Ampere's Law
Andrea Marie Ampere formulated his law by observing a experiment by another scientist named Oersted. Oersted noticed that when a magnetic compass was brought near a current carrying wire that the needle would line up perpendicular to the wire. Oersted was unable to explain this phenomenon. Ampere, however, continued to experiment with this observance. He soon found that not only would a compass needle deflect when brought next to a current carrying wire but also another current carrying wire would have forces exerted on it when brought close to the first. This lead Ampere to believe that the current was generating a magnetic field. Ampere's law states that a electric current produces a magnetic field in the direction your fingers point if you point your right hand thumb in the direction of the current flow. Notice how in the animation that when the current flows toward the bottom left the magnatic field vectors rotate in a counter clock wise direction. The opposite is true when the current reverses dirrection. Try it yourself. Point your right hand thumb in the direction the current is flowing and notice that the magnetic field flows in the direction that your fingers point.