Discharge bell-jars

A sphere, adjustable in height, is fixed in each of the glass bell-jars. The glass bell-jar is hermetically sealed at the top by a brass disk. The bell-jar is seated on the circular plate of the stand by grease or wax, so that the bell-jar is hermetically sealed. When the bell-jar is then connected to an electrostatic generator, a discharge will take place between the sphere and the base plate. By way of the turn-cock in the wooden stand the instrument can be connected to an air pump. At normal air pressure, a jumping spark will appear during discharging. However, when the bell-jar is sucked more vacuum, a glowing light will appear between the sphere and the base plate. By varying the air pressure and the distance between the sphere and the base plate, the resulting, varying light effects could be studied. [See also 534, 536 and 539]