SI unit (symbol S) of electrical conductance,
the reciprocal of the impedance of an
electrical circuit. One siemens equals one
ampere per volt. It was formerly called the
mho or reciprocal ohm.

2.
German family of four brothers, creators of a
vast industrial empire. The eldest, Ernst
Werner von Siemens (1812-92), founded the
original electrical firm of Siemens und
Halske 1847 and made many advances in
telegraphy. William (Karl Wilhelm) (1823-83)
moved to England in 1884 and perfected the
open-hearth production of steel, pioneered
the development of the electric locomotive
and the laying of transoceanic cables, and
improved the electric generator.