1820 From April to July, Oster placed the small magnetic needle under the electrified wires placed in the north and south, and found that the small magnetic needle was deflected, and it was found that the magnetic field generated by the current made the small magnetic needle deflect (the magnetic effect of the current).

On July 2 1 65438, Oster published a paper entitled "Experiment of Current Collision on Magnetic Needle". This paper only used four pages to report his experiment very concisely, and announced the magnetic effect of current to the scientific community. As an epoch-making day,1820 July 2 1 went down in history, which opened the prelude of electromagnetism and marked the arrival of the era of electromagnetism.