An electric discharge will cause several light effects in (rarefied) gases. This instrument was used to demonstrate such effects. The glass bell-jar is hermetically sealed at the top by a brass disk. On the disk is a brass sphere with a rod, ending in the bell-jar. In the base of the bell-jar is a copper hemisphere. The bell-jar is hermetically mounted on a wooden tripod stand.
Via the base plate, air can be drawn out of the bell-jar. When the instrument is then connected to an electrostatic generator, bands of light will appear between the hemisphere and the rod at the top [See also 534, 536, 537 and 538].
Discharge bell-jar with vertical and horizontal ring, with a conductor in between
1775 - 1799