The English physicist Humphry Davy had produced an electric arc for lighting purposes for the first time in 1808, proving that what he called electric “arch” lamps could produce a much brighter and more intense light than other light sources that were used at the time. Electric arc lamps could thus be used to make lighthouses along the coasts much more visible or to illuminate large construction sites or other public areas.

An industrial building was located immediately adjacent to the objects to be lit and used to store the spinning dynamos that powered the arc lamps. These generators – known as magneto-electric machines – were heavy but not very powerful and used permanent magnets. The machines produced barely 700 Watts, although the generators weighed almost 2,000 kilos. In addition, power generation was subject to very strict limits, because the permanent steel magnets that were used produced only a weak magnetic field. They quickly lost their magnetism, too, due to the vibrations caused by operation. That was the situation when Werner von Siemens began his systematic research. A higher rotation speed for the anchor and the generation of stronger magnetic fields were decisive factors in his success at further developing magneto-electric machines. The pioneering double‑T anchor developed by Werner von Siemens for his pointer telegraph was the basis for much higher rotation speeds in dynamos, since his design offered sufficient mechanical strength.

The Englishman Henry Wilde attempted for the first time in 1864 to replace the weak steel magnets used in generators with electromagnets that were in turn produced by the conventional dynamos of that era. However, this technically incomplete solution did not satisfy Werner von Siemens. In September 1866 he had a double-T anchor of a generator connected in series with an electromagnet so he could explore the effect of self-induction. If the double‑T anchor was then cranked by hand, the slight magnetism of the Earth was sufficient for initial low-level generation of electricity (self-induction), which then gained its full strength after a few rotations. As a result, a connected electroscope measuring device immediately burned through, and a one-meter-long iron wire secured between the generator clamps even melted.

In early December 1866, Werner von Siemens reported to his brother Wilhelm about his experiments with the new dynamo. Looking at the commercial potential of his invention, he wrote: “Provided the design is correct, the effects should turn out to be enormous. This concept can well be expanded and may initiate a new era in electromagnetism. Thus magnetic electricity will become available very inexpensively, and lighting, galvanometallurgy, etc., even small electromagnetic machines obtaining their energy from larger ones, may become feasible and useful."

At the same time, Werner von Siemens was preparing his report “On the transformation of mechanical energy into electric current without the application of permanent magnets,” which was presented by his friend Heinrich Gustav Magnus before the Prussian Academy of Sciences on January 17, 1867. This brought the brilliant discovery by Werner von Siemens to the attention of experts in the field.

Volker Leiste