With this 3-D Magnetic Field Demonstrator, the iron filings are suspended in oil in a sealed acrylic container. Insert a cylindrical bar magnet (not included) into the opening, or two magnets with opposing polarities, and watch the filings line up along the magnetic field lines. View the demonstration directly or with an overhead projector. The iron filings move to form shapes consistent with the various magnetic fields applied. The viscous liquid holds the filings in place for a while after removing the magnetic field, making observation easier.