For showing Guericke's method of illustrating atmospheric pressure. The hemispheres are pressed out of thick sheet steel and are flanged and sealed vacuum-tight with a Koroseal gasket. The flange is turned up to form a rim which prevents side slip. The handles are designed so that they will hold a weight hanger or permit hanging from an overhead support. One hemisphere is provided with a metal stopcock which is threaded to fit a standardpump plate. The diameter of the hemisphere gives an effective area of nearly 20 square inches so that the force that holds them together when most of the air has been removed is about 300 pounds.