Geissler tubes are tubes for discharges in rarefied gases which have their electrodes soldered to the glass by means of platinum or tungsten wires; they are fairly small have pressures on the order of a millimetre of mercury or just short of that.
The electrodes are in general threadlike, but they can also have the form of a disk. On connecting them to the poles of an electrostatic generator or a Ruhmkorff coil, there is a discharge of the flash type, the colour of which depends on the gas contained in the tube.
The electrodes are contained in two small, ovoid, spherical or cylindrical bubbles on the sides. In the centre of the tube, which is cylindrical, the section is in general reduced so as to increase its luminosity.
What we present here are two tubes ending with two small lateral ovoid bubbles (maximum outside diameter 2 cm) which are joined to a central part of reduced section (internal diameter about 1 mm) consisting of a spiral with ten spires having an outside diameter of about 8 mm. The wire-like electrodes are soldered to the extremities of the two lateral bubbles and the soldered joints are protected on the outside by semicircular capsules of thin metal plate. The overall length is 14 cm and the length of the spiral is 7 cm. It is finely worked.
One of the two tubes is broken.