Ole Christensen Roemer (1644-1710) was a contemporary (and friend) of Isaac Newton and best remembered for his (controversial for many years) discovery of the finite speed of light. However, Roemer was a most versatile person with many accomplishments for his native Denmark in astromomy, mathematics, engineering, tax reform, weight standards, military ballistics, law, government, international trade, to name a few. He also had another under recognized accomplishment.

It was Roemer who designed and constructed his own more accurate thermometers and was the first to realize and use *two* fixed points (rather than one) to calibrate the scale of a thermometer. Roemer's upper point was the boiling point of water, which he set as 60 degrees. (Roemer apparently did not realize that water's b.p. depended on atmospheric pressure, a fact that Fahrenheit later discovered.)

Roemer's lower calibration point has been the subject of some debate. Some have said that a 0 value was assigned to a mixture of water, ice, and ammonium chloride; others claim Roemer used the melting point of snow (which he marked as 7.5 deg.). Because much of Roemer's records were destroyed in a fire in Copenhagen in 1728, we may never know for sure. (I might note here that 7.5 is one-eighth of 60, and accurately dividing a thermometer scale by powers of 2 is easily accomplished with simple tools.)

In 1708, the German physicist, Daniel Gabriel Fahrenheit (not "Gabriel Daniel"), visited Ole Roemer in Copenhagen. Roemer showed him the two-point calibration system he had developed. Roemer was also testing small thermometers designed for meteorological use which had divisions marked from 0 to 22.5 deg. (normal blood temperature) using Roemer's scale.

Fahrenheit was so impressed with Roemer's thermometers and the two-point calibration scale that he adopted them for use back in Germany. While it appears that Fahrenheit used the same lower calibration point as that of Roemer, it is clear (from a letter written by Fahrenheit to Boerhaave in 1729 and rediscovered in 1936) that Fahrenheit used Roemer's 22.5 deg ("normal body temperature") as the upper point. From a 1724 paper, Fahrenheit determined the upper point either in the mouth or under the armpit (the third alternative technique was not noted :-)). It is not clear whether Fahrenheit (or Roemer) distinguished a male or female body temperature (in his Latin paper Fahrenheit used the word "hominis").

Fahrenheit later multiplied Roemer's scale numbers by four for easier reading. This made the melting point of ice 30 deg. and body temperature 90 deg.

Eventually Fahrenheit adjusted the calibration points to 32 (ice melting point) and 96 (body temperature) to simplify marking the scale divisions (i.e., 64 divisions). Thus the boiling point of water would be measured experimentally near 212 deg. Later, the b.p. of water, at a fixed atmospheric pressure, was used as the upper calibration point of 212, returning to Roemer's initial calibration concept. (With these two calibration points, the experimentally determined temperature of a healthy person is now accepted to be approximately 98.6 deg.)

Thus, as noted by historian I.B. Cohen, Ole Roemer's thermometer scale design is really the basis of the thermometer scale used by Daniel Gabriel Fahrenheit (1686-1736).

For more information on Roemer, the thermometer, and his other accomplishments, see Roemer and the First Determination on the Velocity of Light, I. Bernard Cohen (Burndy Library, New York, 1944). Cohen's short book has many references, mostly in Danish, French, German, or Latin; and mostly very old. Fahrenheit's own acknowledgement of Roemer's contribution is in a letter he wrote in 1729 and reprinted in Kon. Akad. Wet. Verhand., Vol.xvi, 1936, pp.1-37. A more recent discussion of Roemer's temperature scale was given by Robert H. Romer, "Temperature scales: Celsius, Fahrenheit, Kelvin, Reamur, and Romer", The Physics Teacher, 20 (Oct. 1982), pp.450-454)

For the extremely adventurous, one can peruse a bibliography on Roemer by Per Friedrichsen, "Dansk Astronomi Gennem Firhundrede År", Bind 3, ISBN 87-7245-281-1, Produktion Rhodos, 1990, then stop by the Ole Roemer Museum in Tåstrup, Denmark.
 

Allan S. Wagman <Allan_Wagman@cc.chiron.com> sent this letter to Marilyn:

I happened upon your column in the March 22 issue of Parade Magazine which quite incompletely answers to a very good question posed by Baker Smith - What is the logical correlation between the Fahrenheit scale and natural calibration points. The answer is very simple. There are 180 degrees between the melting point of water and the boiling point. This number was considered rational at the time since it was based on the number of degrees in half of a circle. Fahrenheit was an instrument maker in Amsterdam who is famous for inventing the mercury thermometer. He based his temperature scale on the work of many others, but mostly that of Robert Hook and Ole Roemer. Fahrenheit's scale is fixed by the known simple constant temperature baths at the time which were that of melting water-ice in a saturated aqueous salt solution and that of melting water-ice in pure water. The saturated salt bath and ice was assigned the value of 0 degrees while that of ice and pure water was assigned the value of 30 degrees. (see D. G. Fahrenheit Phil. Trans. (London) 1724, 33, 78.) The temperature of the body was measured at 96 degrees. This scale was later arbitrarily changed when the temperature of boiling water was measured at 212 degrees. Fahrenheit changed the value of freezing water from 30 to 32 degrees to achieve the more attractive scale of 180 degrees between the melting point of water and that of boiling water. There are many other interesting connections in the history of thermodynamics and the personalities that are famous for making the great intellectual leaps that drive our science and civilization. (for more information see the references below)

............

• Adkins, C. J., Thermal Physics, 1987 Cambridge University Press, ISBN 0-521-33715-1
• Cork, James M., Heat, 1942, John Wiley & Sons
• Herzfeld, Charles M. Editor, Temperature: Its Measurement and Control in Science and Industry, 1962, Reinhold
• Quinn, T. J., Temperature, 1990, Academic Press, ISBN 0-12-569681-7
• Weber, Robert L., Heat and Temperature Measurement, 1950, Prentice-Hall, Inc

Zemansky, Mark W., Heat and Thermodynamics, 1968, Mc Graw Hill