Svedberg unit: a name from the ultracentrifuge
At the ultracentrifuge, particles, their surrounding solution, and their size become part of a measurement named for Theodor Svedberg. The Svedberg unit, symbol S, measures sedimentation rate and corresponds to 100 femtoseconds. Uppsala University's history links the name to its Nobel Prize-winning professor, who lived from 1884-1971. The university's portrait of him places him beside his ultracentrifuge, the scientific setting in which the unit remains in use. A tiny time equivalent is only the beginning of the story: the measurement belongs to the behavior of particles in a solution, carrying a scientist's name into laboratory vocabulary.
The sedimentation coefficient relates to the extra mass a particle has compared with its solution and to its size. Its equivalent can also be written as ten to the negative thirteenth power of a second. The number is expressed in time units, while its use concerns sedimentation in an ultracentrifuge. That pairing joins a very small scale to a particular kind of laboratory measurement. The name does not stand for an ordinary division of a clock face; it belongs to a coefficient whose meaning depends on the particle and the solution around it.
Svedberg is among five historical Uppsala pioneers whose names became units of measurement. Their work spans temperature, light, radiation, sedimentation, and very small distances. This company gives the Svedberg unit a place within a wider university history, in which scientific names traveled beyond the people who first bore them. Uppsala's scientific vocabulary reaches from a thermometer to an ultracentrifuge, with each name connecting a measured quantity to a person associated with its study rather than to a single shared scale.
Temperature carries the name of Anders Celsius, an astronomer and professor at Uppsala who lived from 1701-44. Several temperature scales were in use during the eighteenth century; four different scales developed in Europe alone. In Uppsala, temperature measurements began with his predecessor, Erik Burman, and an uninterrupted series extends back to 1722. Celsius entered a scientific environment already concerned with observing temperature over time. His name now identifies a scale, but that familiar label grew from a history involving earlier observations and competing ways of assigning numbers to temperature. The measurements preceded the international adoption of the personal name.
Celsius's scale originally ran in the opposite direction from its modern form. In the year after his death, Carl Linnaeus reversed it. International use of the name Celsius did not begin until 1948; before then, C stood for centigrade, meaning one hundred degrees. The Svedberg unit's name points directly toward its laboratory context. The familiar thermometer vocabulary therefore contains contributions made at different times by different people. Its present name sits at the end of a longer sequence of observation, adjustment, and international usage.
The angstrom commemorates Anders Angstrom, who lived from 1814-74 and served as physicist, astronomer, professor, and vice-chancellor at Uppsala. One of the founders of spectroscopy, he determined wavelengths of light and was the first to investigate the spectrum of the northern lights. The unit bearing his name is a very short length, roughly corresponding to the length of an atom. It appeared in writing during the eighteen-sixties, became more widely used around 1905-06, and received its present definition in 1960. Its uses in physics and chemistry connect a scientist's work on light with a scale of exceptionally small distances.
Radiation measurement honors Rolf Sievert, who lived from 1896-1966. He earned his doctorate in Uppsala, then continued his career at Karolinska Institutet and Radiumhemmet. His work made him a pioneer in measuring radiation doses and in diagnosis during cancer treatment. The sievert is the SI unit for equivalent dose and effective dose, quantities used to estimate the risk of damage from ionizing radiation exposure to people and other living organisms. It is generally expressed in millisieverts, thousandths of a sievert. Here the university connection extends through a doctorate into work elsewhere, and the unit's purpose concerns biological consequences rather than particle sedimentation.
Manne Siegbahn, a Nobel Prize-winning professor who lived from 1886-1978, gave his name to another small-distance measure. Introduced in 1925, it was originally called X and served his research in X-ray spectroscopy. The X unit, also called the Siegbahn, could measure wavelengths of gamma rays and X-rays. It remained in use from 1925 onward, but replacement by the angstrom began at the end of the nineteen-sixties. A scientific name could thus survive as part of Uppsala's history even as its unit left active use, giving way to another measure associated with a scientist from the same university.