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Re: MHO to Siemens


I wondered if someone could give me a historical insight on why the
unit of conductance changed from Mho to Siemens ( S) after William Siemens
(1823-83) [ besides the mere fact that it is impolite to distort people's names
- from Ohm to Mho. That seems an unlikely reason ]. Why Siemens, for example.

The name of the SI unit of conductance is siemens (starting with a lower
case s); its symbol is the upper case S.
I don't know why that name was chosen but it continues the SI practice of
naming selected derived units directly after people. It has been the
official SI name for at least 25 years, probably much longer. As far as I
know mho was never an SI name, so as far as the International System is
concerned there was no change from mho to siemens. Since there was no
famous scientist called mho, it is unlikely that the International
Conference on Weights and Measures would have considered mho as a unit
name. I think that mho was introduced by American texts in the olden days
of mixed cgs and mks units, before SI.

Ian Sefton (
School of Physics A28
University of Sydney NSW 2006