It's a magnetic stirring bar for scientific experiments. It sits in liquid and spins around, mixing the contents of the liquid when a magnetic field is applied.
You put your beaker of liquid on a thing that looks like a hot plate. Instead of heat, it has a rotating magnet in it. This causes the stir bar to spin, keeping the liquid contents mixed together without having to constantly use a stirring rod manually.
At first I thought it was a coherer. Radio signal detector for tube radios. Basically it's the ancestor of a diode. But there are no metal ends on it.
