Ernst Werner Siemens (1816-1892) was a German inventor and industrialist. Siemens’s name has been adopted as the SI unit of electrical conductance, the siemens. He was also the founder of the electrical and telecommunications company Siemens.
A dynamo is an electrical generator that produces direct current with the use of a commutator.
Dynamos were the first electrical generators capable of delivering power for industry, and the foundation upon which many other later electric-power conversion devices were based, including the electric motor, the alternating-current alternator, and the rotary converter.
Today, the simpler alternator dominates large scale power generation, for efficiency, reliability and cost reasons.
A dynamo has the disadvantages of a mechanical commutator. Also, converting alternating to direct current using power rectification devices (vacuum tube or more recently solid state) is effective and usually economic.