‘Magnetism and relativity’ considers Albert Einstein's theory of relativity. Electric forces are incredibly strong; they are what hold all rigid objects together — bridges, walls, and human beings. But they all cancel out in a current-carrying wire because all the positive and negative charges balance. However, the tiny relativistic effect, what we call the magnetic field, which is due to the motion of the negatively charged mobile electrons, remains and is not cancelled out. Einstein showed that magnetism is a purely relativistic effect, something that would not even be there without relativity. Magnetic fields are a relativistic correction that you observe when charges move relative to you.