The characteristics of VR-tubes were improved and new types were developed from a study of the phenomena in the glow discharge. A smooth voltage-current characteristic without hysteresis is obtained with noble gases of smaller atomic weight wen the gaseous impurity content is less than one part per million (Penning, F. M., and Moubis, Philips Research Reports, vol. 1, p.119; 1946). Under many conditions, the mean energy per electron freed from a hollow cathode. is less than from a plain cathode, but the problem of cleaning the metal of dis solved gases is increased. Techniques to obtain high purity and.to shorten the life of virtual leaks from the glass and the electrode materials will be presented. In addition, the loss of energy from the discharge through the diffusion of metastable will be discussed, and some of the effects on the characteristics will be illustrated with performance curves.