If you place a wire with a running current in a magnetic field, the magnetic field will excert a force on the wire. So, if you place two wires parallel to each other, the current on each will produce a magnetic field, which in turn will attract or repulse the other wire depending on the direction of the current. What I don't get, is how the magnetic field from wire a reaches wire b. If you look at drawings of magnetic field lines between wires, the total field does not seem to run through the wires at all, as the magnetic field generated from wire a, "deflects" the field generated by wire b. This is what I'm talking about: What am I missing?