FROM OERSTED TO EINSTEIN

In the winter of 1819–1820 Hans Christian Oersted was lecturing on electricity, galvanism, and magnetism to advanced students at the University of Copenhagen. Electricity meant electrostatics; galvanism referred to the effects produced by continuous currents from batteries, a subject opened up by Galvani's chance discovery and the subsequent experiments of Volta; magnetism dealt with the already ancient lore of lodestones, compass needles, and the terrestrial magnetic field. It seemed clear to some that there must be a relation between galvanic currents and electric charge, although there was little more direct evidence than the fact that both could cause shocks. On the other hand, magnetism and electricity appeared to have nothing whatever to do with one another. Still Oersted had a notion, vague perhaps, but tenaciously pursued, that magnetism like the galvanic current might be a sort of “hidden form” of electricity. Groping for some manifestation of this, he tried before his class the experiment of passing a galvanic current through a wire which ran above and at right angles to a compass needle. It had no effect. After the lecture, something impelled him to try the experiment with a wire running parallel to the compass needle. The needle swung wide—and when the galvanic current was reversed it swung the other way!

The scientific world was more than ready for this revelation. A ferment of experimentation and discovery followed as soon as the word reached other laboratories.