Roget’s Spiral

—An experiment to show the attraction of parallel currents; a spiral of copper wire is hung from a binding screw so that its lower end just tips in a mercury - cup. When a current is pa ed through the circuit thus formed, the coils of the spiral attract one another and contract raising the tip from the mercury surface an breaking the zircuit; the circuit’being broken, the coils relax, the circuit is again completed through the mercury, and the performance repeated.