Geissler tube

A Geissler tube is composed of a sealed glass cylinder of various shapes, which is partially evacuated and equipped with a metal electrode at each end.

It contains rarefied gases—such as neon or argon, air, mercury vapor, or other conductive substances, and sometimes ionizable minerals or metals like sodium.

When a high voltage is applied between the electrodes, there is an electric current through the tube, causing gas molecules to ionize by shedding electrons.

Colorful decorative Geissler tubes were made in many artistic designs around the turn of the century, to demonstrate the new technology of electricity.

A novel effect could be obtained by spinning a glowing tube at high speed with a motor; a disk of color was seen due to persistence of vision.