Since many of the inventions of the 19th century exploited the interactions between electricity and magnetism, it was important to give students and understanding of these effects. Here are three devices from the Cabinet of Physics that demonstrate eddy currents: the Arago disk, the Foucault apparatus, and the Ruhmkorff electromagnet.
Eddy currents are currents that flow through a metal object that moves through a magnetic field. Their effects can interfere with the operation of electromagnetic devices, so engineers learn techniques for minimizing eddy currents–examples here are the second Arago disk, which features radial slots cut into it, and the dangling cube made up of many thin layers of copper as opposed to a solid copper cube.
The Foundation for Science and Technics, or Fondazione Scienza e Tecnica, of Florence, Italy, has made available many videos exploring the Cabinet of Physics, a large collection of antique scientific demonstration instruments. The Foundation’s homepage may be found here, and its Youtube channel, florencefst, here.
