18]
