" It’s more than just an electrical conductor, it’s a superconductor. “You might think of it this way: the conductor is a road with lots of obstacles in it. The electrons carrying the charge are deflected from their path so the traffic is slowed up. But this plastic is like a wide speedway. The electrons can move in large loops and avoid all the obstacles. So they go around and around at high speed, and if the speedway is a circle, they will never stop.” “Never?” Danny gazed up at the Professor in wonder. “You mean it would be a kind of perpetual motion? But I thought that wasn’t possible.” “Nevertheless, that’s just what it would be.” Professor Bullfinch leaned forward to inspect the plastic. “Look here. The two ends of this coil are touching. It forms a closed ring. When you dropped the cable, it started a charge going through the coil. Now, my boy, a moving charge of electricity flowing around a circuit produces a magnetic field. What we have here is a very powerful ring magnet, so powerful that when I tried to touch it the magnetic field caught and held the metal of my wrist watch.” “A supermagnet,” said Danny. “That’s right. And it will go on being a magnet, with the current flowing on and on around the circle until I break the current. Like this.” Professor Bullfinch glanced about. He found a pair of heavy rubber gloves and put them on. He seized the coil and pulled its two ends apart. There was a flash and a snap. The Professor turned to Dr. Fenster. “As you can see, this means—” he was beginning. "
― Jay Williams , Danny Dunn and the Swamp Monster (Danny Dunn)