For demonstration of the kinetic theory of gases thinning of air with increasing altitude, etc. Clear, perspex, cylindrical tube with a rubber diaphragm attached to its lower end. Beneath the diaphragm, a piston connected to a 6-V DC motor is fixed for producing agitation. Whole assembly mounted on a circular base with two 4mm-socket terminals for electrical connection to the motor. Metal spheres, â…›”; freely sliding, expanded polystyrene pistons; and 4 card board discs for loading of pistons also included.