Modern views on magnetism
The molecular theory of magnetism was a considerable step forward but later there came an electrical explanation for the magnetism of atoms and this had wider applications. We have already seen that magnets can be made by an electric current. Atoms contain particles of electricity called electrons which move in orbits about a central nucleus. These electrons behave like an electric current in a single turn of wire and so create a magnetic field. More importantly, the electrons are also spinning like tops and this adds further magnetism to the atom.
It may be recalled that, on page 342, we remarked that all substances show some kind of magnetic effect even if it is very small. The apparently non-magnetic substances are classified as either diamagnetic or paramagnetic respectively. We shall explain these terms very briefly before going on to deal with the strongly magnetic or ferromagnetic substances.