This deluxe 3-D set includes 2 plastic viewers containing over 200 miniature compasses each! Each large viewer is 8" / 20cm in height and contains a removable side panel for placement of the included magnets. The default photo shows the set with the magnets in place. Pan over the other photo (clicking on it to enlarge) to see the magnets removed and the side panels open. This set is so simple to use, and it dramatically illustrates magnetic lines of force to students.

 

It is far superior to iron filings both in detail and cleanliness. Ideal for use with an overhead projector. A best seller!