I actually meant to take the demo one step further. Each compass needle has its own magnetic field. Put them close enough together and (with luck) the N end of one needle will attract the S end of the other. Put several of these compases in a ring, and the needles will point around the ring, whether or not there is a current flowing down a wire in the middle. And there are two stable states, just like a core. With (even more) luck, you can flip between states with a current. Just like core. Worth a try? This weekend I shall see if I can find some cheap, small compasses in a toy shop or somewhere... Philip.