i can prove these lines going from north to south externally???but do know the proof internally,
The proof is really only a logical deduction. The external lines of force emanate from the north pole and trace out continuous non-overlapping lines through space back to the south pole. (The external direction from north to south is arbitrarily assigned). It is therefore a logical deduction that the lines of force returning to the south pole trace out continuous non-overlapping lines back to the north pole inside the magnetic material.
