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In this scale, the zero was initially set using freezing brine. The boiling point of water was defined as 60 degrees. Rømer then saw that the freezing point of pure water was roughly one eighth of the way (about 7.5 degrees) between these two points, so he redefined the lower fixed point to be the freezing point of water at precisely 7.5 degrees. This did not greatly change the scale but made it easier to calibrate by defining it by reference to pure water. Thus the unit of this scale, a Rømer degree, is 100/52.5 = 40/21 of a kelvin (or of a Celsius degree). The symbol is sometimes given as °R, but since that is also sometimes used for the Rankine scale, the other symbol °Rø is to be preferred. The name should not be confused with Réaumur.
The inventor of the Fahrenheit scale Daniel Gabriel Fahrenheit learned of Rømer's work and visited him in 1708; in one of his letters Fahrenheit narrates how he borrowed the idea for the scale from this visit, increasing the number of divisions by a factor of four and eventually establishing what is now known as the Fahrenheit scale, in 1724.
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- ↑ Roger W. Coltey, Survey of medical technology, University of Michigan, 1978, p. 29.