8 Apr 2010

Aurorae (see March 29th) has an interesting article on the recognition that aurorae had electro-magnetic properties. In 1740 Anders Celsius, the inventor of the centigrade scale named after him, interpreted aurorae as an electro-magnetic anomaly after he noticed a large compass needle on his desk top changed orientation whenever an aurorae was visible in the sky above Uppsala in Sweden. In 1861 Benjamin Marsh theorised that an auroral streamer is a current of electricity that originates in the upper parts of the atmosphere. In 1883 Selim Lemstrom, a Finnish professor, reported a link between aurorae and electricity - even artificially producing a weak auroral stream that stretched 400 feet into the air from an electrical apparatus he installed on top of a hill near his home. Kristian Birkeland spent a large part of his time investigating aurorae - very often making expeditions into the bleaker and colder regions of Norway in order to study it where it was most common. He set out to seek an electro-magnetic solution and was attracted by the possibility that the sun might throw out electrons towards the earth and these may become trapped in earth's magnetic field where they would congregate near the poles. The same electrons, he thought, might glow as they travelled through the atmosphere = auroral phenomena.

In European countries to the south, where aurorae were not common and therefore not something at hand to research, Birkeland's theories were completely rejected - as these things tend to be. The consensus once again was extraordinarily dogmatic and an electro-magnetic connection was resisted by academic science. Sydney Chapman was attracted by the theory but peer pressure seems to have made him change his mind. An electric current flowing from the sun was considered an impossibility. Alfven replicated Birkeland's experiment but by this time Chapman had been nobbled and would not budge - the heavy brigade had made an impression on him and he did not wish to put his head above the parapet once again. However, in 1961  a Russian spacecraft encountered a stream of electric particles flowing from the sun - which they reported. Western scientists scoffed at this in the age old manner of haughty contempt - fairly easy to achieve in the Cold War era. However, a few years later NASAs Mariner II spacecraft encountered a stream of electrified gas travelling at an enormously fast speed. In addition, the US Navy was collecting consistent evidence of magnetic disturbance in their instruments every time a ship approached one of the poles. Practicalities put a question mark against academia and once satellite data began to report precisely the same kind of thing the guys in the tall spires had to come down to earth and eventually accept Birkeland's theory - now attributed to the Solar Wind.