Rømer temperature conversion formulae
from Rømer to Rømer
Celsius x °Rø ≘ (x − 7.5) × 40/21 °C x °C ≘ (x × 21/40 + 7.5) °Rø
Fahrenheit x °Rø ≘ ((x − 7.5) × 24/7 + 32) °F x °F ≘ ((x − 32) × 7/24 + 7.5) °Rø
Kelvin x °Rø ≘ ((x − 7.5) × 40/21 + 273.15) K x K ≘ ((x − 273.15) × 21/40 + 7.5) °Rø
Rankine x °Rø ≘ ((x − 7.5) × 24/7 + 491.67) °R x °R ≘ ((x − 491.67) × 7/24 + 7.5) °Rø
For temperature intervals rather than specific temperatures,
1 °Rø = 40/21 °C = 24/7 °F
Conversion between temperature scales

The Rømer scale (Danish pronunciation: [ˈʁœˀmɐ]; notated as °Rø), also known as Romer or Roemer, is a temperature scale named after the Danish astronomer Ole Christensen Rømer, who proposed it in 1701. It is based on the freezing point of pure water being 7.5 degrees and the boiling point of water as 60 degrees.

Degree measurements

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 Celsius degree. The symbol is sometimes given as °R, but since that is also sometimes used for the Réaumur and Rankine scales, the other symbol °Rø is to be preferred.

Importance

The Rømer scale is no longer in use, but it is of some historical importance. Alongside the Newton scale, it was the first calibrated scale. Previous thermometers gave only an indication of whether the temperature was rising or falling, or else were highly inaccurate. For instance the top and bottom marks of thermometers were typically set to the hottest and coldest days, respectively, of the current year which clearly would vary from year to year.[1] The idea of using two fiduciary points with equally spaced calibration marks between them was completely new.

Rømer was familiar with Galileo's thermoscope and understood that its large inaccuracies were due to it being affected by air pressure as well as temperature. He followed Ferdinand II of Tuscany's idea of enclosing a liquid in a sealed glass tube which made it immune to pressure changes. Rømer's thermometer was also an improvement in the fluid that he used. He used a mixture of alcohol and water, conveniently available in the form of wine. This avoided the drawbacks of both the low boiling point of pure alcohol and the extreme non-linearity of pure water near freezing.[2][3]

Relationship to other scales

Daniel Gabriel Fahrenheit, inventor of the Fahrenheit scale, visited Copenhagen in 1708. While there, he met Rømer and learned about his work with thermometers and scales. Rømer also told Fahrenheit that demand for accurate thermometers was high.[4]: 4  The visit ignited a keen interest in Fahrenheit to try to improve thermometers.[5]: 71  By 1713, Fahrenheit was creating his own thermometers with a scale heavily borrowed from Rømer that ranged from 0 to 24 degrees but with each degree divided into quarters.[4]: 31 [6] At some point, the quarter degrees became whole degrees and Fahrenheit made other adjustments to Rømer's scale, modifying the freezing point from 7.5 degrees to 8, which, when multiplied by four, correlates to 32 degrees on Fahrenheit's scale.[5]: 73  The 22.5 degree point would have become 90 degrees, however, by 1713, Fahrenheit rounded this up to 24 degrees–96 when multiplied by 4–in order to make calculations easier.[4]: 20 .

Newton published his scale in the same year as Rømer. Newton's system was calibrated between the freezing point of water (0 degrees) and human body temperature (12 degrees); it was a coarser scale, but unlike Rømer's it was not intended for everyday use, as Newton's interest was in determining the melting points of metals, which are not readily accessible with Rømer's system based on liquid thermometers.

See also

Notes and references

  1. ↑ Don Rittner, A to Z of Scientists in Weather and Climate, page 53, Infobase Publishing, 2009, ISBN 1438109245.
  2. ↑ Jonathan Shectman, Groundbreaking Scientific Experiments, Inventions, and Discoveries of the 18th Century, pp. 248–49, Greenwood Publishing Group, 2003 ISBN 0313320152.
  3. ↑ Susan Wills, Steven R. Wills, Meteorology: Predicting the Weather, pp. 19–21, The Oliver Press, Inc., 2003 ISBN 1881508617.
  4. 1 2 3 van der Star, Pieter (1983). Fahrenheit's Letters to Leibniz and Boerhaave (E-book (from hardcover) ed.). Amsterdam: Rodopi. ISBN 978-90-04-62867-0. Retrieved 2 December 2023.
  5. 1 2 Middleton, W. E. K. (1966). A history of the thermometer and its use in meteorology. Internet Archive. Johns Hopkins Press. ISBN 9780801871535.
  6. ↑ Roger W. Coltey, Survey of medical technology, University of Michigan, 1978, p. 29.
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