At the end of the seventeenth century, the French physicist Jean Picard discovered that an electric discharge in an evacuated tube caused a glow of light. In the course of the eighteenth century, various instruments were developed to study and demonstrate this phenomenon. This glass bell-jar is hermetically sealed at the top by a brass disk, from which a brass ring is suspended into the bell-jar. On the base plate a copper ring is mounted and a glass tube with a copper cone. Via the base plate the bell-jar can be connected to an air pump. When the instrument is then connected to an electrostatic generator, discharges between the rings and the cone will appear. The resulting light phenomena differ as the air pressure varies. [See also 534, 537, 538 and 539]
Discharge bell-jar with copper cone and ring
1775 - 1799