Stationary Magnetic Fields 1 (In A Vacuum)

In Programmes 2 and 3 we considered electrostatic fields which we found were produced by charges at rest and in Programme 4 we saw that conduction fields are produced by charges in motion. We now begin a study of magnetic fields ‘at rest’ or ‘steady’ magnetic fields, and the question arises as to how they are produced. Before Oersted’s discovery in 1820 that current-carrying conductors produced magnetic fields in their vicinity the only known magnetism was that of natural magnets. Early experimenters found that the effects of these were greatest near their ends (which were called poles) and that the two ends produced opposite effects. Although it was realised that poles always occurred in pairs. Michell had the idea of considering them separately and showed in 1750 that the inverse square law applied to the forces between them.