Units of measurement named after Uppsala scientists
Five historical pioneers at Uppsala University have so far lent their names to units of measurement. That could be a world record.
Celsius, symbol °C
Unit of temperature named after Anders Celsius (1701–44), astronomer and professor at Uppsala University.
Several different temperature scales were in use in the 18th century. In Europe alone, four different scales were developed. In Uppsala, temperature measurements began with Erik Burman, Celsius’s predecessor. There is an uninterrupted series of temperature measurements dating back to 1722. However, the scale was upside down. It was not until the year after Celsius’s death that Carl Linnaeus turned the scale the right way up from our modern perspective. Internationally, the scale was not used with the name of Celsius until 1948. Before that, the symbol C stood for centigrade (one hundred degrees).
Anders Celsius’ thermometer at Gustavianum.
Angstrom, symbol Å
An old unit of length, primarily used in spectroscopy. The unit is named after Anders Ångström (1814–74), physicist, astronomer, professor, and vice-chancellor at Uppsala University, and one of the founders of spectroscopy.
The unit has to do with the wavelengths of light. Ångström determined the wavelength of light and was the first to investigate the spectrum of the northern lights. An angstrom is 10⁻¹⁰ metres, a very short unit that roughly corresponds to the length of an atom.
The unit was first mentioned in writing in the 1860s, but only began to be used more widely around 1905–06. It obtained its present definition in 1960 and commonly occurs in physics and chemistry.
Detail of portrait of Anders Ångström.
Sievert, symbol Sv
The SI unit for the quantities equivalent dose and effective dose of radiation. The unit is named after Rolf Sievert (1896–1966), a pioneer in the measurement of radiation doses and diagnosis in the treatment of cancer.
Sieverts are generally expressed as millisieverts (thousandths of a sievert). The quantities are used in estimating the risk of damage to a person or other living organism exposed to ionising radiation. The highest permissible dose for anyone working with radiation is 20 millisieverts. An X-ray at the dentist exposes the patient to one hundredth of a millisievert.
Sievert obtained his doctorate in Uppsala but continued his career at Karolinska Institutet and Radiumhemmet.
Rolf Sievert in his office.
Svedberg, symbol S
Measure of sedimentation rate corresponding to 10⁻¹³ seconds or 100 femtoseconds. The measure is named after Nobel Prize winner Professor Theodor (The) Svedberg (1884–1971).
The sedimentation coefficient relates to the extra mass that a particle has compared with its solution and size. The unit is expressed in inverse seconds. One Svedberg is 10⁻¹³ seconds. The unit is still used in ultracentrifuge contexts.
The Svedberg at his ultracentrifuge.
Siegbahn or X unit (XE)
A unit of distance used for very small distances, for example to measure the wavelength of gamma and X-rays. The unit was introduced in 1925 and is named after Nobel Prize winner Professor Manne Siegbahn (1886–1978).
The unit was originally called X. Siegbahn needed it for his research in X-ray spectroscopy and it was perhaps modesty that led him to call it X.
The unit was used from 1925 onwards. At the end of the 1960s, the X unit or Siegbahn began to be replaced by the angstrom. It is therefore no longer in use.
Manne Siegbahn.