When are units that are named after persons given their names?

Question

There are many scientific units named after people, of which most were given their names a relatively long time ago (Watt, Newton, Celsius, etc).

I wonder if the scientists who "discovered" these units/laws usually get to know that their name is being used in such a way, i.e. if it is common to name the discovery while the person is still alive.

Of course I expect there to be many individual cases, but maybe there is some kind of standard or guideline when it comes to naming units. These are the cases I can think of:

• The scientist names the unit after himself. This rarely happens: What famous laws were named by their discoverer?
• The unit is given its name by someone else to honor the discoverer who is still alive.
• The unit is given its name by someone else (a long time) after the discoverer has died. Maybe to honor the person, or just because nobody could come up with a better name.

How is this usually handled, if there is any usual way at all?

Answer 1

Much of the personal naming occured in 1860-70s for CGS and 1870-1880s for SI, see History of the Metric System. Most of the units named referred to deceased people: newtons, volts, ohms, amperes, pascals, coulombs, watts, etc. Some passed away a while ago, like Pascal and Newton, some relatively recently, like Ampere and Ohm.

Farads, joules and webers might have entered discussions while their name bearers were still around, but by the time the names were officially recommended for adoption (informal adoption began earlier) in 1873 for CGS and 1893 for SI they passed away as well (Faraday in 1867, Joule in 1889 and Weber in 1891). None were self-named.

I am not aware of a formal rule but the tradition seems to be that you do have to die to get a unit to your name.

Answer 2

HERE is a listing of the SI derived units. As far as I know, none of these were someone naming it for himself. If your name is Henry Gray then you are a double unit.

Answer 3

Two scientists got a unit named after them while alive: Joule and Weber.

1) Joule: the second International Electrical Congress in 1889 adopted the joule as the practical unit of electrical work. But time flies, and Joule died a few weeks after the event.(Jayson)

2) Weber. Around 1871, Latimer Clark introduced the weber as a name for the practical unit of current, equal to 1 volt per ohm, although the name was not adopted by all (Everett). In 1881 the International Congress of electrical engineers agreed on the name ampere instead of weber.(Borvon) In 1891 Weber died. In 1893 the International Electrical Conference in Chicago officially adopted the name ampere. In 1933, the weber was reintroduced as another unit name, for magnetic flux.

There is no official guideline, but in 1891 the electrical engineer W.H. Preece wrote he thought it would be unwise to use the name of the living, he preferred the names of the dead.

About temperature units: initially, the personal names Fahrenheit and Celsius were not inseparable parts of their temperature units. The unit was 'degree', and mentioning the scale was optional. Today they are inseparable. May be it would help to determine when writers started inserting a space before the degree symbol, for example 40 °C instead of 40° C.