For sale, a Late Victorian Geissler Tube Cross Vacuum Scale
This uncommon set is comprised of an ebonised wood base and upstand. The former has a metal stand which provides a base for holding six Geissler tubes which are in turn fastened at the top by brass electrical connection points secures to the upstand. Each Geissler tube has an attached label numbering successively from 1 to 6 and the base and the side of the upstand are also fitted with a connection point.
The cross-vacuum scale demonstration is to show the variations of electric glow discharge when voltage is applied to a set of glass (Geissler) tubes which are gas filled and all have varying levels of vacuum pressure within them. The glow or plasma is created by applying voltage and the requisite pressure within each will denote how strongly or brightly the tube glows. Different gases will also denote which colour glow is achieved.
This example is unnamed although it does look as though some type of label was once applied to the back edge of the base, however, numerous companies such as Max Kohl of Germany are known to have produced them in latter stages of the Nineteenth Century and early Twentieth Century.