Geomagnetic observation point Vossnacken

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The remains of the geomagnetic observation point at Vossnacken in Velbert in 2015

The Vossnacken Geomagnetic Observatory (also known as the Geomagnetic Observatory or Self-Writing Declinatory) was a building erected in 1912 and used until 1946 in the garden of the former Vossnacker School in Velbert .

Location and description

The district of Vossnacken is on the outskirts of the city of Velbert and is bordered by the Deilbach in the north, east and south. The school building stands on a ridge that can be seen from afar above the Ruhr valley in the middle of the historic farms of the farmers . The control room was built 60 meters to the northeast behind the school on a vacant lot and was surrounded with a fence to shield it.

The building was constructed completely iron-free to avoid magnetic interference. The base and the foundations are made of sandstone , over which a floor made of gravel concrete , screed and asphalt lead plates was laid to protect against rising damp. A two-shell timber structure with a hip roof and slate covering was erected on top. Metal parts such as gutters, door locks and nails were made from brass or copper . It contained an anteroom measuring 4 × 3 meters, from which the observations were made and recorded by a register, and an instrument room measuring 4 × 4 meters. In the instrument room there was a 122 cm high sandstone pillar to safely accommodate the variometer, the actual measuring device. Since the closure of the old Vossnacker School in 1958, the schoolhouse has been used as a private residence. The control room existed until the 1980s and then fell into disrepair.

Measuring device

The measuring device consisted of a variometer for determining the declination and a register located about 2 meters away. In the variometer there was a magnet suspended on a thin thread and a mirror that followed its movement. An electric lamp in the register sent a beam of light concentrated through a converging lens to the mirror in the variometer, which deflected the light beam back to the register , where the point of light hit a roller covered with photographic paper . Since this was moved by a clockwork , the deviation of the magnetic field appeared here as a curve.


Originally, the compass was the only reliable measuring device for determining direction underground . With the introduction of theodolites , polygon courses could be measured. Because of the special conditions in mining when measurements are taken through floating sticks or shafts , magnetic needle measurements were still used to correct angular deviations. Due to the changes and variations in the magnetic axis, however, comparative measurements in geomagnetic observatories had to be used.

From June 1844, the mining offices in Ibbenbüren and Bochum initially carried out measurements with simple compasses. In 1854 the first iron-free house was built to take regular measurements with measuring instruments such as Breitkamp's declinatories. The Westfälische Berggewerkschaftskasse (WBK) set up its first magnetic control room in Bochum in 1888, which, however, had to be relocated in 1895 due to the industrialization of the area with its iron masses and stray currents from the overhead lines of the trams. In July 1912, the control room moved south of the Ruhr to a sparsely populated ridge in Vossnacken , at that time a municipality in the Hardenberg mayor's office . Contrary to a move to the north, in the middle of the mining district, the industrial-free location on the empty ridge seemed more favorable. When choosing the construction site, the decisive factor was that the main teacher at the school could carry out the daily operation of the measuring equipment. The control room was closed in 1946, as the increasing steel expansion of the coal pits made magnetic measurements almost impossible.


  • Glückauf, Berg - und Hüttenmänische Zeitschrift, No. 51, December 21, 1912, Volume 48, page 2061 to page 2070 "The new self-writing declinatorium for the Lower Rhine-Westphalian coal district."
  • Dr. Helmut Grau, Josef Johannes Niedworok, Sven Polkläser: Vossnacker school chronicle - two silver groschen for a pupil - 150 local history and a look into the world in the mirror of the Vossnack primary school chronicle . Scala Verlag, Velbert 2015, ISBN 978-3-9816362-3-9 .

Individual evidence

  1. Researchers discover forgotten history in Langenberg at: from November 3, 2015
  2. Vossnacker school chronicle tells history and stories on: from November 4, 2015