For lectures and demonstrations, our apparatus gives you a more convenient way to do experiments that everyone can see. The Magnetic Field Projectual is a sturdy, transparent acrylic case that holds iron filings in a special viscous fluid. First shake the unit so the internal glass rod distributes the filings evenly. Place any magnet under the unit and set it on an overhead projector and the filings line up along the lines of magnetic force. Size: 25cm x 21cm x 2cm.