Göttingen Magnetic Observatory and Magnetic Union

Measuring the field in absolute units

In 1832 Gauss showed how to express the strength of the Earth's magnetic field in absolute units, based on length, mass and time, instead of comparing needles. He published the method in 1833 as Intensitas vis magneticae terrestris ad mensuram absolutam revocata. A reading in one place could now be compared with a reading anywhere.

With Weber he built a magnetic observatory at Göttingen in 1833, made of copper and brass so that nothing would disturb the instruments, and connected it by a telegraph wire to the physics laboratory, some 1.1 kilometres away. The Gauss–Weber telegraph sent messages between the two buildings, one of the first working electromagnetic telegraphs.

The Magnetic Union

In 1834 Gauss and Weber organised the Göttingen Magnetic Union (Magnetischer Verein), a network of observers in Germany and other European countries who observed on agreed term days, taking readings every five minutes for 24 hours, and sent them to Göttingen. Results were published from 1837 as the Resultate aus den Beobachtungen des magnetischen Vereins, which ran to six volumes.

Weber was dismissed from his chair in 1837 as one of the Göttingen Seven, who had protested against the King of Hanover's abrogation of the constitution, but he continued the magnetic work. In 1838 Gauss published a general theory of terrestrial magnetism that fitted the field with a series of spherical harmonics, and in 1840 the Union published its Atlas des Erdmagnetismus.

Why it counts as an observatory

The Union had no common building. It was a procedure: identical instruments, absolute units, simultaneous observation, a central place that collected and published. It is the template that later networks, from the International Polar Year to INTERMAGNET and the World-Wide Standardized Seismograph Network, rediscovered.

A network without a building

The Union had no site, no common budget and no staff in the modern sense: it was a collaboration of observers, most of whom were at universities and academies, who agreed to follow a method. That makes it unusual among the observatories in the atlas, and a close precedent for the federations of today. It also shows the limit of the form: the Union lasted only a few years after 1840, when its organisers moved on and the telegraph lost its novelty. Its successors, the British colonial observatories, the International Polar Years and later INTERMAGNET, were organised by institutions with budgets. A federation needs a secretariat to survive its founders.

Instruments and technologies

• Magnetometer with mirror reading A heavy magnetised bar hung by a silk thread; a mirror on it reflected a scale into a telescope, so tiny rotations were read as large movements of the scale.
• Iron-free building Copper, brass and wood throughout, with no iron nails, so that the building did not distort the field.
• Electromagnetic telegraph A wire over the rooftops of Göttingen linking the observatory and the physics laboratory, using the induced current from a moving magnet.

The people

• Carl Friedrich Gauss Mathematician; absolute units, the method of least squares, the general theory of the field.
• Wilhelm Eduard Weber Physicist; designed the instruments and organised the observers.

Timeline

• 1833 Gauss publishes Intensitas vis magneticae terrestris ad mensuram absolutam revocata; the iron-free observatory and the Gauss–Weber telegraph are built.
• 1836 First year of network results, published in 1837 as Resultate aus den Beobachtungen des magnetischen Vereins.
• 1837 Weber is dismissed as one of the Göttingen Seven but continues the magnetic work.
• 1840 Gauss and Weber publish the Atlas des Erdmagnetismus.

Key lessons for observation today

• Units come first Absolute units turned incomparable readings into a data set. Any network starts by agreeing on units and reference scales.
• Observe together on a schedule Term days with five-minute readings made distant records comparable in time. Synchronised observing is still done through shared time references.
• Build for quiet The iron-free building kept the instruments clean. A site's electromagnetic environment is a design requirement, as the later move of Kew's magnetic instruments showed.

Sources

• MacTutor History of Mathematics, Wilhelm Weber
• Smithsonian Libraries, Resultate aus den Beobachtungen des Magnetischen Vereins
• Wikipedia, Göttingen Observatory (secondary)