Magnetism and magnetic £elds were one of the oldest physical phenomena investigated and subjected to measurements. The effect of attraction (or repulsion) between pieces of some lodestones has been known as long as iron smelting.* Moreover, it was observed that small pieces of this rock spontaneously rotated along north-south direction. Thus, no wonder that such an effect was applied to pointing north direction in the compass-written records show that ancient Chinese used the compass (Si Nan) between 300 and 200 BC† (Campbell 2001).