Study magnetic fields without the mess of iron filings. The transparent acrylic case is filled with fluid and fine iron filings and then permanently sealed shut. Set the magnetic field demonstrator on an overhead projector. Place a magnet beneath the demonstrator and watch the clear lines of magnetic force become visible through the clear sides of the chamber. Under the bright light of the overhead projector the lines of force are magnified and very clear. Try several arrangements. The magnetic force line patterns will be very interesting to your students. This rugged device measures 12 cm x 22 cm x 1 cm.