The Rømer scale (; notated as °Rø), also known as Romer or Roemer, is a

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

scale named after the Danish

astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either ...

Ole Christensen Rømer, who proposed it in 1701. It is based on the

freezing point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depend ...

of pure

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...

being 7.5 degrees and the

boiling point The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding env ...

of water as 60 degrees.

Degree measurements

In this scale, the zero was initially set using freezing

brine Brine is a high-concentration solution of salt (NaCl) in water (H2O). In diverse contexts, ''brine'' may refer to the salt solutions ranging from about 3.5% (a typical concentration of seawater, on the lower end of that of solutions used for ...

. The boiling point of

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 Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a discrete piece of action (or beat) in a theatrical presentation Music * ''Unit'' (a ...

of this scale, a Rømer degree, is 100/52.5 = 40/21 of a

kelvin The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and ...

Celsius The degree Celsius is the unit of temperature on the Celsius scale (originally known as the centigrade scale outside Sweden), one of two temperature scales used in the International System of Units (SI), the other being the Kelvin scale. The d ...

degree. The symbol is sometimes given as °R, but since that is also sometimes used for the Réaumur and

Rankine scale The Rankine scale () is an absolute scale of thermodynamic temperature named after the University of Glasgow engineer and physicist Macquorn Rankine, who proposed it in 1859. History Similar to the Kelvin scale, which was first proposed in 184 ...

s, 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. 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 Ferdinando II de' Medici (14 July 1610 – 23 May 1670) was grand duke of Tuscany from 1621 to 1670. He was the eldest son of Cosimo II de' Medici and Maria Maddalena of Austria. He was remembered by his contemporaries as a man of culture and ...

'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.

Relationship to other scales

Daniel Gabriel Fahrenheit Daniel Gabriel Fahrenheit FRS (; ; 24 May 1686 – 16 September 1736) was a physicist, inventor, and scientific instrument maker. Born in Poland to a family of German extraction, he later moved to the Dutch Republic at age 15, where he spen ...

, inventor of the

Fahrenheit scale The Fahrenheit scale () is a temperature scale based on one proposed in 1724 by the physicist Daniel Gabriel Fahrenheit (1686–1736). It uses the degree Fahrenheit (symbol: °F) as the unit. Several accounts of how he originally defined h ...

, learned of Rømer's work and visited him in 1708. Fahrenheit described how he borrowed the idea for his scale from this visit, but increased the number of divisions.Roger W. Coltey, ''Survey of medical technology'', University of Michigan, 1978, p. 29. 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.

Notes and references

{{DEFAULTSORT:Romer Scale Obsolete units of measurement Scales of temperature Danish inventions

Degree measurements

Importance

Relationship to other scales

See also

Notes and references