Ampère's force law Updated +Created
Force between two wires carrying an electric current.
Caused by the Lorentz force.
Maxwell's equations require special relativity Updated +Created
When charged particle though experiment are seen from the point of view of special relativity, it becomes clear that magnetism is just a direct side effect of charges being viewed in special relativity. One is philosophically reminded of how spin is the consequence of quantum mechanics + special relativity.