Dramatic demonstration showing the force of air pressure that your students will remember for a long time. Simply hook up the hemispheres to a hand vacuum pump, an aspirator or vacuum pump and evacuate the air. Close the valve and let the pulling begin! Challenge your strongest students to see who can pull the two hemispheres apart. This economical demonstration features a convenient two-way valve for easy operation and release, two tough plastic 11-cm diameter hemispheres with molded handles, and comes complete with directions, experiment suggestions and historical information about Magdeburg hemispheres. Requires a vacuum source for use.