Electromagnetism
in 1873, James Clerk Maxwell summed up these connections in his theory of "classical electromagnetism," electricity and magnetism together.  This theory was based on a set of four equations called Maxwell's equations, and the Lorentz force law. Maxwell's equations told us how to relate electricity and magnetism. They said that charges sitting still could push on other charges, but moving charges could produce magnetic fields that push on magnets. On the other hand, magnets sitting still can only push on moving charges, but moving magnets can push on any electric charges.